Apex Trigger to Update Lookup Field (Contact)

Question

Need some advise on how to populate a lookup field (contact) via apex trigger

I've created a lookup field called Contact__c on Idea object.
I would like to populate the Contact__c with the createdby User if it was originated from the web (CreatedBy.Contact.Account.Name == "Web Ideas") and leave it empty for internal idea creation.
I have read up and created the following trigger and was able to save and run. However, upon saving the idea record, i am getting an error : UpdateContactonComplaints: data changed by trigger for field Contact: id value of incorrect type: 005N0000000l9iMIAQ

trigger UpdateContactonComplaints on Idea (before insert, before Update) {

list<id> oid = new list<id>();
for(Idea o: trigger.new){                   
    oid.add(o.id);
        }
map<id, Idea> ExtendU = new map<id, Idea>(
    [select CreatedbyID from Idea where id in: oid]);

for(Idea o: trigger.new){
    o.Contact__c = ExtendU.get(o.id).CreatedbyID;
}

}

The error is displayed because the Contact__c field seems to be a lookup field to other object instead of User. Also, since Contact is a different entity in Salesforce platform, that field name can be misleading to understand which object are you refering to. — geekymartian

Vinoth Vijayabaskar Vinoth Vijayabaskar · Accepted Answer · 2014-03-27T13:08:01

In the Trigger, the user id(id of the User who created the idea) is assigned to Contact custom lookup field).

So, it throws an error, data changed by trigger for field Contact: id value of incorrect type:

Apex Trigger to Update Lookup Field (Contact)

1 Answers