Query with relationship fields

Question

I read some other questions but I'm still having trouble.

I' ve got Custom object A and B. A has got a LookUp relationship field on B named LookUpB__c.

I'd like to get the value of Name of B. This is the query I'm using:

SELECT Name FROM B WHERE id =: A.LookUpB__c

What am I doing wrong?

Answer 1

// Assuming you are querying object A , need to use (__r) to retrieve Parent fields.

__r is for Custom objects reference For example: Custom_Object__r . It is used for reference custom object relationship name in Apex or visualforce page, formula field etc. Used as suffix.

String strBName = [SELECT Id, LookUpB__c, LookUpB__r.Name FROM A WHERE Id=: 'Id of Record A' limit 1].LookUpB__r.Name;

Answer 2

If you're looking to just grab the Name of Object B when given Object A you should try this:

SELECT Id, LookUpB__c.Name FROM A WHERE Id= [Id of Object A]