### Saxon.Api

- BinaryResource
- CatalogCollection
- DirectoryCollection
- DocumentBuilder
- DomDestination
- DynamicContext
- DynamicError
- EmptyEnumerator<T>
- ErrorReporter
- ErrorReporterToStaticError
- ErrorReporterWrapper
- ExtensionFunction
- ExtensionFunctionCall
- ExtensionFunctionDefinition
- Feature<T>
- FeatureKeys
- HostLanguage
- ICollectionFinder
- IErrorReporter
- IInvalidityHandler
- IMessageListener
- IMessageListener2
- InvalidityHandlerWrapper
- IPredicate<in XdmItem>
- IQueryResolver
- IResource
- IResourceCollection
- IResourceFactory
- IResultDocumentHandler
- IXmlLocation
- JarCollection
- NamespaceConstant
- NullDestination
- Predicate<T>
- Predicates
- Processor
- QName
- RawDestination
- RecoveryPolicy
- Resource
- ResourceCollection
- SchemaManager
- SchemaResolver
- SchemaValidationMode
- SchemaValidator
- Serializer
- StandardCollectionFinder
- StandardLogger
- StaticContext
- StaticError
- Step<TInput, TResult>
- Steps
- TextWriterDestination
- TreeModel
- URIQueryParameters
- ValidationFailure
- WhitespacePolicy
- XdmAnyArrayType
- XdmAnyFunctionType
- XdmAnyItemType
- XdmAnyMapType
- XdmAnyNodeType
- XdmArray
- XdmAtomicType
- XdmAtomicValue
- XdmAxis
- XdmDestination
  - - TreeProtector
- XdmEmptySequence
- XdmExternalObjectValue
- XdmFunctionItem
- XdmItem
- XdmItemType
- XdmMap
- XdmNode
- XdmNodeKind
- XdmSequenceType
- XdmValue
- XmlDestination
- XmlProcessingError
- XmlResource
- XPathCompiler
- XPathExecutable
- XPathSelector
- XQueryCompiler
- XQueryEvaluator
- XQueryExecutable
- Xslt30Transformer
- XsltCompiler
- XsltExecutable
  - - ParameterDetails
- XsltPackage
- XsltTransformer

### Saxon.Api

# Class XQueryEvaluator

public class XQueryEvaluator
implements IEnumerable

An `XQueryEvaluator` represents a compiled and loaded query ready for execution. The `XQueryEvaluator` holds details of the dynamic evaluation context for the query.

An `XQueryEvaluator` must not be used concurrently in multiple threads. It is safe, however, to reuse the object within a single thread to run the same query several times. Running the query does not change the context that has been established.

An `XQueryEvaluator` is always constructed by running the `Load` method of an `XQueryExecutable`.

### Property Summary
XdmItem | ContextItem The context item for the query.
net.sf.saxon.s9api.XQueryEvaluator | Implementation Escape hatch to the `net.sf.saxon.query.DynamicQueryContext` object in the underlying Java implementation
XmlResolver | InputXmlResolver The `XmlResolver` to be used at run-time to resolve and dereference URIs supplied to the `doc()` function.
SchemaValidationMode | SchemaValidationMode The `SchemaValidationMode` to be used in this query, especially for documents loaded using the `doc()`, `document()`, or `collection()` functions.
StandardLogger | TraceFunctionDestination Destination for output of messages produced using the `trace()` function.

### Method Summary
XdmValue | CallFunction(QName function, XdmValue[] arguments) Call a global user-defined function in the compiled query.
XdmValue | Evaluate() Evaluate the query, returning the result as an `XdmValue` (that is, a sequence of nodes and/or atomic values).
XdmItem | EvaluateSingle() Evaluate the query, returning the result as an `XdmItem` (that is, a single node or atomic value).
IEnumerator | GetEnumerator() Evaluate the query, returning the result as an `IEnumerator` (that is, an enumerator over a sequence of nodes and/or atomic values).
void | Run(XmlDestination destination) Evaluate the query, sending the result to a specified destination.
XdmNode[] | RunUpdate() Execute an updating query.
void | SetExternalVariable(QName name, XdmValue value) Set the value of an external variable declared in the query.

## Property Detail

### ContextItem

public XdmItem ContextItem {get; set; }

The context item for the query.

