Using a variable in dynamic sql [duplicate]

You could try this

Set <ID> unwantedIds = ...  // ids I don't want.
String query = 'select Id, ThirdPartyId__c, whatId FROM Task where ThirdPartyId__c not in :unwantedIds ' ;

Not sure what you are looking for .. If you want to build a dynamic query to exclude the unwantedids this should work

I was able to fix this by just building up a string of IDs...

String idList = '';
for (Id id : objectiveIds) {
   idList = idList + ',\'' + id + '\'';
}

and appending that to the dynamic soql as opposed to using a variable. I guess it makes sense that bound variables should not work with dynamic soql and it was thus a bit of a stupid question.

Why use dynamic SOQL at all in this case? If this is in Apex, and your example above is accurate, you shouldn't need to. Think you'd be better off with something like:

List<Task> myTasks = [Select Id,ThirdPartyId__c,WhatId FROM Task where ThirdPartyId__c not in :objectiveIds];

I just tried the following via workbench, and it worked as intended:

Set<Id> contacts = new Set<Id>();
for(Contact c : [Select Id From Contact Limit 10]){
    contacts.add(c.Id);
}
List<Contact> allButFirst10Contacts = [Select Id From Contact Where Id Not In :contacts];
System.debug(allButFirst10Contacts.size());