title: How To Summarize A Rollup Relationship That Cross References A Custom Object?
body: <p>We are trying to implement a University system for students, faculty, and staff to be able to better manage course registrations as well as other enrollment activities.</p>
  <p><strong>Consider the following problem:</strong> When a student registers for a course, the course needs to get added to the students bill as a billing line item. The bill needs to have a total price of all the courses that have been registered for that particular student. Note: We've tried to keep the process manual in order to simplify the requirements.</p>
  <p>We have identified 4 custom objects and some important fields:</p>
  <ol>
  <li><strong>Courses</strong> - <em>Course Name</em>:(Primary Key), <em>Course Size</em>:(Number), <em>Course Price</em>:(Currency), <em>Start Date</em>:(Date), <em>End Date</em>:(Date), <em>Students Enrolled</em>:(Rollup Count)</li>
  <li><strong>Course Registrations</strong> - <em>Course Registration Number</em>:(Primary Key), <em>Course List</em>:(Master-Detail), <em>Student</em>:(Lookup), <em>Course Price</em>:(Formula), <em>Course Credits</em>:(Formula)</li>
  <li><strong>Billing Line Item</strong> - <em>Billing Line Item Number</em>:(Primary Key), <em>Course Registration</em>:(Master-Detail), <em>Bill</em>:(Master-Detail), <em>Course Price</em>:(Formula)</li>
  <li><strong>Bill</strong> - <em>Bill Name</em>:(Primary Key), <em>Student</em>:(Lookup)</li>
  </ol>
  <p>We know in order to summarize the total of all course prices, we need to make the Billing Line Item the detail object and the Bill the master object. We want to perform a Rollup Summary on all the Billing Line Item prices.</p>
  <p>We've also made the Billing Line Item the detail object and the Course Registration a master object. This is because without a Course Registration, there is no need for a Billing Line Item to exist. Also the Course Registration has the <em>Course Price</em> via a formula which needs to be used in order to summarize the total cost of all courses.</p>
  <p>I've seen online that you are unable to summarize a cross-reference object. We are getting confused as to how we should summarize all the prices associated with each course. Any help would be greatly appreciated. We can provide screenshots if requested!</p>