DDL Internals

These are some of the constructs used to generate migration instructions. The APIs here build off of the sqlalchemy.schema.DDLElement and Custom SQL Constructs and Compilation Extension systems.

For programmatic usage of Alembic’s migration directives, the easiest route is to use the higher level functions given by Operation Directives.

class alembic.ddl.base.AddColumn(name: str, column: Column[Any], schema: quoted_name | str | None = None)

class alembic.ddl.base.AlterColumn(name: str, column_name: str, schema: str | None = None, existing_type: TypeEngine | None = None, existing_nullable: bool | None = None, existing_server_default: _ServerDefault | None = None, existing_comment: str | None = None)

class alembic.ddl.base.AlterTable(table_name: str, schema: quoted_name | str | None = None)

Represent an ALTER TABLE statement.

Only the string name and optional schema name of the table is required, not a full Table object.

class alembic.ddl.base.ColumnComment(name: str, column_name: str, comment: str | None, **kw)

class alembic.ddl.base.ColumnDefault(name: str, column_name: str, default: _ServerDefault | None, **kw)

class alembic.ddl.base.ColumnName(name: str, column_name: str, newname: str, **kw)

class alembic.ddl.base.ColumnNullable(name: str, column_name: str, nullable: bool, **kw)

class alembic.ddl.base.ColumnType(name: str, column_name: str, type_: TypeEngine, **kw)

class alembic.ddl.base.ComputedColumnDefault(name: str, column_name: str, default: Computed | None, **kw)

class alembic.ddl.base.DropColumn(name: str, column: Column[Any], schema: str | None = None)

class alembic.ddl.base.IdentityColumnDefault(name: str, column_name: str, default: Identity | None, impl: DefaultImpl, **kw)

class alembic.ddl.base.RenameTable(old_table_name: str, new_table_name: quoted_name | str, schema: quoted_name | str | None = None)

alembic.ddl.base.add_column(compiler: DDLCompiler, column: Column[Any], **kw) → str

alembic.ddl.base.alter_column(compiler: DDLCompiler, name: str) → str

alembic.ddl.base.alter_table(compiler: DDLCompiler, name: str, schema: str | None) → str

alembic.ddl.base.drop_column(compiler: DDLCompiler, name: str, **kw) → str

alembic.ddl.base.format_column_name(compiler: DDLCompiler, name: quoted_name | str | None) → quoted_name | str

alembic.ddl.base.format_server_default(compiler: DDLCompiler, default: _ServerDefault | None) → str

alembic.ddl.base.format_table_name(compiler: Compiled, name: quoted_name | str, schema: quoted_name | str | None) → quoted_name | str

alembic.ddl.base.format_type(compiler: DDLCompiler, type_: TypeEngine) → str

alembic.ddl.base.quote_dotted(name: quoted_name | str, quote: partial) → quoted_name | str

quote the elements of a dotted name

alembic.ddl.base.visit_add_column(element: AddColumn, compiler: DDLCompiler, **kw) → str

alembic.ddl.base.visit_column_default(element: ColumnDefault, compiler: DDLCompiler, **kw) → str

alembic.ddl.base.visit_column_name(element: ColumnName, compiler: DDLCompiler, **kw) → str

alembic.ddl.base.visit_column_nullable(element: ColumnNullable, compiler: DDLCompiler, **kw) → str

alembic.ddl.base.visit_column_type(element: ColumnType, compiler: DDLCompiler, **kw) → str

alembic.ddl.base.visit_computed_column(element: ComputedColumnDefault, compiler: DDLCompiler, **kw)

alembic.ddl.base.visit_drop_column(element: DropColumn, compiler: DDLCompiler, **kw) → str

alembic.ddl.base.visit_identity_column(element: IdentityColumnDefault, compiler: DDLCompiler, **kw)

alembic.ddl.base.visit_rename_table(element: RenameTable, compiler: DDLCompiler, **kw) → str

class alembic.ddl.impl.DefaultImpl(dialect: Dialect, connection: Connection | None, as_sql: bool, transactional_ddl: bool | None, output_buffer: TextIO | None, context_opts: Dict[str, Any])

Provide the entrypoint for major migration operations, including database-specific behavioral variances.

