alembic-postgresql-enum

Alembic autogenerate support for creation, alteration and deletion of enums

Alembic will now automatically:

• Create enums that currently are not in postgres schema
• Remove/add/alter enum values
• Reorder enum values
• Delete unused enums from schema

If you are curious to know about analogs and reasons for this library to exist see alternatives and motivation

Usage

Install library:

pip install alembic-postgresql-enum

Add the line:

# env.py
import alembic_postgresql_enum
...

To the top of your migrations/env.py file.

Features

• Creation of enums
• Deletion of unreferenced enums
• Detection of enum values changes
  • Creation of new enum values
  • Deletion of enums values
  • Renaming of enum values
• Omitting managing enums

Creation of enum

When table is created

class MyEnum(enum.Enum):
    one = 1
    two = 2
    three = 3


class ExampleTable(BaseModel):
    test_field = Column(Integer, primary_key=True, autoincrement=False)
    enum_field = Column(postgresql.ENUM(MyEnum)) 

This code will generate migration given below:

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    # this line is generated by our library
    sa.Enum('one', 'two', 'three', name='myenum').create(op.get_bind())
    op.create_table('example_table',
    sa.Column('test_field', sa.Integer(), nullable=False),
    # create_type=False argument is now present on postgresql.ENUM as library takes care of enum creation
    sa.Column('enum_field', postgresql.ENUM('one', 'two', 'three', name='myenum', create_type=False), nullable=True),
    sa.PrimaryKeyConstraint('test_field')
    )
    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    # drop_table does not drop enum by alembic
    op.drop_table('example_table')
    # It is dropped by us
    sa.Enum('one', 'two', 'three', name='myenum').drop(op.get_bind())
    # ### end Alembic commands ###

When column is added

class MyEnum(enum.Enum):
    one = 1
    two = 2
    three = 3


class ExampleTable(BaseModel):
    test_field = Column(Integer, primary_key=True, autoincrement=False)
    # this column has just been added
    enum_field = Column(postgresql.ENUM(MyEnum)) 

This code will generate migration given below:

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    # this line is generated by our library
    sa.Enum('one', 'two', 'three', name='myenum').create(op.get_bind())
    # create_type=False argument is now present on postgresql.ENUM as library takes care of enum creation
    op.add_column('example_table', sa.Column('enum_field', postgresql.ENUM('one', 'two', 'three', name='myenum', create_type=False), nullable=False))
    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.drop_column('example_table', 'enum_field')
    # enum is explicitly dropped as it is no longer used
    sa.Enum('one', 'two', 'three', name='myenum').drop(op.get_bind())
    # ### end Alembic commands ###

Deletion of unreferenced enum

If enum is defined in postgres schema, but its mentions removed from code - It will be automatically removed

class ExampleTable(BaseModel):
    test_field = Column(Integer, primary_key=True, autoincrement=False)
    # enum_field is removed from table

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.drop_column('example_table', 'enum_field')
    sa.Enum('one', 'two', 'four', name='myenum').drop(op.get_bind())
    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    sa.Enum('one', 'two', 'four', name='myenum').create(op.get_bind())
    op.add_column('example_table', sa.Column('enum_field', postgresql.ENUM('one', 'two', 'four', name='myenum', create_type=False), autoincrement=False, nullable=True))
    # ### end Alembic commands ###

Detection of enum values changes

Can be disabled with detect_enum_values_changes configuration flag turned off

Creation of new enum values

If new enum value is defined sync_enum_values function call will be added to migration to account for it

class MyEnum(enum.Enum):
    one = 1
    two = 2
    three = 3
    four = 4 # New enum value

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.sync_enum_values(
        enum_schema='public', 
        enum_name='myenum', 
        new_values=['one', 'two', 'three', 'four'], 
        affected_columns=[TableReference(table_schema='public', table_name='example_table', column_name='enum_field')],
        enum_values_to_rename=[],
    )
    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.sync_enum_values(
        enum_schema='public', 
        enum_name='myenum', 
        new_values=['one', 'two', 'three'], 
        affected_columns=[TableReference(table_schema='public', table_name='example_table', column_name='enum_field')],
        enum_values_to_rename=[],
    )
    # ### end Alembic commands ###

