Legacy Query API¶
About the Legacy Query API
This page contains the Python generated documentation for the
Query
construct, which for many years was the sole SQL
interface when working with the SQLAlchemy ORM. As of version 2.0, an all
new way of working is now the standard approach, where the same
select()
construct that works for Core works just as well for the
ORM, providing a consistent interface for building queries.
For any application that is built on the SQLAlchemy ORM prior to the
2.0 API, the Query
API will usually represents the vast
majority of database access code within an application, and as such the
majority of the Query
API is
not being removed from SQLAlchemy. The Query
object
behind the scenes now translates itself into a 2.0 style select()
object when the Query
object is executed, so it now is
just a very thin adapter API.
For a guide to migrating an application based on Query
to 2.0 style, see 2.0 Migration - ORM Usage.
For an introduction to writing SQL for ORM objects in the 2.0 style, start with the SQLAlchemy Unified Tutorial. Additional reference for 2.0 style querying is at ORM Querying Guide.
The Query Object¶
Query
is produced in terms of a given Session
, using the Session.query()
method:
q = session.query(SomeMappedClass)
Following is the full interface for the Query
object.
Object Name | Description |
---|---|
ORM-level SQL construction object. |
- class sqlalchemy.orm.Query¶
ORM-level SQL construction object.
Legacy Feature
The ORM
Query
object is a legacy construct as of SQLAlchemy 2.0. See the notes at the top of Legacy Query API for an overview, including links to migration documentation.Query
objects are normally initially generated using theSession.query()
method ofSession
, and in less common cases by instantiating theQuery
directly and associating with aSession
using theQuery.with_session()
method.Members
__init__(), add_column(), add_columns(), add_entity(), all(), apply_labels(), as_scalar(), autoflush(), column_descriptions, correlate(), count(), cte(), delete(), distinct(), enable_assertions(), enable_eagerloads(), except_(), except_all(), execution_options(), exists(), filter(), filter_by(), first(), from_statement(), get(), get_children(), get_execution_options(), get_label_style, group_by(), having(), instances(), intersect(), intersect_all(), is_single_entity, join(), label(), lazy_loaded_from, limit(), merge_result(), offset(), one(), one_or_none(), only_return_tuples(), options(), order_by(), outerjoin(), params(), populate_existing(), prefix_with(), reset_joinpoint(), scalar(), scalar_subquery(), select_from(), selectable, set_label_style(), slice(), statement, subquery(), suffix_with(), tuples(), union(), union_all(), update(), value(), values(), where(), whereclause, with_entities(), with_for_update(), with_hint(), with_labels(), with_parent(), with_session(), with_statement_hint(), with_transformation(), yield_per()
Class signature
class
sqlalchemy.orm.Query
(sqlalchemy.sql.expression._SelectFromElements
,sqlalchemy.sql.annotation.SupportsCloneAnnotations
,sqlalchemy.sql.expression.HasPrefixes
,sqlalchemy.sql.expression.HasSuffixes
,sqlalchemy.sql.expression.HasHints
,sqlalchemy.event.registry.EventTarget
,sqlalchemy.log.Identified
,sqlalchemy.sql.expression.Generative
,sqlalchemy.sql.expression.Executable
,typing.Generic
)-
method
sqlalchemy.orm.Query.
__init__(entities: Sequence[_ColumnsClauseArgument[Any]], session: Optional[Session] = None)¶ Construct a
Query
directly.E.g.:
q = Query([User, Address], session=some_session)
The above is equivalent to:
q = some_session.query(User, Address)
- Parameters:
entities – a sequence of entities and/or SQL expressions.
session – a
Session
with which theQuery
will be associated. Optional; aQuery
can be associated with aSession
generatively via theQuery.with_session()
method as well.
-
method
sqlalchemy.orm.Query.
add_column(column: _ColumnExpressionArgument[Any]) Query[Any] ¶ Add a column expression to the list of result columns to be returned.
Deprecated since version 1.4:
Query.add_column()
is deprecated and will be removed in a future release. Please useQuery.add_columns()
-
method
sqlalchemy.orm.Query.
add_columns(*column: _ColumnExpressionArgument[Any]) Query[Any] ¶ Add one or more column expressions to the list of result columns to be returned.
See also
Select.add_columns()
- v2 comparable method.
-
method
sqlalchemy.orm.Query.
add_entity(entity: _EntityType[Any], alias: Optional[Union[Alias, Subquery]] = None) Query[Any] ¶ add a mapped entity to the list of result columns to be returned.
See also
Select.add_columns()
- v2 comparable method.
-
method
sqlalchemy.orm.Query.
all() List[_T] ¶ Return the results represented by this
Query
as a list.This results in an execution of the underlying SQL statement.
Warning
The
Query
object, when asked to return either a sequence or iterator that consists of full ORM-mapped entities, will deduplicate entries based on primary key. See the FAQ for more details.
-
method
sqlalchemy.orm.Query.
apply_labels() Self ¶ Deprecated since version 2.0: The
Query.with_labels()
andQuery.apply_labels()
method is considered legacy as of the 1.x series of SQLAlchemy and becomes a legacy construct in 2.0. Use set_label_style(LABEL_STYLE_TABLENAME_PLUS_COL) instead. (Background on SQLAlchemy 2.0 at: SQLAlchemy 2.0 - Major Migration Guide)
-
method
sqlalchemy.orm.Query.
as_scalar() ScalarSelect[Any] ¶ Return the full SELECT statement represented by this
Query
, converted to a scalar subquery.Deprecated since version 1.4: The
Query.as_scalar()
method is deprecated and will be removed in a future release. Please refer toQuery.scalar_subquery()
.
-
method
sqlalchemy.orm.Query.
autoflush(setting: bool) Self ¶ Return a Query with a specific ‘autoflush’ setting.
As of SQLAlchemy 1.4, the
Query.autoflush()
method is equivalent to using theautoflush
execution option at the ORM level. See the section Autoflush for further background on this option.
