SQL Expression Language Foundational Constructs¶
Base classes and mixins that are used to compose SQL Expression Language elements.
Object Name | Description |
---|---|
The key used to identify a SQL statement construct in the SQL compilation cache. |
|
Base class for elements of a programmatically constructed SQL expression. |
|
Establish the ability for a class to have dialect-specific arguments with defaults and constructor validation. |
|
Mixin for objects which can produce a cache key. |
|
A SQL construct where the state is stored as an un-invoked lambda. |
|
Represent a composable SQL statement as a |
- class sqlalchemy.sql.expression.CacheKey¶
The key used to identify a SQL statement construct in the SQL compilation cache.
See also
Members
Class signature
class
sqlalchemy.sql.expression.CacheKey
(builtins.tuple
)-
attribute
sqlalchemy.sql.expression.CacheKey.
bindparams: Sequence[BindParameter[Any]]¶ Alias for field number 1
-
attribute
sqlalchemy.sql.expression.CacheKey.
key: Tuple[Any, ...]¶ Alias for field number 0
-
method
sqlalchemy.sql.expression.CacheKey.
to_offline_string(statement_cache: MutableMapping[Any, str], statement: ClauseElement, parameters: _CoreSingleExecuteParams) str ¶ Generate an “offline string” form of this
CacheKey
The “offline string” is basically the string SQL for the statement plus a repr of the bound parameter values in series. Whereas the
CacheKey
object is dependent on in-memory identities in order to work as a cache key, the “offline” version is suitable for a cache that will work for other processes as well.The given
statement_cache
is a dictionary-like object where the string form of the statement itself will be cached. This dictionary should be in a longer lived scope in order to reduce the time spent stringifying statements.
-
attribute
- class sqlalchemy.sql.expression.ClauseElement¶
Base class for elements of a programmatically constructed SQL expression.
Members
compare(), compile(), get_children(), inherit_cache, params(), self_group(), unique_params()
Class signature
class
sqlalchemy.sql.expression.ClauseElement
(sqlalchemy.sql.annotation.SupportsWrappingAnnotations
,sqlalchemy.sql.cache_key.MemoizedHasCacheKey
,sqlalchemy.sql.traversals.HasCopyInternals
,sqlalchemy.sql.visitors.ExternallyTraversible
,sqlalchemy.sql.expression.CompilerElement
)-
method
sqlalchemy.sql.expression.ClauseElement.
compare(other: ClauseElement, **kw: Any) bool ¶ Compare this
ClauseElement
to the givenClauseElement
.Subclasses should override the default behavior, which is a straight identity comparison.
**kw are arguments consumed by subclass
compare()
methods and may be used to modify the criteria for comparison (seeColumnElement
).
-
method
sqlalchemy.sql.expression.ClauseElement.
compile(bind: Optional[Union[Engine, Connection]] = None, dialect: Optional[Dialect] = None, **kw: Any) Compiled ¶ inherited from the
CompilerElement.compile()
method ofCompilerElement
Compile this SQL expression.
The return value is a
Compiled
object. Callingstr()
orunicode()
on the returned value will yield a string representation of the result. TheCompiled
object also can return a dictionary of bind parameter names and values using theparams
accessor.- Parameters:
bind – An
Connection
orEngine
which can provide aDialect
in order to generate aCompiled
object. If thebind
anddialect
parameters are both omitted, a default SQL compiler is used.column_keys – Used for INSERT and UPDATE statements, a list of column names which should be present in the VALUES clause of the compiled statement. If
None
, all columns from the target table object are rendered.dialect – A
Dialect
instance which can generate aCompiled
object. This argument takes precedence over thebind
argument.compile_kwargs –
optional dictionary of additional parameters that will be passed through to the compiler within all “visit” methods. This allows any custom flag to be passed through to a custom compilation construct, for example. It is also used for the case of passing the
literal_binds
flag through:from sqlalchemy.sql import table, column, select t = table('t', column('x')) s = select(t).where(t.c.x == 5) print(s.compile(compile_kwargs={"literal_binds": True}))
-
method
sqlalchemy.sql.expression.ClauseElement.
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).
