Embedded
public
abstract
@interface
Embedded
implements
Annotation
androidx.room.Embedded |
Marks a field of an Entity
or POJO to allow nested fields (i.e. fields of the annotated
field's class) to 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
and 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 fields 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 TypeConverter
s 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
public 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 = "loc_") Coordinates coordinates;The column names for
latitude
and longitude
will be loc_latitude
and
loc_longitude
respectively.
By default, prefix is the empty string.
Returns | |
---|---|
String |
The prefix to be used for the fields of the embedded item. |