-
attribute
sqlalchemy.orm.Query.
column_descriptions¶ Return metadata about the columns which would be returned by this
Query
.Format is a list of dictionaries:
user_alias = aliased(User, name='user2') q = sess.query(User, User.id, user_alias) # this expression: q.column_descriptions # would return: [ { 'name':'User', 'type':User, 'aliased':False, 'expr':User, 'entity': User }, { 'name':'id', 'type':Integer(), 'aliased':False, 'expr':User.id, 'entity': User }, { 'name':'user2', 'type':User, 'aliased':True, 'expr':user_alias, 'entity': user_alias } ]
See also
This API is available using 2.0 style queries as well, documented at:
-
method
sqlalchemy.orm.Query.
correlate(*fromclauses: Union[Literal[None, False], FromClauseRole, Type[Any], Inspectable[_HasClauseElement], _HasClauseElement]) Self ¶ Return a
Query
construct which will correlate the given FROM clauses to that of an enclosingQuery
orselect()
.The method here accepts mapped classes,
aliased()
constructs, andMapper
constructs as arguments, which are resolved into expression constructs, in addition to appropriate expression constructs.The correlation arguments are ultimately passed to
Select.correlate()
after coercion to expression constructs.The correlation arguments take effect in such cases as when
Query.from_self()
is used, or when a subquery as returned byQuery.subquery()
is embedded in anotherselect()
construct.See also
Select.correlate()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
count() int ¶ Return a count of rows this the SQL formed by this
Query
would return.This generates the SQL for this Query as follows:
SELECT count(1) AS count_1 FROM ( SELECT <rest of query follows...> ) AS anon_1
The above SQL returns a single row, which is the aggregate value of the count function; the
Query.count()
method then returns that single integer value.Warning
It is important to note that the value returned by count() is not the same as the number of ORM objects that this Query would return from a method such as the .all() method. The
Query
object, when asked to return full entities, will deduplicate entries based on primary key, meaning if the same primary key value would appear in the results more than once, only one object of that primary key would be present. This does not apply to a query that is against individual columns.For fine grained control over specific columns to count, to skip the usage of a subquery or otherwise control of the FROM clause, or to use other aggregate functions, use
expression.func
expressions in conjunction withSession.query()
, i.e.:from sqlalchemy import func # count User records, without # using a subquery. session.query(func.count(User.id)) # return count of user "id" grouped # by "name" session.query(func.count(User.id)).\ group_by(User.name) from sqlalchemy import distinct # count distinct "name" values session.query(func.count(distinct(User.name)))
See also
-
method
sqlalchemy.orm.Query.
cte(name: Optional[str] = None, recursive: bool = False, nesting: bool = False) CTE ¶ Return the full SELECT statement represented by this
Query
represented as a common table expression (CTE).Parameters and usage are the same as those of the
SelectBase.cte()
method; see that method for further details.Here is the PostgreSQL WITH RECURSIVE example. Note that, in this example, the
included_parts
cte and theincl_alias
alias of it are Core selectables, which means the columns are accessed via the.c.
attribute. Theparts_alias
object is analiased()
instance of thePart
entity, so column-mapped attributes are available directly:from sqlalchemy.orm import aliased class Part(Base): __tablename__ = 'part' part = Column(String, primary_key=True) sub_part = Column(String, primary_key=True) quantity = Column(Integer) included_parts = session.query( Part.sub_part, Part.part, Part.quantity).\ filter(Part.part=="our part").\ cte(name="included_parts", recursive=True) incl_alias = aliased(included_parts, name="pr") parts_alias = aliased(Part, name="p") included_parts = included_parts.union_all( session.query( parts_alias.sub_part, parts_alias.part, parts_alias.quantity).\ filter(parts_alias.part==incl_alias.c.sub_part) ) q = session.query( included_parts.c.sub_part, func.sum(included_parts.c.quantity). label('total_quantity') ).\ group_by(included_parts.c.sub_part)
See also
Select.cte()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
delete(synchronize_session: SynchronizeSessionArgument = 'auto') int ¶ Perform a DELETE with an arbitrary WHERE clause.
Deletes rows matched by this query from the database.
E.g.:
sess.query(User).filter(User.age == 25).\ delete(synchronize_session=False) sess.query(User).filter(User.age == 25).\ delete(synchronize_session='evaluate')
Warning
See the section ORM-Enabled INSERT, UPDATE, and DELETE statements for important caveats and warnings, including limitations when using bulk UPDATE and DELETE with mapper inheritance configurations.
- Parameters:
synchronize_session – chooses the strategy to update the attributes on objects in the session. See the section ORM-Enabled INSERT, UPDATE, and DELETE statements for a discussion of these strategies.
- Returns:
the count of rows matched as returned by the database’s “row count” feature.
-
method
sqlalchemy.orm.Query.
distinct(*expr: _ColumnExpressionArgument[Any]) Self ¶ Apply a
DISTINCT
to the query and return the newly resultingQuery
.Note
The ORM-level
distinct()
call includes logic that will automatically add columns from the ORDER BY of the query to the columns clause of the SELECT statement, to satisfy the common need of the database backend that ORDER BY columns be part of the SELECT list when DISTINCT is used. These columns are not added to the list of columns actually fetched by theQuery
, however, so would not affect results. The columns are passed through when using theQuery.statement
accessor, however.Deprecated since version 2.0: This logic is deprecated and will be removed in SQLAlchemy 2.0. See Using DISTINCT with additional columns, but only select the entity for a description of this use case in 2.0.
See also
Select.distinct()
- v2 equivalent method.- Parameters:
*expr –
optional column expressions. When present, the PostgreSQL dialect will render a
DISTINCT ON (<expressions>)
construct.Deprecated since version 1.4: Using *expr in other dialects is deprecated and will raise
CompileError
in a future version.
-
method
sqlalchemy.orm.Query.
enable_assertions(value: bool) Self ¶ Control whether assertions are generated.
When set to False, the returned Query will not assert its state before certain operations, including that LIMIT/OFFSET has not been applied when filter() is called, no criterion exists when get() is called, and no “from_statement()” exists when filter()/order_by()/group_by() etc. is called. This more permissive mode is used by custom Query subclasses to specify criterion or other modifiers outside of the usual usage patterns.
Care should be taken to ensure that the usage pattern is even possible. A statement applied by from_statement() will override any criterion set by filter() or order_by(), for example.
-
method
sqlalchemy.orm.Query.
enable_eagerloads(value: bool) Self ¶ Control whether or not eager joins and subqueries are rendered.
When set to False, the returned Query will not render eager joins regardless of
joinedload()
,subqueryload()
options or mapper-levellazy='joined'
/lazy='subquery'
configurations.This is used primarily when nesting the Query’s statement into a subquery or other selectable, or when using
Query.yield_per()
.
-
method
sqlalchemy.orm.Query.
except_(*q: Query) Self ¶ Produce an EXCEPT of this Query against one or more queries.
