在 Grails 中使用聚合函数的派生属性

Question

我正在尝试基于包含的对象创建派生属性。

下面的例子：

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
   }
}

我已阅读Derived Properties Documentation，但我的情况比与复杂对象无关的公式要复杂一些。

你可以在上面的代码中找到的解决方案导致错误：：

由 GrailsTagException 引起：执行标签时出错：在第 [23] 行评估表达式 [Generation.findAll()] 时出错：无法执行查询； SQL [select this_.id as id22_0_, this_.version as version22_0_, this_.line_id as line3_22_0_, this_.name as name22_0_, MAX(engines.productionEnd) as formula0_0_, MIN(engines.productionStart) as formula1_0_ from generation this_];嵌套异常是 org.hibernate.exception.SQLGrammarException: could not execute query

Answer 1

另一种尝试方法是创建一个getter而不是派生属性：

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
    }

}