Android Room FOREIGN KEY Constraint Failed: Even though Values are the Same

Are you struggling with implementing a foreign key constraint in your Android Room database? No matter what you try, it seems to always throw an error? Well, you’re not alone! Many developers have faced similar challenges when working with Room and foreign keys. In this blog post, we will explore the issue you’re facing and provide some insights to help you resolve it.

The Problem

You are working on an Android app that involves storing playlists in a Room database. The Playlists table contains information such as the playlist’s name, associated album art, and an ID. On the other hand, the Songs table holds details about individual songs, including the song ID, title, album, artist, album art, duration, and the playlist ID as a foreign key.

However, despite your efforts, the code that inserts data into the Songs table is encountering a FOREIGN KEY constraint failed error, even though the values you’re using for the foreign key match the ones in the Playlists table.

Troubleshooting Steps

You’ve already tried a few potential solutions to fix this issue, but let’s go over them again briefly:

1. Creating a Separate Key: Initially, you attempted to use a separate key for the child table (Songs) instead of relying on the auto-generated primary key from the parent table (Playlists). However, this approach did not resolve the problem.
2. Hard-Coding Values: Another approach you tried was hard-coding the values for the foreign key in an attempt to pinpoint any potential issues. Unfortunately, this did not yield the desired results either.
3. Adding Log Entries: To gain further insight, you added log entries to track the values you’re inserting into the database. These logs confirmed that the value being inserted into the playlist_id column is exactly the same as the one queried from the database, ruling out any value mismatch.

Despite these attempts, the FOREIGN KEY constraint error persists, leaving you perplexed and in need of a solution.

Identifying the Root Cause

After reviewing your code and the scenario you described, there seems to be one key issue that stands out: the usage of two separate databases for the Playlists and Songs entities. This separation is causing the FOREIGN KEY constraint failure because the Songs table is unable to find the corresponding playlist in a different database.

To resolve this, you should have only one database that contains both the Playlists and Songs tables. By storing both entities in the same database, you establish the necessary relationship through the FOREIGN KEY CONSTRAINT and enable seamless operations between them.

Solution: One Database, Two Tables

To address the FOREIGN KEY constraint failure, let’s make the following changes to your code:

1. Merge the Playlists and Songs tables into one database. This will ensure they are in the same database and can reference each other properly.
2. Remove the index column from the Playlists entity, as it seems redundant given that you already have an id column. Keep only the id column as your primary key.

By following these modifications, you’ll have a single database with two related tables, allowing the foreign key constraint to work as intended.

One Database, Two Tables

To address the FOREIGN KEY constraint failure, the recommended solution is to have both the Playlists and Songs tables in a single database. By storing both entities in the same database, you establish a direct relationship between them, enabling the foreign key constraint to work as intended.

1. Merge the Tables: Combine the Playlists and Songs tables into a single database. This can be achieved by creating a single database class that includes both entities.

code





@Database(entities = {Playlists.class, Songs.class}, version = 1)
public abstract class MusicDatabase extends RoomDatabase {
    public abstract PlaylistsDao playlistsDao();
    public abstract SongsDao songsDao();
    // ...
}

2. Remove Redundant Column: Since you already have an id column in the Playlists table, you can remove the index column, as it seems redundant. Keep only the id column as your primary key.

code






@Entity(indices = {@Index(value = {"id"}, unique = true) }, tableName = "playlists")
public class Playlists {
    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "id")
    public int id;
    // ...
}

By implementing these changes, you will have a single database with two related tables, enabling seamless interaction between playlists and songs.

Conclusion

Dealing with foreign key constraints in Android Room databases can be challenging, but by following best practices and ensuring that your entities are stored in the same database, you can overcome these hurdles. The modifications suggested in this article should help you resolve the FOREIGN KEY constraint failure you encountered.

If you have any further questions or face any difficulties, feel free to ask for assistance. Database management and relationship handling are crucial aspects of app development, and it’s important to ensure they are implemented correctly.

We hope this article has provided you with valuable insights and solutions for your Android Room database implementation. Good luck with your playlist storage feature, and happy coding!