Class NullOperator

Represents a part of the algebra that has been determined to not return any results in advance and so can be replaced with this operator which always returns null.

Inheritance
object
NullOperator
Implements
Inherited Members
Namespace: VDS.RDF.Query.Algebra
Assembly: dotNetRdf.dll
Syntax
public class NullOperator : ITerminalOperator, ISparqlAlgebra, IVisitable, IProcessable
Remarks

Primarily intended for use with Algebra Optimisers which are rewriting the algebra to run against an out of memory dataset (e.g. SQL based) where it may be easily possible to determine if a triple pattern will match in advance of actually returning the matches.

Constructors

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NullOperator(IEnumerable<string>)

Creates a new Null Operator.

Declaration
public NullOperator(IEnumerable<string> variables)
Parameters
Type Name Description
IEnumerable<string> variables

Variables in the algebra that this null is replacing.

Properties

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FixedVariables

Gets the enumeration of fixed variables in the algebra i.e. variables that are guaranteed to have a bound value.

Declaration
public IEnumerable<string> FixedVariables { get; }
Property Value
Type Description
IEnumerable<string>
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FloatingVariables

Gets the enumeration of floating variables in the algebra i.e. variables that are not guaranteed to have a bound value.

Declaration
public IEnumerable<string> FloatingVariables { get; }
Property Value
Type Description
IEnumerable<string>
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Variables

Gets the variables used in this algebra.

Declaration
public IEnumerable<string> Variables { get; }
Property Value
Type Description
IEnumerable<string>

Methods

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Accept<T>(ISparqlAlgebraVisitor<T>)

Accept a simple algebra visitor.

Declaration
public T Accept<T>(ISparqlAlgebraVisitor<T> visitor)
Parameters
Type Name Description
ISparqlAlgebraVisitor<T> visitor

The visitor implementation.
Returns
Type Description
T
Type Parameters
Name Description
T

The type returned by the Visit methods of the visitor.
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Accept<TResult, TContext>(ISparqlQueryAlgebraProcessor<TResult, TContext>, TContext)

Called by an algebra visitor to process an item by invoking the appropriate method on the processor passed in.

Declaration
public TResult Accept<TResult, TContext>(ISparqlQueryAlgebraProcessor<TResult, TContext> processor, TContext context)
Parameters
Type Name Description
ISparqlQueryAlgebraProcessor<TResult, TContext> processor

The processor to invoke.
TContext context

The context to pass to the processor.
Returns
Type Description
TResult

The result of invoking the processor method.
Type Parameters
Name Description
TResult

The type of result returned by the processor.
TContext

The type of the context object to be provided to the processor.
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ToGraphPattern()

Throws an error since a null operator cannot be transformed back into a query.

Declaration
public GraphPattern ToGraphPattern()
Returns
Type Description
GraphPattern
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ToQuery()

Throws an error since a null operator cannot be transformed back into a query.

Declaration
public SparqlQuery ToQuery()
Returns
Type Description
SparqlQuery
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ToString()

Gets the string representation of the algebra.

Declaration
public override string ToString()
Returns
Type Description
string
Overrides

Implements

Extension Methods