Works the same way as
Query.union()
. See that method for usage examples.See also
Select.except_()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
except_all(*q: Query) Self ¶ Produce an EXCEPT ALL of this Query against one or more queries.
Works the same way as
Query.union()
. See that method for usage examples.See also
Select.except_all()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
execution_options(**kwargs: Any) Self ¶ Set non-SQL options which take effect during execution.
Options allowed here include all of those accepted by
Connection.execution_options()
, as well as a series of ORM specific options:populate_existing=True
- equivalent to usingQuery.populate_existing()
autoflush=True|False
- equivalent to usingQuery.autoflush()
yield_per=<value>
- equivalent to usingQuery.yield_per()
Note that the
stream_results
execution option is enabled automatically if theQuery.yield_per()
method or execution option is used.New in version 1.4: - added ORM options to
Query.execution_options()
The execution options may also be specified on a per execution basis when using 2.0 style queries via the
Session.execution_options
parameter.Warning
The
Connection.execution_options.stream_results
parameter should not be used at the level of individual ORM statement executions, as theSession
will not track objects from different schema translate maps within a single session. For multiple schema translate maps within the scope of a singleSession
, see Horizontal Sharding.See also
Using Server Side Cursors (a.k.a. stream results)
Select.execution_options()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
exists() Exists ¶ A convenience method that turns a query into an EXISTS subquery of the form EXISTS (SELECT 1 FROM … WHERE …).
e.g.:
q = session.query(User).filter(User.name == 'fred') session.query(q.exists())
Producing SQL similar to:
SELECT EXISTS ( SELECT 1 FROM users WHERE users.name = :name_1 ) AS anon_1
The EXISTS construct is usually used in the WHERE clause:
session.query(User.id).filter(q.exists()).scalar()
Note that some databases such as SQL Server don’t allow an EXISTS expression to be present in the columns clause of a SELECT. To select a simple boolean value based on the exists as a WHERE, use
literal()
:from sqlalchemy import literal session.query(literal(True)).filter(q.exists()).scalar()
See also
Select.exists()
- v2 comparable method.
-
method
sqlalchemy.orm.Query.
filter(*criterion: _ColumnExpressionArgument[bool]) Self ¶ Apply the given filtering criterion to a copy of this
Query
, using SQL expressions.e.g.:
session.query(MyClass).filter(MyClass.name == 'some name')
Multiple criteria may be specified as comma separated; the effect is that they will be joined together using the
and_()
function:session.query(MyClass).\ filter(MyClass.name == 'some name', MyClass.id > 5)
The criterion is any SQL expression object applicable to the WHERE clause of a select. String expressions are coerced into SQL expression constructs via the
text()
construct.
-
method
sqlalchemy.orm.Query.
filter_by(**kwargs: Any) Self ¶ Apply the given filtering criterion to a copy of this
Query
, using keyword expressions.e.g.:
session.query(MyClass).filter_by(name = 'some name')
Multiple criteria may be specified as comma separated; the effect is that they will be joined together using the
and_()
function:session.query(MyClass).\ filter_by(name = 'some name', id = 5)
The keyword expressions are extracted from the primary entity of the query, or the last entity that was the target of a call to
Query.join()
.
-
method
sqlalchemy.orm.Query.
first() Optional[_T] ¶ Return the first result of this
Query
or None if the result doesn’t contain any row.first() applies a limit of one within the generated SQL, so that only one primary entity row is generated on the server side (note this may consist of multiple result rows if join-loaded collections are present).
Calling
Query.first()
results in an execution of the underlying query.
-
method
sqlalchemy.orm.Query.
from_statement(statement: ExecutableReturnsRows) Self ¶ Execute the given SELECT statement and return results.
This method bypasses all internal statement compilation, and the statement is executed without modification.
The statement is typically either a
text()
orselect()
construct, and should return the set of columns appropriate to the entity class represented by thisQuery
.See also
Select.from_statement()
- v2 comparable method.
-
method
sqlalchemy.orm.Query.
get(ident: _PKIdentityArgument) Optional[Any] ¶ Return an instance based on the given primary key identifier, or
None
if not found.Deprecated since version 2.0: The
Query.get()
method is considered legacy as of the 1.x series of SQLAlchemy and becomes a legacy construct in 2.0. The method is now available asSession.get()
(Background on SQLAlchemy 2.0 at: SQLAlchemy 2.0 - Major Migration Guide)E.g.:
my_user = session.query(User).get(5) some_object = session.query(VersionedFoo).get((5, 10)) some_object = session.query(VersionedFoo).get( {"id": 5, "version_id": 10})
Query.get()
is special in that it provides direct access to the identity map of the owningSession
. If the given primary key identifier is present in the local identity map, the object is returned directly from this collection and no SQL is emitted, unless the object has been marked fully expired. If not present, a SELECT is performed in order to locate the object.Query.get()
also will perform a check if the object is present in the identity map and marked as expired - a SELECT is emitted to refresh the object as well as to ensure that the row is still present. If not,ObjectDeletedError
is raised.Query.get()
is only used to return a single mapped instance, not multiple instances or individual column constructs, and strictly on a single primary key value. The originatingQuery
must be constructed in this way, i.e. against a single mapped entity, with no additional filtering criterion. Loading options viaQuery.options()
may be applied however, and will be used if the object is not yet locally present.- Parameters:
ident –
A scalar, tuple, or dictionary representing the primary key. For a composite (e.g. multiple column) primary key, a tuple or dictionary should be passed.
For a single-column primary key, the scalar calling form is typically the most expedient. If the primary key of a row is the value “5”, the call looks like:
my_object = query.get(5)
The tuple form contains primary key values typically in the order in which they correspond to the mapped
Table
object’s primary key columns, or if theMapper.primary_key
configuration parameter were used, in the order used for that parameter. For example, if the primary key of a row is represented by the integer digits “5, 10” the call would look like:my_object = query.get((5, 10))
The dictionary form should include as keys the mapped attribute names corresponding to each element of the primary key. If the mapped class has the attributes
id
,version_id
as the attributes which store the object’s primary key value, the call would look like:my_object = query.get({"id": 5, "version_id": 10})
New in version 1.3: the
Query.get()
method now optionally accepts a dictionary of attribute names to values in order to indicate a primary key identifier.- Returns:
The object instance, or
None
.
