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I have a simple query need: Find a list of users who made an order since Jan 1, 2013.
In SQL, it's a very simple query.
But I'm using Rails and Active Record.
So I wrote: User.joins(:orders).where("orders.created_at >= '2013-01-01 00:00:00'")
In our database, we have 100 orders made since 01/01/2013 by 75 users. (Some users made more than one order apparently.)
However, the expression above returns 100 users. (There must be duplicates.)
I tried User.joins(:orders).where("orders.created_at >= '2013-01-01 00:00:00'").uniq
That doesn't work either.
How can I get the 75 users who've made an order since 01/01/2013?
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The SQL SELECT DISTINCT Statement The SELECT DISTINCT statement is used to return only distinct (different) values. Inside a table, a column often contains many duplicate values; and sometimes you only want to list the different (distinct) values.
ActiveRecord is an ORM. It's a layer of Ruby code that runs between your database and your logic code.
1.2 Object Relational Mapping Object Relational Mapping, commonly referred to as its abbreviation ORM, is a technique that connects the rich objects of an application to tables in a relational database management system.
ActiveRecord::Base indicates that the ActiveRecord class or module has a static inner class called Base that you're extending.
@dbjohn has the right idea, but I assume you want to avoid creating extra objects. Here's a slight variant on his solution, letting the database do the uniq-ing for you:
date = "2013-01-01 00:00:00" User.joins(:orders).where("orders.created_at >= ?", date).distinct Note that you can rearrange the order of methods to fit whatever you think is most semantic, and ActiveRecord will write the same SQL for you.
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