Salesforce检查某字段前后是否被更改的方法 - Trigger & Validation Sample

场景描述：开发中经常遇到记录一旦创建，其中的某个字段就不允许被修改的需求，以保证记录的安全性，以下提供两种解决方案。

方案一：使用Validation Rules实现
Sample：当记录第一次被保存后，就不允许用户修改其中某个字段-isCheck:

Validation Rule:

最终效果：

方案二：使用Trigger实现

Sample：比较old和new fields是否相同：oldMap适用于Update/Delete trigger

for(Opportunity opp : Trigger.new){
	//Create an old and new map so that we can compare values
	Opportunity oldOpp = Trigger.oldMap.get(opp.ID);    
	Opportunity newOpp = Trigger.newMap.get(opp.ID);

	//Retrieve the old and new Reseller Email Field            
	string oldResellerEmail = oldOpp.Reseller_Email__c;
	string newResellerEmail = newOpp.Reseller_Email__c;

	//If the fields are different, the email has changed
	if(oldResellerEmail != newResellerEmail){
	    oppIDs.put(opp.Id,opp.Reseller_Email__c);    
	}
}

注意：在实际运用时，可能会出现下图错误：

我们仅需改进如下：

((Map)Trigger.oldMap).get(l.Id).OwnerId <> l.OwnerId

【Trigger项目实战 - after insert/update/delete/undelete】：

项目中有如下需求：A和B对象为lookup关系，其中A为父，B为子，目前想将B的Name字段拼接到A的某字段上，Code如下：

public class TradingAccountTriggerFunction {
    public static void joinLoginToAccount(Set accSet) {
      Savepoint sp = Database.setSavepoint();
      try{
        List accs = [SELECT Id, Trading_Account_Login__c, (SELECT Id, Name FROM MT4_Accounts__r ORDER BY LastModifiedDate)
                    FROM Account 
                    WHERE Id IN :accSet];  
        for(Account acc : accs) {
          acc.Trading_Account_Login__c = '';
        for(Integer i = 0; i < acc.MT4_Accounts__r.size(); i++) {
          acc.Trading_Account_Login__c += (i == acc.MT4_Accounts__r.size() - 1) ? acc.MT4_Accounts__r[i].Name : acc.MT4_Accounts__r[i].Name + ';';
          System.debug(acc.Trading_Account_Login__c);
        }
        }
        update accs;
      }catch(Exception e) {
        System.debug(e.getMessage());
        Database.rollback(sp);
      }
    }
}

public class TradingAccountTriggerHandler extends TriggerHandler{
    //handle before insert logic
    public override void beforeInsert(){} 
    
    //handle before update logic
    public override void beforeUpdate(){}   
 
    //handle before delete logic    
    public override void beforeDelete(){}
    
    //handle after insert logic
    public override void afterInsert(){
    	System.debug('go into after insert logic.');
    	Set accIdSet = new Set();
    	for(MT4_Accounts__c tAcc : (List)Trigger.new) {
    		accIdSet.add(tAcc.Account__c);
    	}
    	if(accIdSet.size() > 0) {
    		TradingAccountTriggerFunction.joinLoginToAccount(accIdSet);
    	}
    }  
    
    //handle after update logic
    public override void afterUpdate(){
    	System.debug('go into after update logic.');
    	Set accIdSet = new Set();
    	for(MT4_Accounts__c tAcc : (List)Trigger.new) {
    		if(((Map)Trigger.oldMap).get(tAcc.Id).Name <> tAcc.Name) 
    			accIdSet.add(tAcc.Account__c);
    	}
    	if(accIdSet.size() > 0) {
    		TradingAccountTriggerFunction.joinLoginToAccount(accIdSet);
    	}
    }  
 
    //handle after delete logic    
    public override void afterDelete(){
    	System.debug('go into after delete logic.');
    	Set accIdSet = new Set();
    	for(MT4_Accounts__c tAcc : (List)Trigger.old) {
    		accIdSet.add(tAcc.Account__c);
    	}
    	if(accIdSet.size() > 0) {
    		TradingAccountTriggerFunction.joinLoginToAccount(accIdSet);
    	}
    }  
 
    //handle after undelete logic      
    public override void afterUndelete(){
    	System.debug('go into after undelete logic.');
    	Set accIdSet = new Set();
    	for(MT4_Accounts__c tAcc : (List)Trigger.new) {
    		accIdSet.add(tAcc.Account__c);
    	}
    	if(accIdSet.size() > 0) {
    		TradingAccountTriggerFunction.joinLoginToAccount(accIdSet);
    	}
    } 
}