class HasCacheKey(object):
Known subclasses: sqlalchemy.orm.interfaces.MapperProperty, sqlalchemy.orm.interfaces.CompileStateOption, sqlalchemy.orm.path_registry.PathRegistry, sqlalchemy.orm.path_registry.PathToken, sqlalchemy.sql.base.CacheableOptions, sqlalchemy.sql.selectable._MemoizedSelectEntities, sqlalchemy.sql.sqltypes.TableValueType, sqlalchemy.sql.traversals.MemoizedHasCacheKey
Mixin for objects which can produce a cache key.
| Class Variable | inherit_cache |
Indicate if this .HasCacheKey instance should make use of the cache key generation scheme used by its immediate superclass. |
| Class Method | _generate_cache_attrs |
generate cache key dispatcher for a new class. |
| Class Method | _generate_cache_key_for_object |
Undocumented |
| Method | _gen_cache_key |
return an optional cache key. |
| Method | _generate_cache_key |
return a cache key. |
| Class Variable | __slots__ |
Undocumented |
| Class Variable | _hierarchy_supports_caching |
private attribute which may be set to False to prevent the inherit_cache warning from being emitted for a hierarchy of subclasses. |
| Class Variable | _is_has_cache_key |
Undocumented |
sqlalchemy.dialects.mysql.match, sqlalchemy.dialects.postgresql.aggregate_order_by, sqlalchemy.dialects.postgresql.array, sqlalchemy.dialects.postgresql.array, sqlalchemy.orm.attributes.InstrumentedAttribute, sqlalchemy.sql.elements.BindParameter, sqlalchemy.sql.expression.Alias, sqlalchemy.sql.expression.Lateral, sqlalchemy.sql.expression.Subquery, sqlalchemy.sql.schema.Column, sqlalchemy.sql.selectable.Exists, sqlalchemy.sql.selectable.ScalarSelect, sqlalchemy.sql.selectable.ScalarSelect, sqlalchemy.databases.mssql.TryCast, sqlalchemy.orm.interfaces.StrategizedProperty, sqlalchemy.orm.path_registry.CachingEntityRegistry, sqlalchemy.orm.path_registry.PropRegistry, sqlalchemy.orm.path_registry.RootRegistry, sqlalchemy.orm.path_registry.SlotsEntityRegistry, sqlalchemy.orm.path_registry.TokenRegistry, sqlalchemy.orm.query.AliasOption, sqlalchemy.orm.util._ORMJoin, sqlalchemy.sql.elements.AsBoolean, sqlalchemy.sql.elements.BooleanClauseList, sqlalchemy.sql.elements.BooleanClauseList, sqlalchemy.sql.elements.CollectionAggregate, sqlalchemy.sql.elements.IndexExpression, sqlalchemy.sql.elements.ReleaseSavepointClause, sqlalchemy.sql.elements.RollbackToSavepointClause, sqlalchemy.sql.elements.SavepointClauseIndicate 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 to False, 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
:ref:`compilerext_caching` - General guideslines for setting the
.HasCacheKey.inherit_cache attribute for third-party or user
defined SQL constructs.
generate cache key dispatcher for a new class.
This sets the _generated_cache_key_traversal attribute once called so should only be called once per class.
sqlalchemy.orm.mapper.Mapper, sqlalchemy.orm.util.Bundle, sqlalchemy.sql.elements.BindParameter, sqlalchemy.sql.expression.LambdaElement, sqlalchemy.sql.functions.FunctionAsBinary, sqlalchemy.sql.schema.Table, sqlalchemy.orm.path_registry.PathToken, sqlalchemy.orm.strategy_options._UnboundLoad, sqlalchemy.sql.base.CacheableOptionsreturn an optional cache key.
The cache key is a tuple which can contain any series of objects that are hashable and also identifies this object uniquely within the presence of a larger SQL expression or statement, for the purposes of caching the resulting query.
The cache key should be based on the SQL compiled structure that would ultimately be produced. That is, two structures that are composed in exactly the same way should produce the same cache key; any difference in the structures that would affect the SQL string or the type handlers should result in a different cache key.
If a structure cannot produce a useful cache key, the NO_CACHE symbol should be added to the anon_map and the method should return None.
return a cache key.
The cache key is a tuple which can contain any series of objects that are hashable and also identifies this object uniquely within the presence of a larger SQL expression or statement, for the purposes of caching the resulting query.
The cache key should be based on the SQL compiled structure that would ultimately be produced. That is, two structures that are composed in exactly the same way should produce the same cache key; any difference in the structures that would affect the SQL string or the type handlers should result in a different cache key.
The cache key returned by this method is an instance of
.CacheKey, which consists of a tuple representing the
cache key, as well as a list of .BindParameter objects
which are extracted from the expression. While two expressions
that produce identical cache key tuples will themselves generate
identical SQL strings, the list of .BindParameter objects
indicates the bound values which may have different values in
each one; these bound parameters must be consulted in order to
execute the statement with the correct parameters.
a _expression.ClauseElement structure that does not implement
a ._gen_cache_key method and does not implement a
.traverse_internals attribute will not be cacheable; when
such an element is embedded into a larger structure, this method
will return None, indicating no cache key is available.
tuple =
sqlalchemy.orm.interfaces.MapperProperty, sqlalchemy.orm.path_registry.PathRegistry, sqlalchemy.sql.compiler._CompileLabelUndocumented
bool =
sqlalchemy.sql.ddl._DDLCompilesprivate attribute which may be set to False to prevent the inherit_cache warning from being emitted for a hierarchy of subclasses.
Currently applies to the DDLElement hierarchy which does not implement caching.