根据配置服务对命令对象应用默认值

Question

如何将默认值应用于Grails 2.3中的命令对象?

请注意，当相应的url参数未指定时，我需要从服务中检索这些默认值。

我有以下命令对象作为我的操作

的参数

class SearchCommand {
    int page
    int pageSize     // todo: get default from configurationService
    String orderBy   // todo: get default from configurationService
    String search
}

我已经看过@BindUsing，但当相应的请求参数缺失时，它似乎没有被调用，击败了我应用默认值的尝试。

Answer 1

你也可以这样做:

. .

一个控制器

// grails-app/controllers/com/demo/DemoController.groovy
package com.demo
class DemoController {
    def createPerson(Person p) {
        render "First Name: ${p.firstName}, Last Name: ${p.lastName}"
    }
}
class Person {
    String firstName
    String lastName
}

服务……

// grails-app/services/com/demo/MyConfigurationService.groovy
package com.demo
class MyConfigurationService {
    def initializePerson(Person p) {
        p.firstName = 'Default First Name'
        p.lastName = 'Default Last Name'
    }
}

绑定监听器…

// src/groovy/com/demo/PersonBindingListener.groovy
package com.demo
import org.grails.databinding.events.DataBindingListenerAdapter
class PersonBindingListener extends DataBindingListenerAdapter {
    def configService
    Boolean beforeBinding(Object target, Object errors) {
        configService.initializePerson target
        true
    }

    boolean supports(Class<?> clazz) {
        clazz == Person
    }
}

注册listener bean…

// grails-app/conf/spring/resources.groovy
beans = {
    myListener(com.demo.PersonBindingListener) {
        configService = ref('myConfigurationService')
    }
}

Answer 2

这里没有足够的信息来确定最好的做法是什么，但是您有几个选择。没有办法告诉框架，当它创建一个命令对象的实例时，它应该初始化来自某个服务的属性，但是你仍然可以使用你的服务来帮助。

    class MyController {
        // there is no way to cause co to automatically be 
        // initialized with values from your service...
        def someAction(MyCommand co) {
        }
        // something like this might help...
        def someOtherAction() {
            // the service creates an instance of the object
            // and initializes values with
            def myCommand = someService.createCommand()
            // this will do data binding, overriding the default
            // values defined by the service with values that are
            // included in request params...
            bindData myCommand, params
            myCommand.validate()
            // carry on...
        }
    }

Answer 3

@Jeff的回答很好。基于这个答案，我选择了一个更简单的解决方案:

考虑到问题中的设置…:

package com.whatevs
import org.grails.databinding.events.DataBindingListenerAdapter
/**
 * Binds the SearchCommand defaults
 */
class SearchCommandBindingListener extends DataBindingListenerAdapter{
    String ORDER_BY = 'lastName, firstName'
    int PAGE_SIZE = 100
    Boolean beforeBinding(Object target, Object errors) {
        SearchCommand searchCommand = (SearchCommand) target
        searchCommand.pageSize = PAGE_SIZE
        searchCommand.orderBy = ORDER_BY
        true
    }
    boolean supports(Class<?> clazz) {
        clazz == SearchCommand
    }
}

和resources.groovy

searchCommandBindingListener(SearchCommandBindingListener)

您可以覆盖资源中的ORDER_BY和PAGE_SIZE的值。Groovy也是。

searchCommandBindingListener(SearchCommandBindingListener) {
    ORDER_BY = 'firstName, lastName'
    PAGE_SIZE = 41
}