One Round Trip, Top N

One Round Trip, Top N

Logistics opens every review meeting with the same slide: the customers we shipped the most to this period. The code behind it walks every customer, then every shipment document of that customer, then every line of that document — the DBA's trace shows a wall of tiny SELECT statements growing with the customer list. The ranking is right; the report is just having O(customers × documents) little conversations with the database instead of one.

Your job: the same ranking, one conversation.

Requirements

Create a codeunit named "Top Shippers" with one public procedure:

procedure TopShippedCustomers(CustomerNoFilter: Text; FromDate: Date; ToDate: Date; TopCount: Integer): List of [Text]

Rules:

1. Consider every Customer whose "No." matches CustomerNoFilter — an AL filter expression for a Code field. The tests use patterns like TRYAL-T1-*; the filter is never empty.
2. A customer's shipped volume comes from the Sales Shipment Line records of their shipment documents: a Sales Shipment Header belongs to the customer through its "Sell-to Customer No.", and a line belongs to its document through "Document No.".
3. Only lines of documents whose header "Posting Date" lies in FromDate..ToDate count — both boundary dates included. Shipment lines carry a "Posting Date" and a "Sell-to Customer No." of their own — stamps copied at posting time, possibly stale. The tests deliberately seed lines whose stamps contradict their header; the header decides.