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
System.Object
NullOperator
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
Namespace: VDS.RDF.Query.Algebra
Assembly: dotNetRDF.dll
Syntax
public class NullOperator : ITerminalOperator, ISparqlAlgebra
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
System.Collections.Generic.IEnumerable<System.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
System.Collections.Generic.IEnumerable<System.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
System.Collections.Generic.IEnumerable<System.String>
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Variables

Gets the variables used in this algebra.
Declaration
public IEnumerable<string> Variables { get; }
Property Value
Type Description
System.Collections.Generic.IEnumerable<System.String>

Methods

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Evaluate(SparqlEvaluationContext)

Evaluates the Null operator which of course always returns a NullMultiset.
Declaration
public BaseMultiset Evaluate(SparqlEvaluationContext context)
Parameters
Type Name Description
SparqlEvaluationContext context Evaluation Context.
Returns
Type Description
BaseMultiset
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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
System.String
Overrides
System.Object.ToString()

Implements

Extension Methods