CODEWITHSUNDEEP
sqlruby-on-rails
reader1
reader1

Reputation: 93

method for select (column_name) where (some single condition)

I have looked and looked, but I cannot find a method that will allow me to select a specific column based on a single condition (that does not involve a string query). The condition is arbitrary, but the column name is always the same. Below is my most recent (and desperate) attempt to better illustrate what I am trying to do. 

@notExists = Company.select("name").where("name = ?", :company)

Ok, the query was correct, I was forgetting to use the '=>' in the below code. However, that now yeilds an error because :company is evaluating to be 'company'. According to the list of params in the server output window, its value is 'sample'.

Edit: full content

 class User < ActiveRecord::Base
   # Include default devise modules. Others available are:
   # :token_authenticatable, :confirmable, :lockable and :timeoutable

   # Setup accessible (or protected) attributes
   attr_accessible :email, :password, :password_confirmation, :remember_me, :company

   validates :company, :presence => true
   devise :database_authenticatable, :registerable, :recoverable, :rememberable, :trackable, :validatable, :timeoutable

   after_save :correspond


   def correspond
     @notExists = Company.select("name").where("name = ?", :company)

     if @notExists.empty?
       c = Company.new(:name => :company)
       c.save
     end
   end

 end

To see the full solution to this issue, please see dmarkow's answer below. One change was necessary to make it tick:

def correspond
  c = Company.find_or_create_by_name(self.company)
end

Upvotes: 0

Views: 96

Answers (3)

Dylan Markow
Dylan Markow

Reputation: 124419

The only thing that is preventing your code from working is that you're trying to use :company which translates as a string instead of a variable.

Edit:

Your correspond method should be defined with a parameter and the first line of the method should use that parameter like so:

def correspond(user)
  @notExists = Company.select("name").where("name = ?", user.company)

However, this is a much cleaner way of doing this -- it will only create the company if it doesn't exist:

def correspond(user)
  c = Company.find_or_create_by_name(user.company)
end

Upvotes: 2

Chris Turner
Chris Turner

Reputation: 109

@notExists = Company.select("name").where("name = ?", :company)

will return [] if no matching records exist 

@notExists = Company.select("name").where("name = ?", :company).first

will return nil if no matching records exist

so if you are relying on it to be nil if the record does not exist you need the second one.

you could test the first one with @notExists.empty?

Upvotes: 0

Tobias Cohen
Tobias Cohen

Reputation: 20000

The query you have seems fine. If you want to get just the column value, you could do:

company = Company.select("name").where("name = ?", :company).first
value = company && company.name

Upvotes: 0

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