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Through associations

AKA "Has Many Through"

Overview

Many-to-Many through associations behave the same way as many-to-many associations with the exception of the join table being automatically created for you. In a Many-To-Many through assocation you define a model containing two fields that correspond to the two models you will be joining together. When defining an association you will add the through key to show that the model should be used rather than the automatic join table.

Has Many Through Example

// myApp/api/models/User.js
module.exports = {
  attributes: {
    name: {
      type: 'string'
    },
    pets:{
      collection: 'pet',
      via: 'owner',
      through: 'petuser'
    }
  }
}

// myApp/api/models/Pet.js
module.exports = {
  attributes: {
    name: {
      type: 'string'
    },
    color: {
      type: 'string'
    },
    owners:{
      collection: 'user',
      via: 'pet',
      through: 'petuser'
    }
  }
}

// myApp/api/models/PetUser.js
module.exports = {
  attributes: {
    owner:{
      model:'user'
    },
    pet: {
      model: 'pet'
    }
  }
}

By using the PetUser model we can use .populate() on both the User model and Pet model just the same as a normal Many-to-Many association.

Currently if you would like to add additional information to the through table it will not be available when calling .populate. To do this you will need to query the through model manually.

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