While individual SQL/DDL constructs already provide for database-specific implementations, variances here allow for entirely different sequences of operations to take place for a particular migration, such as SQL Server’s special ‘IDENTITY INSERT’ step for bulk inserts.

add_column(table_name: str, column: Column[Any], schema: str | quoted_name | None = None) → None

add_constraint(const: Any) → None

adjust_reflected_dialect_options(reflected_object: Dict[str, Any], kind: str) → Dict[str, Any]

alter_column(table_name: str, column_name: str, nullable: bool | None = None, server_default: _ServerDefault | Literal[False] = False, name: str | None = None, type_: TypeEngine | None = None, schema: str | None = None, autoincrement: bool | None = None, comment: str | Literal[False] | None = False, existing_comment: str | None = None, existing_type: TypeEngine | None = None, existing_server_default: _ServerDefault | None = None, existing_nullable: bool | None = None, existing_autoincrement: bool | None = None, **kw: Any) → None

autogen_column_reflect(inspector, table, column_info)

A hook that is attached to the ‘column_reflect’ event for when a Table is reflected from the database during the autogenerate process.

Dialects can elect to modify the information gathered here.

property bind: Connection | None

bulk_insert(table: TableClause | Table, rows: List[dict], multiinsert: bool = True) → None

cast_for_batch_migrate(existing, existing_transfer, new_type)

command_terminator = ';'

compare_indexes(metadata_index: Index, reflected_index: Index) → ComparisonResult

Compare two indexes by comparing the signature generated by create_index_sig.

This method returns a ComparisonResult.

compare_server_default(inspector_column, metadata_column, rendered_metadata_default, rendered_inspector_default)

compare_type(inspector_column: Column[Any], metadata_column: Column) → bool

Returns True if there ARE differences between the types of the two columns. Takes impl.type_synonyms into account between retrospected and metadata types

compare_unique_constraint(metadata_constraint: UniqueConstraint, reflected_constraint: UniqueConstraint) → ComparisonResult

Compare two unique constraints by comparing the two signatures.

The arguments are two tuples that contain the unique constraint and the signatures generated by create_unique_constraint_sig.

This method returns a ComparisonResult.

correct_for_autogen_constraints(conn_uniques: Set[UniqueConstraint], conn_indexes: Set[Index], metadata_unique_constraints: Set[UniqueConstraint], metadata_indexes: Set[Index]) → None

correct_for_autogen_foreignkeys(conn_fks: Set[ForeignKeyConstraint], metadata_fks: Set[ForeignKeyConstraint]) → None

create_column_comment(column: ColumnElement[Any]) → None

create_index(index: Index, **kw: Any) → None

create_table(table: Table, **kw: Any) → None

create_table_comment(table: Table) → None

drop_column(table_name: str, column: Column[Any], schema: str | None = None, **kw) → None

drop_constraint(const: Constraint) → None

drop_index(index: Index, **kw: Any) → None

drop_table(table: Table, **kw: Any) → None

drop_table_comment(table: Table) → None

emit_begin() → None

Emit the string BEGIN, or the backend-specific equivalent, on the current connection context.

This is used in offline mode and typically via EnvironmentContext.begin_transaction().

emit_commit() → None

Emit the string COMMIT, or the backend-specific equivalent, on the current connection context.

This is used in offline mode and typically via EnvironmentContext.begin_transaction().

execute(sql: Executable | str, execution_options: dict[str, Any] | None = None) → None

classmethod get_by_dialect(dialect: Dialect) → Type[DefaultImpl]

identity_attrs_ignore: Tuple[str, ...] = ('order', 'on_null')

prep_table_for_batch(batch_impl: ApplyBatchImpl, table: Table) → None

perform any operations needed on a table before a new one is created to replace it in batch mode.

the PG dialect uses this to drop constraints on the table before the new one uses those same names.

rename_table(old_table_name: str, new_table_name: str | quoted_name, schema: str | quoted_name | None = None) → None

render_ddl_sql_expr(expr: ClauseElement, is_server_default: bool = False, **kw: Any) → str

Render a SQL expression that is typically a server default, index expression, etc.

render_type(type_obj: TypeEngine, autogen_context: AutogenContext) → str | Literal[False]

requires_recreate_in_batch(batch_op: BatchOperationsImpl) → bool

Return True if the given BatchOperationsImpl would need the table to be recreated and copied in order to proceed.

