Add_column for links (Rails)

Question

I have the following Rails migration that works fine (irrelevant fragments removed):

create_table :comments do |t| t.text :body t.references :post end 

Now I would like to add the author column to my comments table (which is the user ID), but I have no idea how to do this (I am tempted to just write MySql-specific syntax using execute ).

I looked at add_column here which does not mention references . I actually found a TableDefinition # link , but I have no idea how to use it with the add_column .

Is it possible? Is it also true that for MySql, the functionality of “links” does not actually establish relationships between tables?

Answer 1

While it is too late to get any points from this, I thought I would put the best way for posterity :)

use change_table instead of create_table to add columns to a table that already exists, with all the benefits of TableDefinition:

 self.up do change_table :comments do |t| t.references :author end end 

This may seem trivial, but other gems, such as Devise, make heavy use of their own custom table definitions, and so you can still use them.

Answer 2

 add_reference :table_name, :reference, index: true 

Answer 3

Finally he got

 add_column :locations, :state_id , :integer, :references => "states" 

Answer 4

First, do:

 script/generate migration AddAuthorIdToComments 

Open the generated file and add this line:

 add_column :comments, :author_id, :integer 

Then in your model files:

 class User < ActiveRecord::Base has_many :comments, :foreign_key => "author_id" end class Comment belongs_to :author, :class_name => User end 

Answer 5

It has been some time since I looked at this, but the last time I checked the migration did not support the creation of foreign keys. Fortunately, however, there is a plugin for it . I used this and it works well.

Answer 6

You can add the add_column(:table, :column_name, :type, :options) column add_column(:table, :column_name, :type, :options) to the new migration.