Not able to get query results using Room persistence

Question

I am developing an Android app using the Room persistence library. I have a User and a Car entity

@Entity(tableName = "users")
public class User {

    @PrimaryKey
    @NonNull
    private int id;
    private String name;

    public User(@NonNull int id, String name) {
        this.id = id;
        this.name = name;
    }
}

and

@Entity(tableName = "cars", foreignKeys = @ForeignKey(parentColumns  = 
"id", childColumns = "userId", entity = User.class))
public class Car {

    @PrimaryKey(autoGenerate = true)
    private int id;
    private int userId;
    private String brand;

    public Car(int userId, String brand) {
        this.userId = userId;
        this.brand = brand;
    }
}

Also I have created a UserWithCar class as below:

public class UserWithCar {

    @Embedded(prefix = "user_")
    public User user;

    @Embedded(prefix = "car_")
    public Car car;
}

As you can see in the UserWithCar I use a prefix cause if I don't I get the following error:

Multiple fields have the same columnName: id. Field names: user > id, car > id.

I want to get all the UserWithCar using the following query:

@Query("SELECT * FROM users JOIN cars ON users.id = cars.userId")
List<UserWithCar> getUserWithCar();

Using this query I get the following error:

The query returns some columns [id, name, id, userId, brand] which are not use by com.roomdemo.data.models.UserWithCar. You can use @ColumnInfo annotation on the fields to specify the mapping. com.roomdemo.data.models.UserWithCar has some fields [user_id, user_name, car_id, car_userId, car_brand] which are not returned by the query. If they are not supposed to be read from the result, you can mark them with @Ignore annotation. You can suppress this warning by annotating the method with @SuppressWarnings(RoomWarnings.CURSOR_MISMATCH). Columns returned by the query: id, name, id, userId, brand. Fields in com.foodtec.roomdemo.data.models.UserWithCar: user_id, user_name, car_id, car_userId, car_brand.

Can I have some help? Thanks!

Update Using @Wizard help, I removed the prefix from the @Embeded and I added @ColumnInfo "uId" for the User's id and "cId for the Car's id in order to not have the same id field. By this way it works!

Answer 1

Columns returned by the query: id, name, id, userId, brand. Fields in com.foodtec.roomdemo.data.models.UserWithCar: user_id, user_name, car_id, car_userId, car_brand.

Error indicates that, columns returned by query is different from Pojo class. It should be the same. Alternatively you can map your Pojo variable to column name using @ColumnInfo annotation.

For example,

@PrimaryKey
@NonNull
@ColumnInfo(name = "user_id")
private int id;

This way, id will be mapped to user_id.