How do I tell if a custom metadata type field is a Field Definition?

Question

I have the following code:

public static void getFields(){

    SObject obj = (SObject) Type.forName('Health_Cloud_Integration_Settings__mdt').newInstance();
    DescribeSObjectResult describe = obj.getSObjectType().getDescribe();
    Map<String, Schema.SObjectField> fieldMap = describe.fields.getMap();

    for (String fieldName: fieldMap.keySet()) {
        //get all the fields label for Account Object
        String fieldLabel = fieldMap.get(fieldName).getDescribe().getLabel();
        //get data types for each fields
        Schema.DisplayType fielddataType = fieldMap.get(fieldName).getDescribe().getType();
        System.debug(fieldLabel + ' | ' + fielddataType);
        // If fieldtype = field definition add api name to list of strings for soql 


}

However field data type returns string for my Field Definition type fields? How do I do this?

Answer 1

Instead of describe calls, query FieldDefinition object.

There is a field named ExtraTypeInfo that has information to indicate it is an externallookup and also the DataType is Picklist()

The below code is tested in my Dev org and return the info .

for(FieldDefinition field: [Select Id, DataType, QualifiedApiName, ExtraTypeInfo from FieldDefinition where EntityDefinition.QualifiedApiName='Health_Cloud_Integration_Settings__mdt']){
   if(field.ExtraTypeInfo != null && field.ExtraTypeInfo=='externallookup' &&  field.DataType == 'Picklist()') {
       system.debug(field.QualifiedApiName);
  }
}