This is my first ROOM implementation. I have a User class which has a list of Pets as one of its member variables.
public class User {
String id;
String name;
List<Pet> pets;
}
Public class Pets {
String id;
String type;
}
How to create its Entity and DAO classes for Room Database from the following JSON?
{
"users":[
{
"id":"as123",
"name":"John",
"pets":[
{
"id":"p123",
"type":"dog"
}
]
},
{
"id":"as343",
"name":"Mark",
"pets":[
{
"id":"p324",
"type":"dog"
},
{
"id":"p254",
"type":"cat"
}
]
}
]
}
I have created the following but not sure how to create a correct column or Join these tables.
Entity Classes
@Entity(tableName = "user")
public class User {
@PrimaryKey
@NonNull
@ColumnInfo(name = "id")
String id;
@Nullable
@ColumnInfo(name = "name")
String name;
List<Pets> pets; // how to set type for Pets
}
@Entity(tableName = "pets",
foreignKeys = @ForeignKey(entity = User.class,
parentColumns = "id",
childColumns = "userId",
onDelete = CASCADE))
Public class Pets {
@PrimaryKey
@NonNull
@ColumnInfo(name = "id")
String id;
@Nullable
@ColumnInfo(name = "type")
String type;
@NonNull
@ColumnInfo(name = "userId")
String userId; // for accessing pets of a user
}
DAO classes
@Dao
public interface PetsDAO {
@Insert
void insert(Pets pets);
@Update
void update(Pets... pets);
@Delete
void delete(Pets... pets);
@Query("SELECT * FROM pets WHERE id=:userId")
List<Pets> getPetsForUser(final String userId);
}
@Dao
public interface UserDAO {
@Insert
void insert(User pets);
@Update
void update(User... pets);
@Delete
void delete(User... pets);
@Query("SELECT * FROM user)
List<User> getAllUsers(); // should return list of users with all their pets
}
How can I get a List
of users with all of their respective pets?
This is a many-to-many relation so you have to create a join table: UserPetsJoin table with the petId and userId; Here you can find a good topic explaining you're same situation: https://android.jlelse.eu/android-architecture-components-room-relationships-bf473510c14a