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

CQL::Relations::Collection < Reference < Object

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

struct Movie < CQL::Model(Int64)
  property id : Int64
  property title : String

  many_to_many :actors, Actor, join_through: :movies_actors
end

struct Actor < CQL::Model(Int64)
  property id : Int64
  property name : String
end

struct MoviesActors < CQL::Model(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")

Constructors

def 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

Example

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

Instance Methods

def clear

Clears all associated records from the parent record and the database

• return : [] of T

Example

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

def 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

Example

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

def create

Create a new record and associate it with the parent record

• param : attributes (Hash(Symbol, String | Int64))

• return : Array(Target)

• raise : CQL::Error

Example

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

def delete(record : Target)

Delete the associated record from the parent record if it exists

• param : record (Target)

• return : Bool

Example

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

def delete(id : Pk)

Delete the associated record from the parent record if it exists

• param : id (Pk)

• return : Bool

Example

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

def ids=(ids : Array(Int64))

Associates the parent record with the records that match the primary keys provided

• param : ids (Array(Pk))

• return : Array(Target)

Example

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">]