Why I am getting error : System.SObjectException: SObject row was retrieved via SOQL without querying the requested field?

Question

Covered Product is an object and Installed product is a lookup field on Covered product and Status is a picklist field on Installed product.

When I am trying to run the below code in Execute Anonymous window then I am getting error : Line: 4, Column: 1 System.SObjectException: SObject row was retrieved via SOQL without querying the requested field: Service_Contract_Products__c.Installed_Product__r. But when I am running the same code inside a class I am not getting the error.

Can someone please provide the solution how to check the status of Installed product in Covered Product object? And why I am not getting error inside class but getting error in Execute Anonymous window?

List<Service_Contract_Products__c> coveredProducts = [SELECT Id,Installed_Product__c FROM Service_Contract_Products__c];
for(Service_Contract_Products__c coverProd : coveredProducts)
{
    if(coverProd.Installed_Product__r.Status__c != 'OPER - Operational')
    {
        System.debug(coverProd.Installed_Product__r.Status__c);
    }
}

Answer 1

Your query is missing the querying of the related record likely called Installed_Product__c. The field Installed_Product__c is just the Id of that record. To get fields from that object you will need to include _r references e.g. Installed_Product__r.Status__c in the query.

If you haven't already, I suggest you work through e.g. Write SOQL Queries, focusing particularly on the section about related records.

Answer 2

Every field you want to read must be in the SOQL query.
The if condition checks the value of Installed_Product__r.Status__c, so that field must be added to the query in the first list of the snippet:

List<Service_Contract_Products__c> coveredProducts = [SELECT Id, Installed_Product__c, Installed_Product__r.Status__c FROM Service_Contract_Products__c];

If you need only the records related to the Installed Product that are not in 'OPER - Operational' status, you can add that condition in the WHERE clause:

SELECT Id, Installed_Product__c, Installed_Product__r.Status__c
FROM Service_Contract_Products__c
WHERE Installed_Product__r.Status__c != 'OPER - Operational'];

Keep in mind that time spent in SOQL query does't count toward CPU time limit.