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StefanStefan 

Code to test for field change

I am struggling to understand the basics in Apex triggers. Can anyone tell me simply how I  should detect a field change. For example in the below. If the contact name has changed then I want to make some updates to the contact record.

 

trigger AfterUpdate on Contact (before update) {

If (Contact.Name changed)

       }
   
}
 
 


Best Answer chosen by Admin (Salesforce Developers) 
Sebastian75Sebastian75
Hi Stefan,
 
What you need to understand is that the context of the trigger is hold by the Trigger object and that this context can be bulk, i.e. when you insert/update massively data with the dataloader for instance. Hence, this context is not a single object, but a list of objects, or a Map.
So, in you case, you would use it in this way:
 

//Assign the context before and after the change into a Map
Map<Id,Contact> newContactMap = Trigger.newMap;
Map<Id,Contact> oldContactMap = Trigger.oldMap;

//Loop through the map
for(Id contactId:newMap.keySet()){
 Contact myNewContact = newContactMap.get(contactId);
 Contact myOldContact = oldContactMap.get(contactId);

 if (myNewContact.Name<> myOldContact.Name){
   //Here goes your processing
 }

}

 


All Answers
Sebastian75Sebastian75
Hi Stefan,
 
What you need to understand is that the context of the trigger is hold by the Trigger object and that this context can be bulk, i.e. when you insert/update massively data with the dataloader for instance. Hence, this context is not a single object, but a list of objects, or a Map.
So, in you case, you would use it in this way:
 

//Assign the context before and after the change into a Map
Map<Id,Contact> newContactMap = Trigger.newMap;
Map<Id,Contact> oldContactMap = Trigger.oldMap;

//Loop through the map
for(Id contactId:newMap.keySet()){
 Contact myNewContact = newContactMap.get(contactId);
 Contact myOldContact = oldContactMap.get(contactId);

 if (myNewContact.Name<> myOldContact.Name){
   //Here goes your processing
 }

}

 
This was selected as the best answer
StefanStefan
Hi Sebastion, I think there is a syntax error in your code which I am unable to figure out.
 
I am getting this error when tryng to save:
 
ErrorError: Compile Error: Method does not exist or incorrect signature: newMap.keySet() at line 7 column 18
 
 
trigger updateDemo on Contact (before update) {
//Assign the context before and after the change into a Map
Map<Id,Contact> newContactMap = Trigger.newMap;
Map<Id,Contact> oldContactMap = Trigger.oldMap;

//Loop through the map
for(Id contactId:newMap.keySet()){
 Contact myNewContact = newContactMap.get(contactId);
 Contact myOldContact = oldContactMap.get(contactId);

 if (myNewContact.Name<> myOldContact.Name){
   //Here goes your processing
 }

}

}
 
 
 


Sebastian75Sebastian75
Hi,
 
Yeah, inddeed, I wrote this out of the blue ....
 
You need to replace: 
 
 
for(Id contactId:newMap.keySet()){
 with
 
 
for(Id contactId:newContactMap.keySet()){
 
 
 
 
 


StefanStefan
Thanks that did it....