Ruby on Rails Seed Data - ruby-on-rails

Question

I am Ruby/Rails newbie. I am currently learning about the Rails console and databases using Rake and the seeds.rb file.
I am supposed to:
Add a post with a unique title and body to seeds.rb.
Before creating a unique post, verify it exists in the database. Only
seed the post if it doesn't.
Run rake db:seed a couple times, start your Rails console and confirm
that your unique post has only been seeded once.
Repeat to create a unique comment and confirm that it is also only
seeded once.
Honestly I don't know how to start working on this. I am supposed to add a post using the rails console or directly from the seeds.rb file? Any guidance will be greatly appreciated.

Answer 1

Despite the intention of seed-ing - that this is meant to be run once, to populate the database - there is no technical constrain preventing you from running rake db:seed command couple times. Even without cleaning/recreating your database.
In that case, try following code for db/seeds.rb
post_atrributes = [
{ title: "Sample Title 1", body: "Sample body 1" },
{ title: "Sample Title 2", body: "Sample body 2" },
{ title: "Sample Title 3", body: "Sample body 3" },
]
post_attributes.each do |attributes|
Post.create(attributes) unless Post.where(attributes).first
end
First of all, we're defining an array of attributes for each Post, to be created.
Later, we're iterating through that array (with post_attributes.each do |attributes|), and trying create a new Post, unless one with specified attributes found.
In Rails, there is quite fancy method first_or_create, which does exactly that - queries database for specified attributes (where(attributes)), and if nothing found - creates new record based on provided attributes.
post_atrributes = [
{ title: "Sample Title 1", body: "Sample body 1" },
{ title: "Sample Title 2", body: "Sample body 2" },
{ title: "Sample Title 3", body: "Sample body 3" },
]
post_attributes.each do |attributes|
Post.where(attributes).first_or_create
end
At this point, you can "seed" the database with rake db:seed and check what is stored in database (after running rails console) by:
Post.all.map(&:title)
Assuming you had empty database before running rake db:seed, it should contain only 3 Posts. The ones specified with attributes in post_attributes.
Now, if you try to modify your db/seeds.rb again, adding an attributes for one more Post:
post_atrributes = [
{ title: "Sample Title 1", body: "Sample body 1" },
{ title: "Sample Title 2", body: "Sample body 2" },
{ title: "Sample Title 3", body: "Sample body 3" },
{ title: "Another Post", body: "WOW!" },
]
post_attributes.each do |attributes|
Post.where(attributes).first_or_create
end
After running rake db:seed, and checking in console:
Post.all.map(&:title)
You can see, that only one new Post has been created. The one with title "Another Post".
In your question I understood, that when creating new Post, both attributes - title and body have be unique, so if you try to perform the same for attributes like:
post_atrributes = [
{ title: "Sample Title 1", body: "Sample body 1" },
{ title: "Sample Title 1", body: "Sample body 2" },
]
This will create two separate Posts, because they have different body attributes defined.
For Comments you can do similar thing.
Again, as jBeas mentioned earlier - seed-ing has different purpose, but if this is only exercise to play with ActiveRecord - this is one of ways how you can tackle the problem.
Hope that helps!

Answer 2

Seeding is the process of populating a database with data.
There are two methods used to accomplish this.
You can use ActiveRecord Migrations
class AddInitialProducts < ActiveRecord::Migration
def up
5.times do |i|
Product.create(name: "Product ##{i}", description: "A product.")
end
end
def down
Product.delete_all
end
end
Or you can store it in a separate seeds.rb file
5.times do |i|
Product.create(name: "Product ##{i}", description: "A product.")
end
afterwards, run rake db:seed
Source
http://edgeguides.rubyonrails.org/active_record_migrations.html#migrations-and-seed-data