sqlalchemy.orm.properties.ColumnProperty

class documentation

class ColumnProperty(StrategizedProperty):

Describes an object attribute that corresponds to a table column.

Public constructor is the _orm.column_property function.

Class	`Comparator`	Produce boolean, comparison, and other operators for `.ColumnProperty` attributes.
Method	`__clause_element__`	Allow the ColumnProperty to work in expression before it is turned into an instrumented attribute.
Method	`__init__`	Provide a column-level property for use with a mapping.
Method	`__str__`	Undocumented
Method	`_getcommitted`	Undocumented
Method	`_memoized_attr__deferred_column_loader`	Undocumented
Method	`_memoized_attr__raise_column_loader`	Undocumented
Method	`_memoized_attr__renders_in_subqueries`	Undocumented
Method	`copy`	Undocumented
Method	`do_init`	Perform subclass-specific initialization post-mapper-creation steps.
Method	`instrument_class`	Hook called by the Mapper to the property to initiate instrumentation of the class attribute managed by this MapperProperty.
Method	`merge`	Merge the attribute represented by this `MapperProperty` from source to destination object.
Class Variable	`__slots__`	Undocumented
Class Variable	`_links_to_entity`	True if this MapperProperty refers to a mapped entity.
Class Variable	`inherit_cache`	Indicate if this `.HasCacheKey` instance should make use of the cache key generation scheme used by its immediate superclass.
Class Variable	`strategy_wildcard_key`	Undocumented
Instance Variable	`_orig_columns`	Undocumented
Instance Variable	`active_history`	Undocumented
Instance Variable	`columns`	Undocumented
Instance Variable	`comparator_factory`	Undocumented
Instance Variable	`deferred`	Undocumented
Instance Variable	`descriptor`	Undocumented
Instance Variable	`doc`	Undocumented
Instance Variable	`expire_on_flush`	Undocumented
Instance Variable	`group`	Undocumented
Instance Variable	`info`	Undocumented
Instance Variable	`instrument`	Undocumented
Instance Variable	`raiseload`	Undocumented
Instance Variable	`strategy_key`	Undocumented
Property	`expression`	Return the primary column or expression for this ColumnProperty.

Inherited from StrategizedProperty:

Class Method	`strategy_for`	Undocumented
Class Method	`_strategy_lookup`	Undocumented
Method	`_get_context_loader`	Undocumented
Method	`_get_strategy`	Undocumented
Method	`_memoized_attr__default_path_loader_key`	Undocumented
Method	`_memoized_attr__wildcard_token`	Undocumented
Method	`create_row_processor`	Produce row processing functions and append to the given set of populators lists.
Method	`post_instrument_class`	Perform instrumentation adjustments that need to occur after init() has completed.
Method	`setup`	Called by Query for the purposes of constructing a SQL statement.
Class Variable	`_all_strategies`	Undocumented
Instance Variable	`_strategies`	Undocumented
Instance Variable	`strategy`	Undocumented

Inherited from MapperProperty (via StrategizedProperty):

Method	`__repr__`	Undocumented
Method	`_memoized_attr_info`	Info dictionary associated with the object, allowing user-defined data to be associated with this `.InspectionAttr`.
Method	`cascade_iterator`	Iterate through instances related to the given instance for a particular 'cascade', starting with this MapperProperty.
Method	`init`	Called after all mappers are created to assemble relationships between mappers and perform other post-mapper-creation initialization steps.
Method	`set_parent`	Set the parent mapper that references this MapperProperty.
Class Variable	`_cache_key_traversal`	Undocumented
Class Variable	`cascade`	The set of 'cascade' attribute names.
Class Variable	`is_property`	Part of the InspectionAttr interface; states this object is a mapper property.
Instance Variable	`_configure_finished`	Undocumented
Instance Variable	`_configure_started`	Undocumented
Instance Variable	`parent`	Undocumented
Property	`class_attribute`	Return the class-bound descriptor corresponding to this `.MapperProperty`.

Inherited from HasCacheKey (via StrategizedProperty, MapperProperty):

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	`_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

Inherited from InspectionAttr (via StrategizedProperty, MapperProperty):

Class Variable	`_is_internal_proxy`	True if this object is an internal proxy object.
Class Variable	`is_aliased_class`	True if this object is an instance of `.AliasedClass`.
Class Variable	`is_attribute`	True if this object is a Python :term:`descriptor`.
Class Variable	`is_bundle`	True if this object is an instance of `.Bundle`.
Class Variable	`is_clause_element`	True if this object is an instance of `_expression.ClauseElement`.
Class Variable	`is_instance`	True if this object is an instance of `.InstanceState`.
Class Variable	`is_mapper`	True if this object is an instance of `_orm.Mapper`.
Class Variable	`is_selectable`	Return True if this object is an instance of `_expression.Selectable`.

