SFDC之trigger那些事儿

初学Salesforce 的Apex开发，trigger可以说的开发者的基本功了。

trigger的定义模式如下：

trigger TriggerName on ObjectName (trigger_events) {   code_block}

triggerName相当于trigger的命名，ObjectName指trigger绑定的类的名字，trigger_events指能引起代码触发的条件，主要有insert，update，delete，merge，upsert，undelete六种，本文主要介绍insert，update和delete三种。

trigger的类型包括两种

• Before trigger：通常用于在他们被保存在数据库以前更新或者校验数据;
• After Trigger： 通常用于保存后访问系统的字段（Id等）.
  

创建一个测试用例TestTrigger__c，里面含字段status__c，触发器代码如下：

trigger testTrigger on TestTrigger__c (before insert,before update,before delete,after insert,after update,after delete) {if(trigger.isBefore){//插入前if(trigger.isInsert){System.debug('*******插入前trigger.new********' + trigger.new);System.debug('*******插入前trigger.newMap********' + trigger.newMap);System.debug('*******插入前trigger.old********' + trigger.old);System.debug('*******插入前trigger.oldMap********' + trigger.oldMap);}//更新前if(trigger.isUpdate){System.debug('*******更新前trigger.new********' + trigger.new);System.debug('*******更新前trigger.newMap********' + trigger.newMap);System.debug('*******更新前trigger.old********' + trigger.old); System.debug('*******更新前trigger.oldMap********' + trigger.oldMap);}//删除前if(trigger.isDelete){ System.debug('*******删除前trigger.new********' + trigger.new); System.debug('*******删除前trigger.newMap********' + trigger.newMap);System.debug('*******删除前trigger.old********' + trigger.old);System.debug('*******删除前trigger.oldMap********' + trigger.oldMap);}}if(trigger.isAfter){//插入后if(trigger.isInsert){ System.debug('*******插入后trigger.new********' + trigger.new);System.debug('*******插入后trigger.newMap********' + trigger.newMap);System.debug('*******插入后trigger.old********' + trigger.old);System.debug('*******插入后trigger.oldMap********' + trigger.oldMap);}//更新后if(trigger.isUpdate){ System.debug('*******更新后trigger.new********' + trigger.new);System.debug('*******更新后trigger.newMap********' + trigger.newMap);System.debug('*******更新后trigger.old********' + trigger.old); System.debug('*******更新后trigger.oldMap********' + trigger.oldMap);}//删除后if(trigger.isDelete){System.debug('*******删除后trigger.new********' + trigger.new); System.debug('*******删除后trigger.newMap********' + trigger.newMap);System.debug('*******删除后trigger.old********' + trigger.old);System.debug('*******删除后trigger.oldMap********' + trigger.oldMap);}}}

新建一个TestTrigger__c对象，控制台输出可以看到：

*******插入前trigger.new********(TestTrigger__c:{Id=null, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=null, CreatedDate=null, CreatedById=null, LastModifiedDate=null, LastModifiedById=null, SystemModstamp=null, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态一})*******插入前trigger.newMap********null*******插入前trigger.old********null*******插入前trigger.oldMap********null*******插入后trigger.new********(TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:14:49, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:14:49, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态一})*******插入后trigger.newMap********{a007F000003AzKwQAK=TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:14:49, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:14:49, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态一}}*******插入后trigger.old********null*******插入后trigger.oldMap********null

修改对象，控制台输出看到：

*******更新前trigger.new********(TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:14:49, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:14:49, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态二})*******更新前trigger.newMap********{a007F000003AzKwQAK=TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:14:49, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:14:49, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态二}}*******更新前trigger.old********(TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:14:49, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:14:49, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态一})*******更新前trigger.oldMap********{a007F000003AzKwQAK=TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:14:49, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:14:49, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态一}}*******更新后trigger.new********(TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:16:58, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:16:58, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态二})*******更新后trigger.newMap********{a007F000003AzKwQAK=TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:16:58, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:16:58, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态二}}*******更新后trigger.old********(TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:14:49, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:14:49, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态一})*******更新后trigger.oldMap********{a007F000003AzKwQAK=TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:14:49, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:14:49, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态一}}

