Model.reset_column_information does not reload columns in rails migration

问题

I'm using Rails 3.2 and have a migration that contains the code:

add_column :users, :gift_aid, :integer, :default => 2
# reset columns
User.reset_column_information

... code here to load legacy data from sqlite3 database ...

# now create a user with the loaded column data
user = User.create( ...other cols..., 
                    :gift_aid => migrated_gift_aid_column_data,
                    ...other cols... )

and I get unknown attribute: gift_aid when running the migration. User.column_names shows the same list before and after the call to reset_column_information.

Oddly when I manually drop the column in mysql and re-run the migration it works as expected. Starting from the first migration again with an empty database and it doesn't work so it's something to do with running all the migrations rather than the single one.

I have a couple of previous migrations on User model, both include reset_column_information and both work fine.

I'm really scratching my head on this one - anyone got any ideas

回答1:

I think this must be some kind of bug related to schema caching... this might work:

User.connection.schema_cache.clear!
User.reset_column_information

(for Rails 3.2.2)

回答2:

this isn't needed on rails 6 (tested on 6.0.0beta3).

I tried both with update!(new_column: ...) and update_all(new_column: ...)

来源：https://stackoverflow.com/questions/9115347/model-reset-column-information-does-not-reload-columns-in-rails-migration