How to access lookup object field in apex

Question

So, I'm getting the values of the properties of a custom sObject in my org, in an Apex method. So, this is how it works, basically I receive via parameter a list of strings that are the fields that I need to fetch from the sObject. So, the process is this:

for(Item__c item : items){
  for(String field : fields){
     columns.add(String.valueOf(item.get(field)));
  }
}

The fields are being sent from my lightning component, in a way I can directly get them via sObject.get. The thing is, there is a field that is a lookup field (its called listing_type) and I don't know how can I access a field of the listing_type object. I can't access it directly like this, so how can I achieve this? It should be listing_type__r.name, but if I pass that to the item.get() it doesn't work.

Answer 1

You need to "follow the path", like this:

for(Item__c item: items) {
  for(String field: fields) {
    // Temp variable holds current spot in path
    sObject temp = item;
    // Break into parts; we need to escape . because split uses regex.
    String[] path = field.split('\\.');
    // While we have more path to follow, and current step isn't null...
    while(path.size()>1 && temp != null) {
      // Go to the next step
      temp = temp.getsObject(path.remove(0));
    }
    // Assuming we still have a current spot, we can get the end value here
    if(temp != null) {
      columns.add(String.valueOf(temp.get(path[0])));
    }
  }
}

You could even abstract this into a method if you think you might use it frequently.

Answer 2

You need to break up the field label to get the values from the Parent record. First you need to get the parent record using the getSObject method and then you can get the value of the parent field.

You can use the below method to dynamically get those values. Add the below method in your class.

public static string extractFieldValues(sObject sb, string fieldAPIName){
    string fvalue='';
    if(fieldAPIName.contains('.')){
        List<string> splitedFields = fieldAPIName.split('\\.');
        try{
            for(integer i=0;i<splitedFields.size()-1;i++){
                sb=sb.getSobject(splitedFields[i]);   
            }
            fvalue = string.valueof(sb.get(splitedFields[splitedFields.size()-1]));
        }catch(exception ex){
           system.debug('******exception while fetching fieldValues as relationship '+fieldAPIName+'  value is blank.'+ex.getmessage()); 
           fvalue='';
        }
        
    }else if(sb.get(fieldAPIName)!=null){
        fvalue = string.valueOf(sb.get(fieldAPIName));
    }
    return fvalue;
}

And use it like below.

for(Item__c item : items){
  for(String field : fields){
     columns.add(extractFieldValues(item, field));
  }
}

Refer this blog post for more details: Accessing Parent Field Values from sObjects in Dynamic Queries Using Dynamic Apex

Answer 3

You have to use getSObject to get the relationship.

for(Item__c item : items){
     columns.add(String.valueOf(item.getSObject('listing_type__r').get('name'));
  }
}