问题
How can I add an element to an Enum field in an alembic migration when using a version of PostgreSQL older than 9.1 (which adds the ALTER TYPE for enums)? This SO question explains the direct process, but I'm not quite sure how best to translate that using alembic.
This is what I have:
new_type = sa.Enum('nonexistent_executable', 'output_limit_exceeded',
'signal', 'success', 'timed_out', name='status')
old_type = sa.Enum('nonexistent_executable', 'signal', 'success', 'timed_out',
name='status')
tcr = sa.sql.table('testcaseresult',
sa.Column('status', new_type, nullable=False))
def upgrade():
op.alter_column('testcaseresult', u'status', type_=new_type,
existing_type=old_type)
def downgrade():
op.execute(tcr.update().where(tcr.c.status==u'output_limit_exceeded')
.values(status='timed_out'))
op.alter_column('testcaseresult', u'status', type_=old_type,
existing_type=new_type)
The above unfortunately only produces ALTER TABLE testcaseresult ALTER COLUMN status TYPE status upon upgrade, which essentially does nothing.
回答1:
I decided to try to follow the postgres approach as directly as possible and came up with the following migration.
from alembic import op
import sqlalchemy as sa
old_options = ('nonexistent_executable', 'signal', 'success', 'timed_out')
new_options = sorted(old_options + ('output_limit_exceeded',))
old_type = sa.Enum(*old_options, name='status')
new_type = sa.Enum(*new_options, name='status')
tmp_type = sa.Enum(*new_options, name='_status')
tcr = sa.sql.table('testcaseresult',
sa.Column('status', new_type, nullable=False))
def upgrade():
# Create a tempoary "_status" type, convert and drop the "old" type
tmp_type.create(op.get_bind(), checkfirst=False)
op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE _status'
' USING status::text::_status')
old_type.drop(op.get_bind(), checkfirst=False)
# Create and convert to the "new" status type
new_type.create(op.get_bind(), checkfirst=False)
op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE status'
' USING status::text::status')
tmp_type.drop(op.get_bind(), checkfirst=False)
def downgrade():
# Convert 'output_limit_exceeded' status into 'timed_out'
op.execute(tcr.update().where(tcr.c.status==u'output_limit_exceeded')
.values(status='timed_out'))
# Create a tempoary "_status" type, convert and drop the "new" type
tmp_type.create(op.get_bind(), checkfirst=False)
op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE _status'
' USING status::text::_status')
new_type.drop(op.get_bind(), checkfirst=False)
# Create and convert to the "old" status type
old_type.create(op.get_bind(), checkfirst=False)
op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE status'
' USING status::text::status')
tmp_type.drop(op.get_bind(), checkfirst=False)
It appears that alembic has no direct support for the USING statement in its alter_table method.
回答2:
I used a bit simpler approach with less steps than the accepted answer, which I based this on. In this example I will pretend the enum in question is called 'status_enum', because in the accepted answer the use of 'status' for both the column and enum confused me.
from alembic import op
import sqlalchemy as sa
name = 'status_enum'
tmp_name = 'tmp_' + name
old_options = ('nonexistent_executable', 'signal', 'success', 'timed_out')
new_options = sorted(old_options + ('output_limit_exceeded',))
new_type = sa.Enum(*new_options, name=name)
old_type = sa.Enum(*old_options, name=name)
tcr = sa.sql.table('testcaseresult',
sa.Column('status', new_type, nullable=False))
def upgrade():
op.execute('ALTER TYPE ' + name + ' RENAME TO ' + tmp_name)
new_type.create(op.get_bind())
op.execute('ALTER TABLE testcaseresult ALTER COLUMN status ' +
'TYPE ' + name + ' USING status::text::' + name)
op.execute('DROP TYPE ' + tmp_name)
def downgrade():
# Convert 'output_limit_exceeded' status into 'timed_out'
op.execute(tcr.update().where(tcr.c.status=='output_limit_exceeded')
.values(status='timed_out'))
op.execute('ALTER TYPE ' + name + ' RENAME TO ' + tmp_name)
old_type.create(op.get_bind())
op.execute('ALTER TABLE testcaseresult ALTER COLUMN status ' +
'TYPE ' + name + ' USING status::text::' + name)
op.execute('DROP TYPE ' + tmp_name)
回答3:
As of Postgres 9.1 adding a new value to an enum can be done with the ALTER TYPE statement. This is complicated by the fact that it cannot be done in a transaction. However this can be worked around by committing alembic's transaction see here.
I actually had problems using the older, more verbose, solution because Postgres could not automatically convert the default for the column.
