如何在Ruby on Rails中编写连接条件？

Question

what I'm trying to do is to write something like the next query:

SELECT *
FROM Customers c
LEFT JOIN CustomerAccounts ca
    ON ca.CustomerID = c.CustomerID
    AND c.State = 'NY'

Notice that I'm not using any WHERE clause, but I need to my JOIN have a condition. I cannot make it work in Ruby on Rails.

Can you help me out?

Answer 1

You can join the tables with LEFT JOIN . Just pass the join condition in joins and you will get the expected result

Customer.joins("LEFT JOIN CustomerAccounts
                ON CustomerAccounts.CustomerID = Customers.CustomerID
                AND Customers.State = 'NY'")

#=> SELECT * FROM Customers LEFT JOIN CustomerAccounts ON CustomerAccounts.CustomerID = Customers.CustomerID AND Customers.State = 'NY'

Note: just .joins() does INNER JOIN so you need to specify the join with condition

Answer 2

Your SQL code, translated to activerecord, would look as follows (using joins ):

Customer.where(state: 'NY').joins(:customer_accounts)

The code assumes, you have the association set up:

class Customer
  has_many :customer_accounts
end