Android Room Persistence Library: Achieving Upsert Functionality

2024-07-27

In database management, "upsert" (insert or update) is a convenient operation that simplifies data persistence.
It combines the logic of inserting a new row if it doesn't exist or updating an existing row if it does, based on a unique identifier (primary key).
While SQLite (the underlying database used by Android Room) doesn't have a built-in upsert function, Android Room provides annotations and techniques to achieve similar behavior.

Room's Approach to Upsert

Leveraging Annotations (@Insert or @Update):

Room offers @Insert and @Update annotations on DAO (Data Access Object) methods to handle insertions and updates, respectively.
However, using these annotations individually requires you to explicitly check for existing data before deciding between insert or update.

Custom Upsert Logic (For More Control):

For greater control and flexibility, you can create a custom upsert method in your DAO:
- This method typically performs a query to check for the existence of the entity based on its primary key.
- If the entity exists, an update query is executed.
- If not, an insert query is performed.

Here's an example of a custom upsert method:

@Dao
public interface MyDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void upsert(MyEntity entity);

    // Implementation of upsert using query and REPLACE strategy
    @Query("SELECT * FROM MyEntity WHERE id = :id")
    MyEntity findById(long id);

    @Update(onConflict = OnConflictStrategy.REPLACE)
    int update(MyEntity entity);
}

Explanation:

The custom upsert method:
- Takes a MyEntity object as input.
- Calls findById to check if an entity with the same id exists.
- Based on the return value of findById:
  - If findById returns null (entity doesn't exist), insert is called with onConflictStrategy.REPLACE.
- onConflictStrategy.REPLACE ensures that if a row with the same primary key already exists, it's replaced with the new data.

Key Considerations:

Android Version: If you require native upsert functionality (available in SQLite versions 3.24.0 and above), your app needs to target Android 11 (API level 30) or higher, as these versions include the necessary SQLite library by default.
Custom SQLite (Pre-Android 11): For earlier Android versions, you might consider using a custom SQLite library that supports upsert natively (like requery/sqlite-android). However, this introduces additional dependencies and potential maintenance overhead.

In Summary:

Android Room doesn't have a native upsert method, but it provides annotations and workarounds to achieve similar behavior.
Custom upsert logic offers more control over the insertion/update process.
The choice between approaches depends on your specific requirements, Android version support, and complexity trade-offs.

@Entity(tableName = "my_table")
data class MyEntity(
    @PrimaryKey val id: Long,
    val name: String,
    val description: String
)

This code defines the MyEntity class with the following properties:

id: Long (primary key)
name: String
description: String

DAO with Custom Upsert (MyDao.kt):

@Dao
public interface MyDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void upsert(MyEntity entity);

    // Implementation of upsert using query and REPLACE strategy
    @Query("SELECT * FROM MyEntity WHERE id = :id")
    MyEntity findById(long id);

    @Update(onConflict = OnConflictStrategy.REPLACE)
    int update(MyEntity entity);
}

This code defines the MyDao interface:

upsert: This custom method takes a MyEntity object and performs the upsert logic.
findById: This method checks if an entity with the provided id exists in the database.
update: This method updates an existing entity in the database (used by the custom upsert).

Explanation (refer to previous explanation for details):

The upsert method checks for the existence of the entity using findById.
Based on the result, it calls either insert or update with onConflictStrategy.REPLACE.

Using the Upsert Functionality:

// Assuming you have an instance of MyDao (e.g., myDao)
MyEntity newEntity = new MyEntity(10, "New Item", "This is a new item");
myDao.upsert(newEntity);

This code snippet creates a new MyEntity object and calls the upsert method on the myDao instance. This will insert the new entity into the database if it doesn't exist, or update an existing entity with the same id (10).

While not a true upsert, this approach simplifies the code compared to a custom method.
Annotate your insert method in the DAO with @Insert(onConflict = OnConflictStrategy.REPLACE).
This strategy inserts a new row if it doesn't exist, otherwise it replaces the existing row with the new data based on the primary key.

Here's an example:

@Dao
public interface MyDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertOrUpdate(MyEntity entity);
}

The insertOrUpdate method simply inserts the provided MyEntity object.

This method might not be suitable if you need to perform additional logic during updates (e.g., only updating specific fields).

Native Upsert (Android 11 and Above):

If your app targets Android 11 (API level 30) or higher, you can leverage the native upsert functionality available in SQLite version 3.24.0 and above.
However, this approach requires using raw SQL queries and might be less readable than using Room annotations.

Here's an example (replace MyEntity with your actual table name and column names):

@Dao
public interface MyDao {

    @RawQuery(observedMutations = true)
    void upsert(String query, MyEntity entity);
}

The upsert method takes a raw SQL query string and a MyEntity object.
You'll need to construct the appropriate INSERT OR REPLACE query dynamically based on the entity's properties.
observedMutations = true ensures Room is notified of changes made by the raw query.

This approach requires more manual work and can be less maintainable compared to using Room annotations.

Choosing the Right Method:

The best method depends on your specific needs and preferences.
If you need a simple solution and don't require additional logic during updates, @Insert(onConflict = OnConflictStrategy.REPLACE) might be sufficient.
For more granular control or if you're targeting Android versions below 11, the custom upsert logic provides more flexibility.
If targeting Android 11 or higher and are comfortable with raw SQL, the native upsert can be an option, but consider the trade-offs in maintainability.

android sqlite android-room