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: sqlalchemy.sql.schema.Column, schema: Optional[Union[sqlalchemy.sql.elements.quoted_name, str]] = None)
class alembic.ddl.base.AlterColumn(name: str, column_name: str, schema: Optional[str] = None, existing_type: Optional[TypeEngine] = None, existing_nullable: Optional[bool] = None, existing_server_default: Optional[Union[TextClause, FetchedValue, Function, str]] = None, existing_comment: Optional[str] = None)
class alembic.ddl.base.AlterTable(table_name: str, schema: Optional[Union[sqlalchemy.sql.elements.quoted_name, str]] = 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: Optional[str], **kw)
class alembic.ddl.base.ColumnDefault(name: str, column_name: str, default: Optional[Union[TextClause, FetchedValue, Function, str]], **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: Optional[Computed], **kw)
class alembic.ddl.base.DropColumn(name: str, column: sqlalchemy.sql.schema.Column, schema: Optional[str] = None)
class alembic.ddl.base.IdentityColumnDefault(name: str, column_name: str, default: Optional[Identity], impl: DefaultImpl, **kw)
class alembic.ddl.base.RenameTable(old_table_name: str, new_table_name: Union[sqlalchemy.sql.elements.quoted_name, str], schema: Optional[Union[sqlalchemy.sql.elements.quoted_name, str]] = None)
alembic.ddl.base.add_column(compiler: DDLCompiler, column: Column, **kw) str
alembic.ddl.base.alter_column(compiler: DDLCompiler, name: str) str
alembic.ddl.base.alter_table(compiler: DDLCompiler, name: str, schema: Optional[str]) str
alembic.ddl.base.drop_column(compiler: DDLCompiler, name: str, **kw) str
alembic.ddl.base.format_column_name(compiler: DDLCompiler, name: Optional[Union[quoted_name, str]]) Union[quoted_name, str]
alembic.ddl.base.format_server_default(compiler: DDLCompiler, default: Optional[Union[TextClause, FetchedValue, Function, str]]) str
alembic.ddl.base.format_table_name(compiler: Compiled, name: Union[quoted_name, str], schema: Optional[Union[quoted_name, str]]) Union[quoted_name, str]
alembic.ddl.base.format_type(compiler: DDLCompiler, type_: TypeEngine) str
alembic.ddl.base.quote_dotted(name: Union[sqlalchemy.sql.elements.quoted_name, str], quote: functools.partial) Union[sqlalchemy.sql.elements.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: Optional[Connection], as_sql: bool, transactional_ddl: Optional[bool], output_buffer: Optional[StringIO], 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, schema: Optional[Union[quoted_name, str]] = None) None
add_constraint(const: Any) None
alter_column(table_name: str, column_name: str, nullable: Optional[bool] = None, server_default: Union[_ServerDefault, Literal[False]] = False, name: Optional[str] = None, type_: Optional[TypeEngine] = None, schema: Optional[str] = None, autoincrement: Optional[bool] = None, comment: Optional[Union[str, Literal[False]]] = False, existing_comment: Optional[str] = None, existing_type: Optional[TypeEngine] = None, existing_server_default: Optional[_ServerDefault] = None, existing_nullable: Optional[bool] = None, existing_autoincrement: Optional[bool] = 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: Optional[Connection]
bulk_insert(table: Union[TableClause, Table], rows: List[dict], multiinsert: bool = True) None
cast_for_batch_migrate(existing, existing_transfer, new_type)
command_terminator = ';'
compare_server_default(inspector_column, metadata_column, rendered_metadata_default, rendered_inspector_default)
compare_type(inspector_column: Column, 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

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) None
create_index(index: Index) None
create_table(table: Table) None
create_table_comment(table: Table) None
drop_column(table_name: str, column: Column, schema: Optional[str] = None, **kw) None
drop_constraint(const: Constraint) None
drop_index(index: Index) None
drop_table(table: Table) 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: Union[Update, TextClause, str], execution_options: None = None) None
classmethod get_by_dialect(dialect: Dialect) Any
identity_attrs_ignore: Tuple[str, ...] = ('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: Union[str, quoted_name], schema: Optional[Union[quoted_name, str]] = None) None
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.

New in version 1.0.11.

render_type(type_obj: TypeEngine, autogen_context: AutogenContext) Union[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], ...] = ({'NUMERIC', 'DECIMAL'},)
class alembic.ddl.impl.ImplMeta(classname: str, bases: Tuple[Type[alembic.ddl.impl.DefaultImpl]], dict_: Dict[str, Any])
class alembic.ddl.impl.Params(token0, tokens, args, kwargs)

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

property args

Alias for field number 2

property kwargs

Alias for field number 3

property token0

Alias for field number 0

property tokens

Alias for field number 1

MySQL

class alembic.ddl.mysql.MariaDBImpl(dialect: Dialect, connection: Optional[Connection], as_sql: bool, transactional_ddl: Optional[bool], output_buffer: Optional[StringIO], context_opts: Dict[str, Any])

Bases: alembic.ddl.mysql.MySQLImpl

memo: dict
class alembic.ddl.mysql.MySQLAlterDefault(name: str, column_name: str, default: _ServerDefault, schema: Optional[str] = None)

Bases: alembic.ddl.base.AlterColumn

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

Bases: alembic.ddl.base.AlterColumn

class alembic.ddl.mysql.MySQLImpl(dialect: Dialect, connection: Optional[Connection], as_sql: bool, transactional_ddl: Optional[bool], output_buffer: Optional[StringIO], context_opts: Dict[str, Any])