This may be a node, an atomic value, or a function item such as a map or array. Most commonly it will be a document node, which might be constructed using a `DocumentBuilder` created from the `Processor` object.

### Implementation

public net.sf.saxon.s9api.XQueryEvaluator Implementation {get; }

Escape hatch to the `net.sf.saxon.query.DynamicQueryContext` object in the underlying Java implementation

### InputXmlResolver

public XmlResolver InputXmlResolver {get; set; }

The `XmlResolver` to be used at run-time to resolve and dereference URIs supplied to the `doc()` function.

### SchemaValidationMode

public SchemaValidationMode SchemaValidationMode {get; set; }

The `SchemaValidationMode` to be used in this query, especially for documents loaded using the `doc()`, `document()`, or `collection()` functions.

This does not affect any document supplied as the context item for the query, or as the values of external variables.

### TraceFunctionDestination

public StandardLogger TraceFunctionDestination {get; set; }

Destination for output of messages produced using the `trace()` function.

If no specific destination is supplied by the caller, message information will be written to the standard error stream.

The supplied destination is ignored if a `TraceListener` is in use.

## Method Detail

### CallFunction

public XdmValue CallFunction(QName function,
XdmValue[] arguments)
throws
ArgumentException,
DynamicError

Call a global user-defined function in the compiled query.

If this is called more than once (to evaluate the same function repeatedly with different arguments, or to evaluate different functions) then the sequence of evaluations uses the same values of global variables including external variables (query parameters); the effect of any changes made to query parameters between calls is undefined.

Parameters:

`function` - The name of the function to be called
`arguments` - The values of the arguments to be supplied to the function. These must be of the correct type as defined in the function signature (there is no automatic conversion to the required type).

Throws:

ArgumentException - If no function has been defined with the given name and arity or if any of the arguments does not match its required type according to the function signature.
DynamicError - If a dynamic error occurs in evaluating the function.

### Evaluate

public XdmValue Evaluate()
throws
DynamicError

Evaluate the query, returning the result as an `XdmValue` (that is, a sequence of nodes and/or atomic values).

Returns:

An `XdmValue` representing the results of the query

Throws:

DynamicError - Throws a `DynamicError` if any run-time failure occurs while evaluating the query.

### EvaluateSingle

public XdmItem EvaluateSingle()
throws
DynamicError

Evaluate the query, returning the result as an `XdmItem` (that is, a single node or atomic value).

Returns:

An `XdmItem` representing the result of the query, or null if the query returns an empty sequence. If the query returns a sequence of more than one item, any items after the first are ignored.

Throws:

DynamicError - Throws a `DynamicError` if any run-time failure occurs while evaluating the expression.

### GetEnumerator

public IEnumerator GetEnumerator()
throws
DynamicError

Evaluate the query, returning the result as an `IEnumerator` (that is, an enumerator over a sequence of nodes and/or atomic values).

Returns:

An enumerator over the sequence that represents the results of the query. Each object in this sequence will be an instance of `XdmItem`. Note that the query may be evaluated lazily, which means that a successful response from this method does not imply that the query has executed successfully: failures may be reported later while retrieving items from the iterator.

Throws:

DynamicError - Throws a `DynamicError` if any run-time failure occurs while evaluating the expression.

### Run

public void Run(XmlDestination destination)
throws
DynamicError

Evaluate the query, sending the result to a specified destination.

Parameters:

`destination` - The destination for the results of the query. The class `XmlDestination` is an abstraction that allows a number of different kinds of destination to be specified.

Throws:

DynamicError - Throws a `DynamicError` if any run-time failure occurs while evaluating the expression.

### RunUpdate

public XdmNode[] RunUpdate()
throws
DynamicError

Execute an updating query.

Returns:

An array containing the root nodes of documents that have been updated by the query.

Throws:

DynamicError - Throws a `DynamicError` if any run-time failure occurs while evaluating the expression, or if the expression is not an updating query.

### SetExternalVariable

public void SetExternalVariable(QName name,
XdmValue value)

Set the value of an external variable declared in the query.

Parameters:

`name` - The name of the external variable, expressed as a `QName`. If an external variable of this name has been declared in the query prolog, the given value will be assigned to the variable. If the variable has not been declared, calling this method has no effect (it is not an error).
`value` - The value to be given to the external variable. If the variable declaration defines a required type for the variable, then this value must match the required type: no conversions are applied.