-
method
sqlalchemy.orm.Query.
get_children(*, omit_attrs: Tuple[str, ...] = (), **kw: Any) Iterable[HasTraverseInternals] ¶ inherited from the
HasTraverseInternals.get_children()
method ofHasTraverseInternals
Return immediate child
HasTraverseInternals
elements of thisHasTraverseInternals
.This is used for visit traversal.
**kw may contain flags that change the collection that is returned, for example to return a subset of items in order to cut down on larger traversals, or to return child items from a different context (such as schema-level collections instead of clause-level).
-
method
sqlalchemy.orm.Query.
get_execution_options() _ImmutableExecuteOptions ¶ Get the non-SQL options which will take effect during execution.
New in version 1.3.
-
attribute
sqlalchemy.orm.Query.
get_label_style¶ Retrieve the current label style.
New in version 1.4.
See also
Select.get_label_style()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
group_by(_Query__first: Union[Literal[None, False, _NoArg.NO_ARG], _ColumnExpressionOrStrLabelArgument[Any]] = _NoArg.NO_ARG, *clauses: _ColumnExpressionOrStrLabelArgument[Any]) Self ¶ Apply one or more GROUP BY criterion to the query and return the newly resulting
Query
.All existing GROUP BY settings can be suppressed by passing
None
- this will suppress any GROUP BY configured on mappers as well.See also
These sections describe GROUP BY in terms of 2.0 style invocation but apply to
Query
as well:Aggregate functions with GROUP BY / HAVING - in the SQLAlchemy Unified Tutorial
Ordering or Grouping by a Label - in the SQLAlchemy Unified Tutorial
Select.group_by()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
having(*having: _ColumnExpressionArgument[bool]) Self ¶ Apply a HAVING criterion to the query and return the newly resulting
Query
.Query.having()
is used in conjunction withQuery.group_by()
.HAVING criterion makes it possible to use filters on aggregate functions like COUNT, SUM, AVG, MAX, and MIN, eg.:
q = session.query(User.id).\ join(User.addresses).\ group_by(User.id).\ having(func.count(Address.id) > 2)
See also
Select.having()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
instances(result_proxy: CursorResult[Any], context: Optional[QueryContext] = None) Any ¶ Return an ORM result given a
CursorResult
andQueryContext
.Deprecated since version 2.0: The
Query.instances()
method is deprecated and will be removed in a future release. Use the Select.from_statement() method or aliased() construct in conjunction with Session.execute() instead.
-
method
sqlalchemy.orm.Query.
intersect(*q: Query) Self ¶ Produce an INTERSECT of this Query against one or more queries.
Works the same way as
Query.union()
. See that method for usage examples.See also
Select.intersect()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
intersect_all(*q: Query) Self ¶ Produce an INTERSECT ALL of this Query against one or more queries.
Works the same way as
Query.union()
. See that method for usage examples.See also
Select.intersect_all()
- v2 equivalent method.
-
attribute
sqlalchemy.orm.Query.
is_single_entity¶ Indicates if this
Query
returns tuples or single entities.Returns True if this query returns a single entity for each instance in its result list, and False if this query returns a tuple of entities for each result.
New in version 1.3.11.
See also
-
method
sqlalchemy.orm.Query.
join(target: _JoinTargetArgument, onclause: Optional[_OnClauseArgument] = None, *, isouter: bool = False, full: bool = False) Self ¶ Create a SQL JOIN against this
Query
object’s criterion and apply generatively, returning the newly resultingQuery
.Simple Relationship Joins
Consider a mapping between two classes
User
andAddress
, with a relationshipUser.addresses
representing a collection ofAddress
objects associated with eachUser
. The most common usage ofQuery.join()
is to create a JOIN along this relationship, using theUser.addresses
attribute as an indicator for how this should occur:q = session.query(User).join(User.addresses)
Where above, the call to
Query.join()
alongUser.addresses
will result in SQL approximately equivalent to:SELECT user.id, user.name FROM user JOIN address ON user.id = address.user_id
In the above example we refer to
User.addresses
as passed toQuery.join()
as the “on clause”, that is, it indicates how the “ON” portion of the JOIN should be constructed.To construct a chain of joins, multiple
Query.join()
calls may be used. The relationship-bound attribute implies both the left and right side of the join at once:q = session.query(User).\ join(User.orders).\ join(Order.items).\ join(Item.keywords)
Note
as seen in the above example, the order in which each call to the join() method occurs is important. Query would not, for example, know how to join correctly if we were to specify
User
, thenItem
, thenOrder
, in our chain of joins; in such a case, depending on the arguments passed, it may raise an error that it doesn’t know how to join, or it may produce invalid SQL in which case the database will raise an error. In correct practice, theQuery.join()
method is invoked in such a way that lines up with how we would want the JOIN clauses in SQL to be rendered, and each call should represent a clear link from what precedes it.Joins to a Target Entity or Selectable
A second form of
Query.join()
allows any mapped entity or core selectable construct as a target. In this usage,Query.join()
will attempt to create a JOIN along the natural foreign key relationship between two entities:q = session.query(User).join(Address)
In the above calling form,
Query.join()
is called upon to create the “on clause” automatically for us. This calling form will ultimately raise an error if either there are no foreign keys between the two entities, or if there are multiple foreign key linkages between the target entity and the entity or entities already present on the left side such that creating a join requires more information. Note that when indicating a join to a target without any ON clause, ORM configured relationships are not taken into account.Joins to a Target with an ON Clause
The third calling form allows both the target entity as well as the ON clause to be passed explicitly. A example that includes a SQL expression as the ON clause is as follows:
q = session.query(User).join(Address, User.id==Address.user_id)
The above form may also use a relationship-bound attribute as the ON clause as well:
q = session.query(User).join(Address, User.addresses)
The above syntax can be useful for the case where we wish to join to an alias of a particular target entity. If we wanted to join to
Address
twice, it could be achieved using two aliases set up using thealiased()
function:a1 = aliased(Address) a2 = aliased(Address) q = session.query(User).\ join(a1, User.addresses).\ join(a2, User.addresses).\ filter(a1.email_address=='ed@foo.com').\ filter(a2.email_address=='ed@bar.com')
The relationship-bound calling form can also specify a target entity using the
PropComparator.of_type()
method; a query equivalent to the one above would be:a1 = aliased(Address) a2 = aliased(Address) q = session.query(User).\ join(User.addresses.of_type(a1)).\ join(User.addresses.of_type(a2)).\ filter(a1.email_address == 'ed@foo.com').\ filter(a2.email_address == 'ed@bar.com')
Augmenting Built-in ON Clauses
As a substitute for providing a full custom ON condition for an existing relationship, the
PropComparator.and_()
function may be applied to a relationship attribute to augment additional criteria into the ON clause; the additional criteria will be combined with the default criteria using AND:q = session.query(User).join( User.addresses.and_(Address.email_address != 'foo@bar.com') )
New in version 1.4.