Deletion of enums values

If enum value is removed it also will be detected

class MyEnum(enum.Enum):
    one = 1
    two = 2
    # three = 3 removed

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.sync_enum_values(
        enum_schema='public', 
        enum_name='myenum', 
        new_values=['one', 'two'], 
        affected_columns=[TableReference(table_schema='public', table_name='example_table', column_name='enum_field')],
        enum_values_to_rename=[],
    )
    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.sync_enum_values(
        enum_schema='public', 
        enum_name='myenum', 
        new_values=['one', 'two', 'three'], 
        affected_columns=[TableReference(table_schema='public', table_name='example_table', column_name='enum_field')],
        enum_values_to_rename=[],
    )
    # ### end Alembic commands ###

Rename enum value

In this case you must manually edit migration

class MyEnum(enum.Enum):
    one = 1
    two = 2
    three = 3 # renamed from `tree`

This code will generate this migration:

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.sync_enum_values(
        enum_schema='public', 
        enum_name='myenum', 
        new_values=['one', 'two', 'three'], 
        affected_columns=[TableReference(table_schema='public', table_name='example_table', column_name='enum_field')],
        enum_values_to_rename=[],
    )
    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.sync_enum_values(
        enum_schema='public', 
        enum_name='myenum', 
        new_values=['one', 'two', 'tree'], 
        affected_columns=[TableReference(table_schema='public', table_name='example_table', column_name='enum_field')],
        enum_values_to_rename=[],
    )
    # ### end Alembic commands ###

This migration will cause problems with existing rows that references MyEnum

So adjust migration like that

def upgrade():
    op.sync_enum_values(
        enum_schema='public', 
        enum_name='myenum', 
        new_values=['one', 'two', 'three'], 
        affected_columns=[TableReference(table_schema='public', table_name='example_table', column_name='enum_field')],
        enum_values_to_rename=[('tree', 'three')],
    )


def downgrade():
    op.sync_enum_values(
        enum_schema='public', 
        enum_name='myenum', 
        new_values=['one', 'two', 'tree'], 
        affected_columns=[TableReference(table_schema='public', table_name='example_table', column_name='enum_field')],
        enum_values_to_rename=[('three', 'tree')],
    )

Do not forget to switch places old and new values for downgrade

All defaults in postgres will be renamed automatically as well

Omitting managing enums

If configured include_name function returns False given enum will be not managed.

import alembic_postgresql_enum

def include_name(name: str) -> bool:
    return name not in ['enum-to-ignore', 'some-internal-enum']

alembic_postgresql_enum.set_configuration(
    alembic_postgresql_enum.Config(
        include_name=include_name,
    )
)

Feature is similar to sqlalchemy feature for tables

Configuration

You can configure this extension to disable parts of it, or to enable some feature flags

To do so you need to call set_configuration function after the import:

import alembic_postgresql_enum

alembic_postgresql_enum.set_configuration(
    alembic_postgresql_enum.Config(
        add_type_ignore=True,
    )
)

Available options:

• add_type_ignore (False by default) - flag that can be turned on to add # type: ignore[attr-defined] at the end of generated op.sync_enum_values calls. This is helpful if you are using type checker such as mypy. type: ignore is needed because there is no way to add new function to an existing alembic's op.

• include_name (lambda _: True bby default) - it adds ability to ignore process enum by name in similar way alembic allows to define include_name function. This property accepts function that takes enum name and returns whether it should be processed.

• drop_unused_enums (True by default) - feature flag that can be turned off to disable clean up of undeclared enums

• detect_enum_values_changes (True by default) - feature flag that can be turned off to disable generation of op.sync_enum_values.