class Cql::Relations::ManyCollection(Target, Through, Pk)

• Cql::Relations::ManyCollection(Target, Through, Pk)
• Cql::Relations::Collection(Target, Pk)
• Reference
• Object

Overview

A collection of records for a many to many relationship This class is used to manage the relationship between two tables through a join table (through)

A many-to-many association occurs when multiple records of one model can be associated with multiple records of another model, and vice versa. Typically, it requires a join table (or a junction table) to store the relationships between the records of the two models.

Here’s how a many-to-many association is commonly implemented in CQL using Crystal.

Example

class Movie
  include Cql::Model(Movie, Int64)

  property id : Int64
  property title : String

  many_to_many :actors, Actor, join_through: :movies_actors
end

class Actor
  include Cql::Model(Actor, Int64)
  property id : Int64
  property name : String
end

class MoviesActors
  include Cql::Model(MoviesActors, Int64)
  property id : Int64
  property movie_id : Int64
  property actor_id : Int64
end

movie = Movie.create(title: "The Matrix")
actor = Actor.create(name: "Keanu Reeves")

Defined in:

Constructors

• .new(key : Symbol, id : Pk, target_key : Symbol, cascade : Bool = false, query : Cql::Query = (Cql::Query.new(Target.schema)).from(Target.table))

  Initialize the many-to-many association collection class - param : key (Symbol) - The key for the parent record - param : id (Pk) - The id value for the parent record - param : target_key (Symbol) - The key for the associated record - param : cascade (Bool) - Delete associated records - param : query (Cql::Query) - Query object - return : ManyCollection

Instance Method Summary

• #clear

  Clears all associated records from the parent record and the database - return : [] of T

• #create(record : Target)

  Create a new record and associate it with the parent record - param : attributes (Hash(Symbol, String | Int64)) - return : Array(Target) - raise : Cql::Error

• #create(**attributes)

  Create a new record and associate it with the parent record - param : attributes (Hash(Symbol, String | Int64)) - return : Array(Target) - raise : Cql::Error

• #delete(record : Target)

  Delete the associated record from the parent record if it exists - param : record (Target) - return : Bool

• #delete(id : Pk)

  Delete the associated record from the parent record if it exists - param : id (Pk) - return : Bool

• #ids=(ids : Array(Int64))

  Associates the parent record with the records that match the primary keys provided - param : ids (Array(Pk)) - return : Array(Target)

Constructor Detail

ManyCollection.new(
  :movie_id,
  1,
  :actor_id,
  false,
  Cql::Query.new(Actor.schema).from(Actor.table)
)

Instance Method Detail

movie.actors.create(name: "Carrie-Anne Moss")
movie.actors.reload
movie.actors.all => 1
movie.actors.clear
movie.actors.reload
movie.actors.all => []

movie.actors.create!(name: "Hugo Weaving")
movie.actors.reload
movie.actors.all
=> [#<Actor:0x00007f8b3b1b3f00 @id=1, @name="Hugo Weaving">]

movie.actors.create(name: "Carrie-Anne Moss")
movie.actors.reload
movie.actors.all
=> [#<Actor:0x00007f8b3b1b3f00 @id=1, @name="Carrie-Anne Moss">]

movie.actors.create(name: "Carrie-Anne Moss")
movie.actors.reload
movie.actors.all => 1

movie.actors.delete(Actor.find(1))
movie.actors.reload
movie.actors.all

=> [] of Actor

movie.actors.create(name: "Carrie-Anne Moss")
movie.actors.reload
movie.actors.all => 1
movie.actors.delete(1)
movie.actors.reload
movie.actors.all => []

movie.actors.ids = [1, 2, 3]
movie.actors.reload
movie.actors.all => [
#<Actor:0x00007f8b3b1b3f00 @id=1, @name="Carrie-Anne Moss">,
   #<Actor:0x00007f8b3b1b3f00 @id=2, @name="Hugo Weaving">,
  #<Actor:0x00007f8b3b1b3f00 @id=3, @name="Laurence Fishburne">]