Joining to Tables and Subqueries
The target of a join may also be any table or SELECT statement, which may be related to a target entity or not. Use the appropriate
.subquery()
method in order to make a subquery out of a query:subq = session.query(Address).\ filter(Address.email_address == 'ed@foo.com').\ subquery() q = session.query(User).join( subq, User.id == subq.c.user_id )
Joining to a subquery in terms of a specific relationship and/or target entity may be achieved by linking the subquery to the entity using
aliased()
:subq = session.query(Address).\ filter(Address.email_address == 'ed@foo.com').\ subquery() address_subq = aliased(Address, subq) q = session.query(User).join( User.addresses.of_type(address_subq) )
Controlling what to Join From
In cases where the left side of the current state of
Query
is not in line with what we want to join from, theQuery.select_from()
method may be used:q = session.query(Address).select_from(User).\ join(User.addresses).\ filter(User.name == 'ed')
Which will produce SQL similar to:
SELECT address.* FROM user JOIN address ON user.id=address.user_id WHERE user.name = :name_1
See also
Select.join()
- v2 equivalent method.- Parameters:
*props – Incoming arguments for
Query.join()
, the props collection in modern use should be considered to be a one or two argument form, either as a single “target” entity or ORM attribute-bound relationship, or as a target entity plus an “on clause” which may be a SQL expression or ORM attribute-bound relationship.isouter=False – If True, the join used will be a left outer join, just as if the
Query.outerjoin()
method were called.full=False – render FULL OUTER JOIN; implies
isouter
.
-
method
sqlalchemy.orm.Query.
label(name: Optional[str]) Label[Any] ¶ Return the full SELECT statement represented by this
Query
, converted to a scalar subquery with a label of the given name.See also
Select.label()
- v2 comparable method.
-
attribute
sqlalchemy.orm.Query.
lazy_loaded_from¶ An
InstanceState
that is using thisQuery
for a lazy load operation.Deprecated since version 1.4: This attribute should be viewed via the
ORMExecuteState.lazy_loaded_from
attribute, within the context of theSessionEvents.do_orm_execute()
event.See also
-
method
sqlalchemy.orm.Query.
limit(limit: _LimitOffsetType) Self ¶ Apply a
LIMIT
to the query and return the newly resultingQuery
.See also
Select.limit()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
merge_result(iterator: Union[FrozenResult[Any], Iterable[Sequence[Any]], Iterable[object]], load: bool = True) Union[FrozenResult[Any], Iterable[Any]] ¶ Merge a result into this
Query
object’s Session.Deprecated since version 2.0: The
Query.merge_result()
method is considered legacy as of the 1.x series of SQLAlchemy and becomes a legacy construct in 2.0. The method is superseded by themerge_frozen_result()
function. (Background on SQLAlchemy 2.0 at: SQLAlchemy 2.0 - Major Migration Guide)Given an iterator returned by a
Query
of the same structure as this one, return an identical iterator of results, with all mapped instances merged into the session usingSession.merge()
. This is an optimized method which will merge all mapped instances, preserving the structure of the result rows and unmapped columns with less method overhead than that of callingSession.merge()
explicitly for each value.The structure of the results is determined based on the column list of this
Query
- if these do not correspond, unchecked errors will occur.The ‘load’ argument is the same as that of
Session.merge()
.For an example of how
Query.merge_result()
is used, see the source code for the example Dogpile Caching, whereQuery.merge_result()
is used to efficiently restore state from a cache back into a targetSession
.
-
method
sqlalchemy.orm.Query.
offset(offset: _LimitOffsetType) Self ¶ Apply an
OFFSET
to the query and return the newly resultingQuery
.See also
Select.offset()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
one() _T ¶ Return exactly one result or raise an exception.
Raises
sqlalchemy.orm.exc.NoResultFound
if the query selects no rows. Raisessqlalchemy.orm.exc.MultipleResultsFound
if multiple object identities are returned, or if multiple rows are returned for a query that returns only scalar values as opposed to full identity-mapped entities.Calling
one()
results in an execution of the underlying query.
-
method
sqlalchemy.orm.Query.
one_or_none() Optional[_T] ¶ Return at most one result or raise an exception.
Returns
None
if the query selects no rows. Raisessqlalchemy.orm.exc.MultipleResultsFound
if multiple object identities are returned, or if multiple rows are returned for a query that returns only scalar values as opposed to full identity-mapped entities.Calling
Query.one_or_none()
results in an execution of the underlying query.See also
Result.one_or_none()
- v2 comparable method.Result.scalar_one_or_none()
- v2 comparable method.
-
method
sqlalchemy.orm.Query.
only_return_tuples(value: bool) Query ¶ When set to True, the query results will always be a
Row
object.This can change a query that normally returns a single entity as a scalar to return a
Row
result in all cases.See also
Query.tuples()
- returns tuples, but also at the typing level will type results asTuple
.Result.tuples()
- v2 comparable method.
-
method
sqlalchemy.orm.Query.
options(*args: ExecutableOption) Self ¶ Return a new
Query
object, applying the given list of mapper options.Most supplied options regard changing how column- and relationship-mapped attributes are loaded.
-
method
sqlalchemy.orm.Query.
order_by(_Query__first: Union[Literal[None, False, _NoArg.NO_ARG], _ColumnExpressionOrStrLabelArgument[Any]] = _NoArg.NO_ARG, *clauses: _ColumnExpressionOrStrLabelArgument[Any]) Self ¶ Apply one or more ORDER BY criteria to the query and return the newly resulting
Query
.e.g.:
q = session.query(Entity).order_by(Entity.id, Entity.name)
Calling this method multiple times is equivalent to calling it once with all the clauses concatenated. All existing ORDER BY criteria may be cancelled by passing
None
by itself. New ORDER BY criteria may then be added by invokingQuery.order_by()
again, e.g.:# will erase all ORDER BY and ORDER BY new_col alone q = q.order_by(None).order_by(new_col)
See also
These sections describe ORDER BY in terms of 2.0 style invocation but apply to
Query
as well:ORDER BY - in the SQLAlchemy Unified Tutorial
Ordering or Grouping by a Label - in the SQLAlchemy Unified Tutorial
Select.order_by()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
outerjoin(target: _JoinTargetArgument, onclause: Optional[_OnClauseArgument] = None, *, full: bool = False) Self ¶ Create a left outer join against this
Query
object’s criterion and apply generatively, returning the newly resultingQuery
.Usage is the same as the
join()
method.See also
Select.outerjoin()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
params(_Query__params: Optional[Dict[str, Any]] = None, **kw: Any) Self ¶ Add values for bind parameters which may have been specified in filter().
