Question

我遇到标题中所述的问题。我有以下实体：

@Entity(tableName = "Person")
data class Person(@PrimaryKey var id: Int,
              var firstName: String,
              var surname: String,
              var age: Int,
              var numberOfHobbies: Int) {
    @Ignore
    constructor() : this(0, "", "", 0, 0)
}

@Entity(tableName = "Skill")
data class Skill(@PrimaryKey var id: Int,
             var skillName: String) {
    @Ignore
    constructor() : this(0, "")
}

@Entity(tableName = "PersonSkill")
data class PersonSkill(var personId: Int,
                   var skillId: Int) {
    @Ignore
    constructor() : this(0, 0)

    @field:PrimaryKey(autoGenerate = true)
    var id: Int = 0
}

以下关系：

data class SkillWithPersons(
    @Embedded var skill: Skill = Skill(0, "UNKNOWN"),
    @Relation(
            parentColumn = "id",
            entityColumn = "skillId",
            entity = PersonSkill::class,
            projection = arrayOf("personId")
    ) var personIds: List<Int> = emptyList()
) {
      constructor() : this(Skill(0, "UNKNOWN"), emptyList())
 }

data class PersonWithSkills(
    @Embedded var person: Person = Person(0, "UNKNOWN", "UNKNOWN", 0, 0),
    @Relation(
            parentColumn = "id",
            entityColumn = "personId",
            entity = PersonSkill::class,
            projection = arrayOf("skillId")
    ) var skillIds: List<Int> = emptyList()
) {
      constructor(): this(Person(0, "UNKNOWN", "UNKNOWN", 0, 0), emptyList())
}

我已经尝试了一切，但它不起作用。我一直在用kotlin-kapt得到以下错误：

e: 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).
e: 

e:   Tried the following constructors but they failed to match:
e:   Integer(int) : [value : null]
e:   Integer(java.lang.String) : [s : null]
e: 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).
e: 

e: java.lang.IllegalStateException:

我使用以下版本：

带Gradle 4的Android Studio 3.0，房间：1.0.0-alpha9-1，构建工具：26.0.2，科特林：1.1.51

使用@Relation似乎存在一个错误，因为kotin-kapt似乎没有处理它。有没有人遇到过这种情况？我甚至试图从projection中移除@Relation，但即使这样做似乎没有什么区别。

Answer 1

现在，房间里的@Relation标签只支持＃34; Florina Muntenescu＆＃34;提到的一对多关系。在她的博客post

中

同样对于上述问题，请在下面提到的数据类中进行更改

@Entity(tableName = "Person")
data class Person(@PrimaryKey 
                  var id: Int = 0,
                  var firstName: String = "",
                  var surname: String = "",
                  var age: Int = 0,
                  var numberOfHobbies: Int = 0)

@Entity(tableName = "Skill")
data class Skill(@PrimaryKey 
                 var id: Int = 0,
                 var skillName: String = "")

@Entity(tableName = "PersonSkill")
data class PersonSkill(@PrimaryKey 
                       var id: Int = 0
                       var personId: Int = 0,
                       var skillId: Int = 0)



data class SkillWithPersons(
    @Embedded 
    var skill: Skill? = null 
    @Relation(
            parentColumn = "id",
            entityColumn = "skillId",
            entity = PersonSkill::class,
            projection = arrayOf("personId")) 
            var personIds: List<Int> = ArrayList()
            )

data class PersonWithSkills(
    @Embedded 
    var person: Person? = null
    @Relation(
            parentColumn = "id",
            entityColumn = "personId",
            entity = PersonSkill::class,
            projection = arrayOf("skillId")) 
            var skillIds: List<Int> = ArrayList()
)

这样你就可以摆脱错误。

与Room的多对多关系导致错误：实体和Pojos必须具有可用的公共构造函数

1 个答案: