Realm database in React Native - Build, Publish & Deploy

Build & Publish - Realm database

Performance Impact of Realm Database

Realm is designed for fast local data storage on mobile devices. It offers near-native speed with low latency for read and write operations, helping maintain smooth UI animations at 60fps or higher. Realm uses zero-copy architecture, which reduces memory overhead and CPU usage compared to traditional SQLite or JSON storage. This efficiency helps save battery life by minimizing background processing.

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How to Optimize Realm for 60fps Rendering

To keep your app smooth, avoid blocking the main thread with heavy Realm queries. Use asynchronous Realm APIs to fetch or write data without freezing the UI. Batch writes together instead of many small writes to reduce disk I/O. Also, use Realm's live objects and notifications to update UI reactively, so you only re-render components when data changes, saving CPU cycles.

Impact on App Bundle Size and Startup Time

Adding Realm to a React Native app increases the bundle size by about 5-10MB depending on platform and configuration. This is moderate and usually acceptable for apps needing local database features. Realm's native libraries are loaded on startup, which can add a small delay (under 500ms) to app launch time. To minimize impact, initialize Realm lazily after the splash screen or use code splitting.

iOS vs Android Differences for Realm Database

Realm uses native libraries on both iOS and Android, but setup differs. On iOS, Realm integrates with Swift/Objective-C runtime and requires CocoaPods or Swift Package Manager. On Android, it uses native JNI bindings and Gradle dependencies. iOS apps require code signing for Realm binaries, while Android apps need proper ABI splits to reduce APK size. Performance is similar, but Android devices vary more in hardware, so test on multiple devices.

Relevant Store Review Guidelines and Requirements

Both Apple App Store and Google Play require apps to handle user data securely. Realm stores data locally, so ensure you encrypt sensitive information using Realm's encryption features. Follow platform privacy policies by disclosing data storage in your privacy policy. Also, avoid excessive background data access to comply with battery and performance guidelines. For iOS, Realm binaries must be properly signed to pass App Store review.

Self-Check: Your App Takes 5 Seconds to Load This Screen. What's Likely Wrong?

Long load times often happen if you perform heavy Realm queries or data migrations on the main thread during screen load. Also, initializing Realm synchronously before UI renders can block the app. To fix this, move Realm initialization and queries to background threads or use async APIs. Avoid large data reads at startup; load data incrementally or on demand.

Key Result

Realm database offers fast, efficient local storage with minimal impact on UI smoothness and battery life. Optimize by using async queries and batching writes. It adds moderate bundle size and small startup delay. iOS and Android require different native setups and signing. Secure data and follow privacy rules to pass store reviews.

Practice

1. What is the primary purpose of using Realm database in a React Native app?

easy

A. To handle app navigation between screens

B. To store data locally on the device for fast access

C. To style the app's user interface

D. To connect the app to a remote SQL server

Solution

1. Step 1: Understand Realm's role

   Realm is a local database designed to store data on the device itself.

2. Step 2: Compare options

   Options A, B, and C describe unrelated functions like navigation, remote servers, and UI styling, which Realm does not handle.

3. Final Answer:

   To store data locally on the device for fast access -> Option B

4. Quick Check:

   Realm = local data storage [OK]

Hint: Realm is for local data, not UI or navigation [OK]

Common Mistakes:

• Confusing Realm with remote databases
• Thinking Realm manages UI or navigation
• Assuming Realm is a cloud service

2. Which of the following is the correct way to define a Realm schema for a Task object with a string name and a boolean completed property?

easy

A. const TaskSchema = {name: 'Task', properties: {name: 'string', completed: 'bool'}};

B. const TaskSchema = {name: 'Task', properties: {name: 'string', completed: 'boolean'}};

C. const TaskSchema = {name: 'Task', properties: {name: 'String', completed: 'Bool'}};

D. const TaskSchema = {name: 'Task', properties: {name: String, completed: Boolean}};

Solution

1. Step 1: Check Realm property types

   Realm expects property types as lowercase strings like 'string' and 'bool'.

