Sorry for the beginner question -- I'm generating a Map<ID,String> where the ID is an OpportunityId and the String is the value of a custom field on the Opportunity that I want updated. How would I go about updating the records via the contents of the map?

  • 1
    Please update this question with your existing code so that we can quickly identify problem and propose better solution
    – Himanshu
    Sep 20, 2016 at 18:27

2 Answers 2


You can do it like this:

// Your map
Map<Id, String> m = new Map<Id, String>();

// Update needs to know the type so create objects of the right type
Opportunity[] updates = new Opportunity[] {};
for (Id id : m.keySet()) {
    updates.add(new Opportunity(Id = id, FieldName__c = m.get(id)));
update updates;

Note that there is also a put(String fieldName, Object value) method available so if you didn't want to hard code the field name you could use that to set the value by name.

  • what is this declaring: Opportunity[] updates = new Opportunity[] {}; ? thanks
    – jaw999
    Jun 8, 2017 at 18:10
  • @jaw999 That is exactly the same as List<Opportunity> updates = new List<Opportunity>(); but using the more compact (and interchangeable) array syntax.
    – Keith C
    Jun 9, 2017 at 8:14

The put method of maps update an item when it finds the item: From the documentation: https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_methods_system_map.htm

"If the map previously contained a mapping for this key, the old value is returned by the method and then replaced."

Here you have an example:

Note: myList is String and myMap is String, Integer

List myList = new List();

Map myMap = new Map();
for (String item : myList)
    if (myMap.containsKey(item))
        Integer contador = myMap.get(item);
        myMap.put(item, contador + 1);
        myMap.put(item, 1);

System.debug('$$$$$$$$$ myMap: Size: ' + myMap.size() + ' ; ' + myMap);

It prints the following:

$$$$$$$$$ myMap: Size: 2 ; {key1=2, key2=1}

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