una - convertir tipos de datos en postgresql

Alambique: modifique el tipo de columna con USING

Question

Intento usar alambic para convertir un campo SQLAlchemy PostgreSQL ARRAY (Texto) en un campo BIT (variable = Verdadero) para una de las columnas de mi tabla.

La columna se define actualmente como:

cols = Column(ARRAY(TEXT), nullable=False, index=True)

Quiero cambiarlo a:

cols = Column(BIT(varying=True), nullable=False, index=True)

Cambiar los tipos de columna no parece ser compatible por defecto, por lo que estoy editando el script alambique a mano. Esto es lo que tengo actualmente:

def upgrade():
    op.alter_column(
        table_name=''views'',
        column_name=''cols'',
        nullable=False,
        type_=postgresql.BIT(varying=True)
    )


def downgrade():
    op.alter_column(
        table_name=''views'',
        column_name=''cols'',
        nullable=False,
        type_=postgresql.ARRAY(sa.Text())
    )

Sin embargo, al ejecutar este script se obtiene el error:

Traceback (most recent call last):
  File "/home/home/.virtualenvs/deus_lex/bin/alembic", line 9, in <module>
    load_entry_point(''alembic==0.7.4'', ''console_scripts'', ''alembic'')()
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/config.py", line 399, in main
    CommandLine(prog=prog).main(argv=argv)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/config.py", line 393, in main
    self.run_cmd(cfg, options)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/config.py", line 376, in run_cmd
    **dict((k, getattr(options, k)) for k in kwarg)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/command.py", line 165, in upgrade
    script.run_env()
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/script.py", line 382, in run_env
    util.load_python_file(self.dir, ''env.py'')
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/util.py", line 242, in load_python_file
    module = load_module_py(module_id, path)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/compat.py", line 79, in load_module_py
    mod = imp.load_source(module_id, path, fp)
  File "./scripts/env.py", line 83, in <module>
    run_migrations_online()
  File "./scripts/env.py", line 76, in run_migrations_online
    context.run_migrations()
  File "<string>", line 7, in run_migrations
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/environment.py", line 742, in run_migrations
    self.get_context().run_migrations(**kw)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/migration.py", line 305, in run_migrations
    step.migration_fn(**kw)
  File "/home/home/deus_lex/winslow/scripts/versions/2644864bf479_store_caselist_column_views_as_bits.py", line 24, in upgrade
    type_=postgresql.BIT(varying=True)
  File "<string>", line 7, in alter_column
  File "<string>", line 1, in <lambda>
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/util.py", line 387, in go
    return fn(*arg, **kw)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/operations.py", line 470, in alter_column
    existing_autoincrement=existing_autoincrement
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/ddl/impl.py", line 147, in alter_column
    existing_nullable=existing_nullable,
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/alembic/ddl/impl.py", line 105, in _exec
    return conn.execute(construct, *multiparams, **params)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 729, in execute
    return meth(self, multiparams, params)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/sqlalchemy/sql/ddl.py", line 69, in _execute_on_connection
    return connection._execute_ddl(self, multiparams, params)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 783, in _execute_ddl
    compiled
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 958, in _execute_context
    context)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1159, in _handle_dbapi_exception
    exc_info
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/sqlalchemy/util/compat.py", line 199, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 951, in _execute_context
    context)
  File "/home/home/.virtualenvs/deus_lex/local/lib/python2.7/site-packages/sqlalchemy/engine/default.py", line 436, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.ProgrammingError: (ProgrammingError) column "cols" cannot be cast automatically to type bit varying
HINT:  Specify a USING expression to perform the conversion.
 ''ALTER TABLE views ALTER COLUMN cols TYPE BIT VARYING'' {}

¿Cómo puedo cambiar mi script con la expresión USING?

Answer 1

Desafortunadamente necesita usar SQL sin procesar ya que el alambique no emite una instrucción USING al cambiar los tipos.

Sin embargo, escribir SQL personalizado para esto es bastante fácil:

op.execute(''ALTER TABLE views ALTER COLUMN cols TYPE bit varying USING expr'')

Por supuesto, debe reemplazar expr con una expresión que convierta el tipo de datos anterior al nuevo tipo de datos.

Answer 2

Desde la versión 0.8.8, el alambic admite USING de PostgreSQL con el parámetro postgresql_using :

op.alter_column(''views'', ''cols'', type_=postgresql.BIT(varying=True), postgresql_using=''expr'')