Functional constructs for ORM configuration.
See the SQLAlchemy object relational tutorial and mapper configuration documentation for an overview of how this module is used.
Create a BackRef object with explicit arguments, which are the same arguments one can send to relation().
Used with the backref keyword argument to relation() in place of a string argument.
Given a class (or an object), return the primary Mapper associated with the key.
If no mapper can be located, raises InvalidRequestError.
Remove all mappers that have been created thus far.
The mapped classes will return to their initial "unmapped" state and can be re-mapped with new mappers.
Provide a column-level property for use with a Mapper.
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.
Columns that aren't present in the mapper's selectable won't be persisted by the mapper and are effectively "read-only" attributes.
- *cols
- list of Column objects to be mapped.
- 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 deferred().
- extension
- an AttributeExtension instance, or list of extensions, which will be prepended to the list of attribute listeners for the resulting descriptor placed on the class. These listeners will receive append and set events before the operation proceeds, and may be used to halt (via exception throw) or change the value used in the operation.
Provide query semantics for an unmanaged attribute.
Allows a regular Python @property (descriptor) to be used in Queries and SQL constructs like a managed attribute. comparable_property wraps a descriptor with a proxy that directs operator overrides such as == (__eq__) to the supplied comparator but proxies everything else through to the original descriptor:
class MyClass(object): @property def myprop(self): return 'foo' class MyComparator(sqlalchemy.orm.interfaces.PropComparator): def __eq__(self, other): .... mapper(MyClass, mytable, properties=dict( 'myprop': comparable_property(MyComparator)))
Used with the properties dictionary sent to mapper().
Optional when used in a properties={} declaration. The Python descriptor or property to layer comparison behavior on top of.
The like-named descriptor will be automatically retreived from the mapped class if left blank in a properties declaration.
Compile all mappers that have been defined.
This is equivalent to calling compile() on any individual mapper.
Return a composite column-based property for use with a Mapper.
This is very much like a column-based property except the given class is used to represent "composite" values composed of one or more columns.
The class must implement a constructor with positional arguments matching the order of columns supplied here, as well as a __composite_values__() method which returns values in the same order.
A simple example is representing separate two columns in a table as a single, first-class "Point" object:
class Point(object): def __init__(self, x, y): self.x = x self.y = y def __composite_values__(self): return self.x, self.y def __eq__(self, other): return other is not None and self.x == other.x and self.y == other.y # and then in the mapping: ... composite(Point, mytable.c.x, mytable.c.y) ...
The composite object may have its attributes populated based on the names of the mapped columns. To override the way internal state is set, additionally implement __set_composite_values__:
- class Point(object):
- def __init__(self, x, y):
- self.some_x = x self.some_y = y
- def __composite_values__(self):
- return self.some_x, self.some_y
- def __set_composite_values__(self, x, y):
- self.some_x = x self.some_y = y
- def __eq__(self, other):
- return other is not None and self.some_x == other.x and self.some_y == other.y
Arguments are:
Return a MapperOption that will indicate to the query that the main table has been aliased.
alias is the string name or Alias object representing the alias.
Return a MapperOption that will indicate to the query that the given attribute will be eagerly loaded.
Used when feeding SQL result sets directly into query.instances(). Also bundles an EagerLazyOption to turn on eager loading in case it isn't already.
alias is the string name of an alias, or an sql.Alias object, which represents the aliased columns in the query. This argument is optional.
create a new Session.
The defaults of create_session() are the opposite of that of sessionmaker(); autoflush and expire_on_commit are false, autocommit is True. In this sense the session acts more like the "classic" SQLAlchemy 0.3 session with these defaults.
It is recommended to use the sessionmaker() function instead of create_session().
Return a MapperOption that will convert the column property of the given name into a deferred load.
Used with query.options()
Return a DeferredColumnProperty, which indicates this object attributes should only be loaded from its corresponding table column when first accessed.
Used with the properties dictionary sent to mapper().
Construct a dynamically-loading mapper property.
