Rails Arel joins with where condition on joined table

问题

I'm trying to convert the following Rails where clause to use Arel, mostly to take advantage of the or method that Arel provides.

Post model

class Post
  belongs_to :user
end

User model

class User
  has_many :posts
end

I'm looking for posts posted by Mark.

This is the Rails Query:

Post.joins(:user).where(users: { first_name: 'Mark' })

I need to convert this query with Arel.

Thanks in advance!

回答1:

This should do it.

# Generate Arel tables for both
posts = Arel::Table.new(:posts)
users = Arel::Table.new(:users)

# Make a join and add a where clause
posts.join(:users).on(posts[:user_id].eq(users[:id])).where(users[:first_name].eq('Mark'))

回答2:

If you only need Arel for the where part (not for the join), I think this would be a better solution (will wield Activerecord results):

Post.joins(:user).where(User.arel_table[:first_name].eq('Mark'))

来源：https://stackoverflow.com/questions/39236293/rails-arel-joins-with-where-condition-on-joined-table