如何在Ruby On Rails中使用内部联接

Question

I am working on rails.

my need is,

@accountUrl = Account.find_by_id(current_account_id)

@details = Detail.find_by_acc_id(@accountUrl.id)

How to write inner join query from above example

Can any one.

Answer 1

In this simple case Rails does not use a join, it joins "in code":

Account.includes(:details).where(:id => current_account_id).first

It will make two separate queries.

If you need a condition for the select, you have to join "by hand" (or through a scope)

Account.joins(:details).where("details.name" => selected_detail).first

This will make an INNER JOIN and return only accounts satistfying the conditions.

Answer 2

model A
  has_many :bs

model B
  has_many :cs

in model A, u can write

has_many :cs, :through => :bs #uses inner join to fetch the records.

check out http://guides.rubyonrails.org/active_record_querying.html and http://asciicasts.com/episodes/215-advanced-queries-in-rails-3

Answer 3

INNER JOIN is by default in Rails Example from Rails doc

User.joins(:posts)
=> SELECT "users".* FROM "users" INNER JOIN "posts" ON "posts"."user_id" = "users"."id"

In your case it will be something like that:

Account.joins(:details)
       .where(id: current_account_id)