This property is similar to relation(), except read operations return an active Query object, which reads from the database in all cases. Items may be appended to the attribute via append(), or removed via remove(); changes will be persisted to the database during a flush(). However, no other list mutation operations are available.
A subset of arguments available to relation() are available here.
Return a MapperOption that will convert the property of the given name into an eager load.
Used with query.options().
Return a MapperOption that will convert all properties along the given dot-separated path into an eager load.
For example, this:
query.options(eagerload_all('orders.items.keywords'))...
will set all of 'orders', 'orders.items', and 'orders.items.keywords' to load in one eager load.
Used with query.options().
Return a MapperOption that will insert the given MapperExtension to the beginning of the list of extensions that will be called in the context of the Query.
Used with query.options().
Return a MapperOption that will convert the property of the given name into a lazy load.
Used with query.options().
Return a new Mapper object.
Return a MapperOption that will convert the property of the given name into a non-load.
Used with query.options().
Given an object, return the primary Mapper associated with the object instance.
Create a UNION statement used by a polymorphic mapper.
See the SQLAlchemy advanced mapping docs for an example of how this is used.
Decorate a method as the 'reconstructor' hook.
Designates a method as the "reconstructor", an __init__-like method that will be called by the ORM after the instance has been loaded from the database or otherwise reconstituted.
The reconstructor will be invoked with no arguments. Scalar (non-collection) database-mapped attributes of the instance will be available for use within the function. Eagerly-loaded collections are generally not yet available and will usually only contain the first element. ORM state changes made to objects at this stage will not be recorded for the next flush() operation, so the activity within a reconstructor should be conservative.
Provide a relationship of a primary Mapper to a secondary Mapper.
This corresponds to a parent-child or associative table relationship. The constructed class is an instance of PropertyLoader.
- argument
- a class or Mapper instance, representing the target of the relation.
- secondary
- for a many-to-many relationship, specifies the intermediary table. The secondary keyword argument should generally only be used for a table that is not otherwise expressed in any class mapping. In particular, using the Association Object Pattern is generally mutually exclusive against using the secondary keyword argument.
**kwargs follow:
- backref
- indicates the name of a property to be placed on the related mapper's class that will handle this relationship in the other direction, including synchronizing the object attributes on both sides of the relation. Can also point to a backref() construct for more configurability.
- cascade
a comma-separated list of cascade rules which determines how Session operations should be "cascaded" from parent to child. This defaults to "False", which means the default cascade should be used. The default value is "save-update, merge". Available cascades are:
save-update - cascade the "add()" operation (formerly known as save() and update())
merge - cascade the "merge()" operation
expunge - cascade the "expunge()" operation
delete - cascade the "delete()" operation
delete-orphan - if an item of the child's type with no parent is detected, mark it for deletion. Note that this option prevents a pending item of the child's class from being persisted without a parent present.
refresh-expire - cascade the expire() and refresh() operations
all - shorthand for "save-update,merge, refresh-expire, expunge, delete"
- collection_class
- a class or function that returns a new list-holding object. will be used in place of a plain list for storing elements.
- extension
- an AttributeExtension instance, or list of extensions, which will be prepended to the list of attribute listeners for the resulting descriptor placed on the class. These listeners will receive append and set events before the operation proceeds, and may be used to halt (via exception throw) or change the value used in the operation.
- foreign_keys
- a list of columns which are to be used as "foreign key" columns. this parameter should be used in conjunction with explicit primaryjoin and secondaryjoin (if needed) arguments, and the columns within the foreign_keys list should be present within those join conditions. Normally, relation() will inspect the columns within the join conditions to determine which columns are the "foreign key" columns, based on information in the Table metadata. Use this argument when no ForeignKey's are present in the join condition, or to override the table-defined foreign keys.
- join_depth=None
- when non-None, an integer value indicating how many levels deep eagerload joins should be constructed on a self-referring or cyclical relationship. The number counts how many times the same Mapper shall be present in the loading condition along a particular join branch. When left at its default of None, eager loads will automatically stop chaining joins when they encounter a mapper which is already higher up in the chain.
