Question

我得到Error:(55, 41) Kotlin: Type inference failed. Expected type mismatch: inferred type is (Mutable)List<Optional<Address!>!>! but List<Address>? was expected

我将数据保存到我的build.gradle具有的mongoDB文档中：

implementation 'org.springframework.boot:spring-boot-starter-actuator'
implementation 'org.springframework.boot:spring-boot-starter-data-mongodb'
implementation 'org.springframework.boot:spring-boot-starter-data-rest'
implementation 'org.springframework.boot:spring-boot-starter-hateoas'
implementation 'org.springframework.boot:spring-boot-starter-web'
implementation 'com.fasterxml.jackson.module:jackson-module-kotlin'

我的文档对象

@Document(collection = "address")
class Address {
    @Id
    var id: String? = null
    var number: String? = null
    var street: String? = null
    var neighborhood: String? = null
    var locality: String? = null
    var region: String? = null
    var country: String? = null
    var code: String? = null
    var google_place_id: String? = null

    constructor()
}

和

@Document(collection = "person")
class Person {
    @Id
    var id: String? = null
    var name: String? = null
    var lastName: String? = null
    var phone: String? = null
    var email: String? = null
    var password: String? = null
    @DBRef(db = "mlm")
    var address: List<Address>? = null

    constructor()
}

我有界面

@Repository
interface PersonRepository : MongoRepository<Person, String>

和

@Repository
interface AddressRepository : MongoRepository<Address, String>

我的控制器正常工作
我的Seeder /油井测试真的可以看到如何做到这一点，而这正是我遇到的问题

class DbSeeder {
    @Autowired
    private val personRepository: PersonRepository? = null
    @Autowired
    private val addressRepository: AddressRepository? = null

    fun addressLoading() {
        val address1 = Address()
        address1.id = "5cb2e9424274072ec4bb4199"
        address1.number = "1"
        address1.street = "Microsoft Way"
        address1.neighborhood = "Redmond"
        address1.locality = "King County"
        address1.region = "Washington"
        address1.code = "425"
        address1.country = "United States"
        address1.google_place_id = "5644+83 Centurion"

        val address2 = Address()
        address2.id = "5cb2e9424274072ec4bb4198"
        address2.number = "1600"
        address2.street = "Amphitheatre Parkway"
        address2.neighborhood = ""
        address2.locality = "Mountain View"
        address2.region = "California"
        address2.country = "United States"
        address2.code = "94043"
        address2.google_place_id = "CWC8+Q9 Mountain View, California, USA"

        val address = Arrays.asList(address1, address2)
        this.addressRepository!!.insert(address)
    }

    fun personLoading() {
        val personDocument = Person()
        personDocument.id = "5cb2e9424274072ec4bb4197"
        personDocument.name = "William"
        personDocument.lastName = "Gates"
        personDocument.phone = "1081010810"
        personDocument.email = "bill.gates@gmail.com"
        personDocument.password = "bill-secret"

        val personAddressDBRef = addressRepository!!.findById("5cb2e9424274072ec4bb4199")

        personDocument.address = Arrays.asList(personAddressDBRef)

    //  val personDBRef = personRepository!!.save(personDocument)  // If the ObjectID is requires else ware
        personRepository!!.save(personDocument)
    }
}

要保存我的地址，我需要找到与ObjectID相关的地址，然后将ObjectID作为DBRef保存在个人文档中

val personAddressDBRef = addressRepository!!.findById("5cb2e9424274072ec4bb4199")
personDocument.address = Arrays.asList(personAddressDBRef) // << Error here

在最后一行，我得到错误Error:(55, 41) Kotlin: Type inference failed. Expected type mismatch: inferred type is (Mutable)List<Optional<Address!>!>! but List<Address>? was expected 我似乎不知道如何进行
我在GitHub https://github.com/Morons/gofetchbyidandinsertdbref.git上发布了它
任何帮助都会被

Answer 1

您需要阅读https://kotlinlang.org/docs/reference/java-interop.html#null-safety-and-platform-types才能了解推断类型的写入方式。但是问题很简单：

personAddressDBRef的类型为Optional<Address>，因为findById返回的类型。
所以Arrays.asList(personAddressDBRef)是List<Optional<Address>>（同样，请参见上面的链接以了解为什么看到更复杂的类型）。
您无法将personDocument.address设置为List<Optional<Address>>，而需要使用List<Address>。

因此，您需要确定如何将Optional<Address>转换为List<Address>。一种方法是

personDocument.address = personAddressDBRef.map { listOf(it) }.orElseGet { listOf() }

得到错误：（55，41）Kotlin：类型推断失败

1 个答案: