当尝试从JHipster Kotlin中的另一个实体引用一个JDL实体时，抛出"Parameter specified as non-null is null“。

Question

我正在尝试用JDL Kotlin建立一个网站，但我在JDL生成的实体和编辑表单方面遇到了问题。我有一个名为Provider的JDL实体，一个名为Plan的实体，它需要引用它所属的提供者，还有一个名为PerDayPricing的实体，它同时引用Provider和Plan，所有这些都符合以下JDL配置：

entity Provider {
    // [...]
}

entity Plan {
    // [...]
}

entity PerDayPricing {
    // [...]
}

relationship OneToMany {
    Provider to Plan
}

relationship OneToMany {
    Provider to PerDayPricing
    Plan to PerDayPricing
}

service all with serviceImpl

但是，当我尝试在Plan item上创建或设置Provider字段时，它显示以下错误：

WARN [PID] --- [ XNIO-1 task-10] .m.m.a.ExceptionHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageConversionException: JSON conversion problem: Parameter specified as non-null is null: method com.example.project.domain.Plan.setPerDayPricings, parameter <set-?>; nested exception is com.fasterxml.jackson.databind.JsonMappingException: Parameter specified as non-null is null: method com.example.project.domain.Plan.setPerDayPricings, parameter <set-?> (through reference chain: com.example.project.domain.Plan["perDayPricings"])]

这里引用了PerDayPricing，尽管我没有更改它的任何项。当我尝试在PerDayPricing项上设置Provider字段时，出现以下错误：

WARN [PID] --- [ XNIO-1 task-32] .m.m.a.ExceptionHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageConversionException: JSON conversion problem: Parameter specified as non-null is null: method com.example.project.domain.Provider.setPlans, parameter <set-?>; nested exception is com.fasterxml.jackson.databind.JsonMappingException: Parameter specified as non-null is null: method com.example.project.domain.Provider.setPlans, parameter <set-?> (through reference chain: com.example.project.domain.PerDayPricing["provider"]->com.example.project.domain.Provider["plans"])]

我实际上不知道这里发生了什么，因为我没有太多使用JHipster的经验。我只是导入了JDL源文件，并让JHipster基于其配置创建文件，而无需更改任何文件，而且这种情况已经发生了。在代码库中甚至不存在对方法名setPlans和setPerDayPricings的引用，所以我假设它们是由Kotlin在后台生成的？

有没有人知道发生了什么事，我该怎么解决它？

编辑:以下是实体类的签名(为简洁起见，删除了常规字段)：

// src/main/kotlin/domain/Provider.kt

@Entity
@Table(name = "plan")
@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
data class Plan(
    // [...]

    @OneToMany(mappedBy = "plan")
    @Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
    var perDayPricings: MutableSet<PerDayPricing> = mutableSetOf(),

    @OneToMany(mappedBy = "plan")
    @Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
    var fixedDurationPricings: MutableSet<FixedDurationPricing> = mutableSetOf(),

    @ManyToOne @JsonIgnoreProperties("plans")
    var provider: Provider? = null

    // jhipster-needle-entity-add-field - JHipster will add fields here, do not remove
) : Serializable

// src/main/kotlin/domain/Plan.kt

@Entity
@Table(name = "provider")
@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
data class Provider(
    // [...]

    @OneToMany(mappedBy = "provider")
    @Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
    var plans: MutableSet<Plan> = mutableSetOf(),

    @OneToMany(mappedBy = "provider")
    @Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
    var perDayPricings: MutableSet<PerDayPricing> = mutableSetOf(),

    @OneToMany(mappedBy = "provider")
    @Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
    var fixedDurationPricings: MutableSet<FixedDurationPricing> = mutableSetOf()

    // jhipster-needle-entity-add-field - JHipster will add fields here, do not remove
) : Serializable

// src/main/kotlin/domain/PerDayPricing.kt

/**
 * A PerDayPricing.
 */
@Entity
@Table(name = "per_day_pricing")
@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
data class PerDayPricing(
    // [...]

    @ManyToOne @JsonIgnoreProperties("perDayPricings")
    var provider: Provider? = null,

    @ManyToOne @JsonIgnoreProperties("perDayPricings")
    var plan: Plan? = null

    // jhipster-needle-entity-add-field - JHipster will add fields here, do not remove
) : Serializable

Answer 1

如果编译器生成数据类，那么编译器将为您生成setter和getter。我想，当您想要将实体彼此设置时，您没有提供异常中的那些字段。默认情况下，Kotlin不支持空值。所以要么必须提供这些字段，要么将类型标记为可空？(问号)在类型的和处。例如

var perDayPricings:String?

您应该使用给定的代码更新问题，这样我们就可以看到问题出在哪里。