- lazy=(True|False|None|'dynamic')
specifies how the related items should be loaded. Values include:
- True - items should be loaded lazily when the property is first
- accessed.
- False - items should be loaded "eagerly" in the same query as that
- of the parent, using a JOIN or LEFT OUTER JOIN.
- None - no loading should occur at any time. This is to support
- "write-only" attributes, or attributes which are populated in some manner specific to the application.
- 'dynamic' - a DynaLoader will be attached, which returns a
- Query object for all read operations. The dynamic- collection supports only append() and remove() for write operations; changes to the dynamic property will not be visible until the data is flushed to the database.
- order_by
- indicates the ordering that should be applied when loading these items.
- passive_deletes=False
Indicates loading behavior during delete operations.
A value of True indicates that unloaded child items should not be loaded during a delete operation on the parent. Normally, when a parent item is deleted, all child items are loaded so that they can either be marked as deleted, or have their foreign key to the parent set to NULL. Marking this flag as True usually implies an ON DELETE <CASCADE|SET NULL> rule is in place which will handle updating/deleting child rows on the database side.
Additionally, setting the flag to the string value 'all' will disable the "nulling out" of the child foreign keys, when there is no delete or delete-orphan cascade enabled. This is typically used when a triggering or error raise scenario is in place on the database side. Note that the foreign key attributes on in-session child objects will not be changed after a flush occurs so this is a very special use-case setting.
- passive_updates=True
Indicates loading and INSERT/UPDATE/DELETE behavior when the source of a foreign key value changes (i.e. an "on update" cascade), which are typically the primary key columns of the source row.
When True, it is assumed that ON UPDATE CASCADE is configured on the foreign key in the database, and that the database will handle propagation of an UPDATE from a source column to dependent rows. Note that with databases which enforce referential integrity (i.e. Postgres, MySQL with InnoDB tables), ON UPDATE CASCADE is required for this operation. The relation() will update the value of the attribute on related items which are locally present in the session during a flush.
When False, it is assumed that the database does not enforce referential integrity and will not be issuing its own CASCADE operation for an update. The relation() will issue the appropriate UPDATE statements to the database in response to the change of a referenced key, and items locally present in the session during a flush will also be refreshed.
This flag should probably be set to False if primary key changes are expected and the database in use doesn't support CASCADE (i.e. SQLite, MySQL MyISAM tables).
- post_update
- this indicates that the relationship should be handled by a second UPDATE statement after an INSERT or before a DELETE. Currently, it also will issue an UPDATE after the instance was UPDATEd as well, although this technically should be improved. This flag is used to handle saving bi-directional dependencies between two individual rows (i.e. each row references the other), where it would otherwise be impossible to INSERT or DELETE both rows fully since one row exists before the other. Use this flag when a particular mapping arrangement will incur two rows that are dependent on each other, such as a table that has a one-to-many relationship to a set of child rows, and also has a column that references a single child row within that list (i.e. both tables contain a foreign key to each other). If a flush() operation returns an error that a "cyclical dependency" was detected, this is a cue that you might want to use post_update to "break" the cycle.
- primaryjoin
- a ClauseElement that will be used as the primary join of this child object against the parent object, or in a many-to-many relationship the join of the primary object to the association table. By default, this value is computed based on the foreign key relationships of the parent and child tables (or association table).
- remote_side
- used for self-referential relationships, indicates the column or list of columns that form the "remote side" of the relationship.
- secondaryjoin
- a ClauseElement that will be used as the join of an association table to the child object. By default, this value is computed based on the foreign key relationships of the association and child tables.
- uselist=(True|False)
- a boolean that indicates if this property should be loaded as a list or a scalar. In most cases, this value is determined automatically by relation(), based on the type and direction of the relationship - one to many forms a list, many to one forms a scalar, many to many is a list. If a scalar is desired where normally a list would be present, such as a bi-directional one-to-one relationship, set uselist to False.
- viewonly=False
- when set to True, the relation is used only for loading objects within the relationship, and has no effect on the unit-of-work flush process. Relations with viewonly can specify any kind of join conditions to provide additional views of related objects onto a parent object. Note that the functionality of a viewonly relationship has its limits - complicated join conditions may not compile into eager or lazy loaders properly. If this is the case, use an alternative method.
