Rails | Add condition in join query - ruby-on-rails

Question

Is it possible, to add condition in join query?
For example I want to build next query:
select * from clients
left join comments on comments.client_id = clients.id and comments.type = 1
Client.joins(:comments).all generates only:
select * from clients
left join comments on comments.client_id = clients.id
PS. Client.joins("LEFT JOIN comments on comments.client_id = clients.id and comment.type = 1") isn't nice.

Answer 1

You can do:
Client.left_outer_joins(:comments)
.where(comments: { id: nil })
.or(Client.left_outer_joins(:comments)
.where.not(comments: { id: nil })
.where(comments: { type: 1 }))
what gives you something equivalent to what you want:
SELECT "clients".*
FROM "clients"
LEFT OUTER JOIN "comments"
ON "comments"."client_id" = "clients"."id"
WHERE "comments"."id" IS NULL
OR ("comments"."id" IS NOT NULL) AND "comments"."type" = 1
UPDATE
Actually, this does not work because rails close the parenthesis leaving outside the evaluation of type.
UPDATE 2
If yours comment types are few and is not probable its values will change, you can solve it with this way:
class Client < ApplicationRecord
has_many :comments
has_many :new_comments, -> { where comments: { type: 1 } }, class_name: Comment
has_many :spam_comments, -> { where comments: { type: 2 } }, class_name: Comment
end
class Comment < ApplicationRecord
belongs_to :client
end
With this new relationships in your model now you can do:
Client.left_joins(:comments)
gives:
SELECT "clients".*
FROM "clients"
LEFT OUTER JOIN "comments"
ON "comments"."client_id" = "clients"."id"
Client.left_joins(:new_comments)
gives:
SELECT "clients".*
FROM "clients"
LEFT OUTER JOIN "comments"
ON "comments"."client_id" = "clients"."id" AND "comments"."type" = ?
/*[["type", 1]]*/
Client.left_joins(:spam_comments)
gives the same query:
SELECT "clients".*
FROM "clients"
LEFT OUTER JOIN "comments"
ON "comments"."client_id" = "clients"."id" AND "comments"."type" = ?
/*[["type", 2]]*/
Client.left_joins(:new_comments).where name: 'Luis'
gives:
SELECT "clients".*
FROM "clients"
LEFT OUTER JOIN "comments"
ON "comments"."client_id" = "clients"."id" AND "comments"."type" = ?
WHERE "clients"."name" = ?
/*[["type", 1], ["name", "Luis"]]*/
NOTE:
I try to use a parameter in the original has_many relationship like...
has_many :comments, -> (t) { where comments: { type: t } }
but this give me an error:
ArgumentError: The association scope 'comments' is instance dependent (the scope block takes an argument). Preloading instance dependent scopes is not supported.

Answer 2

I ended up doing this:
meals_select = Meal.left_outer_joins(:dish_quantities).arel
on_expression = meals_select.source.right.first.right.expr
on_expression.children.push(DishQuantity.arel_table[:date].eq(delivery_date))
on_expression.children.push(DishQuantity.arel_table[:dish_id].eq(Dish.arel_table[:id]))
ON "dish_quantities"."meal_id" = "meals"."id" AND "dish_quantities"."date" = '2022-08-05' AND "dish_quantities"."dish_id" = "dishes"."id"

Answer 3

Client.joins(:comments).where(comments: {type: 1})
Try this