I am using alembic to generate database migration scripts for a mysql database. I've noticed that the syntax of the generated upgrade and downgrade scripts differ slightly, whereas I thought they would basically be the same.
models.py- before
class Message_User(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(20), nullable=True)
models.py-after table modification
class Message_User(db.Model):
id = db.Column(db.Integer, primary_key=True)
tag = db.Column(db.String(15), nullable=True)
migration file - original - shows table creation
def upgrade():
op.create_table('message_user',
sa.Column('id', sa.Integer(), nullable=False),
sa.Column('name', sa.String(length=20), nullable=True)
sa.PrimaryKeyConstraint('id', name=op.f('pk_message_user'))
)
def downgrade():
op.drop_table('message_user')
migration file - after - shows table modification
def upgrade():
op.add_column('message_user', sa.Column('tag', sa.String(length=15), nullable=True))
op.drop_column('message_user', 'name')
def downgrade():
op.add_column('message_user', sa.Column('name', mysql.VARCHAR(collation='utf8_bin',
length=20), nullable=True))
op.drop_column('message_user', 'tag')
The upgrade scripts describe the changes purely in sqlalchemy terms, whereas the downgrade scripts add mysql dialect specific changes. Specifically, the upgrade script defines the type as sa.String(length=15) whereas the downgrade defines it as mysql.VARCHAR(collation='utf8_bin', length=20). In create table statements in the downgrade scripts, the autogenerated script also includes mysql_collate, mysql_default_charset and mysql_engine whereas these aren't in create table statements for upgrade scripts. I didn't see any mention of this in the alembic documentation. Does anyone know why this differs?