Normally, only returns True on SQLite when operations other than add_column are present.

start_migrations() → None

A hook called when EnvironmentContext.run_migrations() is called.

Implementations can set up per-migration-run state here.

static_output(text: str) → None

transactional_ddl = False

type_arg_extract: Sequence[str] = ()

type_synonyms: Tuple[Set[str], ...] = ({'DECIMAL', 'NUMERIC'},)

version_table_impl(*, version_table: str, version_table_schema: str | None, version_table_pk: bool, **kw: Any) → Table

Generate a Table object which will be used as the structure for the Alembic version table.

Third party dialects may override this hook to provide an alternate structure for this Table; requirements are only that it be named based on the version_table parameter and contains at least a single string-holding column named version_num.

New in version 1.14.

class alembic.ddl.impl.ImplMeta(classname: str, bases: Tuple[Type[DefaultImpl]], dict_: Dict[str, Any])

class alembic.ddl.impl.Params(token0, tokens, args, kwargs)

Create new instance of Params(token0, tokens, args, kwargs)

args: List[str]

Alias for field number 2

kwargs: Dict[str, str]

Alias for field number 3

token0: str

Alias for field number 0

tokens: List[str]

Alias for field number 1

MySQL

class alembic.ddl.mysql.MariaDBImpl(dialect: Dialect, connection: Connection | None, as_sql: bool, transactional_ddl: bool | None, output_buffer: TextIO | None, context_opts: Dict[str, Any])

Bases: MySQLImpl

memo: dict

class alembic.ddl.mysql.MySQLAlterDefault(name: str, column_name: str, default: _ServerDefault, schema: str | None = None)

Bases: AlterColumn

class alembic.ddl.mysql.MySQLChangeColumn(name: str, column_name: str, schema: str | None = None, newname: str | None = None, type_: TypeEngine | None = None, nullable: bool | None = None, default: _ServerDefault | Literal[False] | None = False, autoincrement: bool | None = None, comment: str | Literal[False] | None = False)

Bases: AlterColumn

class alembic.ddl.mysql.MySQLImpl(dialect: Dialect, connection: Connection | None, as_sql: bool, transactional_ddl: bool | None, output_buffer: TextIO | None, context_opts: Dict[str, Any])

Bases: DefaultImpl

alter_column(table_name: str, column_name: str, nullable: bool | None = None, server_default: _ServerDefault | Literal[False] = False, name: str | None = None, type_: TypeEngine | None = None, schema: str | None = None, existing_type: TypeEngine | None = None, existing_server_default: _ServerDefault | None = None, existing_nullable: bool | None = None, autoincrement: bool | None = None, existing_autoincrement: bool | None = None, comment: str | Literal[False] | None = False, existing_comment: str | None = None, **kw: Any) → None

compare_server_default(inspector_column, metadata_column, rendered_metadata_default, rendered_inspector_default)

correct_for_autogen_constraints(conn_unique_constraints, conn_indexes, metadata_unique_constraints, metadata_indexes)

correct_for_autogen_foreignkeys(conn_fks, metadata_fks)

drop_constraint(const: Constraint) → None

memo: dict

transactional_ddl = False

type_arg_extract: Sequence[str] = ['character set ([\\w\\-_]+)', 'collate ([\\w\\-_]+)']

type_synonyms: Tuple[Set[str], ...] = ({'DECIMAL', 'NUMERIC'}, {'BOOL', 'TINYINT'}, {'JSON', 'LONGTEXT'})

class alembic.ddl.mysql.MySQLModifyColumn(name: str, column_name: str, schema: str | None = None, newname: str | None = None, type_: TypeEngine | None = None, nullable: bool | None = None, default: _ServerDefault | Literal[False] | None = False, autoincrement: bool | None = None, comment: str | Literal[False] | None = False)

Bases: MySQLChangeColumn

MS-SQL

class alembic.ddl.mssql.MSSQLImpl(*arg, **kw)

