• Realm >
• MongoDB Data Access >
• CRUD Operations

Delete Documents

Overview

The code snippets on this page demonstrate how to delete documents that are stored in a MongoDB collection. Delete operations use a query filter to specify which documents to delete.

Data Model

The examples on this page use a collection named store.items that models various items available for purchase in an online store. Each item has a name, an inventory quantity, and an array of customer reviews.

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// store.items
{
    "_id": { "bsonType": "objectId" },
    name: { "bsonType": "string" },
    quantity: { "bsonType": "int" },
    reviews: {
      "bsonType": "array",
      "items": {
        "username": { "bsonType": "string" },
        "comment": { "bsonType": "string" }
      }
    }
}

Snippet Setup

• Functions
• iOS SDK
• Android SDK
• JavaScript SDKs

To use a code snippet in a function, you must first instantiate a MongoDB collection handle:

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exports = function() {
  const mongodb = context.services.get("mongodb-atlas");
  const itemsCollection = mongodb.db("store").collection("items");
  const purchasesCollection = mongodb.db("store").collection("purchases");
}

To use a code snippet in an iOS project, you must first do the following:

1

Set Up Your Project

Follow the steps in the Install Realm for iOS, macOS, tvOS, and watchOS guide.

2

Import Realm Dependencies

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In scope (e.g. UIViewController)

import RealmCore
import RealmCoreRemoteMongoDBService
import RealmRemoteMongoDBService

3

Initialize the MongoDB Realm iOS SDK

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Application Startup (e.g. AppDelegate.didFinishLaunchingWithOptions())

do {
    let _ = try Realm.initializeDefaultAppClient(
        withClientAppID: "YOUR-APP-ID"
    )
} catch {
    print("Failed to initialize MongoDB Realm iOS SDK: \(error)")
}

4

Instantiate a MongoDB Collection Handle

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In scope (e.g. UIViewController)

// Variables in scope:
private lazy var realmClient = Realm.defaultAppClient!
private var mongoClient: RemoteMongoClient?
private var itemsCollection: RemoteMongoCollection<Document>?

// Set the realm variables declared above in viewDidLoad()
mongoClient = realmClient.serviceClient(
    fromFactory: remoteMongoClientFactory,
    withName: "mongodb-atlas"
)
itemsCollection = mongoClient?.db("store").collection("items")
purchasesCollection = mongoClient?.db("store").collection("purchases")

To use a code snippet in an Android project, you must first do the following:

1

Set Up Your Project

Follow the steps in the Install Realm for Android guide.

2

Import Realm Dependencies

For CRUD operations on a remote MongoDB collection, you will use one or more of the following import statements:

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// Base Realm Packages
import com.mongodb.realm.android.core.Realm;
import com.mongodb.realm.android.core.RealmAppClient;
// Realm Authentication Packages
import com.mongodb.realm.android.core.auth.RealmUser;
import com.mongodb.realm.core.auth.providers.anonymous.AnonymousCredential;

// MongoDB Service Packages
import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoCollection;
// Utility Packages
import com.mongodb.realm.core.internal.common.BsonUtils;

To Sync documents between a remote and a local MongoDB instance, you will also need to import the following packages:

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// Realm Sync Packages
import com.mongodb.realm.core.services.mongodb.remote.sync.ChangeEventListener;
import com.mongodb.realm.core.services.mongodb.remote.sync.DefaultSyncConflictResolvers;
import com.mongodb.realm.core.services.mongodb.remote.sync.ErrorListener;
import com.mongodb.realm.core.services.mongodb.remote.sync.internal.ChangeEvent;

Important

If you use Sync, be sure to add .sync() before every remote database call in the examples below, as in the following:

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itemsCollections.sync().find()

To perform CRUD operations only on the local (on-device) database, import the following packages:

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// MongoDB Mobile Local Database Packages
import com.mongodb.realm.android.services.mongodb.local.LocalMongoDbService;

3

Instantiate a MongoDB Collection Handle

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Top of Activity File

private RealmAppClient realmClient;
private RemoteMongoClient mongoClient;
private RemoteMongoCollection itemsCollection;

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In Activity.onCreate()

realmClient = Realm.getDefaultAppClient();
mongoClient = realmClient.getServiceClient(RemoteMongoClient.factory, "mongodb-atlas");

itemsCollection = mongoClient.getDatabase("store").getCollection("items");
purchasesCollection = mongoClient.getDatabase("store").getCollection("purchases");

