Embedded

@Target(allowedTargets = [AnnotationTarget.FIELD, AnnotationTarget.FUNCTION])
@Retention(value = AnnotationRetention.BINARY)
public annotation Embedded

Marks a property of an Entity or data object to allow nested properties (i.e. properties of the annotated property's class) to be referenced directly in the SQL queries.

If the container is an Entity, these sub properties will be columns in the Entity's database table.

For example, if you have 2 classes:

data class Coordinates (
  val latitude: Double,
  val longitude: Double
)

data class Address (
  val street: String,
  @Embedded
  val coordinates: Coordinates
)

Room will consider latitude and longitude as if they are properties of the Address class when mapping an SQLite row to Address.

So if you have a query that returns street, latitude, longitude, Room will properly construct an Address object.

If the Address class is annotated with Entity, its database table will have 3 columns: street, latitude and longitude.

If there is a name conflict with the properties of the sub data object and the owner object, you can specify a prefix for the properties of the sub object. Note that the prefix is always applied to sub properties even if they have a ColumnInfo with a specific name.

If sub properties of an embedded property has PrimaryKey annotation, they will not be considered as primary keys in the owner Entity.

Nullable Embedded Properties

When constructing an embedded property that is nullable, if all columns in the row for the properties of the embedded (and its sub properties) are null then the embedded property will be set to null. Otherwise, it is constructed.

Note that even if you have TypeConverters that converts a null column into a non-nullvalue, if all columns of the embedded property are null, the TypeConverter will never be used and the embedded property will not be constructed.

This behavior only applies to nullable embedded properties and can be overridden by making the property non-null.

Summary

public Embedded(@NonNull String prefix)

public final @NonNull String getPrefix()

@Embedded(prefix = "loc_")
val coordinates: Coordinates