回答4:
This runs without problems:
from alembic import op
def upgrade():
op.execute("COMMIT")
op.execute("ALTER TYPE enum_type ADD VALUE 'new_value'")
def downgrade():
...
Reference
回答5:
I had the same issue trying to migrate a column type to another. I use the following requirements:
Alembic==0.9.4
SQLAlchemy==1.1.12
You can provide the argument postgresql_using as a kwarg of alembic.op.alter_column.
from alembic import op
import sqlalchemy as types
op.alter_column(
table_name='my_table',
column_name='my_column',
type_=types.NewType,
# allows to use postgresql USING
postgresql_using="my_column::PostgesEquivalentOfNewType",
)
I hope it can help.
回答6:
In straight SQL, this would work for Postgres, if the order of the things in your enum doesn't need to be exactly as above:
ALTER TYPE status ADD value 'output_limit_exceeded' after 'timed_out';
回答7:
I needed to move data while migrating types, including deleting some old types, so I figured I'd write up a more general way of doing this based on the (awesome) accepted answer (https://stackoverflow.com/a/14845740/629272). Hopefully this helps someone else in the same boat!
# This migration will move data from one column to two others based on the type
# for a given row, and modify the type of each row.
from alembic import op
import sqlalchemy as sa
from sqlalchemy.dialects import postgresql
revision = '000000000001'
down_revision = '000000000000'
branch_labels = None
depends_on = None
# This set of options makes up the old type.
example_types_old = (
'EXAMPLE_A',
'EXAMPLE_B',
'EXAMPLE_C',
)
example_type_enum_old = postgresql.ENUM(*example_types_old, name='exampletype')
# This set of options makes up the new type.
example_types_new = (
'EXAMPLE_C',
'EXAMPLE_D',
'EXAMPLE_E',
)
example_type_enum_new = postgresql.ENUM(*example_types_new, name='exampletype')
# This set of options includes everything from the old and new types.
example_types_tmp = set(example_types_old + example_types_new)
example_type_enum_tmp = postgresql.ENUM(*example_types_tmp, name='_exampletype')
# This is a table view from which we can select and update as necessary. This
# only needs to include the relevant columns which are in either the old or new
# version of the table.
examples_view = sa.Table(
# Use the name of the actual table so it is modified in the upgrade and
# downgrade.
'examples',
sa.MetaData(),
sa.Column('id', sa.Integer, primary_key=True),
# Use the _tmp type so all types are usable.
sa.Column('example_type', example_type_enum_tmp),
# This is a column from which the data will be migrated, after which the
# column will be removed.
sa.Column('example_old_column', sa.Integer),
# This is a column to which data from the old column will be added if the
# type is EXAMPLE_A.
sa.Column('example_new_column_a', sa.Integer),
# This is a column to which data from the old column will be added if the
# type is EXAMPLE_B.
sa.Column('example_new_column_b', sa.Integer),
)
def upgrade():
connection = op.get_bind()
# Add the new column to which data will be migrated.
example_new_column_a = sa.Column(
'example_new_column_a',
sa.Integer,
nullable=True
)
op.add_column('examples', example_new_column_a)
# Add the new column to which data will be migrated.
example_new_column_b = sa.Column(
'example_new_column_b',
sa.Integer,
nullable=True
)
op.add_column('examples', example_new_column_b)
# Create the temporary enum and change the example_type column to use the
# temporary enum.
# The USING statement automatically maps the old enum to the temporary one.
example_type_enum_tmp.create(connection, checkfirst=False)
# Change to the temporary type and map from the old type to the temporary
# one.
op.execute('''
ALTER TABLE examples
ALTER COLUMN example_type
TYPE _exampletype
USING example_type::text::_exampletype
''')
# Move data from example_old_column to example_new_column_a and change its
# type to EXAMPLE_D if the type is EXAMPLE_A.
connection.execute(
examples_view.update().where(
examples_view.c.example_type == 'EXAMPLE_A'
).values(
example_type='EXAMPLE_D',
example_new_column_a=examples_view.c.example_old_column,
)
)
# Move data from example_old_column to example_new_column_b and change its
# type to EXAMPLE_E if the type is EXAMPLE_B.
connection.execute(
examples_view.update().where(
examples_view.c.example_type == 'EXAMPLE_B'
).values(
example_type='EXAMPLE_E',
example_new_column_b=examples_view.c.example_old_column,
)
)
# Move any remaining data from example_old_column to example_new_column_a
# and keep its type as EXAMPLE_C.
connection.execute(
examples_view.update().where(
examples_view.c.example_type == 'EXAMPLE_C'
).values(
example_type='EXAMPLE_C',
example_new_column_a=examples_view.c.example_old_column,
)
)
# Delete the old enum now that the data with the old types have been moved.
example_type_enum_old.drop(connection, checkfirst=False)
