派生属性在Grails中使用集合函数 [英] Derived Properties using aggregate functions in Grails
问题描述
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
}
}
我试过了派生属性文档，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::
由GrailsTagException引发：执行标记时出错：在[23]行上计算表达式[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：无法执行查询
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::
Caused by GrailsTagException: Error executing tag : Error evaluating expression [Generation.findAll()] on line [23]: could not execute query; 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_]; nested exception is org.hibernate.exception.SQLGrammarException: could not execute query
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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