Ruby Rails Active Record Query on two columns

Question

Lets say we have following table:
Employee
ID Name Sick_Leaves Casual_Leaves
1 John 4 8
2 Nancy 5 2
3 Matthew 2 9

Now if I want to get a list of all the Employess who have taken more sick leaves than casual, its straight forward in SQL:
Select * from Employee Where Sick_Leaves > Casual_Leave

Now considering that I have a Rails Active Record Model class defined for Employee, how can I execute the same query using model class itself ? I am getting stuck in how to define the WHERE clause. If it had been Sick_Leaves > 5 (or some fixed number), then its simple, but what now when we want to compare two columns itself ?

Any help will be appreciated.

Answer 1

您可以使用以下ActiveRecord查询：

Employee.where('sick_leaves > casual_leaves')

Answer 2

Rails' interface to Active Relation doesn't have a simple syntax for expressing "greater than" (amongst other things). So you can either use hand-written SQL (as @JKen12579 suggested) or you can step down into the bowels of using ARel syntax. (It's weird at first but gives you the full power of SQL still.)

Employee.where(arel_table[:Sick_Leaves].gt(arel_table[:Casual_Leaves]))

I'd recommend this approach because it keeps you writing Ruby code, it alleviates issues with having to write the table name or not (eg "Do I need to use employees.<column> ?"), and it is database agnostic (which may not be important here but maybe later... so get used to the syntax and never worry).