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hybin joseph 2hybin joseph 2 

I am getting a run time error on one of the triggers I wrote

The error I am getting is  :

Error: Invalid Data.
Review all error messages below to correct your data.
Apex trigger hybinjoseph1.AcctTrigger caused an unexpected exception, contact your administrator: hybinjoseph1.AcctTrigger: execution of AfterInsert caused by: System.FinalException: Cannot modify a collection while it is being iterated.: Trigger.hybinjoseph1.AcctTrigger: line 9, column 1

and my tirgger is :

trigger AcctTrigger on Account (After Insert) {

list<contact> conlist = new list<contact>();

for(Account a : trigger.new){

conlist = [SELECT AccountID, Name from Contact WHERE Mailingcity = :a.Billingcity];

for(contact con : conlist){
con.AccountId = a.Id;
conlist.add(con);

}


}
update conlist;

}



I am new to writing triggers so cant understand whats wrong here.Please help
Best Answer chosen by hybin joseph 2
Amit Chaudhary 8Amit Chaudhary 8
Hi hybin joseph ,

Never exeucte SOQL inside the for loop because once you will upload data from data loader your trigger will fail

Please update your code like below
trigger AcctTrigger on Account (After Insert) 
{

	Set<String> setBillingCity = new Set<String>();
	
	for(Account a : trigger.new)
	{
		if(a.Billingcity != null)
		{
			setBillingCity.add(a.Billingcity);
		}		
	}
	
	if(setBillingCity.size() > 0 )
	{
		list<Contact> lstContact = [ SELECT AccountID,Mailingcity, Name from Contact WHERE Mailingcity = :setBillingCity ];
		Map<String,List<Contact>> mapCityWiseContact = new Map<String,List<Contact>> ();
		for( Contact cont : lstContact)
		{
			if(mapCityWiseContact.containsKey(cont.Mailingcity))
			{
				List<Contact> lstCont = mapCityWiseContact.get(cont.Mailingcity);
				lstCont.add(cont);
			}
			else
			{
				List<Contact> lstCont= new List<Contact>();
				lstCont.add(cont);
				mapCityWiseContact.put(cont.Mailingcity,lstCont);
			}
		}
		
	
		list<contact> listContactToUpdate = new list<contact>();
		for(Account a : trigger.new)
		{
			if(a.Billingcity != null)
			{
				if(mapCityWiseContact.containsKey(a.Billingcity))
				{
					List<Contact> lstCOnt = mapCityWiseContact.get(a.Billingcity);
					for(Contact cont: lstCOnt)
					{
						con.AccountId = a.Id;
						listContactToUpdate.add(con);
					}	
				}	
			}
		}
		if(listContactToUpdate.size() > 0 )
		{
			update listContactToUpdate;
		}	
	}
}
1) http://amitsalesforce.blogspot.com/2015/06/trigger-best-practices-sample-trigger.html

Trigger Best Practices | Sample Trigger Example | Implementing Trigger Framework

1) One Trigger Per Object
A single Apex Trigger is all you need for one particular object. If you develop multiple Triggers for a single object, you have no way of controlling the order of execution if those Triggers can run in the same contexts

2) Logic-less Triggers
If you write methods in your Triggers, those can’t be exposed for test purposes. You also can’t expose logic to be re-used anywhere else in your org. 

3) Context-Specific Handler Methods
Create context-specific handler methods in Trigger handlers


4) Bulkify your Code
Bulkifying Apex code refers to the concept of making sure the code properly handles more than one record at a time.

5) Avoid SOQL Queries or DML statements inside FOR Loops
An individual Apex request gets a maximum of 100 SOQL queries before exceeding that governor limit. So if this trigger is invoked by a batch of more than 100 Account records, the governor limit will throw a runtime exception

6) Using Collections, Streamlining Queries, and Efficient For Loops
It is important to use Apex Collections to efficiently query data and store the data in memory. A combination of using collections and streamlining SOQL queries can substantially help writing efficient Apex code and avoid governor limits

7) Querying Large Data Sets
The total number of records that can be returned by SOQL queries in a request is 50,000. If returning a large set of queries causes you to exceed your heap limit, then a SOQL query for loop must be used instead. It can process multiple batches of records through the use of internal calls to query and queryMore

8) Use @future Appropriately
It is critical to write your Apex code to efficiently handle bulk or many records at a time. This is also true for asynchronous Apex methods (those annotated with the @future keyword). The differences between synchronous and asynchronous Apex can be found

9) Avoid Hardcoding IDs
When deploying Apex code between sandbox and production environments, or installing Force.com AppExchange packages, it is essential to avoid hardcoding IDs in the Apex code. By doing so, if the record IDs change between environments, the logic can dynamically identify the proper data to operate against and not fail


