Schema.getGlobalDescribe().get(objectType); doesn't work with custom objects

Question

I have a method that returns a map of all the fields where the field's API name is the key and the object Schema.SObjectField is the value.

    private static Map<String, Schema.SObjectField> fieldMap(String objectType){
         Map<String, Schema.SObjectType> schemaMap = Schema.getGlobalDescribe();
         Schema.SObjectType objectSchema = schemaMap.get(objectType);
         Map<String, Schema.SObjectField> fieldMap = objectSchema?.getDescribe().fields.getMap();
         return fieldMap;
    }

It works well with standard objects but it won't with custom objects. The line Map<String, Schema.SObjectField> fieldMap = objectSchema?.getDescribe().fields.getMap(); throws the error Attempt to de-reference a null object.

Any idea why? The Object's API Name is CO_Shuttle__c.

Thank you,

Answer 1

Is your object part of a managed package? If so, you may need to deal with the namespace as well.

Map<String, sObjectField> mapping = fieldMap('myNs__CO_Shuttle__c');

You can avoid a lot of this hassle by using an sObjectType token if you have it:

static Map<String, Schema.SObjectField> fieldMap(sObjectType token) {
  return token?.getDescribe().fields.getMap();
}

But at that point, it's a one-liner; you can just use this directly.

Map<String, sObjectField> fieldMap = sObjectType.CO_Shuttle__c.fields.getMap();

Note that using a token guarantees you will find the sObjectType or you'll get a compilation error. Always prefer to use hard-coded tokens whenever possible.

If you absolutely need it to be dynamic, you can also use Type.forName:

static Map<String, sObjectField> fieldMap(String objectApiName);
  Type sType = Type.forName('Schema', objectApiName);
  if(sType == null) {
    throw new IllegalArgumentException('Unable to find '+objectApiName);
  }
  sObject template = (sObject)sType.newInstance();
  sObjectType sType = template.getSobjectType();
  return sType.getDescribe().fields.getMap();
}

I would strongly advise against using your method as written, as Schema.getGlobalDescribe() is very expensive in CPU time, and may even time out in large orgs.