Inherited from MemoizedSlots (via StrategizedProperty, MapperProperty):

Method	`__getattr__`	Undocumented
Method	`_fallback_getattr`	Undocumented

def __clause_element__(self):

Allow the ColumnProperty to work in expression before it is turned into an instrumented attribute.

def __init__(self, *columns, **kwargs):

overrides sqlalchemy.orm.interfaces.MapperProperty.__init__

Provide a column-level property for use with a mapping.

Column-based properties can normally be applied to the mapper's properties dictionary using the _schema.Column element directly. Use this function when the given column is not directly present within the mapper's selectable; examples include SQL expressions, functions, and scalar SELECT queries.

The _orm.column_property function returns an instance of .ColumnProperty.

Columns that aren't present in the mapper's selectable won't be persisted by the mapper and are effectively "read-only" attributes.

See Also

:ref:`column_property_options` - to map columns while including mapping options

:ref:`mapper_column_property_sql_expressions` - to map SQL expressions

Parameters
*columns	Undocumented
**kwargs	Undocumented
cols	list of Column objects to be mapped.
active_history=False	When `True`, indicates that the "previous" value for a scalar attribute should be loaded when replaced, if not already loaded. Normally, history tracking logic for simple non-primary-key scalar values only needs to be aware of the "new" value in order to perform a flush. This flag is available for applications that make use of `.attributes.get_history` or `.Session.is_modified` which also need to know the "previous" value of the attribute.
comparator_factory	a class which extends `.ColumnProperty.Comparator` which provides custom SQL clause generation for comparison operations.
group	a group name for this property when marked as deferred.
deferred	when True, the column property is "deferred", meaning that it does not load immediately, and is instead loaded when the attribute is first accessed on an instance. See also `~sqlalchemy.orm.deferred`.
doc	optional string that will be applied as the doc on the class-bound descriptor.
expire_on_flush=True	Disable expiry on flush. A column_property() which refers to a SQL expression (and not a single table-bound column) is considered to be a "read only" property; populating it has no effect on the state of data, and it can only return database state. For this reason a column_property()'s value is expired whenever the parent object is involved in a flush, that is, has any kind of "dirty" state within a flush. Setting this parameter to `False` will have the effect of leaving any existing value present after the flush proceeds. Note however that the `.Session` with default expiration settings still expires all attributes after a `.Session.commit` call, however.
info	Optional data dictionary which will be populated into the `.MapperProperty.info` attribute of this object.
raiseload	if True, indicates the column should raise an error when undeferred, rather than loading the value. This can be altered at query time by using the `.deferred` option with raiseload=False. New in version 1.4. See Also :ref:`deferred_raiseload`

def __str__(self):

Undocumented

def _getcommitted(self, state, dict_, column, passive=attributes.PASSIVE_OFF):

Undocumented

@util.preload_module('sqlalchemy.orm.state', 'sqlalchemy.orm.strategies')
def _memoized_attr__deferred_column_loader(self):

Undocumented

@util.preload_module('sqlalchemy.orm.state', 'sqlalchemy.orm.strategies')
def _memoized_attr__raise_column_loader(self):

Undocumented

def _memoized_attr__renders_in_subqueries(self):

Undocumented

def copy(self):

Undocumented

def do_init(self):

overrides sqlalchemy.orm.interfaces.StrategizedProperty.do_init

Perform subclass-specific initialization post-mapper-creation steps.

This is a template method called by the MapperProperty object's init() method.

def instrument_class(self, mapper):

overrides sqlalchemy.orm.interfaces.MapperProperty.instrument_class

Hook called by the Mapper to the property to initiate instrumentation of the class attribute managed by this MapperProperty.

The MapperProperty here will typically call out to the attributes module to set up an InstrumentedAttribute.

This step is the first of two steps to set up an InstrumentedAttribute, and is called early in the mapper setup process.

The second step is typically the init_class_attribute step, called from StrategizedProperty via the post_instrument_class() hook. This step assigns additional state to the InstrumentedAttribute (specifically the "impl") which has been determined after the MapperProperty has determined what kind of persistence management it needs to do (e.g. scalar, object, collection, etc).

def merge(self, session, source_state, source_dict, dest_state, dest_dict, load, _recursive, _resolve_conflict_map):

overrides sqlalchemy.orm.interfaces.MapperProperty.merge

Merge the attribute represented by this MapperProperty from source to destination object.

__slots__: tuple[str, ...] =

overrides sqlalchemy.orm.interfaces.StrategizedProperty.__slots__

Undocumented

_links_to_entity: bool =

overrides sqlalchemy.orm.interfaces.MapperProperty._links_to_entity

True if this MapperProperty refers to a mapped entity.

Should only be True for RelationshipProperty, False for all others.

inherit_cache: bool =

overrides sqlalchemy.orm.interfaces.StrategizedProperty.inherit_cache

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 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.