Querying a lookup relationship

Question

I have two Objects object1 & object2.

In object1 there is a field, field1 with Lookup to object2. Now what I need to do is query object2 fields based on the id of field1 How can I perform this query?

Answer 1

UPDATE:

Let say you know the Id of Object1. So you can read the Field1__c from that Object1 - this will be Id of the Object2.

Id idOfObject2 = [ Select Field1__r.Id From Object1 Where Id = :someVar ].Field1__r.Id;

Now we reading Object2 fields:

Object2 obj2 = [ Select Field1__c, Field2__c From Object2 Where Id = :idOfObject2 ];

Or we can do the same simpler:

Object2 obj2 = [ Select Field1__c, Field2__c From Object2 
                 Where Id IN (Select Field1__c From Object1 Where Id = :someVar) ];

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I think you can do it like this:

Select Id, Name From Object2 Where Id = :Object1.field1__c

You can read more about lookup relationships at the official doc site: Relationship Queries

Answer 2

You can also do this thriugh one single query -

[Select  Field2__r.Field2_field__c FROM Object1 obj where obj.id = :Object1ID];