Question

I’ve been working through some issues getting rails to behave nicely with sqllite, and decided to move over to mysql.

I ran my rake db:create and rake db:schema, and assumed everything was ok, but then mysql show tables displayed a complete table was missing.

I created a migration with the create table details and ran rake db:migrate, and now the all the tables show up.

Unfortunately, it appears that the link between the tables didn’t work.

The app is a fairly simple recipe app.
The tables are

recipes
ingredients
steps

the ingredients table was the one which was not created in the db:create or db:schema.

I created the ingredients table with

class AddIngredientsTable < ActiveRecord::Migration
  def self.up
        create_table :ingredients do |t|
            t.string    :ingredient
            t.float     :amount
            t.string    :measure
            t.string    :description
        end
  end

In my recipes model i have has_many :ingredients, and my ingredients model has belongs_to :recipe

The error I’m getting is

Mysql::Error: Unknown column 'ingredients.recipe_id' in 'where clause': SELECT     `ingredients`.* FROM       `ingredients`  WHERE     (`ingredients`.recipe_id = 1)

and of course, the error is correct that a recipe_id field does not exist in either table. But I don’t have such a request in the controller either which reads simply

  def show
    @recipe = Recipe.find(params[:id])

    respond_to do |format|
      format.html # show.html.erb
      format.xml  { render :xml => @recipe }
    end
  end

Any suggestions as to what to look for and why this problem might have occured, and how to fix it?

I’d prefer not to manually write out the sql as my understanding is that at this stage that isn’t the rails way, though I am familiar with sql so could do this.

Answer 1

Rails uses a lot of conventions. In this case you’re hitting the rule that has_many :ingredients on Recipe means that the ingredients table must have recipe_id. Obviously you probably want ingredients shared between many recipes, and so for that you’ll want has_and_belongs_to_many with a join table (which you will create another migration for).

I suggest you start with this guide for a comprehensive overview of how this works in Rails.