Relationship with First Matching Record

Good morning!

I'm trying to create a relationship between two objects based on some criteria, and I'm having some difficulty coming up with the right definition for their relationship. In my data set I have Cases and Work Orders, where I might have many work orders to any one case. The important part of the data looks like this:

Case:

• ID

Work Order:

• Case ID
• Engineer Assigned
• Created Date

I need to create a one-to-one relationship between the two using only the first work order chronologically (by created date) where engineer assigned isn't blank. I've attempted to solve this myself by creating a custom table using the following:

FirstSiteVisitWO = SUMMARIZE(FILTER('Work Order', 'Work Order'[Engineer_Assigned] <> BLANK()), 'Work Order'[Case_ID],"FirstWO",MIN('Work Order'[Created_Date]))

The problem I've got now is that a good number of cases I'm expecting to see have been filtered out of my data set by this, and the ones I am seeing don't seem to consistently be the right work order associated. Can anyone suggest the correct way to make this related table?

Thanks!