APEX初步 [3] —— Apex触发器

触发器概念

apex触发器就像数据库中的触发器一样，用来在增删改之前或之后对记录执行自定义的操作，也可以添加触发的条件。它可以做任何apex能做的功能，比如执行SOQL语句或者调用其他apex方法。它可以被定义在Sobejct上，比如account,contact或者自定义对象上。

尽量在无法通过普通的点击操作的设置完成的情况下才使用触发器，比如如果要验证一个字段的值或更新一条记录上的某个字段，就应该使用validation rule 和 workflow。

触发器格式

trigger TriggerName on ObjectName (trigger_events) {
code_block
}

　　

有下面的trigger_events

before insert
before update
before delete
after insert
after update
after delete
after undelete

触发器分为两种：before和after

before发生在记录被更新到数据库之前，可以用来更新和验证数据。

after在记录保存之后，可以获得比如record id ,lastmodifiedDate之类的数据

Context Variables 上下文变量

Trigger.New 用来获取新插入或者新更新的记录

Trigger.Old 用来获取被更新或被删除签的记录。

这些记录有可能是批量操作的，可以对他们进行枚举来获得里面的每一条记录。

trigger HelloWorldTrigger on Account (before insert) {
    for(Account a : Trigger.New) {
        a.Description = 'New description';
    }   
}

还有一些变量的值可以判断触发器是在哪个事件下被触发的

trigger ContextExampleTrigger on Account (before insert, after insert, after delete) {
    if (Trigger.isInsert) {
        if (Trigger.isBefore) {
            // Process before insert
        } else if (Trigger.isAfter) {
            // Process after insert
        }        
    }
    else if (Trigger.isDelete) {
        // Process after delete
    }
}

Variable	Usage
isExecuting	Returns true if the current context for the Apex code is a trigger, not a Visualforce page, a Web service, or an executeanonymous()API call.
isInsert	Returns true if this trigger was fired due to an insert operation, from the Salesforce user interface, Apex, or the API.
isUpdate	Returns true if this trigger was fired due to an update operation, from the Salesforce user interface, Apex, or the API.
isDelete	Returns true if this trigger was fired due to a delete operation, from the Salesforce user interface, Apex, or the API.
isBefore	Returns true if this trigger was fired before any record was saved.
isAfter	Returns true if this trigger was fired after all records were saved.
isUndelete	Returns true if this trigger was fired after a record is recovered from the Recycle Bin (that is, after an undelete operation from the Salesforce user interface, Apex, or the API.)
new	Returns a list of the new versions of the sObject records. This sObject list is only available in insert, update, andundelete triggers, and the records can only be modified inbefore triggers.
newMap	A map of IDs to the new versions of the sObject records. This map is only available in before update, after insert,after update, and after undelete triggers.
old	Returns a list of the old versions of the sObject records. This sObject list is only available in update and delete triggers.
oldMap	A map of IDs to the old versions of the sObject records. This map is only available in update and delete triggers.
size	The total number of records in a trigger invocation, both old and new.

触发器和工作流的选择

工作流

• 不能创建记录
• 只能做task, email, field update和outbound message
• 跨对象只能在master detail关系中,从detail 到 master, 而且只能在有限的场景下 (所有自定义到自定义, 某些自定义到标准, 少数标准到标准) https://help.salesforce.com/HTViewHelpDoc?id=workflow_cross_object_field_updates.htm&language=en_US

触发器

• 用apex做apex能做的任何事情
• 经常被用在当roll up summary字段不能用的情况下来代替它的作用
• 经常被用在要在其他对象上创建记录的场合