2. Step 2: Compare options

   const TaskSchema = {name: 'Task', properties: {name: 'string', completed: 'bool'}}; uses correct lowercase strings. Options A, C, and D use incorrect types or JavaScript types instead of strings.

3. Final Answer:

   const TaskSchema = {name: 'Task', properties: {name: 'string', completed: 'bool'}}; -> Option A

4. Quick Check:

   Property types are lowercase strings [OK]

Hint: Use lowercase strings for property types in schema [OK]

Common Mistakes:

• Using JavaScript types instead of strings
• Capitalizing type names incorrectly
• Omitting the 'properties' key

3. Given the following code snippet, what will be the output of console.log(tasks.length);?

const realm = await Realm.open({schema: [TaskSchema]});
realm.write(() => {
  realm.create('Task', {name: 'Buy milk', completed: false});
  realm.create('Task', {name: 'Walk dog', completed: true});
});
const tasks = realm.objects('Task');
console.log(tasks.length);

medium

A. 0

B. 1

C. 2

D. Undefined

Solution

1. Step 1: Analyze write transaction

   Two Task objects are created inside the write block, so two entries are added.

2. Step 2: Check objects query

   realm.objects('Task') returns all Task objects, so length should be 2.

3. Final Answer:

   2 -> Option C

4. Quick Check:

   Created 2 tasks, length = 2 [OK]

Hint: Count created objects inside write block [OK]

Common Mistakes:

• Forgetting to use write block for create
• Assuming objects() returns empty before commit
• Confusing length with undefined

4. What is wrong with this Realm write transaction code? (Assume the TaskSchema defines name as the primary key)

realm.write(() => {
  realm.create('Task', {name: 'Read book', completed: false});
});
realm.write(() => {
  realm.create('Task', {name: 'Read book', completed: true});
});

medium

A. The second create will throw an error because a Task with the same primary key already exists

B. You cannot call realm.write() more than once

C. The second create will update the existing object automatically

D. There is no error; this code works fine

Solution

1. Step 1: Check schema requirements

   With name as primary key, creating an object with the same primary key without update flag causes error.

2. Step 2: Analyze code behavior

   The first create succeeds. The second create uses the same name (primary key) without update flag, so it throws an error.

3. Final Answer:

   The second create will throw an error because a Task with the same primary key already exists -> Option A

4. Quick Check:

   Duplicate primary key without update flag causes error [OK]

Hint: Use primary key and update flag to avoid create errors [OK]

Common Mistakes:

• Assuming multiple writes are forbidden
• Thinking create auto-updates without flags
• Ignoring primary key requirements

5. You want to update the completed status of a Task object named 'Laundry' to true. (Assume the Task schema defines name as the primary key) Which code snippet correctly performs this update in Realm?

hard

A. realm.write(() => { realm.objects('Task').filtered('name == "Laundry"').completed = true; });

B. realm.write(() => { realm.create('Task', {name: 'Laundry', completed: true}); });

C. realm.write(() => { realm.update('Task', {name: 'Laundry', completed: true}); });

D. realm.write(() => { realm.create('Task', {name: 'Laundry', completed: true}, true); });

Solution

1. Step 1: Understand update with create

   Realm updates existing objects if you pass true as the third argument to create.

2. Step 2: Check each option

   realm.write(() => { realm.create('Task', {name: 'Laundry', completed: true}, true); }); uses true flag correctly. realm.write(() => { realm.create('Task', {name: 'Laundry', completed: true}); }); tries to create without update flag, causing error. realm.write(() => { realm.objects('Task').filtered('name == "Laundry"').completed = true; }); tries to assign directly to filtered results, which is invalid. realm.write(() => { realm.update('Task', {name: 'Laundry', completed: true}); }); uses a non-existent update method.

3. Final Answer:

   realm.write(() => { realm.create('Task', {name: 'Laundry', completed: true}, true); }); -> Option D

4. Quick Check:

   Use create with true flag to update [OK]

Hint: Use true flag in create to update existing objects [OK]

Common Mistakes:

• Forgetting the update flag for updates
• Trying to assign directly to query results
• Using non-existent Realm methods