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EmberJS – Relationships

Relationship

Ember.js provides relationship types to specify how the models are related to each other. There are different relationship types such as One-to-One relationship can be used with DS.belongsTo, One-to-Many relationship can be used with DS.hasMany along with DS.belongsTo and Many-to-Many relationship can be used with DS.hasMany.

Syntax

import DS from 'ember-data';

export default DS.Model.extend ({
   var_name1: DS.belongsTo('model_name1'),
   var_name2: DS.hasMany('model_name2')
});

Example

The example given below shows the use of relationship types. Create two adapters with the names account and staff by using the following command −

ember generate adapter adapter_name

Now open the app/adapters/account.js file and add the following code −

import ApplicationAdapter from './application';

//created an "account" array to store relationship data 
const account = {
   "data": {
      "type": "account",
      "id": "100",

      "relationships": {
         "secondVal": {
            "data": {
               "type": "staff",
               "id": "2"
            }
         },
         "firstVal": {
            "data": {
               "type": "staff",
               "id": "1"
            }
         }
      }
   }
};

export default ApplicationAdapter.extend ({
   //this method fetches data from 'staff' adapter
   findRecord() {
      //returns the data from array
      return account;
   }
});

Open the app/adapters/staff.js file and add the following code −

import ApplicationAdapter from './application';
import Ember from 'ember';

//values given for type and id
const relval1 = {
   data: {
      type: "staff",
      id: "1",
      attributes: {
         name: 'JavaScript'
      }
   }
};

const relval2 = {
   data: {
      type: "staff",
      id: "2",
      attributes: {
         name: 'jQuery'
      }
   }
};

//the variable 'relval3' pushes the data to 'relval1' and 'relval2'
const relval3 = Ember.A();
relval3.pushObject(relval1);
relval3.pushObject(relval2);

export default ApplicationAdapter.extend ({
   findRecord(store, type, id) {
      //finds the item id and returns to 'relval3' variable
      let valret = relval3.find(function (item) {
         return id === Ember.get(item, 'data.id');
      });
      //the searched item will passed to 'relval3' from 'valret' variable
      return valret;
   }
});

Create two models with the names account and staff. Open the app/models/account.js file and include the following code −

import DS from 'ember-data';
import Model from "ember-data/model";
import attr from "ember-data/attr";

//defines one-to-one and one-to-many relationship between models
import { belongsTo, hasMany } from "ember-data/relationships";

export default DS.Model.extend({
   //when async is 'true', it will fetch related entries
   firstVal: belongsTo('staff', {async: true}),
   secondVal: belongsTo('staff', {async: true})
});

Now open the app/models/staff.js file and include the following code −

import DS from 'ember-data';
import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default DS.Model.extend ({
   //specifying attributes using 'attr()' method
   name: attr()
});

Next, create a route and name it as application.js. Open this file, which is created under app/routes/ and add the following code −

import Ember from 'ember';

export default Ember.Route.extend ({
   model(){
      //returns the value of model() hook
      return this.get('store').findRecord('account', 100);  //retrieve a record for specific id        
   }
});

Create a serializer with the name application by using the following command −

ember generate serializer serializer_name

Open the app/serializers/application.js file and add the following code −

import DS from 'ember-data';

//it is the default serializer and works with JSON API backends
export default DS.JSONAPISerializer.extend ({
   
   //keyForRelationship() method overwrites the naming conventions
   keyForRelationship: function(key, relationship, method) {
      return Ember.String.camelize(key);  //returns the lowerCamelCase form of a string
   }
});

Open the application.hbs file created under app/templates/ with the following code −

<h2>Model Relationships</h2>
//display the id along with the name
{{model.firstVal.id}} : {{model.firstVal.name}}
<br>
{{model.secondVal.id}} : {{model.secondVal.name}}
{{outlet}}

Output

Run the ember server; you will receive the following output −

Relationship

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