Question

我有两个简单的location和houses表。我希望能够获取location及其所有相关信息，并将house计数添加到该查询中。 houseCount字段标记为@Ignored，因为我不想保存此字段。然而，房间似乎无法使用该字段从查询中返回数据，就像为查询指定为返回对象类型的任何其他类一样。

我的领域：

@Ignore
@ColumnInfo(name = EXTRA_COLUMN_LOCATION_HOUSE_COUNT)
public int houseCount;

我的位置构造函数：

public Location(long id, String name, LatLng location, long defaultRent, Date synced, int houseCount) {...}

我的查询：

SELECT locations.*, COUNT(DISTINCT houses.id) AS house_count FROM locations, houses WHERE locations.id = :id AND houses.location_id = :id

警告：

Warning:(37, 14) The query returns some columns [house_count] which are not use by ug.karuhanga.logrealty.Models.Entities.Location. You can use @ColumnInfo annotation on the fields to specify the mapping.  You can suppress this warning by annotating the method with @SuppressWarnings(RoomWarnings.CURSOR_MISMATCH). Columns returned by the query: id, name, location, default_rent, synced, house_count. Fields in ug.karuhanga.logrealty.Models.Entities.Location: id, name, location, default_rent, synced.

和错误：

Error:(33, 8) error: Entities and Pojos must have a usable public constructor. You can have an empty constructor or a constructor whose parameters match the fields (by name and type).
Tried the following constructors but they failed to match:
Location(long,java.lang.String,ug.karuhanga.logrealty.Utils.LocationUtils.LatLng,long,java.util.Date,int) : [id : id, name : name, location : location, defaultRent : defaultRent, synced : synced, houseCount : null]

Answer 1

有关在Room db中使用@Ignore的解决方法，请参阅此。 Room database build errors for @Ignore annotation

Answer 2

对于Kotlin，这对我有用：

1。像这样将@JvmOverloads添加到您的数据类：

@Entity(tableName = "student")
data class Student @JvmOverloads constructor(
    ...
)

2。将@PrimaryKey字段放置在构造函数的末尾，如下所示：

@Entity(tableName = "student")
data class Student @JvmOverloads constructor(    
    var name: String,            
    var age: Int,                 
    var gpa: Double,
    var isSingle: Boolean,

    @Ignore                            
    var isSelected: Boolean = false,      

    @PrimaryKey(autoGenerate = true)        //must be placed at the end!!
    var id: Long = 0                        
)

使用Room在`@ Query`结果中使用`@ Ignore`字段

2 个答案: