Android room does not trigger when child table is changed on join query

Question

Imagine we have one to many relationship. Two tables, one is parent_table and another is child_table. Two entity classes called ParentEntity and ChildEntity. And one embeded class called ParentWithChild using it on join query result.

ParentEntity Class

@Entity(tableName = "parent_table")
data class ChildEntity(
        @ColumnInfo(name = "parent_id")
        @PrimaryKey(autoGenerate = false)
        val id: String,
        @ColumnInfo(name = "parent_name")
        val name: String,
)

ChildEntity Class

@Entity(
    tableName = "child_table",
    foreignKeys = [ForeignKey(
        entity = ParentEntity::class,
        parentColumns = ["parent_id"],
        childColumns = ["parent_owner_id"],
        onDelete = ForeignKey.CASCADE,
        onUpdate = ForeignKey.CASCADE,
        deferred = false
    )])
data class ChildEntity(
    @ColumnInfo(name = "child_id")
    @PrimaryKey(autoGenerate = false)
    val id: String,
    @ColumnInfo(name = "parent_owner_id")
    val childId: String,
    @ColumnInfo(name = "child_name")
    val name: String,
)

ParentWithChild Class

data class ParentWithChild(
    @Embedded
    val parent: ParentEntity?,
    @Embedded
    val child : ChildEntity?,
)

And the sample query in dao class is

@Query("""
       select * 
       from parent_table left join child_table on parent_table.parent_id = child_table.parent_owner_id 
    """)
abstract fun loadParentsWithChildren(): Flow<List<ParentWithChild>>

Now two scenarios come to play, if we use loadParentsWithChildren() mehtod.

1- If parent table is updated the trigger happens and the new data stream emitted by room.

2- If the child table is updated the room does not re fetch the join query statements.

My problem is the second scenario, what am I doing wrong ?

• Using Room Stable Release 2.2.6

Thanks in advance.

Answer 1

By adding enableMultiInstanceInvalidation() when creating room database, my problem solved.

@InstallIn(SingletonComponent::class)
@Module
class DatabaseModule {

    @Provides
    fun provideDatabase(@ApplicationContext context: Context): AppDatabase {
        return Room
            .databaseBuilder(context, AppDatabase::class.java, "app.db")
            .fallbackToDestructiveMigration()
            .enableMultiInstanceInvalidation()
            .build()
    }

}

But still I wonder that how I'm using different database instance since I'm using Hilt library and following singletone pattern, and I'm also not using database in multi process ...