sqlite - Android Room Persistence Library: Upsert

Question

Android's Room persistence library graciously includes the @Insert and @Update annotations that work for objects or collections. I however have a use case (push notifications containing a model) that would require an UPSERT as the data may or may not exist in the database.

Sqlite doesn't have upsert natively, and workarounds are described in this SO question. Given the solutions there, how would one apply them to Room?

To be more specific, how can I implement an insert or update in Room that would not break any foreign key constraints? Using insert with onConflict=REPLACE will cause the onDelete for any foreign key to that row to be called. In my case onDelete causes a cascade, and reinserting a row will cause rows in other tables with the foreign key to be deleted. This is NOT the intended behavior.

Answer 1

Perhaps you can make your BaseDao like this.

secure the upsert operation with @Transaction, and try to update only if insertion is failed.

@Dao
public abstract class BaseDao<T> {
    /**
    * Insert an object in the database.
    *
     * @param obj the object to be inserted.
     * @return The SQLite row id
     */
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    public abstract long insert(T obj);

    /**
     * Insert an array of objects in the database.
     *
     * @param obj the objects to be inserted.
     * @return The SQLite row ids   
     */
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    public abstract List<Long> insert(List<T> obj);

    /**
     * Update an object from the database.
     *
     * @param obj the object to be updated
     */
    @Update
    public abstract void update(T obj);

    /**
     * Update an array of objects from the database.
     *
     * @param obj the object to be updated
     */
    @Update
    public abstract void update(List<T> obj);

    /**
     * Delete an object from the database
     *
     * @param obj the object to be deleted
     */
    @Delete
    public abstract void delete(T obj);

    @Transaction
    public void upsert(T obj) {
        long id = insert(obj);
        if (id == -1) {
            update(obj);
        }
    }

    @Transaction
    public void upsert(List<T> objList) {
        List<Long> insertResult = insert(objList);
        List<T> updateList = new ArrayList<>();

        for (int i = 0; i < insertResult.size(); i++) {
            if (insertResult.get(i) == -1) {
                updateList.add(objList.get(i));
            }
        }

        if (!updateList.isEmpty()) {
            update(updateList);
        }
    }
}