-
attribute
sqlalchemy.sql.expression.ClauseElement.
inherit_cache: Optional[bool] = None¶ inherited from the
HasCacheKey.inherit_cache
attribute ofHasCacheKey
Indicate if this
HasCacheKey
instance should make use of the cache key generation scheme used by its immediate superclass.The attribute defaults to
None
, which indicates that a construct has not yet taken into account whether or not its appropriate for it to participate in caching; this is functionally equivalent to setting the value toFalse
, except that a warning is also emitted.This flag can be set to
True
on a particular class, if the SQL that corresponds to the object does not change based on attributes which are local to this class, and not its superclass.See also
Enabling Caching Support for Custom Constructs - General guideslines for setting the
HasCacheKey.inherit_cache
attribute for third-party or user defined SQL constructs.
-
method
sqlalchemy.sql.expression.ClauseElement.
params(_ClauseElement__optionaldict: Optional[Mapping[str, Any]] = None, **kwargs: Any) Self ¶ Return a copy with
bindparam()
elements replaced.Returns a copy of this ClauseElement with
bindparam()
elements replaced with values taken from the given dictionary:>>> clause = column('x') + bindparam('foo') >>> print(clause.compile().params) {'foo':None} >>> print(clause.params({'foo':7}).compile().params) {'foo':7}
-
method
sqlalchemy.sql.expression.ClauseElement.
self_group(against: Optional[OperatorType] = None) ClauseElement ¶ Apply a ‘grouping’ to this
ClauseElement
.This method is overridden by subclasses to return a “grouping” construct, i.e. parenthesis. In particular it’s used by “binary” expressions to provide a grouping around themselves when placed into a larger expression, as well as by
select()
constructs when placed into the FROM clause of anotherselect()
. (Note that subqueries should be normally created using theSelect.alias()
method, as many platforms require nested SELECT statements to be named).As expressions are composed together, the application of
self_group()
is automatic - end-user code should never need to use this method directly. Note that SQLAlchemy’s clause constructs take operator precedence into account - so parenthesis might not be needed, for example, in an expression likex OR (y AND z)
- AND takes precedence over OR.The base
self_group()
method ofClauseElement
just returns self.
-
method
sqlalchemy.sql.expression.ClauseElement.
unique_params(_ClauseElement__optionaldict: Optional[Dict[str, Any]] = None, **kwargs: Any) Self ¶ Return a copy with
bindparam()
elements replaced.Same functionality as
ClauseElement.params()
, except adds unique=True to affected bind parameters so that multiple statements can be used.
-
method
- class sqlalchemy.sql.base.DialectKWArgs¶
Establish the ability for a class to have dialect-specific arguments with defaults and constructor validation.
The
DialectKWArgs
interacts with theDefaultDialect.construct_arguments
present on a dialect.Members
See also
-
classmethod
sqlalchemy.sql.base.DialectKWArgs.
argument_for(dialect_name, argument_name, default)¶ Add a new kind of dialect-specific keyword argument for this class.
E.g.:
Index.argument_for("mydialect", "length", None) some_index = Index('a', 'b', mydialect_length=5)
The
DialectKWArgs.argument_for()
method is a per-argument way adding extra arguments to theDefaultDialect.construct_arguments
dictionary. This dictionary provides a list of argument names accepted by various schema-level constructs on behalf of a dialect.New dialects should typically specify this dictionary all at once as a data member of the dialect class. The use case for ad-hoc addition of argument names is typically for end-user code that is also using a custom compilation scheme which consumes the additional arguments.
- Parameters:
dialect_name – name of a dialect. The dialect must be locatable, else a
NoSuchModuleError
is raised. The dialect must also include an existingDefaultDialect.construct_arguments
collection, indicating that it participates in the keyword-argument validation and default system, elseArgumentError
is raised. If the dialect does not include this collection, then any keyword argument can be specified on behalf of this dialect already. All dialects packaged within SQLAlchemy include this collection, however for third party dialects, support may vary.argument_name – name of the parameter.
default – default value of the parameter.
-
attribute
sqlalchemy.sql.base.DialectKWArgs.
dialect_kwargs¶ A collection of keyword arguments specified as dialect-specific options to this construct.
The arguments are present here in their original
<dialect>_<kwarg>
format. Only arguments that were actually passed are included; unlike theDialectKWArgs.dialect_options
collection, which contains all options known by this dialect including defaults.The collection is also writable; keys are accepted of the form
<dialect>_<kwarg>
where the value will be assembled into the list of options.See also
DialectKWArgs.dialect_options
- nested dictionary form
-
attribute
sqlalchemy.sql.base.DialectKWArgs.
dialect_options¶ A collection of keyword arguments specified as dialect-specific options to this construct.
This is a two-level nested registry, keyed to
<dialect_name>
and<argument_name>
. For example, thepostgresql_where
argument would be locatable as:arg = my_object.dialect_options['postgresql']['where']
New in version 0.9.2.
