postgresqlsqlalchemyalembic

Alembic: Detected added unique constraint None on '('id',)

I am trying to use alembic in my FastAPI/SQLAlchemy app I have a strange code in migration (more details below)

INFO  [alembic.autogenerate.compare] Detected added unique constraint None on '('id',)'

Why do I have this line in migration?

All actions:

Created and applied initial migration (looks good)

alembic revision --autogenerate -m "InitialMigration"
---Connecting to PostgreSQL---
INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Will assume transactional DDL.
INFO  [alembic.autogenerate.compare] Detected added table 'tasks'
INFO  [alembic.autogenerate.compare] Detected added table 'solutions'
INFO  [alembic.autogenerate.compare] Detected added table 'tasks_files'
  Generating /usr/src/app/app/alembic/versions/05f3f7393aa7_initialmigration.py ...  done

alembic upgrade head
---Connecting to PostgreSQL---
INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Will assume transactional DDL.
INFO  [alembic.runtime.migration] Running upgrade  -> 05f3f7393aa7, InitialMigration

Migration file looks valid

def upgrade() -> None:
    # ### commands auto generated by Alembic - please adjust! ###
    op.create_table('tasks',
    sa.Column('id', sa.String(), nullable=False),
    sa.Column('external_id', sa.String(), nullable=False),
    ...
    sa.PrimaryKeyConstraint('id'),
    sa.UniqueConstraint('id')
    )

Then I added new_field column to tasks table

And migration looks strange

alembic revision --autogenerate -m "AddNewField"
---Connecting to PostgreSQL---
INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Will assume transactional DDL.
INFO  [alembic.autogenerate.compare] Detected added unique constraint None on '('id',)'
INFO  [alembic.autogenerate.compare] Detected added column 'tasks.new_field'
INFO  [alembic.autogenerate.compare] Detected added unique constraint None on '('id',)'
INFO  [alembic.autogenerate.compare] Detected added unique constraint None on '('id',)'

Migration file

def upgrade() -> None:
    # ### commands auto generated by Alembic - please adjust! ###
    op.create_unique_constraint(None, 'solutions', ['id'])
    op.add_column('tasks', sa.Column('new_field', sa.String(), nullable=True))
    op.create_unique_constraint(None, 'tasks', ['id'])
    op.create_unique_constraint(None, 'tasks_files', ['id'])
    # ### end Alembic commands ###

My model:

class Task(Base):
    __tablename__ = 'tasks'

    id = Column(String, unique=True, nullable=False, primary_key=True)
    external_id = Column(String, nullable=False)
    ...
    new_field = Column(String)
Solution

  • Removed unique=True

    from

     id = Column(String, unique=True, nullable=False, primary_key=True)

    and it solved the problem