Realm read data with relationship

Question

I'm working on realm to make it work offline as local db in Electron. Now I want to make join(aggregation), so I defined a relationship between two schema's but then the data is not getting synced. It would be great to get help.

Here's my schema:

const articleMetaSchema = {
    name: 'articlemeta',
    properties: {
      _id: 'objectId?',
      catalog_id: 'objectId?',
      content: 'objectId?',
      createdAt: 'date?',
      description: 'string?',
      main_image_url: 'string?',
      origin_type: 'string?',
      pub_date: 'date?',
      publication: 'objectId?',
      sub_title: 'string?',
      title: 'string?',
      updatedAt: 'date?',
      url: 'string?'
    },
    primaryKey: '_id'
  }

const articleSchema = {
    name: 'article',
    properties: {
      _id: 'objectId?',
      active_search: 'bool?',
      article_meta: 'articlemeta?',
      catalog_id: 'objectId?',
      content: 'objectId?',
      createdAt: 'date?',
      flagged: 'bool?',
      owner_id: 'objectId?',
      rating: 'int?',
      read: 'bool?',
      status: 'string?',
      status_updated_at: 'date?',
      updatedAt: 'date?'
    },
    primaryKey: '_id'
  }


config = {
            schema,
            path: getDBPath(),
            sync: {
              user: app.currentUser,
              partitionValue: new ObjectID(getCatalogId()),
              error: (error) => {
                console.log(error.name, error.message)
              }
            }
        }
        let realm = await Realm.open(config)
        // query

I want to query and get the article result and in article schema we have defined a key 'article_meta' which is and objectId. Now I want article result with all the properties with article_meta as an object fetched on the basis of (article.article_meta = articlemeta._id)

Expected result:

[{ _id: '1', catalog_id: '', content: '', createdAt: '', main_image_url: '', origin_type: '', pub_date: '', publication: '', sub_title: '', title: '', updatedAt: '', url: '', article_meta: {} }, {..}, {..}]

user_2851937 · Answer

Realm objects can reference 'joined' realm objects via dot notation. from the docs

Filter on Related and Embedded Object Properties

To filter a query based on a property of an embedded object or a related object, use dot-notation as if it were in a regular, nested object.

So for example, a Person object has a Dog object as one of it's properties and you want to get that pesons' dogs name.

Let's get a specific person by their _id

const person = realm.objectForPrimaryKey("Person", 1234)

if we then want the persons dogs name

const dogName = person.dog.dog_name

In your case you can get a specific article, and then access all of the articlemeta properties using dot notation

const article = realm.objectForPrimaryKey("article", 1234)

and then access the rest of the properties through dot notiation

const id = article._id
const catalogId = article.catalog_id
const mainImageUrl = article.article_meta.main_image_url

As you can see, a query is not needed (for this example) as the Realm objects know their own child properties and can be accessed via dot notation.

Realm read data with relationship

1 Answers