Rails 4 Generating Invalid Column Names

问题

I have a fairly simple query to return the first record in a many-to-many relation or create one if it doesn't exist.

UserCategorization.where(category_id: 3, user_id: 5).first_or_create

My model looks like:

class UserCategorization < ActiveRecord::Base
    belongs_to :user
    belongs_to :category

    self.primary_key = [:user_id, :category_id]
end

However it generates an invalid column name in the SQL:

SQLite3::SQLException: no such column: user_categorizations.[:user_id, :category_id]:

SELECT  "user_categorizations".* FROM "user_categorizations"  WHERE
"user_categorizations"."category_id" = 3 AND "user_categorizations"."user_id" = 5
ORDER BY "user_categorizations"."[:user_id, :category_id]" ASC LIMIT 1

If I remove self.primary_key = [:user_id, :category_id] from the model, it can retrieve the record correctly but cannot save because it doesn't know what to use in the WHERE clause:

SQLite3::SQLException: no such column: user_categorizations.: 

UPDATE "user_categorizations" SET "score" = ? 
WHERE "user_categorizations"."" IS NULL

Has anyone seen this before?

回答1:

I think one of these two suggestions will work:

First, try adding the following migration:

add_index :user_categorizations, [:user_id, :category_id]

Make sure to keep self.primary_key = [:user_id, :category_id] in your UserCategorization model.

If that doesn't work, destroy the UserCategorization table and run this migration:

def change
    create_table :user_categorizations do |t|
      t.references :user
      t.references :category
      t.timestamps
    end
end

references are new to Rails 4. They add a foreign key and index to the specified columns.

Good Luck!

回答2:

So it looks like Rails 4 ActiveRecord doesn't do composite keys very well so many-to-many models create the issues above. I fixed it by using this extension to ActiveRecord: http://compositekeys.rubyforge.org/

来源：https://stackoverflow.com/questions/18905945/rails-4-generating-invalid-column-names