Provides thread-local management of Sessions.
This is a front-end function to the ScopedSession class.
Usage:
Session = scoped_session(sessionmaker(autoflush=True))
To instantiate a Session object which is part of the scoped context, instantiate normally:
session = Session()
Most session methods are available as classmethods from the scoped session:
Session.commit() Session.close()
To map classes so that new instances are saved in the current Session automatically, as well as to provide session-aware class attributes such as "query", use the mapper classmethod from the scoped session:
mapper = Session.mapper mapper(Class, table, ...)
Generate a custom-configured Session class.
The returned object is a subclass of Session, which, when instantiated with no arguments, uses the keyword arguments configured here as its constructor arguments.
It is intended that the sessionmaker() function be called within the global scope of an application, and the returned class be made available to the rest of the application as the single class used to instantiate sessions.
e.g.:
# global scope Session = sessionmaker(autoflush=False) # later, in a local scope, create and use a session: sess = Session()
Any keyword arguments sent to the constructor itself will override the "configured" keywords:
Session = sessionmaker() # bind an individual session to a connection sess = Session(bind=connection)
The class also includes a special classmethod configure(), which allows additional configurational options to take place after the custom Session class has been generated. This is useful particularly for defining the specific Engine (or engines) to which new instances of Session should be bound:
Session = sessionmaker() Session.configure(bind=create_engine('sqlite:///foo.db')) sess = Session()
Options:
Defaults to False. When True, the Session does not keep a persistent transaction running, and will acquire connections from the engine on an as-needed basis, returning them immediately after their use. Flushes will begin and commit (or possibly rollback) their own transaction if no transaction is present. When using this mode, the session.begin() method may be used to begin a transaction explicitly.
Leaving it on its default value of False means that the Session will acquire a connection and begin a transaction the first time it is used, which it will maintain persistently until rollback(), commit(), or close() is called. When the transaction is released by any of these methods, the Session is ready for the next usage, which will again acquire and maintain a new connection/transaction.
An optional dictionary, which contains more granular "bind" information than the bind parameter provides. This dictionary can map individual Table instances as well as Mapper instances to individual Engine or Connection objects. Operations which proceed relative to a particular Mapper will consult this dictionary for the direct Mapper instance as well as the mapper's mapped_table attribute in order to locate an connectable to use. The full resolution is described in the get_bind() method of Session. Usage looks like:
sess = Session(binds={ SomeMappedClass: create_engine('postgres://engine1'), somemapper: create_engine('postgres://engine2'), some_table: create_engine('postgres://engine3'), })
Also see the bind_mapper() and bind_table() methods.
Set up name as a synonym to another mapped property.
Used with the properties dictionary sent to mapper().
Any existing attributes on the class which map the key name sent to the properties dictionary will be used by the synonym to provide instance-attribute behavior (that is, any Python property object, provided by the property builtin or providing a __get__(), __set__() and __del__() method). If no name exists for the key, the synonym() creates a default getter/setter object automatically and applies it to the class.
name refers to the name of the existing mapped property, which can be any other MapperProperty including column-based properties and relations.
If map_column is True, an additional ColumnProperty is created on the mapper automatically, using the synonym's name as the keyname of the property, and the keyname of this synonym() as the name of the column to map. For example, if a table has a column named status:
class MyClass(object): def _get_status(self): return self._status def _set_status(self, value): self._status = value status = property(_get_status, _set_status) mapper(MyClass, sometable, properties={ "status":synonym("_status", map_column=True) })
The column named status will be mapped to the attribute named _status, and the status attribute on MyClass will be used to proxy access to the column-based attribute.
The proxy keyword argument is deprecated and currently does nothing; synonyms now always establish an attribute getter/setter function if one is not already available.
Return a MapperOption that will convert the column property of the given name into a non-deferred (regular column) load.
Used with query.options().
Return a MapperOption that will convert the given group of deferred column properties into a non-deferred (regular column) load.
