无法使用会议室持久性获取查询结果 [英] Not able to get query results using Room persistence

问题描述

我正在使用Room Persistence库开发一个Android应用.我有一个用户和一个汽车实体

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;
    }
}

和

@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;
    }
}

我还创建了一个UserWithCar类，如下所示:

Also I have created a UserWithCar class as below:

public class UserWithCar {

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

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

正如您在UserWithCar中看到的那样，如果没有得到以下错误，我会使用前缀原因:

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

多个字段具有相同的columnName:id.字段名称:用户> ID， 汽车> ID.

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

我想使用以下查询获取所有UserWithCar:

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();

使用此查询，我收到以下错误:

Using this query I get the following error:

查询返回一些列[id，name，id，userId，brand] 不被com.roomdemo.data.models.UserWithCar使用.您可以使用 在字段上使用@ColumnInfo批注指定映射. com.roomdemo.data.models.UserWithCar有一些字段[user_id， user_name，car_id，car_userId，car_brand]不会返回 查询.如果不应该从结果中读取它们，则您 可以使用@Ignore批注对其进行标记.您可以禁止显示此警告 通过用 @SuppressWarnings(RoomWarnings.CURSOR_MISMATCH).传回的栏 查询:id，名称，id，userId，品牌.领域 com.foodtec.roomdemo.data.models.UserWithCar:user_id，user_name， car_id，car_userId，car_brand.

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.

我可以帮忙吗?谢谢！

更新 在@Wizard帮助下，我从@Embeded中删除了前缀，并为用户ID添加了@ColumnInfo"uId"，为汽车ID添加了"cId"，以便没有相同的ID字段.这样，它就可以工作了！

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!

推荐答案

查询返回的列:ID，名称，ID，用户ID，品牌.领域 com.foodtec.roomdemo.data.models.UserWithCar:user_id，user_name， car_id，car_userId，car_brand.

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.

错误表明，查询返回的列与Pojo类不同.应该是一样的.或者，您可以使用@ColumnInfo批注将Pojo变量映射到列名.

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.

例如，

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

这样，id将被映射到user_id.

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