Parameters may be specified using **kwargs, or optionally a single dictionary as the first positional argument. The reason for both is that **kwargs is convenient, however some parameter dictionaries contain unicode keys in which case **kwargs cannot be used.
-
method
sqlalchemy.orm.Query.
populate_existing() Self ¶ Return a
Query
that will expire and refresh all instances as they are loaded, or reused from the currentSession
.As of SQLAlchemy 1.4, the
Query.populate_existing()
method is equivalent to using thepopulate_existing
execution option at the ORM level. See the section Populate Existing for further background on this option.
-
method
sqlalchemy.orm.Query.
prefix_with(*prefixes: _TextCoercedExpressionArgument[Any], dialect: str = '*') Self ¶ inherited from the
HasPrefixes.prefix_with()
method ofHasPrefixes
Add one or more expressions following the statement keyword, i.e. SELECT, INSERT, UPDATE, or DELETE. Generative.
This is used to support backend-specific prefix keywords such as those provided by MySQL.
E.g.:
stmt = table.insert().prefix_with("LOW_PRIORITY", dialect="mysql") # MySQL 5.7 optimizer hints stmt = select(table).prefix_with( "/*+ BKA(t1) */", dialect="mysql")
Multiple prefixes can be specified by multiple calls to
HasPrefixes.prefix_with()
.- Parameters:
*prefixes – textual or
ClauseElement
construct which will be rendered following the INSERT, UPDATE, or DELETE keyword.dialect – optional string dialect name which will limit rendering of this prefix to only that dialect.
-
method
sqlalchemy.orm.Query.
reset_joinpoint() Self ¶ Return a new
Query
, where the “join point” has been reset back to the base FROM entities of the query.This method is usually used in conjunction with the
aliased=True
feature of theQuery.join()
method. See the example inQuery.join()
for how this is used.
-
method
sqlalchemy.orm.Query.
scalar() Any ¶ Return the first element of the first result or None if no rows present. If multiple rows are returned, raises MultipleResultsFound.
>>> session.query(Item).scalar() <Item> >>> session.query(Item.id).scalar() 1 >>> session.query(Item.id).filter(Item.id < 0).scalar() None >>> session.query(Item.id, Item.name).scalar() 1 >>> session.query(func.count(Parent.id)).scalar() 20
This results in an execution of the underlying query.
See also
Result.scalar()
- v2 comparable method.
-
method
sqlalchemy.orm.Query.
scalar_subquery() ScalarSelect[Any] ¶ Return the full SELECT statement represented by this
Query
, converted to a scalar subquery.Analogous to
SelectBase.scalar_subquery()
.Changed in version 1.4: The
Query.scalar_subquery()
method replaces theQuery.as_scalar()
method.See also
Select.scalar_subquery()
- v2 comparable method.
-
method
sqlalchemy.orm.Query.
select_from(*from_obj: Union[FromClauseRole, Type[Any], Inspectable[_HasClauseElement], _HasClauseElement]) Self ¶ Set the FROM clause of this
Query
explicitly.Query.select_from()
is often used in conjunction withQuery.join()
in order to control which entity is selected from on the “left” side of the join.The entity or selectable object here effectively replaces the “left edge” of any calls to
Query.join()
, when no joinpoint is otherwise established - usually, the default “join point” is the leftmost entity in theQuery
object’s list of entities to be selected.A typical example:
q = session.query(Address).select_from(User).\ join(User.addresses).\ filter(User.name == 'ed')
Which produces SQL equivalent to:
SELECT address.* FROM user JOIN address ON user.id=address.user_id WHERE user.name = :name_1
- Parameters:
*from_obj – collection of one or more entities to apply to the FROM clause. Entities can be mapped classes,
AliasedClass
objects,Mapper
objects as well as coreFromClause
elements like subqueries.
-
attribute
sqlalchemy.orm.Query.
selectable¶ Return the
Select
object emitted by thisQuery
.Used for
inspect()
compatibility, this is equivalent to:query.enable_eagerloads(False).with_labels().statement
-
method
sqlalchemy.orm.Query.
set_label_style(style: SelectLabelStyle) Self ¶ Apply column labels to the return value of Query.statement.
Indicates that this Query’s statement accessor should return a SELECT statement that applies labels to all columns in the form <tablename>_<columnname>; this is commonly used to disambiguate columns from multiple tables which have the same name.
When the Query actually issues SQL to load rows, it always uses column labeling.
Note
The
Query.set_label_style()
method only applies the output ofQuery.statement
, and not to any of the result-row invoking systems ofQuery
itself, e.g.Query.first()
,Query.all()
, etc. To execute a query usingQuery.set_label_style()
, invoke theQuery.statement
usingSession.execute()
:result = session.execute( query .set_label_style(LABEL_STYLE_TABLENAME_PLUS_COL) .statement )
New in version 1.4.
See also
Select.set_label_style()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
slice(start: int, stop: int) Self ¶ Computes the “slice” of the
Query
represented by the given indices and returns the resultingQuery
.The start and stop indices behave like the argument to Python’s built-in
range()
function. This method provides an alternative to usingLIMIT
/OFFSET
to get a slice of the query.For example,
session.query(User).order_by(User.id).slice(1, 3)
renders as
SELECT users.id AS users_id, users.name AS users_name FROM users ORDER BY users.id LIMIT ? OFFSET ? (2, 1)
-
attribute
sqlalchemy.orm.Query.
statement¶ The full SELECT statement represented by this Query.
The statement by default will not have disambiguating labels applied to the construct unless with_labels(True) is called first.
-
method
sqlalchemy.orm.Query.
subquery(name: Optional[str] = None, with_labels: bool = False, reduce_columns: bool = False) Subquery ¶ Return the full SELECT statement represented by this
Query
, embedded within anAlias
.Eager JOIN generation within the query is disabled.
