Trigger to copy ID from text field to lookup field on same object (Account)

Question

Text_ID__c - text field with id of an Opportunity

A_Opportunity__c - lookup field to Opportunity

Both fields are in standard Account object. How can I populate the lookup field with the id in the text field? Will not work with workflow or process builder, guess I need Apex trigger (with which I have little experience). Can anyone provide code for this to at least put me on the right track? Would greatly appreciate it :)

Answer 1

Something like this?

    trigger AccountTrigger on Account (before update,before insert) {
         for(account a : Trigger.New)
        {
            a.lookupField__c = a.FieldWithID__c;
       }
     }