Bases: DefaultImpl

adjust_reflected_dialect_options(reflected_object: Dict[str, Any], kind: str) → Dict[str, Any]

alter_column(table_name: str, column_name: str, nullable: bool | None = None, server_default: _ServerDefault | Literal[False] | None = False, name: str | None = None, type_: TypeEngine | None = None, schema: str | None = None, existing_type: TypeEngine | None = None, existing_server_default: _ServerDefault | None = None, existing_nullable: bool | None = None, **kw: Any) → None

batch_separator = 'GO'

bulk_insert(table: TableClause | Table, rows: List[dict], **kw: Any) → None

compare_server_default(inspector_column, metadata_column, rendered_metadata_default, rendered_inspector_default)

create_index(index: Index, **kw: Any) → None

drop_column(table_name: str, column: Column[Any], schema: str | None = None, **kw) → None

emit_begin() → None

Emit the string BEGIN, or the backend-specific equivalent, on the current connection context.

This is used in offline mode and typically via EnvironmentContext.begin_transaction().

emit_commit() → None

Emit the string COMMIT, or the backend-specific equivalent, on the current connection context.

This is used in offline mode and typically via EnvironmentContext.begin_transaction().

identity_attrs_ignore: Tuple[str, ...] = ('order', 'on_null', 'minvalue', 'maxvalue', 'nominvalue', 'nomaxvalue', 'cycle', 'cache')

memo: dict

transactional_ddl = True

type_synonyms: Tuple[Set[str], ...] = ({'DECIMAL', 'NUMERIC'}, {'NVARCHAR', 'VARCHAR'})

alembic.ddl.mssql.mssql_add_column(compiler: MSDDLCompiler, column: Column[Any], **kw) → str

alembic.ddl.mssql.visit_add_column(element: AddColumn, compiler: MSDDLCompiler, **kw) → str

alembic.ddl.mssql.visit_column_default(element: ColumnDefault, compiler: MSDDLCompiler, **kw) → str

alembic.ddl.mssql.visit_column_nullable(element: ColumnNullable, compiler: MSDDLCompiler, **kw) → str

alembic.ddl.mssql.visit_column_type(element: ColumnType, compiler: MSDDLCompiler, **kw) → str

alembic.ddl.mssql.visit_rename_column(element: ColumnName, compiler: MSDDLCompiler, **kw) → str

alembic.ddl.mssql.visit_rename_table(element: RenameTable, compiler: MSDDLCompiler, **kw) → str

Postgresql

class alembic.ddl.postgresql.CreateExcludeConstraintOp(constraint_name: sqla_compat._ConstraintName, table_name: str | quoted_name, elements: Sequence[Tuple[str, str]] | Sequence[Tuple[ColumnClause[Any], str]], where: ColumnElement[bool] | str | None = None, schema: str | None = None, _orig_constraint: ExcludeConstraint | None = None, **kw)

Bases: AddConstraintOp

Represent a create exclude constraint operation.

classmethod batch_create_exclude_constraint(operations: BatchOperations, constraint_name: str, *elements: Any, **kw: Any) → Table | None

This method is proxied on the BatchOperations class, via the BatchOperations.create_exclude_constraint() method.

constraint_type = 'exclude'

classmethod create_exclude_constraint(operations: Operations, constraint_name: str, table_name: str, *elements: Any, **kw: Any) → Table | None

This method is proxied on the Operations class, via the Operations.create_exclude_constraint() method.

classmethod from_constraint(constraint: ExcludeConstraint) → CreateExcludeConstraintOp

to_constraint(migration_context: MigrationContext | None = None) → ExcludeConstraint

class alembic.ddl.postgresql.PostgresqlColumnType(name: str, column_name: str, type_: TypeEngine, **kw)

Bases: AlterColumn

class alembic.ddl.postgresql.PostgresqlImpl(dialect: Dialect, connection: Connection | None, as_sql: bool, transactional_ddl: bool | None, output_buffer: TextIO | None, context_opts: Dict[str, Any])

Bases: DefaultImpl

adjust_reflected_dialect_options(reflected_options: Dict[str, Any], kind: str) → Dict[str, Any]

alter_column(table_name: str, column_name: str, nullable: bool | None = None, server_default: _ServerDefault | Literal[False] = False, name: str | None = None, type_: TypeEngine | None = None, schema: str | None = None, autoincrement: bool | None = None, existing_type: TypeEngine | None = None, existing_server_default: _ServerDefault | None = None, existing_nullable: bool | None = None, existing_autoincrement: bool | None = None, **kw: Any) → None

autogen_column_reflect(inspector, table, column_info)

A hook that is attached to the ‘column_reflect’ event for when a Table is reflected from the database during the autogenerate process.