Let us know if this will help you

All Answers

PavanKPavanK
PLease try below
trigger AcctTrigger on Account (After Insert) {

list<contact> conlist = new list<contact>();

for(Account a : trigger.new){
    for(contact con : [SELECT AccountID, Name from Contact WHERE Mailingcity = :a.Billingcity]){
               con.AccountId = a.Id;
               conlist.add(con);
      }
}
if(conlist.size()>0)
update conlist;

}

 
hybin joseph 2hybin joseph 2
Hi Pavan,

Thanks for ur reponse it worked
Amit Chaudhary 8Amit Chaudhary 8
Hi hybin joseph ,

Never exeucte SOQL inside the for loop because once you will upload data from data loader your trigger will fail

Please update your code like below
trigger AcctTrigger on Account (After Insert) 
{

	Set<String> setBillingCity = new Set<String>();
	
	for(Account a : trigger.new)
	{
		if(a.Billingcity != null)
		{
			setBillingCity.add(a.Billingcity);
		}		
	}
	
	if(setBillingCity.size() > 0 )
	{
		list<Contact> lstContact = [ SELECT AccountID,Mailingcity, Name from Contact WHERE Mailingcity = :setBillingCity ];
		Map<String,List<Contact>> mapCityWiseContact = new Map<String,List<Contact>> ();
		for( Contact cont : lstContact)
		{
			if(mapCityWiseContact.containsKey(cont.Mailingcity))
			{
				List<Contact> lstCont = mapCityWiseContact.get(cont.Mailingcity);
				lstCont.add(cont);
			}
			else
			{
				List<Contact> lstCont= new List<Contact>();
				lstCont.add(cont);
				mapCityWiseContact.put(cont.Mailingcity,lstCont);
			}
		}
		
	
		list<contact> listContactToUpdate = new list<contact>();
		for(Account a : trigger.new)
		{
			if(a.Billingcity != null)
			{
				if(mapCityWiseContact.containsKey(a.Billingcity))
				{
					List<Contact> lstCOnt = mapCityWiseContact.get(a.Billingcity);
					for(Contact cont: lstCOnt)
					{
						con.AccountId = a.Id;
						listContactToUpdate.add(con);
					}	
				}	
			}
		}
		if(listContactToUpdate.size() > 0 )
		{
			update listContactToUpdate;
		}	
	}
}
1) http://amitsalesforce.blogspot.com/2015/06/trigger-best-practices-sample-trigger.html

Trigger Best Practices | Sample Trigger Example | Implementing Trigger Framework

1) One Trigger Per Object
A single Apex Trigger is all you need for one particular object. If you develop multiple Triggers for a single object, you have no way of controlling the order of execution if those Triggers can run in the same contexts

2) Logic-less Triggers
If you write methods in your Triggers, those can’t be exposed for test purposes. You also can’t expose logic to be re-used anywhere else in your org. 

3) Context-Specific Handler Methods
Create context-specific handler methods in Trigger handlers


4) Bulkify your Code
Bulkifying Apex code refers to the concept of making sure the code properly handles more than one record at a time.

5) Avoid SOQL Queries or DML statements inside FOR Loops
An individual Apex request gets a maximum of 100 SOQL queries before exceeding that governor limit. So if this trigger is invoked by a batch of more than 100 Account records, the governor limit will throw a runtime exception

6) Using Collections, Streamlining Queries, and Efficient For Loops
It is important to use Apex Collections to efficiently query data and store the data in memory. A combination of using collections and streamlining SOQL queries can substantially help writing efficient Apex code and avoid governor limits

7) Querying Large Data Sets
The total number of records that can be returned by SOQL queries in a request is 50,000. If returning a large set of queries causes you to exceed your heap limit, then a SOQL query for loop must be used instead. It can process multiple batches of records through the use of internal calls to query and queryMore

8) Use @future Appropriately
It is critical to write your Apex code to efficiently handle bulk or many records at a time. This is also true for asynchronous Apex methods (those annotated with the @future keyword). The differences between synchronous and asynchronous Apex can be found

9) Avoid Hardcoding IDs
When deploying Apex code between sandbox and production environments, or installing Force.com AppExchange packages, it is essential to avoid hardcoding IDs in the Apex code. By doing so, if the record IDs change between environments, the logic can dynamically identify the proper data to operate against and not fail


Let us know if this will help you
This was selected as the best answer
hybin joseph 2hybin joseph 2
Thanks Amit.I took a look at ur code but I am new to coding so its a lil tought o read through the code but I am sure I will get there.Do u have any tips for a newbie like me as to where and how to start ????
Amit Chaudhary 8Amit Chaudhary 8
Hi hybin joseph 2,

I will suggest you to start with trailhead
1) https://developer.salesforce.com/trailhead/trails