[SalesForce] trigger to find change in contact role for an opportunity

Rather than try and populate a field with the count, detect when the Opportunity is changing into the won stage and then enforce the check then. You can use addError to stop the update occurring.

I've mocked out an example trigger below. This was done by hand, so it is probably full of typos and things that might not compile. Hopefully it demonstrates the idea.

I've extended the example to update the count field as you originally wanted. The issue here is that this field will only be set when the Opportunity is changed. It won't automatically update with changes to the OpportunityContactRole records. Unfortunately you can't put a trigger on them. Ref. Ideas:Allow APEX Trigger on OpportunityContactRole.

trigger fulfillmentcontactcreatedopp on Opportunity (before insert, before update) {

    // Only need to enforce rule if going into the "Win" stage

    Map<Id, Opportunity> oppsToCheckMap = new Map<Id, Opportunity>();

    for(Opportunity opp : trigger.new) {
        // Add the opp Id to a Map(Id to Opp) if it is an insert trigger with a won stage 
        // or if it is an update changing into a won stage (use trigger.oldMap to find the value before the change.
        if(opp.Stage == 'Closed Won') { // <== Your "Won" stage name here.
            if(trigger.isInsert || 
               trigger.isUpdate && trigger.oldMap.get(opp.Id).Stage != opp.Stage)
                oppsToCheckMap.put(opp.Id, opp);
            }
        }            

    }

    // For each Opportunity in the map keyset get the count of the
    // OpportunityContactRole with role = fulfillment.
    List<AggregateResult> result = [
             select OpportunityId, count(Id)
             from OpportunityContactRole
             where (Role = 'Fulfillment') and
                    OpportuntiyId in :oppsToCheckMap.keySet() group by OpportunityId];

    // If the count is zero use addError to prevent the insert/update from committing.
    for(AggregateResult aggCount : result) {
        // Here expr0 should be the count(Id) result. 
        // I.e. How many Fulfillment Contact Roles each Opportunity has.
        integer roleCount = (integer)aggCount.get('expr0');
        if(roleCount == 0) {
            Id oppId = (Id)aggCount.get('OpportunityId');
            Opportunity opp = oppsToCheckMap.get(oppId);
            opp.Stage.addError('Requires Fulfillment Contact Role to be Won');
        }

        // If you don't want to use addError you can also update the count field here
        // The problem is that this won't update the count when the
        // OpportunityContactRole records change.
        opp.Number_of_Fulfillment_Contacts__c = roleCount;
    }
}

Yes, it is possible.

The object to import into is Opportunity Contact Role. You will need to mark the "Show all objects in Salesforce" checkbox to be able to select Opportunity Contact Role.

The .CSV file will need the following columns;

1. ContactID - ID of the Contact you are adding to the Opportunity Contact Roles related list
2. OpportunityID - ID of the Opportunity you are adding the Contact to
3. Role - Name of the role you are assigning to the Contact. This needs to be a value from the Role picklist
4. IsPrimary - This will mark the Primary checkbox on the Contact role.

It will be an insert to OpportunityContactRole.