Alembic: zmień typ kolumny za pomocą UŻYWANIA

Question

Próbuję użyć programu alembic do przekonwertowania pola SQLAlchemy PostgreSQL ARRAY (Text) do pola BIT (varying = True) dla jednej z kolumn tabeli.

Kolumna jest obecnie definiowany jako:

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

chcę go zmienić na:

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

Zmiana typów kolumn nie wydaje się być obsługiwane domyślnie, więc jestem edycji pismo alembikie ręcznie. To jest to, co mam obecnie:

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()) 
    ) 

jednak działa ten skrypt daje błąd:

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' {} 

Jak mogę zmienić mój skrypt z wyrażeniu?

Answer 1

Niestety trzeba użyć surowego SQL, ponieważ alembik nie wypowiada instrukcji USING podczas zmiany typów.

Jednak pisząc niestandardowy SQL do tego jest dość proste:

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

Oczywiście trzeba zastąpić expr z wyrazem, który przekształca stary typ danych do nowego typu danych.

Answer 2

Od wersji 0.8.8, alembic obsługuje PostgreSQL USING z parametrem postgresql_using:

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