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Create a Schema

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  • Overview
  • Create a Realm Object Model from an App Services Schema
  • Create an App Services Schema from a Realm Object Model

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

  • Create a Realm Object Model from an App Services Schema: If you have data in your MongoDB Atlas cluster already, MongoDB generates an App Services Schema by sampling your data. Atlas App Services can then translate that App Services Schema into a Realm Object Model to use in your mobile application.
  • Create an App Services 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 an App Services 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.
Note
Link a MongoDB Atlas Data Source

Your app must have at least one linked data source in order to define an App Services data model.

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

1

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

Important
Primary Key _id Required

To work with Atlas Device 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.

2

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 App Services Schema as a generated Realm Object Model in your language of choice.

The generated Realm Object Models and associated warnings in the UI
click to enlarge
3

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

A detailed list in the UI of warnings and errors that occurred during model
click to enlarge
4

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 an App Services 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
Note
Link a MongoDB Atlas Data Source

Your App must have at least one linked data source in order to define an App Services Data Model.

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

1

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 Atlas App Services UI. Atlas App Services will reflect these changes to your Realm Object Model in your App Services Schema used for Atlas.

2

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 Atlas App Services does not accept changes to your Realm Object Model while Development Mode is not on.

Important
Primary Key _id Required

To work with Atlas Device 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 Atlas App Services 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'
};
App Services.open({schema: realmObjectModel, sync: {/*...*/}})
.then(realm => {
// ... use the realm instance to read and modify data
})
3

While Development Mode is on, Atlas App Services doesn't validate writes against your data model, allowing you to freely update your Realm Object Model. When you turn off Development Mode, MongoDB App Services automatically updates your App Services 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 Atlas App Services has stopped accepting new data model changes from clients. Click the "View my App Services Schema" button on the modal to view your updated App Services Schema.

Note

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

The banner in the UI that shows Development Mode is enabled
click to enlarge
The modal that confirms turning off Development Mode in the UI
click to enlarge
←  Sync Schema OverviewEnable or Disable Development Mode →
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