Alembic: alter tipo di colonna con l'utilizzo di

Question

Sto tentando di usare alambicco per convertire un campo SQLAlchemy PostgreSQL ARRAY (Testo) per un campo di bit (variabile = True) per una delle mie colonne della tabella.

La colonna è attualmente definito come:

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

voglio cambiarlo:

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

Modifica tipi di colonna non sembra essere supportata di default, quindi sto modificando il copione alambicco a mano. Questo è quello che ho attualmente:

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()) 
    ) 

Tuttavia, l'esecuzione di questo script dà l'errore:

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' {} 

Come posso cambiare il mio script con l'espressione utilizzando?

Answer 1

Purtroppo è necessario utilizzare SQL crudo come alambicco non emette una dichiarazione USING mai quando si cambia tipo.

Tuttavia, la scrittura SQL personalizzato per questo è abbastanza facile:

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

Ovviamente dovete sostituire expr con un'espressione che converte il vecchio tipo di dati per il nuovo tipo di dati.

Answer 2

A partire dalla versione 0.8.8, alambicco supporta PostgreSQL di USING con il parametro postgresql_using:

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