PhoenixmlDb.Core

XdmValue

Represents an XDM atomic value — a typed, immutable value from the XPath/XQuery type system.

#XdmValue

Namespace: PhoenixmlDb.Xdm

Represents an XDM atomic value — a typed, immutable value from the XPath/XQuery type system.

XdmValue pairs a CLR value (boxed in XdmValue.RawValue) with an XdmType tag that identifies its XSD type. This enables type-aware operations such as comparisons, arithmetic, and casting as defined by the XPath/XQuery Functions and Operators specification.

Construction: Use the static factory methods (XdmValue.UntypedAtomic, XdmValue.XsString, XdmValue.XsInteger, XdmValue.Boolean, etc.) to create values. These ensure the correct XdmType tag is applied.

Access: Use the typed accessor methods (XdmValue.AsString, XdmValue.AsLong, XdmValue.AsDouble, XdmValue.AsBoolean, etc.) to extract the value. These perform type coercion following XPath casting rules and throw InvalidCastException for incompatible types.

Equality: Two values are equal if and only if they have the same XdmValue.Type and the same underlying value.

#Example

csharp 
var price = XdmValue.XsDecimal(19.99m);
var name = XdmValue.XsString("Widget");
var active = XdmValue.Boolean(true);

Console.WriteLine(price.AsDecimal()); // 19.99
Console.WriteLine(name.AsString());   // Widget
Console.WriteLine(active.AsBoolean()); // True

#Properties

Name Description
RawValue Gets the raw value object.

#Methods

#From``1(``0)

Converts a supported CLR value to its XDM representation. This is the single conversion point from .NET types to XDM values.

Parameters:

  • value — The value to convert. Dispatch is on the value's runtime type, so From<object>("x") and From<string>("x") both produce XdmValue.XsString — a metadata value's XDM type is a property of what it actually holds, not of how it happens to be typed at the call site. A null reference or unset Nullable<T> produces XdmValue.Empty.

Exceptions:

  • NotSupportedException — The CLR type has no XDM equivalent.

PhoenixmlDb.Linq

delegates to this instead of maintaining its own parallel

Type

-to-XDM map, so the two projects cannot drift apart on how a given CLR type is represented.

#IsSupportedClrType(Type)

Determines whether

and

support the given CLR type.

Nullable<T>

wrappers are supported wherever their underlying type is.

and

are always reported as supported:

dispatches on the value's runtime type rather than the compile-time type argument, so a caller guarding a call with

IsSupportedClrType(typeof(T))

before invoking

From<T>

must not be turned away just because

T

is

— whether the call actually succeeds still depends on what the value holds at run time.

#To``1(PhoenixmlDb.Xdm.XdmValue)

Converts this value to a supported CLR type. The stored

must match

's XDM family — this is a strict, storage-boundary read, not the coercive casting the

As*

accessors perform for XPath expression evaluation. Numeric widening/narrowing within a family is still permitted (an

xs:integer

reads back as

,

,

, or

; an

xs:double

/

xs:float

reads back as either

or

).

Type parameters:

  • T — The requested CLR type. Nullable<T> wrappers are supported wherever their underlying type is; requesting XdmValue itself returns the value unchanged; requesting Object returns whatever CLR value the stored XdmType naturally boxes to (the mirror image of XdmValue.From``1 dispatching on the runtime value for T = object), or null for XdmValue.Empty.

Exceptions:

  • NotSupportedException — The CLR type has no XDM equivalent.

  • InvalidCastException — Either the stored XdmType is not one T can be read from (e.g. requesting Int32 from a value stored as xs:string), or this value is XdmValue.Empty and T is a non-nullable value type with no meaningful empty representation.

  • OverflowException — The stored integer does not fit in the requested narrower CLR type (e.g. requesting Byte for a stored xs:integer of 300).

XdmValue.Empty is handled by whether T has a value that can genuinely mean "absent": if T is a reference type or Nullable<V>, converting an empty value returns null — this is what keeps From<string>(null) (which produces XdmValue.Empty) and To<string>() genuine inverses of each other. If T is a non-nullable value type (Int64, DateTimeOffset, etc.), there is no such thing as "the empty Int64" — returning a default like 0 or year 1 would be a silently wrong value indistinguishable from genuine data, so this throws InvalidCastException instead.