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Advanced Rails model generators

There are some people who give advice to not use rails generators and create models, controllers and etc. things manually. I don’t agree with them and my advice here is to figure out deeply how they work and then make conclusion.

In this post I will describe the most often and useful generator - it’s a model generator. I bet if you don’t use rails generators yet this post will make you to change your work. Using Rails generators saves your time, increases performance, helps to get consistent data for your application.

Basic usage

Let’s start with simple example:

$ rails g model user email

This command will generate user model with email field type of string, migration which creates users table, test for model and factory (if you have it). You are able to generate model with few fields like this:

$ rails g model user first_name last_name email

This example will generate yet model with 3 string fields: first_name, last_name and email.

If you want to have model with different type of string pass type after field name following by : and type. Example:

$ rails g model user email age:integer

The whole list of available types:


You are able to pass –option parameter to generator. It will inherit generating class from passed name to achieve STI (sing table inheritance):

$ rails g model admin --parent user

This example generates model:

class Admin < User

Interesting fact that if you generate model in some scope passing model like admin/user or Admin::User:

$ rails g model admin/user

you will get generated model in scope app/models/admin/user.rb, defined scope app/models/admin.rb which is requred to define module. Let’s see to the content of generated module:

module Admin
  def self.table_name_prefix

It means that generated table name for Admin::User starts with prefix admin_users. This feature allows to have separated namespaced models as in rails code as in db schema. Very convenient and useful feature for multimodule applications for my opinion.

Advanced usage

Sometimes you have to automatically add index for columns in your migration. It’s not a problem:

$ rails g model user email:index location_id:integer:index

Or uniq index:

$ rails g model user pseudo:string:uniq

Set limit for field of integer, string, text and binary fields:

$ rails generate model user pseudo:string{30}

Special syntax to generate decimal field with scale and precision:

$ rails generate model product 'price:decimal{10,2}'

Pay attention that you have to wrap parameter price:decimal{10,2} to quotes. It’s vital and you may have incorrect behavior of generator if you don’t do it. Full explanation of this case is here.

You can combine any single curly brace option with the index options:

$ rails generate model user username:string{30}:uniq

And the last useful feature of generators - it’s options to generate reference columns (fields which are used in rails as foreign keys):

$ rails generate model photo album:references

This command will generate photos table with integer field album_id and also it will add index for this field automatically. Make sure in it by looking at generated migration:

class CreatePhotos < ActiveRecord::Migration
  def change
    create_table :photos do |t|
      t.references :album

    add_index :photos, :album_id

For polymorphic reference use this syntax:

$ rails generate model product supplier:references{polymorphic}

Polymorphic reference with indexes:

$ rails generate model product supplier:references{polymorphic}:index


As you see there a lot of useful things in rails model generator which can decrease your developing time. Thank you for reading this trolling post but anyway I hope you find it useful because I didn’t find any similar post or literature which describes rails model generator fully.

PS. Foundation for this post was got from this rails description usage which is located only in sources of rails on github.

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