Query Records Through Its Belongs_To Relation in Rails

Query records through its belongs_to relation in Rails

With the latest rails versions you can do:

Activity.joins(:location).where(locations: { country: "Australia" })

Beware:

it is location (singular) in joins(:location) because it references the belongs_to relationship name
it is locations (plural) in where(…) because it references the table name

The latter means that if you had the following:

belongs_to :location, class_name: "PublicLocation"

the query would be:

 Activity.joins(:location).where(public_locations: { country: "Australia" })

Query records through its belongs_to relation in Rails 4

Your belongs_to association name is singular (which is correct, as it the standard) in the Part model, but you tried to join using the pluralized association name (you tried :categories). A common mistake; you probably got mixed up between the database naming convention, and the rails association naming convention. Try instead this:

Part.joins(:category).where('categories.name = "cars"').first

Side note:
This is not related to the question, but in case you did not already know, you can use a hash in the where clause if you like as well. It would look like:

where(categories: {name: "cars"})

And the result would be the same. In your case, it is not relevant since you're clearly passing a literal string, but it may come in handy when you're using form data, or something equally non-secure, since the hash method will properly treat the parameter as text, rather than dangerously placing it in the query as-is.

Rails find records by HABTM relation

This is what you need:

BlogPost.joins(blog_categories).where(blog_categories: { id: params[:id] })

Note that you can pass an array of ids via params[:id] if you need to look up multiple categories.

activerecord where clause on relation belongs_to

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)

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

Rails 4 where -query with has_many belongs_to -relationship, searching with specific count

Should use "companies.id" instead of "company.id".

Company.joins(:users).group("companies.id").having("count(users.id)>5")

And if you want to get company with 0 users, you have to use LEFT JOIN:

Company.joins('LEFT JOIN users ON companies.id = users.company_id').group("companies.id").having("count(users.id) = 0")

How to write where condition for Ruby ApplicationRecord belongs to relationship

You can try something as follow:

product_categories = Admin::ProductCategory.joins(:category)
  .where(product_type_id: self.product_type_id)
  .where(categoires: { type_id: self.category.type_id })
  .where(categoires: { type_id: 4 })

And this is a nice explanation of ActiveRecord join with belongs_to relationship https://stackoverflow.com/a/33266583/7338180.

ActiveRecord Query for Present belongs_to ID but belongs_to Object is Nil

Following should get you telephones with user_id present but corresponding user object is nil.

Telephone.left_outer_joins(:user).where("users.id is NULL AND telephones.user_id is NOT NULL")

searching records in rails include belongs_to or has_many

You can do the following:

Product.includes(:producer)
        .where('products.name LIKE ? OR producers.name LIKE ?', "%#{params[:q]}%", "%#{params[:q]}%")

You can make a scope with it:

class Product < ActiveRecord::Base

  scope :with_name_like, lambda { |name| 
            includes(:producer).where('products.name LIKE ? OR producers.name LIKE ?', "%#{name}%", "%#{name}%") 
  }

And use it like this:

@products = Product.with_name_like('Chair')

Rails - Get all records for has many through relationship including unassociated records

You can use single query with left join:

res = Movie.left_joins(:favourites).where(fauvorites:{ user_id: [current_user.id, nil]}).
       select(Movie.arel_table[Arel.star], "(favourites.id is null) as is_favourited_by_user")
res.first.is_favourited_by_user # 0/1

returned Movie objects will have generated is_favorited_by_user field that indicates if particular movie is favourited by that user.