Question

I have an attribue attempts in database of integer type (initial value is 0 )

When I do @user.attempts += 1 , it throws TypeError: can't convert Fixnum into String

So, I conclude that rails does not convert attributes automatically according to their datatype.

When I do

@user.attempts.to_i +=1

it throws NoMethodError: undefined method 'to_i=' for "0":String

and when I do,

@user.attempts.to_i = @user.attempts.to_i + 1

it throws NoMethodError: undefined method 'to_i=' for "0":String again.

And this,

@user.attempts = @user.attempts.to_i + 1

works fine.

I think the reason is that when I do @user.attempts.to_i + 1 , it actually changes the @user.attempts on left side .

Can somebody throw some light on this behavior ?

EDIT

Migration

    class CreateUsers < ActiveRecord::Migration
      def change
        create_table :users do |t|
          t.string :email 
          t.string :email_pass 
          t.integer :attempts 
          t.timestamps
        end
      end
    end

Create table script

-- Table: users

-- DROP TABLE users;

CREATE TABLE users
(
  id serial NOT NULL,
  email character varying(255), 
  email_pass character varying(255), 
  attempts character varying(255),
  created_at timestamp without time zone NOT NULL,
  updated_at timestamp without time zone NOT NULL, 
  CONSTRAINT users_pkey PRIMARY KEY (id )
)
WITH (
  OIDS=FALSE
);
ALTER TABLE users
  OWNER TO jashwant;

I see that in db attempts is character type.

So, what should be the proper way to alter its datatype.
And I also stand out for my first question, whats the reason for that type conversion ?

Answer 1

When you use += like this :

something += 1

it is the same as :

something = something + 1

And when you do,

obj.method = val

it is the same as :

obj.method=(val)

So you are actually calling #to_i= on @user.attempts which does not exist.

When you do @user.attempts = @user.attempts.to_i + 1, your call is the same as this one :

@user.attempts=(@user.attempts.to_i + 1)

which exists and so works fine.