Realm Database Basics: Offline-First Storage Quiz Quiz

Explore key concepts of offline-first storage and essential features of Realm database with this quiz. Assess your understanding of data persistence, synchronization, and schema in offline-enabled database solutions.

1. Understanding Realm Data Persistence

   Which of the following best describes how Realm stores data on a device for offline-first use?

   1. It stores everything in RAM memory and clears data when the app closes.
   2. It encrypts data but does not save it persistently on the device.
   3. It saves data directly to the device’s local storage so it remains accessible without an internet connection.
   4. It transfers data to cloud only and deletes local copies immediately.

   Explanation: Realm is designed for offline-first scenarios by storing data directly on the device’s storage, making it available without a network. The cloud-only, RAM-only, and non-persistent encryption options do not offer true offline capability since they lack persistent device storage. This ensures users can always access their data, even when disconnected.

2. Defining a Data Schema

   What is required before you can store structured data in a Realm database, for example saving a 'Book' with fields like title and author?

   1. You must define a data schema to describe the structure of your objects.
   2. You must enable background internet access.
   3. You need to pre-insert sample data.
   4. You have to use unstructured plain text blobs.

   Explanation: A data schema defines the structure of each object—such as field names and types—in Realm storage. Without a schema, the database cannot know what to expect when saving data. Pre-inserting data, requiring internet, or using unstructured blobs does not establish a predictable data format. Having a schema ensures data integrity and querying reliability.

3. Basic Data Operations

   Which of the following is a data operation that Realm allows you to perform offline?

   1. Scheduling cloud-only backup routines.
   2. Streaming real-time updates from a remote server.
   3. Running SQL commands directly on the device.
   4. Reading and writing data synchronously to local storage.

   Explanation: Realm supports reading and writing data directly to local device storage without needing a constant internet connection. Scheduling cloud backups or streaming updates are network-dependent and not true offline operations. Realm does not use traditional SQL commands, as it relies on its own methods for data manipulation.

4. Data Synchronization Principles

   In an offline-first architecture, what usually happens when the device regains connectivity after a period offline?

   1. Only new server data is downloaded, ignoring local edits.
   2. All local data is deleted and restarted from the server.
   3. Locally stored changes are synchronized with the server.
   4. Synchronization is permanently disabled after any offline session.

   Explanation: When reconnecting, offline-first storage typically synchronizes local changes with the server to ensure everything stays up to date. Deleting local data or ignoring local edits would risk data loss. Synchronization isn't permanently disabled, as ongoing sync is a core offline-first feature.

5. Querying Data When Offline

   If a user wants to retrieve all 'Task' entries marked as completed, how does Realm handle this when the device is offline?

   1. It sends an empty result, assuming no data can be found.
   2. It blocks the query until internet returns.
   3. It refreshes all data from the cloud first before querying.
   4. It queries the local database and returns all matching entries.

   Explanation: Realm stores data locally, so users can execute queries like retrieving completed tasks even without the internet. Blocking or refreshing via the network would undermine offline-first performance. Always returning an empty result is incorrect since objects are available offline.

6. Atomic Transactions

   What is the benefit of performing data writes in an atomic transaction in Realm?

   1. It ensures all changes succeed together or are completely rolled back if there’s an error.
   2. It increases network speed.
   3. It helps prevent organizing data into tables.
   4. It limits storage size artificially.

   Explanation: Atomic transactions mean that either all write operations succeed, or if an error occurs, none of the changes are applied. Enhancing network speed, preventing tables, or limiting storage are unrelated to transaction atomicity. This benefits data consistency and prevents partial updates.

7. Supported Data Types

   Which of the following is a commonly supported data type for object fields in Realm?

   1. String
   2. Server
   3. Thread
   4. Socket

   Explanation: Realm supports common data types like String for storing text values. Socket, Thread, and Server are unrelated to stored field types; they relate to networking, execution, or infrastructure instead. Using supported types ensures data can be efficiently stored and queried.

8. Relationship Modeling

   How do you typically represent a one-to-many relationship, such as a 'User' with multiple 'Notes', in Realm?

   1. Reference 'User' from each 'Note' only.
   2. Save all notes in one unstructured text blob field.
   3. Use an array or list property in 'User' that points to multiple 'Notes'.
   4. Use a single text field that concatenates all 'Notes'.

   Explanation: A one-to-many relationship in Realm is modeled by adding a list or array property to the 'User' object referencing multiple 'Notes'. Concatenated text fields, referencing only from 'Note', or saving as unstructured blobs lose structure and query flexibility. Arrays or lists keep relationships clear and navigable.

9. Data Synchronization Conflict Resolution

   When two devices update the same record offline and later reconnect, how does a database like Realm typically handle such conflicts?

   1. It crashes the app to avoid data issues.
   2. It always picks the older value and deletes new updates.
   3. It silently discards all user changes.
   4. It merges changes based on resolve policies such as last-write-wins or custom logic.

   Explanation: Conflict resolution is handled by merging changes according to predefined or custom rules, ensuring data consistency. Simply choosing older values, crashing, or discarding data compromises reliability and user trust. Proper conflict management is crucial for syncing in offline-first systems.

10. Zero-Copy Reads

    What does it mean that Realm uses zero-copy reads for accessing stored data?

    1. Data is accessed directly from storage without being copied into memory unless needed.
    2. Data must be fully decrypted into RAM before every read.
    3. Each read requires making a backup to external drives.
    4. Data is always moved into cloud before reading.

    Explanation: Zero-copy reads mean that queries access data directly from the local storage, improving performance and memory usage. Always moving to the cloud, forcing decryption into RAM for every read, or backing up before reading are inefficient or unnecessary. Direct, efficient access is a key feature for speedy offline-first storage.