See also
Select.subquery()
- v2 comparable method.- Parameters:
name – string name to be assigned as the alias; this is passed through to
FromClause.alias()
. IfNone
, a name will be deterministically generated at compile time.with_labels – if True,
with_labels()
will be called on theQuery
first to apply table-qualified labels to all columns.reduce_columns – if True,
Select.reduce_columns()
will be called on the resultingselect()
construct, to remove same-named columns where one also refers to the other via foreign key or WHERE clause equivalence.
-
method
sqlalchemy.orm.Query.
suffix_with(*suffixes: _TextCoercedExpressionArgument[Any], dialect: str = '*') Self ¶ inherited from the
HasSuffixes.suffix_with()
method ofHasSuffixes
Add one or more expressions following the statement as a whole.
This is used to support backend-specific suffix keywords on certain constructs.
E.g.:
stmt = select(col1, col2).cte().suffix_with( "cycle empno set y_cycle to 1 default 0", dialect="oracle")
Multiple suffixes can be specified by multiple calls to
HasSuffixes.suffix_with()
.- Parameters:
*suffixes – textual or
ClauseElement
construct which will be rendered following the target clause.dialect – Optional string dialect name which will limit rendering of this suffix to only that dialect.
-
method
sqlalchemy.orm.Query.
tuples() Query ¶ return a tuple-typed form of this
Query
.This method invokes the
Query.only_return_tuples()
method with a value ofTrue
, which by itself ensures that thisQuery
will always returnRow
objects, even if the query is made against a single entity. It then also at the typing level will return a “typed” query, if possible, that will type result rows asTuple
objects with typed elements.This method can be compared to the
Result.tuples()
method, which returns “self”, but from a typing perspective returns an object that will yield typedTuple
objects for results. Typing takes effect only if thisQuery
object is a typed query object already.New in version 2.0.
See also
Result.tuples()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
union(*q: Query) Self ¶ Produce a UNION of this Query against one or more queries.
e.g.:
q1 = sess.query(SomeClass).filter(SomeClass.foo=='bar') q2 = sess.query(SomeClass).filter(SomeClass.bar=='foo') q3 = q1.union(q2)
The method accepts multiple Query objects so as to control the level of nesting. A series of
union()
calls such as:x.union(y).union(z).all()
will nest on each
union()
, and produces:SELECT * FROM (SELECT * FROM (SELECT * FROM X UNION SELECT * FROM y) UNION SELECT * FROM Z)
Whereas:
x.union(y, z).all()
produces:
SELECT * FROM (SELECT * FROM X UNION SELECT * FROM y UNION SELECT * FROM Z)
Note that many database backends do not allow ORDER BY to be rendered on a query called within UNION, EXCEPT, etc. To disable all ORDER BY clauses including those configured on mappers, issue
query.order_by(None)
- the resultingQuery
object will not render ORDER BY within its SELECT statement.See also
Select.union()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
union_all(*q: Query) Self ¶ Produce a UNION ALL of this Query against one or more queries.
Works the same way as
Query.union()
. See that method for usage examples.See also
Select.union_all()
- v2 equivalent method.
-
method
sqlalchemy.orm.Query.
update(values: Dict[_DMLColumnArgument, Any], synchronize_session: SynchronizeSessionArgument = 'auto', update_args: Optional[Dict[Any, Any]] = None) int ¶ Perform an UPDATE with an arbitrary WHERE clause.
Updates rows matched by this query in the database.
E.g.:
sess.query(User).filter(User.age == 25).\ update({User.age: User.age - 10}, synchronize_session=False) sess.query(User).filter(User.age == 25).\ update({"age": User.age - 10}, synchronize_session='evaluate')
Warning
See the section ORM-Enabled INSERT, UPDATE, and DELETE statements for important caveats and warnings, including limitations when using arbitrary UPDATE and DELETE with mapper inheritance configurations.
- Parameters:
values – a dictionary with attributes names, or alternatively mapped attributes or SQL expressions, as keys, and literal values or sql expressions as values. If parameter-ordered mode is desired, the values can be passed as a list of 2-tuples; this requires that the
update.preserve_parameter_order
flag is passed to theQuery.update.update_args
dictionary as well.synchronize_session – chooses the strategy to update the attributes on objects in the session. See the section ORM-Enabled INSERT, UPDATE, and DELETE statements for a discussion of these strategies.
update_args – Optional dictionary, if present will be passed to the underlying
update()
construct as the**kw
for the object. May be used to pass dialect-specific arguments such asmysql_limit
, as well as other special arguments such asupdate.preserve_parameter_order
.
- Returns:
the count of rows matched as returned by the database’s “row count” feature.
-
method
sqlalchemy.orm.Query.
value(column: _ColumnExpressionArgument[Any]) Any ¶ Return a scalar result corresponding to the given column expression.
Deprecated since version 1.4:
Query.value()
is deprecated and will be removed in a future release. Please useQuery.with_entities()
in combination withQuery.scalar()
-
method
sqlalchemy.orm.Query.
values(*columns: _ColumnsClauseArgument[Any]) Iterable[Any] ¶ Return an iterator yielding result tuples corresponding to the given list of columns
Deprecated since version 1.4:
Query.values()
is deprecated and will be removed in a future release. Please useQuery.with_entities()
-
method
sqlalchemy.orm.Query.
where(*criterion: _ColumnExpressionArgument[bool]) Self ¶ A synonym for
Query.filter()
.New in version 1.4.
See also
Select.where()
- v2 equivalent method.
-
attribute
sqlalchemy.orm.Query.
whereclause¶ A readonly attribute which returns the current WHERE criterion for this Query.
This returned value is a SQL expression construct, or
None
if no criterion has been established.See also
Select.whereclause
- v2 equivalent property.
-
method
sqlalchemy.orm.Query.
with_entities(*entities: _ColumnsClauseArgument[Any], **_Query__kw: Any) Query[Any] ¶ Return a new
Query
replacing the SELECT list with the given entities.e.g.:
# Users, filtered on some arbitrary criterion # and then ordered by related email address q = session.query(User).\ join(User.address).\ filter(User.name.like('%ed%')).\ order_by(Address.email) # given *only* User.id==5, Address.email, and 'q', what # would the *next* User in the result be ? subq = q.with_entities(Address.email).\ order_by(None).\ filter(User.id==5).\ subquery() q = q.join((subq, subq.c.email < Address.email)).\ limit(1)
See also
Select.with_only_columns()
- v2 comparable method.
