How to check if a record exists before creating a new one in rails3?

Question

Heres what I\'m trying to accomplish:

• I have a tagging system in place.
• Tags are created, when Posts are created (posts has_many :tags, :through => :tag

Answer 1

You're going to find it hard to to this from within the Tag model. It seems like what you want is to update the Post using nested attributes, like so:

post = Post.create
post.update_attributes(:tags_attributes=>{"0"=>{:name=>"fish",:user_id=>"37"}})

This is actually pretty simple to do by using a virtual attribute setter method:

class Post < AR::Base
  has_many :tags

  def tags_attributes=(hash)
    hash.each do |sequence,tag_values|
      tags <<  Tag.find_or_create_by_name_and_user_id(tag_values[:name],\
        tag_values[:user_id])
    end
  end

> post = Post.create
> post.update_attributes(:tags_attributes=>{"0"=>{:name=>"fish",:user_id=>"37"}})
> Tag.count # => 1
# updating again does not add dups
> post.update_attributes(:tags_attributes=>{"0"=>{:name=>"fish",:user_id=>"37"}})
> Tag.count # => 1

Answer 2

You want to use the magic method find_or_create_by

def check_exists
    tag = Tag.find_or_create_by_name_and_user_id(:name => self.name, :user_id => current_user.id)
end

Check out the ActiveRecord::Base docs for more info

Answer 3

where returns an empty ActiveRecord on finding no match.

Answer 4

There's a find_or_create_by_ function built right in to Rails

# No 'Summer' tag exists
Tag.find_or_create_by_name("Summer") # equal to Tag.create(:name => "Summer")

# Now the 'Summer' tag does exist
Tag.find_or_create_by_name("Summer") # equal to Tag.find_by_name("Summer")

http://api.rubyonrails.org/classes/ActiveRecord/Base.html (under Dynamic attribute-based finders)

Answer 5

I believe the other answers are a bit dated. Here's how you should probably accomplish this for Rails 4

tag = Tag.first_or_initialize(:name => self.name, :user_id => current_user.id)
if !tag.new_record?
    tag.id = self.id
    tag.save
end

Answer 6

try this

  def check_exists
    tag = Tag.where(:name => self.name, :user_id => current_user.id).first
    tag = Tag.new({:name => self.name, :user_id => current_user.id}) unless tag
  end

use Tag.new instead of Tag.create