See also
DialectKWArgs.dialect_kwargs
- flat dictionary form
-
attribute
sqlalchemy.sql.base.DialectKWArgs.
kwargs¶ A synonym for
DialectKWArgs.dialect_kwargs
.
-
classmethod
- class sqlalchemy.sql.traversals.HasCacheKey¶
Mixin for objects which can produce a cache key.
This class is usually in a hierarchy that starts with the
HasTraverseInternals
base, but this is optional. Currently, the class should be able to work on its own without includingHasTraverseInternals
.Members
-
attribute
sqlalchemy.sql.traversals.HasCacheKey.
inherit_cache: Optional[bool] = None¶ Indicate if this
HasCacheKey
instance should make use of the cache key generation scheme used by its immediate superclass.The attribute defaults to
None
, which indicates that a construct has not yet taken into account whether or not its appropriate for it to participate in caching; this is functionally equivalent to setting the value toFalse
, except that a warning is also emitted.This flag can be set to
True
on a particular class, if the SQL that corresponds to the object does not change based on attributes which are local to this class, and not its superclass.See also
Enabling Caching Support for Custom Constructs - General guideslines for setting the
HasCacheKey.inherit_cache
attribute for third-party or user defined SQL constructs.
-
attribute
- class sqlalchemy.sql.expression.LambdaElement¶
A SQL construct where the state is stored as an un-invoked lambda.
The
LambdaElement
is produced transparently whenever passing lambda expressions into SQL constructs, such as:stmt = select(table).where(lambda: table.c.col == parameter)
The
LambdaElement
is the base of theStatementLambdaElement
which represents a full statement within a lambda.New in version 1.4.
Class signature
class
sqlalchemy.sql.expression.LambdaElement
(sqlalchemy.sql.expression.ClauseElement
)
- class sqlalchemy.sql.expression.StatementLambdaElement¶
Represent a composable SQL statement as a
LambdaElement
.The
StatementLambdaElement
is constructed using thelambda_stmt()
function:from sqlalchemy import lambda_stmt stmt = lambda_stmt(lambda: select(table))
Once constructed, additional criteria can be built onto the statement by adding subsequent lambdas, which accept the existing statement object as a single parameter:
stmt += lambda s: s.where(table.c.col == parameter)
New in version 1.4.
Class signature
class
sqlalchemy.sql.expression.StatementLambdaElement
(sqlalchemy.sql.roles.AllowsLambdaRole
,sqlalchemy.sql.lambdas.LambdaElement
,sqlalchemy.sql.expression.Executable
)-
method
sqlalchemy.sql.expression.StatementLambdaElement.
add_criteria(other: Callable[[Any], Any], enable_tracking: bool = True, track_on: Optional[Any] = None, track_closure_variables: bool = True, track_bound_values: bool = True) StatementLambdaElement ¶ Add new criteria to this
StatementLambdaElement
.E.g.:
>>> def my_stmt(parameter): ... stmt = lambda_stmt( ... lambda: select(table.c.x, table.c.y), ... ) ... stmt = stmt.add_criteria( ... lambda: table.c.x > parameter ... ) ... return stmt
The
StatementLambdaElement.add_criteria()
method is equivalent to using the Python addition operator to add a new lambda, except that additional arguments may be added includingtrack_closure_values
andtrack_on
:>>> def my_stmt(self, foo): ... stmt = lambda_stmt( ... lambda: select(func.max(foo.x, foo.y)), ... track_closure_variables=False ... ) ... stmt = stmt.add_criteria( ... lambda: self.where_criteria, ... track_on=[self] ... ) ... return stmt
See
lambda_stmt()
for a description of the parameters accepted.
-
attribute
sqlalchemy.sql.expression.StatementLambdaElement.
is_delete¶
-
attribute
sqlalchemy.sql.expression.StatementLambdaElement.
is_dml¶
-
attribute
sqlalchemy.sql.expression.StatementLambdaElement.
is_insert¶
-
attribute
sqlalchemy.sql.expression.StatementLambdaElement.
is_select¶
-
attribute
sqlalchemy.sql.expression.StatementLambdaElement.
is_text¶
-
attribute
sqlalchemy.sql.expression.StatementLambdaElement.
is_update¶
-
method
sqlalchemy.sql.expression.StatementLambdaElement.
spoil() NullLambdaStatement ¶ Return a new
StatementLambdaElement
that will run all lambdas unconditionally each time.
-
method