Create a Schema

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Overview

Create a Realm Object Model from a Realm Schema
Create a Realm Schema from a Realm Object Model

Overview

You can create a schema for your Realm app in one of two ways:

Create a Realm Object Model from a Realm Schema: If you have data in your MongoDB Atlas cluster already, MongoDB generates a Realm Schema by sampling your data. MongoDB Realm can then translate that Realm Schema into a Realm Object Model to use in your mobile application.
Create a Realm Schema from a Realm Object Model: Alternatively, if you are developing mobile-first and do not already have data in your Atlas cluster, you can translate your Realm Object Model into a Realm Schema for use with Atlas. Regardless of the approach that you take, when you configure both your Atlas cluster and Mobile application to use the respective data model, changes to the data model between the server and client are auto-updated.

Create a Realm Object Model from a Realm Schema

Note

Link a MongoDB Atlas Data Source

Your app must have at least one linked data source in order to define a Realm data model.

You cannot use sync with a serverless instance or data lake.

Define a Realm Schema

To get started, ensure you have a Realm Schema defined. MongoDB Realm will translate this Realm Schema into a Realm Object Model to be configured and utilized in your mobile application.

Important

Primary Key _id Required

To work with Realm Sync, your data model must have a primary key field called _id. _id can be of type string, int, uuid, ObjectId, or objectId.

Note

To learn how to define a schema for a collection in the synced cluster, see Enforce a Schema.

View the Realm Object Model

The Realm Object Model defines and validates your data in your mobile client application. To view your Realm Object Model, navigate to the SDKs page, where you can view your Realm Schema as a generated Realm Object Model in your language of choice.

The generated Realm Object Models and associated warnings in the UI

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View and Fix Schema Errors

Realm may fail to generate some or all of your Realm Object Model based on your Realm Schema. You can view a list of the errors in your Realm Schema that prevented Realm from generating the Realm Object Model on the SDKs page of the Realm UI.

Common errors include mismatched types, and differences in the way relationships are represented in the two respective models. For each error or warning, modify your Realm Schema to fix the specified issue.

A detailed list in the UI of warnings and errors that occurred during model

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Open a Realm with the Realm Object Model

You can immediately use the generated Realm Object Model in your client application. In order to begin enforcing data validation with your data model, you can open a Realm with the Realm Object Model. This will prevent improper data from entering your database from your mobile client. Click Copy on the right-hand side of the Realm Object Model for the Object Model you want to integrate into your mobile application code. This will copy the Realm Object Model code for the SDK of your choice into your clipboard. Open your mobile application code in your IDE and paste the Realm Object Model code in.

Tip

Create a Realm Schema from a Realm Object Model

Note

Link a MongoDB Atlas Data Source

Your Realm app must have at least one linked data source in order to define a Realm Data Model.

You cannot use sync with a serverless instance or data lake.

Enable Development Mode Sync

First, enable Development Mode sync.

You can alter or define a Realm Object Model through your mobile client SDK. Changes to your Realm Object Model are only allowed when Development Mode is on in the MongoDB Realm UI. MongoDB Realm will reflect these changes to your Realm Object Model in your Realm Schema used for Atlas.

Edit Your Realm Object Model

As you continue to develop your application, you will need to modify your data model with it to enforce different data validation rules based on those changes. While Development Mode is on, you can edit your Realm Object Model in your client code. Data Validation occurs when Development Mode is off, so MongoDB Realm does not accept changes to your Realm Object Model while Development Mode is not on.

Important

Primary Key _id Required

To work with Realm Sync, your data model must have a primary key field called _id. _id can be of type string, int, or objectId.

Example

A group is developing a social media application. When the group first developed their application, a user's birthday was a required field of the User's data model. However, due to privacy concerns over the amount of user data that is stored, management creates a new requirement to make the user's birthday field an optional field. Application developers turn on Development Mode in the MongoDB Realm UI and then edit their user model within their client code.

const realmObjectModel = {
  name: 'User',
  properties: {
    _id: 'objectId',
    _partition: 'string',
    name: 'string',
    birthday: {type: 'date', optional: true}, // developers set optional: true to adhere to the new requirement
  },
  primaryKey: '_id'
};
Realm.open({schema: realmObjectModel, sync: {/*...*/}})
  .then(realm => {
    // ... use the realm instance to read and modify data
  })

Tip

Update Your Realm Schema with the Realm Object Model Changes

While Development Mode is on, MongoDB Realm doesn't validate writes against your data model, allowing you to freely update your Realm Object Model. When you turn off Development Mode, MongoDB Realm automatically updates your Realm Schema and starts to enforce data validation for your Atlas cluster based on it.

Click the "Turn Dev Mode Off" button on the top banner or in the Sync screen to turn off Development Mode. Once you turn off Development Mode, the "Development Mode is OFF" modal will appear. The modal indicates that MongoDB Realm has stopped accepting new data model changes from clients. Click the "View my Realm Schema" button on the modal to view your updated Realm Schema.

Note

To make future data model updates from your mobile client code, you can follow this procedure again.