Difference between ActiveRecord and ActiveRecord::Relation objects

Question

I have searched but not able to find the brief explanation for the difference between ActiveRecord and ActiveRecord::relation object.

I have understand that ActiveRecord is the single object find by something like

User.find(1)

And ActiveRecord::Relation is the array like object Find by something like

User.where(id: 1)

I am looking for the difference between them in terms of query execution or deep explanation about them, so it will clear the whole concept behind it.

Thanks in advance!

Answer 1

An instance of ActiveRecord::Base is an object that represents a specific row of your database (or might be saved into the database).

Whereas an instance of ActiveRecord::Relation is a representation of a query that can be run against your database (but wasn't run yet). Once you run that query by calling to_a, each, first etc. on that Relation a single instance or an array of ActiveRecord::Base instances will be returned.

Answer 2

Rails uses activerecord as standard ORM but the same applies for activerecord on its own.

In short: all queries that yield multiple records like scopes, all, where, and joins return an ActiveRecord::Relation object. You can chain these together, and it is only when you use a method like to_sql, first, each, any, to_a, take, last etc that the query is executed and returns an array of ActiveRecord::Base instead

---

• All this is explained on the following site

  • Especially the section on scopes, query methods and the examples for pluck show all the details on the main differences

• See also the rails API for reference