Embedded

public abstract @interface Embedded
implements Annotation

android.arch.persistence.room.Embedded

Can be used as an annotation on a field of an Entity or Pojo to signal that nested fields (i.e. fields of the annotated field's class) can be referenced directly in the SQL queries.

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

For example, if you have 2 classes: 

   public class Coordinates {
       double latitude;
       double longitude;
   }
   public class Address {
       String street;
       @Embedded
       Coordinates coordinates;
   }
Room will consider latitude and longitude as if they are fields 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 class.

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

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

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

When an embedded field is read, if all fields of the embedded field (and its sub fields) are null in the Cursor, it is set to null. Otherwise, it is constructed.

Note that even if you have TypeConverters that convert a null column into a non-null value, if all columns of the embedded field in the Cursor are null, the TypeConverter will never be called and the embedded field will not be constructed.

You can override this behavior by annotating the embedded field with NonNull.

Summary

Public methods

String prefix()

Specifies a prefix to prepend the column names of the fields in the embedded fields.

Inherited methods

Public methods

prefix

String prefix ()

Specifies a prefix to prepend the column names of the fields in the embedded fields.

For the example above, if we've written: 

   @Embedded(prefix = "foo_")
   Coordinates coordinates;
The column names for latitude and longitude will be foo_latitude and foo_longitude respectively.

By default, prefix is the empty string.

Returns
String The prefix to be used for the fields of the embedded item.