Parse XML That Has Namespaces

Hard

xml

xpath

namespaces

Parse XML That Has Namespaces

Your company just went live with the FreightEx carrier network, and their gateway pushes a shipment status message — an XML document — after every package scan.

The previous developer's parser worked perfectly against the sandbox samples; then production traffic arrived and every field started coming back empty: no errors, no crashes, just nothing found. The difference is one attribute at the top of the message — the sandbox samples carried no namespace declarations, production messages do, and the FreightEx spec says they are entirely within their rights to.

The message

A typical production message:

<?xml version="1.0" encoding="UTF-8"?>
<ShipmentStatus xmlns="urn:tryal:freight:shipping:v2">
  <Header>
    <ShipmentNo>SHP-10412</ShipmentNo>
  </Header>
  <Packages>
    <Package>
      <trk:TrackingNo xmlns:trk="urn:tryal:freight:tracking:v1">1Z-00443-7</trk:TrackingNo>
      <Weight unit="kg">12.5</Weight>
    </Package>
    <Package>
      <trk:TrackingNo xmlns:trk="urn:tryal:freight:tracking:v1">1Z-00443-8</trk:TrackingNo>
      <Weight unit="kg">3.25</Weight>
    </Package>
  </Packages>
</ShipmentStatus>

What the FreightEx spec guarantees — and nothing more:

The elements ShipmentStatus, Header, ShipmentNo, Packages, Package and Weight belong to the namespace urn:tryal:freight:shipping:v2.
The element TrackingNo belongs to the namespace urn:tryal:freight:tracking:v1.
Namespace prefixes are the sender's choice and change between messages: either namespace may appear under any prefix, or as a default (xmlns="...") declaration, on any element. Only the two URIs above carry stable identity.
The unit attribute on Weight never carries a prefix.
Messages may also carry elements from other partners' namespaces — sometimes with the very same local names (ShipmentNo, Package, TrackingNo) — anywhere in the document, including inside Packages. They are not yours and must be ignored.
Shipping-namespace Package elements appear only inside Packages; Header and Packages each appear at most once, directly under the root.
Every message is well-formed XML, and element content is plain text.

Requirements

Create a codeunit named "Shipment Status Parser" with four public procedures:

procedure GetShipmentNo(XmlPayload: Text): Text
procedure CountPackages(XmlPayload: Text): Integer
procedure GetTrackingNumbers(XmlPayload: Text): List of [Text]
procedure GetWeightUnit(XmlPayload: Text): Text

Rules:

GetShipmentNo returns the text content of the shipping-namespace ShipmentNo element inside Header; '' if the message has none.
CountPackages returns how many shipping-namespace Package elements the message contains; 0 for an empty shipment.
GetTrackingNumbers returns the text content of every tracking-namespace TrackingNo element, in document order; an empty list when there are none.
GetWeightUnit returns the value of the first unit attribute found on a shipping-namespace Weight element, in document order; '' when no Weight carries one (or there is no Weight at all).
Elements with the right local name but the wrong namespace never count, are never returned, and never mask the real ones.
None of the procedures may raise an error on a message that satisfies the spec above.

What the tests check

The grading tests feed your parser generated messages: with the shipping namespace declared as default and declared under a prefix, with the tracking namespace under changing prefixes (including a default declaration placed directly on TrackingNo), with foreign-namespace ShipmentNo/Package/TrackingNo/Weight decoys under the root and inside Packages (including a foreign Weight carrying its own unit attribute ahead of the real one), with a unit-less shipping Weight placed before one that carries the unit, and with shipment numbers, counts, tracking numbers and units randomized so pattern-matching the sample above cannot pass. Comparisons and counts are exact — over-matching a decoy fails just as hard as finding nothing. The empty cases are graded too: a missing ShipmentNo, an empty shipment, tracking-free packages and a Weight without a unit must come back as '', 0 or an empty list — never as an error.

Learn More

Hint 1

The starter's XPath queries are syntactically fine and match nothing. In XPath, an unprefixed name like ShipmentStatus means 'ShipmentStatus in NO namespace' — but a default xmlns declaration puts an element and its whole subtree in a namespace even though you see no prefixes anywhere. The document and the query disagree about identity, and XPath resolves that disagreement silently: zero matches.

Hint 2

AL ships an XmlNamespaceManager: AddNamespace binds a prefix of your choosing to a namespace URI, and SelectNodes / SelectSingleNode have overloads that take the manager and resolve those prefixes inside your XPath. After ReadFrom, associate the manager with the document via its NameTable. The prefixes you register are private aliases — they never have to match the sender's, which is exactly what makes prefix-shuffling senders harmless.

Hint 3

Register one prefix per URI — say sh for the shipping namespace and trk for the tracking namespace — then query with those prefixes on every element step: the header path, //sh:Package, //trk:TrackingNo. One last trap: an attribute without a prefix belongs to NO namespace even when a default namespace is in force, so the weight's unit is selected as @unit, never @sh:unit.

ALBusiness Central 28.5

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