Used with query.options().
Decorate a method as a 'validator' for one or more named properties.
Designates a method as a validator, a method which receives the name of the attribute as well as a value to be assigned, or in the case of a collection to be added to the collection. The function can then raise validation exceptions to halt the process from continuing, or can modify or replace the value before proceeding. The function should otherwise return the given value.
User-defined class instrumentation extension.
Base implementation for customizing Mapper behavior.
For each method in MapperExtension, returning a result of EXT_CONTINUE will allow processing to continue to the next MapperExtension in line or use the default functionality if there are no other extensions.
Returning EXT_STOP will halt processing of further extensions handling that method. Some methods such as load have other return requirements, see the individual documentation for details. Other than these exception cases, any return value other than EXT_CONTINUE or EXT_STOP will be interpreted as equivalent to EXT_STOP.
Receive an object instance after that instance is DELETEed.
Receive an object instance after that instance is INSERTed.
Receive an object instance after that instance is UPDATEed.
Receive an object instance before that instance is appended to a result list.
If this method returns EXT_CONTINUE, result appending will proceed normally. if this method returns any other value or None, result appending will not proceed for this instance, giving this extension an opportunity to do the appending itself, if desired.
Receive an object instance before that instance is DELETEed.
Note that no changes to the overall flush plan can be made here; this means any collection modification, save() or delete() operations which occur within this method will not take effect until the next flush call.
Receive an object instance before that instance is INSERTed into its table.
This is a good place to set up primary key values and such that aren't handled otherwise.
Column-based attributes can be modified within this method which will result in the new value being inserted. However no changes to the overall flush plan can be made; this means any collection modification or save() operations which occur within this method will not take effect until the next flush call.
Receive an object instance before that instance is UPDATEed.
Note that this method is called for all instances that are marked as "dirty", even those which have no net changes to their column-based attributes. An object is marked as dirty when any of its column-based attributes have a "set attribute" operation called or when any of its collections are modified. If, at update time, no column-based attributes have any net changes, no UPDATE statement will be issued. This means that an instance being sent to before_update is not a guarantee that an UPDATE statement will be issued (although you can affect the outcome here).
To detect if the column-based attributes on the object have net changes, and will therefore generate an UPDATE statement, use object_session(instance).is_modified(instance, include_collections=False).
Column-based attributes can be modified within this method which will result in their being updated. However no changes to the overall flush plan can be made; this means any collection modification or save() operations which occur within this method will not take effect until the next flush call.
Receive a row when a new object instance is about to be created from that row.
The method can choose to create the instance itself, or it can return EXT_CONTINUE to indicate normal object creation should take place.
Receive an instance before that instance has its attributes populated.
This usually corresponds to a newly loaded instance but may also correspond to an already-loaded instance which has unloaded attributes to be populated. The method may be called many times for a single instance, as multiple result rows are used to populate eagerly loaded collections.
If this method returns EXT_CONTINUE, instance population will proceed normally. If any other value or None is returned, instance population will not proceed, giving this extension an opportunity to populate the instance itself, if desired.
As of 0.5, most usages of this hook are obsolete. For a generic "object has been newly created from a row" hook, use reconstruct_instance(), or the @orm.reconstructor decorator.
Receive an object instance after it has been created via __new__, and after initial attribute population has occurred.
This typicically occurs when the instance is created based on incoming result rows, and is only called once for that instance's lifetime.
Note that during a result-row load, this method is called upon the first row received for this instance. If eager loaders are set to further populate collections on the instance, those will not yet be completely loaded.
Perform pre-processing on the given result row and return a new row instance.
This is called when the mapper first receives a row, before the object identity or the instance itself has been derived from that row.
defines comparison operations for MapperProperty objects.
PropComparator instances should also define an accessor 'property' which returns the MapperProperty associated with this PropComparator.
Return true if this collection contains any member that meets the given criterion.
Return true if this element references a member which meets the given criterion.
Redefine this object in terms of a polymorphic subclass.
