more straightforward would be a pull request that adds "mysql_after" keyword to both op.add_column() and op.modify_column().
On Fri, Jul 7, 2017 at 1:33 AM, <tjhn...@gmail.com> wrote: > > > On Tuesday, August 27, 2013 at 9:31:29 AM UTC-5, Michael Bayer wrote: >> >> >> On Aug 26, 2013, at 11:49 PM, Samer Atiani <sat...@gmail.com> wrote: >> >> Hello, >> >> All my tables have create_date and update_date columns in them, and I like >> to keep these columns as the last two columns in any table for convention >> reasons. However, when you use alembic autogenerate to generate schema >> migrations to add columns, the columns are always added to the end of the >> table. With time, the create_date and update_date columns in my tables will >> end up being in the middle of the column list in my MySQL database. >> >> So I was trying to alter this behavior by making alembic use MySQL's >> "ALTER TABLE x ADD COLUMN y AFTER z" feature to always try to add columns >> before create_date or update_date. The only way I could find out how is to >> override the visit_add_column method after EnvironmentContext configuration. >> I achieved this by changing the "run_migrations_online()" method in >> alembic/env.py so that it looks like: >> >> >> However, this feels quite brittle and is probably touching internal stuff >> that it shouldn't touch. My question to you is: is there a better way to >> achieve this? I looked at SQLAlchemy Core Events, but I couldn't find an >> event that could correspond to adding columns, nor is the alembic code >> firing any events I could see when it add columns (unlike, for example, when >> it emits a CREATE TABLE statements). >> >> >> >> AddColumn is a SQL expression element so the standard way we want to >> override those is to use @compiles >> (http://docs.sqlalchemy.org/en/rel_0_8/core/compiler.html#changing-the-default-compilation-of-existing-constructs). >> As you might have noticed, Alembic is already using that system internally >> in order to provide compile rules for constructs. So we want to override >> that, however the roadblock is that the @compiles system currently doesn't >> have a nice way of letting us override the @compiles of an existing >> @compiles (should be added as a feature). So there's a slight bit of >> internals we need to get at Alembic's already present @compiles rule for >> now, but the rest is straightforward: >> >> from sqlalchemy.ext.compiler import compiles >> from alembic.ddl.base import AddColumn >> >> # ideally, the @compiles system would have some way of getting >> # us the "existing" @compiles decorator, so this part is the >> # hack >> specs = AddColumn.__dict__.get('_compiler_dispatcher').specs >> existing_dispatch = specs.get('mysql', specs['default']) >> >> @compiles(AddColumn, "mysql") >> def add_column(element, compiler, **kw): >> text = existing_dispatch(element, compiler, **kw) >> if "after" in element.column.info: >> text += " AFTER %s" % element.column.info['after'] >> return text >> >> from sqlalchemy import Column, Integer >> from alembic.migration import MigrationContext >> from alembic.operations import Operations >> >> ctx = MigrationContext.configure(dialect_name="mysql", opts={"as_sql": >> True}) >> op = Operations(ctx) >> >> op.add_column("t", Column('y', Integer)) >> >> op.add_column("t", Column('x', Integer, info={"after": "y"})) > > > > I'm interested in applying a similar solution to handle alter columns. > > The problem I'm seeing is that MySQLImpl.alter_column() does not pass *kw > to MySQLChangeColumn or MySQLModifyColumn. So there doesn't seem to be a > simple way that I can write a @compiles(MySQLChangeColumn, 'mysql') > decorated function, and the interface would have to be something like > element.info instead of element.column.info too. Also, can you explain > why I have to use MySQLChangeColumn/MySQLModifyColumn instead of AlterColumn > in the @compiles decorator? > > Would it be possible to get support for this into alembic proper? I can get > it to work, but I have to monkey patch MySQLImpl. > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy-alembic" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sqlalchemy-alembic+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "sqlalchemy-alembic" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy-alembic+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
