派生属性在Grails中使用集合函数

问题描述

我试图根据包含的对象创建派生属性。

下面的例子：

  class Generation {
 
字符串名称
 
 DateTime productionStart 
 
 DateTime productionEnd 
 
 static belongsTo = [line：Line] 
 
 static hasMany = [bodyStyles：BodyStyle，engines：Engine，models：Model] 
 $ b static constraints = {
 line nullable： false 
 name nullable：false，unique：['line']，maxSize：255，blank：false 
} 
 
 static mapping = {
 // I'已经尝试过，但这种解决方案导致错误
 productionStart公式：'MIN（engines.productionstart）'
 //我试过了，但是这个解决方案导致错误
 productionEnd公式：'MAX（engines.productionEnd ）'
} 
} 
 
类引擎{
 
字符串名称
 
整数horsePower 
 
 DateTime productionStar t 
 
 DateTime productionEnd 
 
 static belongsTo = [generation：Generation] 
 
 static hasMany = [models：Model] 
 
静态约束= {
生成可空：false 
名称可空：false，唯一：['generation'，'horsePower']，maxSize：255，空白：false 
 horsePower可空：false 
 productionStart可为空：false 
 productionEnd可为空：true 
} 
 
静态映射= {
 productionStart类型：PersistentDateTime 
 productionEnd类型：PersistentDateTime 
} 
} 
  

我试过了，但我的情况比复杂对象不复杂的公式稍微复杂一些。

您可以在上面的代码中找到的解决方案导致错误::

解决方案

尝试它是创建一个getter而不是派生属性：

  class Generation {
 
字符串名称
 
 DateTime productionStart 
 
 DateTime productionEnd 
 
 static transients = ['productionStart'，'productionEnd'] 
 
 static belongsTo = [line：行] 
 
 static hasMany = [bodyStyles：BodyStyle，引擎：Engine，models：Model] 
 
 static constraints = {
 line nullable：false 
 name nullable：false，unique：['line']，maxSize：255，blank：false 
} 
 
 
 DateTime getProductionStart（）{
 def datetime = Engine.createCriteria（）。get {
 eq（'generation'，this）
 projections {
 min（'productionStart'）
} 
} 
 
返回日期时间
 
} 
 
 DateTime getProductionEnd（）{
 def datetime = Engine.createCriteria（）。get {
 eq（'generation'，this）
预测{
 max（'productionEnd'）
} 
} 
 
 return datetime 
} 
 
} 
  

I'm trying to create derived properties based on contained objects.

Example below:

class Generation {

    String name

    DateTime productionStart

    DateTime productionEnd

    static belongsTo = [line: Line]

    static hasMany = [bodyStyles: BodyStyle, engines: Engine, models: Model]

    static constraints = {
        line nullable: false
        name nullable: false, unique: ['line'], maxSize: 255, blank: false
    }

    static mapping = {
        // I've tried but this solution causes errors
        productionStart formula: 'MIN(engines.productionStart)'
        // I've tried but this solution causes errors
        productionEnd formula: 'MAX(engines.productionEnd)'
    }
}

class Engine {

    String name

    Integer horsePower

    DateTime productionStart

    DateTime productionEnd

    static belongsTo = [generation: Generation]

    static hasMany = [models: Model]

    static constraints = {
        generation nullable: false
        name nullable: false, unique: ['generation', 'horsePower'], maxSize: 255, blank: false
        horsePower nullable: false
        productionStart nullable: false
        productionEnd nullable: true
    }

    static mapping = {
        productionStart type: PersistentDateTime
        productionEnd type: PersistentDateTime
   }
}

I've readed Derived Properties Documentation but my case is a little bit more complicated than formulas not associated with complex objects.

The solution that you can find in the code above results in an error::

解决方案

Another way to try it is to create a getter instead of derived properties:

class Generation {

    String name

    DateTime productionStart

    DateTime productionEnd

    static transients = ['productionStart','productionEnd']

    static belongsTo = [line: Line]

    static hasMany = [bodyStyles: BodyStyle, engines: Engine, models: Model]

    static constraints = {
        line nullable: false
        name nullable: false, unique: ['line'], maxSize: 255, blank: false
    }


    DateTime getProductionStart() {
      def datetime = Engine.createCriteria().get {
        eq('generation',this)
        projections {
          min('productionStart')
        }
      }

      return datetime

    }

    DateTime getProductionEnd() {
      def datetime = Engine.createCriteria().get {
        eq('generation',this)
        projections {
          max('productionEnd')
        }
      }

      return datetime
    }

}

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