Returns a new PropComparator from which further criterion can be evaluated.
e.g.:
query.join(Company.employees.of_type(Engineer)).\ filter(Engineer.name=='foo')
Encapsulates the object-fetching operations provided by Mappers.
add a mapped entity to the list of result columns to be returned.
Return the results represented by this Query as a list.
This results in an execution of the underlying query.
Return a Query with a specific 'autoflush' setting.
Note that a Session with autoflush=False will not autoflush, even if this flag is set to True at the Query level. Therefore this flag is usually used only to disable autoflush for a specific Query.
Perform a bulk delete query.
Deletes rows matched by this query from the database. The synchronize_session parameter chooses the strategy for the removal of matched objects from the session. Valid values are:
experimental feature. Tries to evaluate the querys criteria in Python straight on the objects in the session. If evaluation of the criteria isn't implemented, the 'fetch' strategy will be used as a fallback.
The expression evaluator currently doesn't account for differing string collations between the database and Python.
Returns the number of rows deleted, excluding any cascades.
Warning - this currently doesn't account for any foreign key/relation cascades.
apply the given filtering criterion to the query and return the newly resulting Query
the criterion is any sql.ClauseElement applicable to the WHERE clause of a select.
apply the given filtering criterion to the query and return the newly resulting Query.
Return the first result of this Query or None if the result doesn't contain any row.
This results in an execution of the underlying query.
return a Query that selects from this Query's SELECT statement.
*entities - optional list of entities which will replace those being selected.
Execute the given SELECT statement and return results.
This method bypasses all internal statement compilation, and the statement is executed without modification.
The statement argument is either a string, a select() construct, or a text() construct, and should return the set of columns appropriate to the entity class represented by this Query.
Also see the instances() method.
Return an instance of the object based on the given identifier, or None if not found.
The ident argument is a scalar or tuple of primary key column values in the order of the table def's primary key columns.
apply one or more GROUP BY criterion to the query and return the newly resulting Query
apply a HAVING criterion to the query and return the newly resulting Query.
Given a ResultProxy cursor as returned by connection.execute(), return an ORM result as an iterator.
e.g.:
result = engine.execute("select * from users") for u in session.query(User).instances(result): print u
Given a ResultProxy cursor as returned by connection.execute(), return an ORM result as an iterator.
Deprecated.
e.g.:
result = engine.execute("select * from users") for u in session.query(User).instances(result): print u
Create a join against this Query object's criterion and apply generatively, returning the newly resulting Query.
Each element in *props may be:
- a string property name, i.e. "rooms". This will join along the relation of the same name from this Query's "primary" mapper, if one is present.
- a class-mapped attribute, i.e. Houses.rooms. This will create a join from "Houses" table to that of the "rooms" relation.
- a 2-tuple containing a target class or selectable, and an "ON" clause. The ON clause can be the property name/ attribute like above, or a SQL expression.
e.g.:
# join along string attribute names session.query(Company).join('employees') session.query(Company).join('employees', 'tasks') # join the Person entity to an alias of itself, # along the "friends" relation PAlias = aliased(Person) session.query(Person).join((Palias, Person.friends)) # join from Houses to the "rooms" attribute on the # "Colonials" subclass of Houses, then join to the # "closets" relation on Room session.query(Houses).join(Colonials.rooms, Room.closets) # join from Company entities to the "employees" collection, # using "people JOIN engineers" as the target. Then join # to the "computers" collection on the Engineer entity. session.query(Company).join((people.join(engineers), 'employees'), Engineer.computers) # join from Articles to Keywords, using the "keywords" attribute. # assume this is a many-to-many relation. session.query(Article).join(Article.keywords) # same thing, but spelled out entirely explicitly # including the association table. session.query(Article).join( (article_keywords, Articles.id==article_keywords.c.article_id), (Keyword, Keyword.id==article_keywords.c.keyword_id) )
**kwargs include:
aliased - when joining, create anonymous aliases of each table. This is used for self-referential joins or multiple joins to the same table. Consider usage of the aliased(SomeClass) construct as a more explicit approach to this.
from_joinpoint - when joins are specified using string property names, locate the property from the mapper found in the most recent previous join() call, instead of from the root entity.
