activerecord where clause on relation belongs_to

Question

I'm not strong in sql and relatively new to rails. The

Case
  attr_accessible client_id
  belongs_to Client

Client
  attr_accessibe name
  has_many Cases

I can query directly by client_id and get a record back as expected

Case.where(client_id: 1)

But I would like to query by client.name

Case.where(client.name => "Foo")

This give me an error that tells me that client is not a method of case.

Undefined method or local variable 

Ultimately, what I'm trying to do is very simple: get the first Case that belongs to client "Foo". The query I would expect to use is this.

Case.where(client.name => "Foo").first

What should it be?

Answer 1

Case.joins(:client).where(clients: { name: 'foo' })

This query will joins the clients on the case table (eliminates the Cases without any client associated) and add the where clause "where clients.name = 'foo'"

In human language, this query does:

Get the Cases having at least one Client having the name strictly equal (case-sensitive) to 'foo'

---

Pay attention to the plural/singular:

• in the joins/includes, use the same name as the relation is declared in the model

• in the where clause, always use the pluralized version of the relation (actually the table's name)

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Additionnal informations:

• You can use an array of values in the where clause:

  Case.joins(:client).where(clients: { id: [1,2,5] })
  

• Difference between .joins and .includes: Rails :include vs. :joins

Answer 2

Depending on what you're doing it may be easier to go about it this way:

Client.where(:name => "foo").first.cases

This will return all the cases for the client.