-
method
sqlalchemy.orm.Query.
with_for_update(*, nowait: bool = False, read: bool = False, of: Optional[Union[_ColumnExpressionArgument[Any], Sequence[_ColumnExpressionArgument[Any]]]] = None, skip_locked: bool = False, key_share: bool = False) Self ¶ return a new
Query
with the specified options for theFOR UPDATE
clause.The behavior of this method is identical to that of
GenerativeSelect.with_for_update()
. When called with no arguments, the resultingSELECT
statement will have aFOR UPDATE
clause appended. When additional arguments are specified, backend-specific options such asFOR UPDATE NOWAIT
orLOCK IN SHARE MODE
can take effect.E.g.:
q = sess.query(User).populate_existing().with_for_update(nowait=True, of=User)
The above query on a PostgreSQL backend will render like:
SELECT users.id AS users_id FROM users FOR UPDATE OF users NOWAIT
Warning
Using
with_for_update
in the context of eager loading relationships is not officially supported or recommended by SQLAlchemy and may not work with certain queries on various database backends. Whenwith_for_update
is successfully used with a query that involvesjoinedload()
, SQLAlchemy will attempt to emit SQL that locks all involved tables.Note
It is generally a good idea to combine the use of the
Query.populate_existing()
method when using theQuery.with_for_update()
method. The purpose ofQuery.populate_existing()
is to force all the data read from the SELECT to be populated into the ORM objects returned, even if these objects are already in the identity map.See also
GenerativeSelect.with_for_update()
- Core level method with full argument and behavioral description.Query.populate_existing()
- overwrites attributes of objects already loaded in the identity map.
-
method
sqlalchemy.orm.Query.
with_hint(selectable: _FromClauseArgument, text: str, dialect_name: str = '*') Self ¶ inherited from the
HasHints.with_hint()
method ofHasHints
Add an indexing or other executional context hint for the given selectable to this
Select
or other selectable object.The text of the hint is rendered in the appropriate location for the database backend in use, relative to the given
Table
orAlias
passed as theselectable
argument. The dialect implementation typically uses Python string substitution syntax with the token%(name)s
to render the name of the table or alias. E.g. when using Oracle, the following:select(mytable).\ with_hint(mytable, "index(%(name)s ix_mytable)")
Would render SQL as:
select /*+ index(mytable ix_mytable) */ ... from mytable
The
dialect_name
option will limit the rendering of a particular hint to a particular backend. Such as, to add hints for both Oracle and Sybase simultaneously:select(mytable).\ with_hint(mytable, "index(%(name)s ix_mytable)", 'oracle').\ with_hint(mytable, "WITH INDEX ix_mytable", 'mssql')
See also
-
method
sqlalchemy.orm.Query.
with_labels() Self ¶ Deprecated since version 2.0: The
Query.with_labels()
andQuery.apply_labels()
method is considered legacy as of the 1.x series of SQLAlchemy and becomes a legacy construct in 2.0. Use set_label_style(LABEL_STYLE_TABLENAME_PLUS_COL) instead. (Background on SQLAlchemy 2.0 at: SQLAlchemy 2.0 - Major Migration Guide)
-
method
sqlalchemy.orm.Query.
with_parent(instance: object, property: Optional[attributes.QueryableAttribute[Any]] = None, from_entity: Optional[_ExternalEntityType[Any]] = None) Self ¶ Add filtering criterion that relates the given instance to a child object or collection, using its attribute state as well as an established
relationship()
configuration.Deprecated since version 2.0: The
Query.with_parent()
method is considered legacy as of the 1.x series of SQLAlchemy and becomes a legacy construct in 2.0. Use thewith_parent()
standalone construct. (Background on SQLAlchemy 2.0 at: SQLAlchemy 2.0 - Major Migration Guide)The method uses the
with_parent()
function to generate the clause, the result of which is passed toQuery.filter()
.Parameters are the same as
with_parent()
, with the exception that the given property can be None, in which case a search is performed against thisQuery
object’s target mapper.- Parameters:
instance – An instance which has some
relationship()
.property – Class bound attribute which indicates what relationship from the instance should be used to reconcile the parent/child relationship.
from_entity – Entity in which to consider as the left side. This defaults to the “zero” entity of the
Query
itself.
-
method
sqlalchemy.orm.Query.
with_session(session: Session) Self ¶ Return a
Query
that will use the givenSession
.While the
Query
object is normally instantiated using theSession.query()
method, it is legal to build theQuery
directly without necessarily using aSession
. Such aQuery
object, or anyQuery
already associated with a differentSession
, can produce a newQuery
object associated with a target session using this method:from sqlalchemy.orm import Query query = Query([MyClass]).filter(MyClass.id == 5) result = query.with_session(my_session).one()
-
method
sqlalchemy.orm.Query.
with_statement_hint(text: str, dialect_name: str = '*') Self ¶ inherited from the
HasHints.with_statement_hint()
method ofHasHints
Add a statement hint to this
Select
or other selectable object.This method is similar to
Select.with_hint()
except that it does not require an individual table, and instead applies to the statement as a whole.Hints here are specific to the backend database and may include directives such as isolation levels, file directives, fetch directives, etc.
See also
Select.prefix_with()
- generic SELECT prefixing which also can suit some database-specific HINT syntaxes such as MySQL optimizer hints
-
method
sqlalchemy.orm.Query.
with_transformation(fn: Callable[[Query], Query]) Query ¶ Return a new
Query
object transformed by the given function.E.g.:
def filter_something(criterion): def transform(q): return q.filter(criterion) return transform q = q.with_transformation(filter_something(x==5))
This allows ad-hoc recipes to be created for
Query
objects.
-
method
sqlalchemy.orm.Query.
yield_per(count: int) Self ¶ Yield only
count
rows at a time.The purpose of this method is when fetching very large result sets (> 10K rows), to batch results in sub-collections and yield them out partially, so that the Python interpreter doesn’t need to declare very large areas of memory which is both time consuming and leads to excessive memory use. The performance from fetching hundreds of thousands of rows can often double when a suitable yield-per setting (e.g. approximately 1000) is used, even with DBAPIs that buffer rows (which are most).
As of SQLAlchemy 1.4, the
Query.yield_per()
method is equivalent to using theyield_per
execution option at the ORM level. See the section Fetching Large Result Sets with Yield Per for further background on this option.
-
method
ORM-Specific Query Constructs¶
This section has moved to Additional ORM API Constructs.