attr_accessor is used to define an attribute for object of Model which is not mapped with any column in database. This answers question - What is attr_accessor in Rails.
1. attr_accessor Methods
attr_accessor creates two methods i.e. getter method and setter method.
getter method - it is used to retrieve value of the attribute
setter method - it is used to set value to the attribute
When to use attr_accessor in Rails?
Whenever you want to show certain attribute for particular form but you do not want to store it’s value in the database then you use attr_accessor for that model as follows,
Suppose we have a Model called user in out database with following fields,
And we define attr_accessor :type_of_user as follows,
Now, whenever you create a object of the class User then you can assign a value to it’s attr_accessor.
This will create new object of class User and assign given attribute values. You can assign value to attr_accessor variable as follows,
This assigns ‘middle-aged’ value to the attribute type_of_user attr_accessor.
getter and setter in Action
For attribute type_of_user getter and setter methods are created as follows,
And these are used whenever we assign or retrieve values from the attr_accessor.
2. Usage in Classes
Whenever changing value of the attr_accessor variables, we need to use
self.variable_name = to assign new value to the variable.
Otherwise, it will consider it as a local variable resulting into incorrect values.
Here, it the above service class we have defined
name as the attr_accessor.
We need to change it’s value based on some condition. And we return it’s value
When we execute this class as,
We can see that
process method has returned
In the block,
As the if condition is false, and value of
name is returned from the process method,
name is considered as the local variable. Local variable
name does not have any value.
Thus, it returns
To correct the above service class, we need to use explicity
self when assigning
value to the
attr_accessor variable as given below,
Now if we execute this class, we will get expected result as given below.
3. Lifetime of attr_accessor
attr_accessor is accessible throughout object’s lifecycle. When object is saved using any of ActiveRecord method, save, update etc. all attributes of Model other than attr_accessor are saved in the database.
How to Access
Throughout lifecycle of object, you can access the value of attribute accessor as follows,
and can be used for any operation as you do with normal attribute value.
We learned what is attr_accessor in Rails and how to use it with Rails Application. You can refer APIDock of attr_accessor for more information.