sqlalchemy.sql.ddl

module documentation

Provides the hierarchy of DDL-defining schema items as well as routines to invoke them for a create/drop call.

Class	`AddConstraint`	Represent an ALTER TABLE ADD CONSTRAINT statement.
Class	`CreateColumn`	Represent a `_schema.Column` as rendered in a CREATE TABLE statement, via the `.CreateTable` construct.
Class	`CreateIndex`	Represent a CREATE INDEX statement.
Class	`CreateSchema`	Represent a CREATE SCHEMA statement.
Class	`CreateSequence`	Represent a CREATE SEQUENCE statement.
Class	`CreateTable`	Represent a CREATE TABLE statement.
Class	`DDL`	A literal DDL statement.
Class	`DDLElement`	Base class for DDL expression constructs.
Class	`DropConstraint`	Represent an ALTER TABLE DROP CONSTRAINT statement.
Class	`DropIndex`	Represent a DROP INDEX statement.
Class	`DropSchema`	Represent a DROP SCHEMA statement.
Class	`DropSequence`	Represent a DROP SEQUENCE statement.
Class	`DropTable`	Represent a DROP TABLE statement.
Class	`_CreateDropBase`	Base class for DDL constructs that represent CREATE and DROP or equivalents.
Class	`_DDLCompiles`	No class docstring; 1/1 class variable, 1/2 method documented
Class	`_DropView`	Semi-public 'DROP VIEW' construct.
Class	`DDLBase`	Undocumented
Class	`DropColumnComment`	Represent a COMMENT ON COLUMN IS NULL statement.
Class	`DropTableComment`	Represent a COMMENT ON TABLE '' statement.
Class	`SchemaDropper`	Undocumented
Class	`SchemaGenerator`	Undocumented
Class	`SetColumnComment`	Represent a COMMENT ON COLUMN IS statement.
Class	`SetTableComment`	Represent a COMMENT ON TABLE IS statement.
Function	`sort_tables`	Sort a collection of `_schema.Table` objects based on dependency.
Function	`sort_tables_and_constraints`	Sort a collection of `_schema.Table` / `_schema.ForeignKeyConstraint` objects.

def sort_tables(tables, skip_fn=None, extra_dependencies=None):

Sort a collection of _schema.Table objects based on dependency.

This is a dependency-ordered sort which will emit _schema.Table objects such that they will follow their dependent _schema.Table objects. Tables are dependent on another based on the presence of _schema.ForeignKeyConstraint objects as well as explicit dependencies added by _schema.Table.add_is_dependent_on.

Warning

The ._schema.sort_tables function cannot by itself accommodate automatic resolution of dependency cycles between tables, which are usually caused by mutually dependent foreign key constraints. When these cycles are detected, the foreign keys of these tables are omitted from consideration in the sort. A warning is emitted when this condition occurs, which will be an exception raise in a future release. Tables which are not part of the cycle will still be returned in dependency order.

To resolve these cycles, the :paramref:`_schema.ForeignKeyConstraint.use_alter` parameter may be applied to those constraints which create a cycle. Alternatively, the _schema.sort_tables_and_constraints function will automatically return foreign key constraints in a separate collection when cycles are detected so that they may be applied to a schema separately.

Changed in version 1.3.17: - a warning is emitted when _schema.sort_tables cannot perform a proper sort due to cyclical dependencies. This will be an exception in a future release. Additionally, the sort will continue to return other tables not involved in the cycle in dependency order which was not the case previously.

See Also

.sort_tables_and_constraints

_schema.MetaData.sorted_tables - uses this function to sort

Parameters
tables	a sequence of `_schema.Table` objects.
skip_fn	optional callable which will be passed a `_schema.ForeignKey` object; if it returns True, this constraint will not be considered as a dependency. Note this is different from the same parameter in `.sort_tables_and_constraints`, which is instead passed the owning `_schema.ForeignKeyConstraint` object.
extra_dependencies	a sequence of 2-tuples of tables which will also be considered as dependent on each other.

def sort_tables_and_constraints(tables, filter_fn=None, extra_dependencies=None, _warn_for_cycles=False):

Sort a collection of _schema.Table / _schema.ForeignKeyConstraint objects.

This is a dependency-ordered sort which will emit tuples of (Table, [ForeignKeyConstraint, ...]) such that each _schema.Table follows its dependent _schema.Table objects. Remaining _schema.ForeignKeyConstraint objects that are separate due to dependency rules not satisfied by the sort are emitted afterwards as (None, [ForeignKeyConstraint ...]).

Tables are dependent on another based on the presence of _schema.ForeignKeyConstraint objects, explicit dependencies added by _schema.Table.add_is_dependent_on, as well as dependencies stated here using the :paramref:`~.sort_tables_and_constraints.skip_fn` and/or :paramref:`~.sort_tables_and_constraints.extra_dependencies` parameters.

New in version 1.0.0.