redb.Route.XPath2 4.2.2

redb.Route.XPath2

XPath 2.0 expressions for redb.Route, usable in every position that takes an expression.

using static redb.Route.XPath2.XPath2Dsl;

From("direct:orders")
    .Filter(XPath2("some $o in /orders/order satisfies number($o/total) > 100"))
        .SetHeader("ids", XPath2("string-join(/orders/order[number(total) > 100]/@id, ',')"))
        .To("direct:large-orders")
    .EndFilter();

What it adds over the built-in XPath 1.0

XPath 1.0 has no regular expressions, no sequences, no date arithmetic and no conditional, so a route that needs one of those has to leave the language. XPath 2.0 has them:

What it is not

This is XPath 2.0, not XQuery. let, where and order by are XQuery clauses and the engine rejects them — when the route is built, not on the first message. So there is no sorting and no grouping here. Filtering goes in a predicate rather than in a where:

XPath2("for $o in /orders/order[number(total) > 8] return string($o/@id)")   // yes
XPath2("for $o in /orders/order where number($o/total) > 8 return $o")       // rejected: XQuery

A full XQuery processor is not shipped because every .NET implementation of one is commercial. If you have a licence for one, the XSLT engine seam (IXsltEngineFactory) is the place to plug it in for transformation; see docs/V4/12-XQUERY.md.

There is also no xpath2() function in the ${…} expression language: that language lives in the core assembly, which does not know this package exists. Use the expression object.

The rest of the surface

Everything the XPath 1.0 expression grew is here too, with one deliberate difference.

XPath2("/invoice/id").From(Header("original-request"))        // read something other than the body
XPath2("/orders/order[@id=$id]").WithParameters(("id", Header("orderId")))   // bound, never concatenated
XPath2("/order/name").Trimmed()                                // trim extracted text
XPath2("/s:Envelope/s:Body", ("s", "http://schemas.xmlsoap.org/soap/envelope/"))  // namespaces

Namespaces are given at construction rather than through a fluent WithNamespaces(...), because XPath 2.0 resolves prefixes while compiling, and this expression compiles as soon as it exists so that a bad path fails the route build. A fluent method could only run after the constructor had already rejected the path.

Bound parameters are compared, never parsed: a header holding B-2' or '1'='1 selects an order with that literal id and matches nothing.

A namespace trap

If your own code lives in a namespace under redb.Route, the simple name XPath2 resolves to this package's namespace and shadows the imported factory. Spell it XPath2Dsl.XPath2(…) there. Code in any other namespace is unaffected.

Licence and dependencies

The package is Apache-2.0, like the rest of redb.Route. It depends on XPath2.Net (XPath2, MS-PL), which has no dependencies of its own — so the whole graph is two assemblies. XPath2.Extensions is deliberately not referenced: it is MIT but pulls in Newtonsoft.Json, which this framework removed on purpose, and it adds only non-official extras.

MS-PL is a permissive, OSI-approved licence: it allows commercial and closed-source use and grants patent rights. It is not GPL-compatible, which matters only if you intend to combine it with GPL-licensed code. XPath2.Net reports conformance of 12954 of 15133 XQTS 1.0.2 cases (85.6%).