Bases: alembic.ddl.impl.DefaultImpl

alter_column(table_name: str, column_name: str, nullable: Optional[bool] = None, server_default: Union[_ServerDefault, Literal[False]] = False, name: Optional[str] = None, type_: Optional[TypeEngine] = None, schema: Optional[str] = None, existing_type: Optional[TypeEngine] = None, existing_server_default: Optional[_ServerDefault] = None, existing_nullable: Optional[bool] = None, autoincrement: Optional[bool] = None, existing_autoincrement: Optional[bool] = None, comment: Optional[Union[str, Literal[False]]] = False, existing_comment: Optional[str] = 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], ...] = ({'NUMERIC', 'DECIMAL'}, {'TINYINT', 'BOOL'}, {'JSON', 'LONGTEXT'})
class alembic.ddl.mysql.MySQLModifyColumn(name: str, column_name: str, schema: Optional[str] = None, newname: Optional[str] = None, type_: Optional[TypeEngine] = None, nullable: Optional[bool] = None, default: Optional[Union[_ServerDefault, Literal[False]]] = False, autoincrement: Optional[bool] = None, comment: Optional[Union[str, Literal[False]]] = False)

Bases: alembic.ddl.mysql.MySQLChangeColumn

MS-SQL

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

Bases: alembic.ddl.impl.DefaultImpl

alter_column(table_name: str, column_name: str, nullable: Optional[bool] = None, server_default: Optional[Union[_ServerDefault, Literal[False]]] = False, name: Optional[str] = None, type_: Optional[TypeEngine] = None, schema: Optional[str] = None, existing_type: Optional[TypeEngine] = None, existing_server_default: Optional[_ServerDefault] = None, existing_nullable: Optional[bool] = None, **kw: Any) None
batch_separator = 'GO'
bulk_insert(table: Union[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) None
drop_column(table_name: str, column: sqlalchemy.sql.schema.Column, schema: Optional[str] = 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, ...] = ('minvalue', 'maxvalue', 'nominvalue', 'nomaxvalue', 'cycle', 'cache', 'order', 'on_null', 'order')
memo: dict
transactional_ddl = True
type_synonyms: Tuple[Set[str], ...] = ({'NUMERIC', 'DECIMAL'}, {'VARCHAR', 'NVARCHAR'})
alembic.ddl.mssql.mssql_add_column(compiler: MSDDLCompiler, column: Column, **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: Optional[str], table_name: Union[str, quoted_name], elements: Union[Sequence[Tuple[str, str]], Sequence[Tuple[ColumnClause, str]]], where: Optional[Union[BinaryExpression, str]] = None, schema: Optional[str] = None, _orig_constraint: Optional[ExcludeConstraint] = None, **kw)

Bases: alembic.operations.ops.AddConstraintOp

Represent a create exclude constraint operation.

classmethod batch_create_exclude_constraint(operations, constraint_name, *elements, **kw)

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) Optional[Table]

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

classmethod from_constraint(constraint: sqlalchemy.dialects.postgresql.ext.ExcludeConstraint) alembic.ddl.postgresql.CreateExcludeConstraintOp
to_constraint(migration_context: Optional[MigrationContext] = None) ExcludeConstraint
class alembic.ddl.postgresql.PostgresqlColumnType(name: str, column_name: str, type_: TypeEngine, **kw)

Bases: alembic.ddl.base.AlterColumn

class alembic.ddl.postgresql.PostgresqlImpl(dialect: Dialect, connection: Optional[Connection], as_sql: bool, transactional_ddl: Optional[bool], output_buffer: Optional[StringIO], context_opts: Dict[str, Any])

Bases: alembic.ddl.impl.DefaultImpl

alter_column(table_name: str, column_name: str, nullable: Optional[bool] = None, server_default: Union[_ServerDefault, Literal[False]] = False, name: Optional[str] = None, type_: Optional[TypeEngine] = None, schema: Optional[str] = None, autoincrement: Optional[bool] = None, existing_type: Optional[TypeEngine] = None, existing_server_default: Optional[_ServerDefault] = None, existing_nullable: Optional[bool] = None, existing_autoincrement: Optional[bool] = 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_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)
create_index(index)
identity_attrs_ignore: Tuple[str, ...] = ('on_null', 'order')
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_type(type_: TypeEngine, autogen_context: AutogenContext) Union[str, Literal[False]]
transactional_ddl = True
type_synonyms: Tuple[Set[str], ...] = ({'NUMERIC', 'DECIMAL'}, {'DOUBLE PRECISION', 'FLOAT'})
alembic.ddl.postgresql.visit_column_comment(element: ColumnComment, compiler: PGDDLCompiler, **kw) str
alembic.ddl.postgresql.visit_column_type(element: alembic.ddl.postgresql.PostgresqlColumnType, compiler: PGDDLCompiler, **kw) str
alembic.ddl.postgresql.visit_identity_column(element: IdentityColumnDefault, compiler: PGDDLCompiler, **kw)
alembic.ddl.postgresql.visit_rename_table(element: alembic.ddl.base.RenameTable, compiler: PGDDLCompiler, **kw) str

SQLite

class alembic.ddl.sqlite.SQLiteImpl(dialect: Dialect, connection: Optional[Connection], as_sql: bool, transactional_ddl: Optional[bool], output_buffer: Optional[StringIO], context_opts: Dict[str, Any])

Bases: alembic.ddl.impl.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, existing_transfer: Dict[str, Union[TypeEngine, Cast]], new_type: TypeEngine) None
compare_server_default(inspector_column: Column, metadata_column: Column, rendered_metadata_default: Optional[str], rendered_inspector_default: Optional[str]) bool
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.

New in version 1.0.11.

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