Dialects can elect to modify the information gathered here.

compare_indexes(metadata_index: Index, reflected_index: Index) → ComparisonResult

Compare two indexes by comparing the signature generated by create_index_sig.

This method returns a ComparisonResult.

compare_server_default(inspector_column, metadata_column, rendered_metadata_default, rendered_inspector_default)

compare_unique_constraint(metadata_constraint: UniqueConstraint, reflected_constraint: UniqueConstraint) → ComparisonResult

Compare two unique constraints by comparing the two signatures.

The arguments are two tuples that contain the unique constraint and the signatures generated by create_unique_constraint_sig.

This method returns a ComparisonResult.

correct_for_autogen_constraints(conn_unique_constraints, conn_indexes, metadata_unique_constraints, metadata_indexes)

create_index(index: Index, **kw: Any) → None

memo: dict

prep_table_for_batch(batch_impl, table)

perform any operations needed on a table before a new one is created to replace it in batch mode.

the PG dialect uses this to drop constraints on the table before the new one uses those same names.

render_ddl_sql_expr(expr: ClauseElement, is_server_default: bool = False, is_index: bool = False, **kw: Any) → str

Render a SQL expression that is typically a server default, index expression, etc.

render_type(type_: TypeEngine, autogen_context: AutogenContext) → str | Literal[False]

transactional_ddl = True

type_synonyms: Tuple[Set[str], ...] = ({'DECIMAL', 'NUMERIC'}, {'DOUBLE PRECISION', 'FLOAT'})

alembic.ddl.postgresql.visit_column_comment(element: ColumnComment, compiler: PGDDLCompiler, **kw) → str

alembic.ddl.postgresql.visit_column_type(element: PostgresqlColumnType, compiler: PGDDLCompiler, **kw) → str

alembic.ddl.postgresql.visit_identity_column(element: IdentityColumnDefault, compiler: PGDDLCompiler, **kw)

alembic.ddl.postgresql.visit_rename_table(element: RenameTable, compiler: PGDDLCompiler, **kw) → str

SQLite

class alembic.ddl.sqlite.SQLiteImpl(dialect: Dialect, connection: Connection | None, as_sql: bool, transactional_ddl: bool | None, output_buffer: TextIO | None, context_opts: Dict[str, Any])

Bases: DefaultImpl

add_constraint(const: Constraint)

autogen_column_reflect(inspector: Inspector, table: Table, column_info: Dict[str, Any]) → None

A hook that is attached to the ‘column_reflect’ event for when a Table is reflected from the database during the autogenerate process.

Dialects can elect to modify the information gathered here.

cast_for_batch_migrate(existing: Column[Any], existing_transfer: Dict[str, TypeEngine | Cast], new_type: TypeEngine) → None

compare_server_default(inspector_column: Column[Any], metadata_column: Column[Any], rendered_metadata_default: str | None, rendered_inspector_default: str | None) → bool

correct_for_autogen_constraints(conn_unique_constraints, conn_indexes, metadata_unique_constraints, metadata_indexes)

drop_constraint(const: Constraint)

memo: dict

render_ddl_sql_expr(expr: ClauseElement, is_server_default: bool = False, **kw) → str

Render a SQL expression that is typically a server default, index expression, etc.

requires_recreate_in_batch(batch_op: BatchOperationsImpl) → bool

Return True if the given BatchOperationsImpl would need the table to be recreated and copied in order to proceed.

Normally, only returns True on SQLite when operations other than add_column are present.

transactional_ddl = False

SQLite supports transactional DDL, but pysqlite does not: see: http://bugs.python.org/issue10740

alembic.ddl.sqlite.visit_column_name(element: ColumnName, compiler: DDLCompiler, **kw) → str

alembic.ddl.sqlite.visit_rename_table(element: RenameTable, compiler: DDLCompiler, **kw) → str