To use a code snippet in a JavaScript project, you must first do the following:

1

Import Realm Dependencies

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Import from CDN

<!-- Import the Realm JS SDK at the top of the file -->
<script src="https://s3.amazonaws.com/realm-sdks/js/bundles/4/realm.js"></script>
<script>
  // Destructure Realm JS SDK Components
  const { Realm, RemoteMongoClient, BSON } = realm;
</script>

– or –

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Import from Module

// Import components of the Realm JS SDK at the top of the file
import {
  Realm,
  RemoteMongoClient,
  BSON
} from "mongodb-realm-browser-sdk";

2

Instantiate a MongoDB Remote Collection Handle

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const realmApp = Realm.initializeDefaultAppClient("<Your App ID>");
const mongodb = realmApp.getServiceClient(RemoteMongoClient.factory, "mongodb-atlas");

const itemsCollection = mongodb.db("store").collection("items");
const purchasesCollection = mongodb.db("store").collection("purchases");

Methods

Delete a Single Document

You can delete a single document from a collection using the collection.deleteOne() action.

The following snippet deletes one document in the items collection that has a name value of legos:

• Functions
• iOS SDK
• Android SDK
• JavaScript SDKs

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const query = { "name": "legos" };

itemsCollection.deleteOne(query)
  .then(result => console.log(`Deleted ${result.deletedCount} item.`))
  .catch(err => console.error(`Delete failed with error: ${err}`))

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let query : Document = ["name": "legos"];

itemsCollection?.deleteOne(query) { result in
    switch result {
    case .success(let result):
        print("Deleted \(result.deletedCount) item.");
    case .failure(let error):
        print("Delete failed with error: \(error)");
    }
}

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Document filterDoc = new Document().append("name", "legos");

final Task<RemoteDeleteResult> deleteTask = itemsCollection.deleteOne(filterDoc);
deleteTask.addOnCompleteListener(new OnCompleteListener <RemoteDeleteResult> () {
    @Override
    public void onComplete(@NonNull Task <RemoteDeleteResult> task) {
        if (task.isSuccessful()) {
            long numDeleted = task.getResult().getDeletedCount();
            Log.d("app", String.format("successfully deleted %d documents", numDeleted));
        } else {
            Log.e("app", "failed to delete document with: ", task.getException());
        }
    }
});

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const query = { "name": "legos" };

itemsCollection.deleteOne(query)
  .then(result => console.log(`Deleted ${result.deletedCount} item.`))
  .catch(err => console.error(`Delete failed with error: ${err}`))

Delete One or More Documents

You can delete multiple items from a collection using the collection.deleteMany() action.

The following snippet deletes all documents in the items collection that do not have any reviews:

• Functions
• iOS SDK
• Android SDK
• JavaScript SDKs

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const query = { "reviews": { "$size": 0 } };

itemsCollection.deleteMany(query)
  .then(result => console.log(`Deleted ${result.deletedCount} item(s).`))
  .catch(err => console.error(`Delete failed with error: ${err}`))

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let query : Document = ["reviews": ["$size": 0] as Document];

itemsCollection?.deleteMany(query) { result in
    switch result {
    case .success(let result):
        print("Deleted \(result.deletedCount) item(s).");
    case .failure(let error):
        print("Delete failed with error: \(error)");
    }
}

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Document filterDoc = new Document().append("reviews", new Document().append("$size", 0));

final Task <RemoteDeleteResult> deleteTask = itemsCollection.deleteMany(filterDoc);
deleteTask.addOnCompleteListener(new OnCompleteListener <RemoteDeleteResult> () {
    @Override
    public void onComplete(@NonNull Task <RemoteDeleteResult> task) {
        if (task.isSuccessful()) {
            long numDeleted = task.getResult().getDeletedCount();
            Log.d("app", String.format("successfully deleted %d documents", numDeleted));
        } else {
            Log.e("app", "failed to delete document with: ", task.getException());
        }
    }
});

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const query = { "reviews": { "$size": 0 } };

itemsCollection.deleteMany(query)
  .then(result => console.log(`Deleted ${result.deletedCount} item(s).`))
  .catch(err => console.error(`Delete failed with error: ${err}`))

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