Return exactly one result or raise an exception.
Raises sqlalchemy.orm.NoResultError if the query selects no rows. Raisees sqlalchemy.orm.MultipleResultsError if multiple rows are selected.
This results in an execution of the underlying query.
apply one or more ORDER BY criterion to the query and return the newly resulting Query
Create a left outer join against this Query object's criterion and apply generatively, retunring the newly resulting Query.
Usage is the same as the join() method.
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.
Return a Query that will refresh all instances loaded.
This includes all entities accessed from the database, including secondary entities, eagerly-loaded collection items.
All changes present on entities which are already present in the session will be reset and the entities will all be marked "clean".
An alternative to populate_existing() is to expire the Session fully using session.expire_all().
Return a new Query with criterion corresponding to a parent instance.
Deprecated. Use sqlalchemy.orm.with_parent in conjunction with filter().
Return a newly constructed Query object, with criterion corresponding to a relationship to the given parent instance.
a persistent or detached instance which is related to class represented by this query.
return a new Query reset the 'joinpoint' of this Query reset back to the starting mapper. Subsequent generative calls will be constructed from the new joinpoint.
Note that each call to join() or outerjoin() also starts from the root.
Return the first element of the first result or None.
>>> session.query(Item).scalar() <Item> >>> session.query(Item.id).scalar() 1 >>> 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.
Set the from_obj parameter of the query and return the newly resulting Query. This replaces the table which this Query selects from with the given table.
from_obj is a single table or selectable.
apply LIMIT/OFFSET to the Query based on a range and return the newly resulting Query.
return the full SELECT statement represented by this Query, embedded within an Alias.
Perform a bulk update query.
Updates rows matched by this query in the database. The values parameter takes a dictionary with object attributes as keys and literal values or sql expressions as values. The synchronize_session parameter chooses the strategy to update the attributes on objects in the session. Valid values are:
experimental feature. Tries to evaluate the querys criteria in Python straight on the objects in the session. If evaluation of the criteria isn't implemented, the 'expire' strategy will be used as a fallback.
The expression evaluator currently doesn't account for differing string collations between the database and Python.
Returns the number of rows matched by the update.
Warning - this currently doesn't account for any foreign key/relation cascades.
Return an iterator yielding result tuples corresponding to the given list of columns
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.
Add a join criterion corresponding to a relationship to the given parent instance.
Currently, this method only works with immediate parent relationships, but in the future may be enhanced to work across a chain of parent mappers.
Load columns for descendant mappers of this Query's mapper.
Using this method will ensure that each descendant mapper's tables are included in the FROM clause, and will allow filter() criterion to be used against those tables. The resulting instances will also have those columns already loaded so that no "post fetch" of those columns will be required.
cls_or_mappers is a single class or mapper, or list of class/mappers, which inherit from this Query's mapper. Alternatively, it may also be the string '*', in which case all descending mappers will be added to the FROM clause.
selectable is a table or select() statement that will be used in place of the generated FROM clause. This argument is required if any of the desired mappers use concrete table inheritance, since SQLAlchemy currently cannot generate UNIONs among tables automatically. If used, the selectable argument must represent the full set of tables and columns mapped by every desired mapper. Otherwise, the unaccounted mapped columns will result in their table being appended directly to the FROM clause which will usually lead to incorrect results.
Yield only count rows at a time.
WARNING: use this method with caution; if the same instance is present in more than one batch of rows, end-user changes to attributes will be overwritten.
In particular, it's usually impossible to use this setting with eagerly loaded collections (i.e. any lazy=False) since those collections will be cleared for a new load when encountered in a subsequent result batch.
Runs a validation method on an attribute value to be set or appended.
Construct a new Validator.
key - name of the attribute to be validated; will be passed as the second argument to the validation method (the first is the object instance itself).
validator - an function or instance method which accepts three arguments; an instance (usually just 'self' for a method), the key name of the attribute, and the value. The function should return the same value given, unless it wishes to modify it.