[SalesForce] How to associate contacts to opportunities

This is a bit of a pain as you can't use a roll up summary field or write a trigger on the OpportunityContactRole object. This is a free, unmanaged, Appexchange product that does this:

https://appexchange.salesforce.com/listingDetail?listingId=a0N300000025Vs1EAE

Note the most helpful negative review:

https://appexchange.salesforce.com/listingDetail?listingId=a0N300000025Vs1EAE&tab=r

The issue is the trigger fires on Opportunity updates so the user will have to cancel out and add a OCR (potentially having to create a Contact first etc).

I have used a modified version of this in combination with a validation rule so that a OCR must be present at a certain stage, but we have actually adopted a different approach. We replaced the New Opportunity screen with a custom VisualForce page that included a section dedicated to making it easy to add an existing Contact as an OCR or creating a brand new Contact all from the same screen.

We decided this was more user friendly as well making all the Opportunities populated with an OCR from the start - so better data quality earlier.

This field is a bug and should not be used. It is technical debt that SFDC has not cleaned up yet. Mary Scotton at SFDC commented on this here: http://gokubi.com/archives/mystery-contact-id-field-on-opportunity

You should query against Opportuinty, Contact, and OpportunityContactRole to get the related SObjects.

This SOQL will work and get you what you want:

List<Contact> contactObj = [SELECT Id,
                      (SELECT Id,Status,CaseNumber,LastModifiedDate FROM Cases),
                      (SELECT Id,OpportunityId,Opportunity.StageName, Opportunity.Amount, ContactId FROM OpportunityContactRoles) 
                     FROM Contact ];

System.debug(JSON.serialize(contactObj));