删除对象，控制台输出可以看到：

*******删除前trigger.new********null*******删除前trigger.newMap********null*******删除前trigger.old********(TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:16:58, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:16:58, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态二})*******删除前trigger.oldMap********{a007F000003AzKwQAK=TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:16:58, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:16:58, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态二}}*******删除后trigger.new********null*******删除后trigger.newMap********null*******删除后trigger.old********(TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:16:58, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:16:58, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态二})*******删除后trigger.oldMap********{a007F000003AzKwQAK=TestTrigger__c:{Id=a007F000003AzKwQAK, OwnerId=0057F000000ySVPQA2, IsDeleted=false, Name=R-0006, CreatedDate=2017-08-21 03:14:49, CreatedById=0057F000000ySVPQA2, LastModifiedDate=2017-08-21 03:16:58, LastModifiedById=0057F000000ySVPQA2, SystemModstamp=2017-08-21 03:16:58, LastActivityDate=null, LastViewedDate=null, LastReferencedDate=null, address__c=触发器测试数据, status__c=状态二}}

上述结果可以看到，trigger.new等变量不是在任何时候都会有值，当它实际上等于null的时候，在trigger_events下是没有意义的。

对于trigger中的new/old变量需要注意的是，它的实质的一个List集合的存储形式，里面包含的不仅只是一个对象的值，更多的是针对批处理的情况、Apex开发后期使用DataLoader导入用户数据就是很典型的一种批处理场景。所以在开发的时候，我们更多的要针对多条数据进行处理。

List<TestTrigger__c>  list_test = trigger.new

if(trigger.isBefore){//插入前if(trigger.isInsert){for(TestTrigger__c test: trigger.new){test.status__c = '状态二';}}}

每次新建TestTrigger__c对象的时候，将状态都修改为“状态二”

而对于trigger中的newmap/oldmap变量，实质是一个map存储了对象的ID和对象，通过ID可以取出对应的SObject。

下面举个例子

trigger testTrigger on TestTrigger__c (after update) {TestTriggerHandle handler =  new  TestTriggerHandle();if(trigger.IsUpdate && trigger.isAfter)}             handler.OnAfterUpdate(trigger.new,trigger.oldMap);}}

/** *  Author:小青  *  Time:2017-8-21 *  Function：TestTrigger__c的状态发生变化 * */public class TestTriggerHandle {    public void OnAfterUpdate(List<TestTrigger__c> list_test,Map<Id,TestTrigger__c> map_old){               Set<Id>  set_id = new Set<Id>();//记录被修改的TestTrigger__c的ID        for(TestTrigger__c test : list_test){                set_id.add(test.Id);                    }                List<TestTrigger__c> list_update = [Select Id,status__c From TestTrigger__c  where Id in :set_id];              for(TestTrigger__c test : advList){                       TestTrigger__c oldTest = map_old.get(ad.Id);             if(test.status__c != oldTest.status__c){            System.debug('测试数据的状态发生了修改，原状态为：' + oldTest.status__c + '新的状态为' + test.status__c);            }        }}

以上是常用的触发器开发的方法，逻辑处理放在一个Handler类中，在触发器中调用handler类的方法进行处理，从而实现代码的分离，便于控制代码的执行顺序以及避免业务逻辑过于复杂。

最后，对于触发器的开发需要理解，例如trigger.new在before insert中，不需要进行DML操作就可以直接修改记录的数据，然后就能进行保存，而在After Update中，并不能直接使用trigger.new所代表是数据，因为这条记录已经被插入到数据库中，这时候直接进行DML操作会报错，所以需要我们用一个set记录下对应的ID然后再进行一次查询，对这个查询出来的集合重新DML操作就没有问题了。