# Create the new enum and change the example_type column to use the new
# enum.
# The USING statement automatically maps the temporary enum to the new one.
example_type_enum_new.create(connection, checkfirst=False)
op.execute('''
ALTER TABLE examples
ALTER COLUMN example_type
TYPE exampletype
USING example_type::text::exampletype
''')
# Delete the temporary enum.
example_type_enum_tmp.drop(connection, checkfirst=False)
# Remove the old column.
op.drop_column('examples', 'example_old_column')
# The downgrade just performs the opposite of all the upgrade operations but in
# reverse.
def downgrade():
connection = op.get_bind()
example_old_column = sa.Column(
'example_old_column',
sa.Integer,
nullable=True
)
op.add_column('examples', example_old_column)
example_type_enum_tmp.create(connection, checkfirst=False)
op.execute('''
ALTER TABLE examples
ALTER COLUMN example_type
TYPE _exampletype
USING example_type::text::_exampletype
''')
connection.execute(
examples_view.update().where(
examples_view.c.example_type == 'EXAMPLE_C'
).values(
example_type='EXAMPLE_C',
example_old_column=examples_view.c.example_new_column_b,
)
)
connection.execute(
examples_view.update().where(
examples_view.c.example_type == 'EXAMPLE_E'
).values(
example_type='EXAMPLE_B',
example_old_column=examples_view.c.example_new_column_b,
)
)
connection.execute(
examples_view.update().where(
examples_view.c.example_type == 'EXAMPLE_D'
).values(
example_type='EXAMPLE_A',
example_old_column=examples_view.c.example_new_column_a,
)
)
example_type_enum_old.create(connection, checkfirst=False)
op.execute('''
ALTER TABLE examples
ALTER COLUMN example_type
TYPE exampletype
USING example_type::text::exampletype
''')
example_type_enum_tmp.drop(connection, checkfirst=False)
op.drop_column('examples', 'example_new_column_b')
op.drop_column('examples', 'example_new_column_a')
回答8:
Since I got conversion errors and problems with default values, I wrote an even more generalised answer based on the accepted one:
def replace_enum_values(
name: str,
old: [str],
new: [str],
modify: [(str, str, str)]
):
"""
Replaces an enum's list of values.
Args:
name: Name of the enum
new: New list of values
old: Old list of values
modify: List of tuples of table name
and column to modify (which actively use the enum).
Assumes each column has a default val.
"""
connection = op.get_bind()
tmp_name = "{}_tmp".format(name)
# Rename old type
op.execute(
"ALTER TYPE {} RENAME TO {};"
.format(name, tmp_name)
)
# Create new type
lsl = sa.Enum(*new, name=name)
lsl.create(connection)
# Replace all usages
for (table, column) in modify:
# Get default to re-set later
default_typed = connection.execute(
"SELECT column_default "
"FROM information_schema.columns "
"WHERE table_name='{table}' "
"AND column_name='{column}';"
.format(table=table, column=column)
).first()[0] # type: str
# Is bracketed already
default = default_typed[:default_typed.index("::")]
# Set all now invalid values to default
connection.execute(
"UPDATE {table} "
"SET {column}={default} "
"WHERE {column} NOT IN {allowed};"
.format(
table=table,
column=column,
# Invalid: What isn't contained in both new and old
# Can't just remove what's not in new because we get
# a type error
allowed=tuple(set(old).intersection(set(new))),
default=default
)
)
op.execute(
"ALTER TABLE {table} "
# Default needs to be dropped first
"ALTER COLUMN {column} DROP DEFAULT,"
# Replace the tpye
"ALTER COLUMN {column} TYPE {enum_name} USING {column}::text::{enum_name},"
# Reset default
"ALTER COLUMN {column} SET DEFAULT {default};"
.format(
table=table,
column=column,
enum_name=name,
default=default
)
)
# Remove old type
op.execute("DROP TYPE {};".format(tmp_name))
This can be called from upgrade / downgrade as such:
replace_enum_values(
name='enum_name',
new=["A", "B"],
old=["A", "C"],
modify=[('some_table', 'some_column')]
)
All invalidated values will be set to server_default.
来源：https://stackoverflow.com/questions/14845203/altering-an-enum-field-using-alembic