Class FieldMaskingSpanQuery

Wrapper to allow SpanQuery objects participate in composite single-field SpanQueries by 'lying' about their search field. That is, the masked SpanQuery will function as normal, but Field simply hands back the value supplied in this class's constructor.

This can be used to support Queries like SpanNearQuery or SpanOrQuery across different fields, which is not ordinarily permitted.

This can be useful for denormalized relational data: for example, when indexing a document with conceptually many 'children': 

 teacherid: 1
 studentfirstname: james
 studentsurname: jones

 teacherid: 2
 studenfirstname: james
 studentsurname: smith
 studentfirstname: sally
 studentsurname: jones

A SpanNearQuery with a slop of 0 can be applied across two SpanTermQuery objects as follows: 

    SpanQuery q1  = new SpanTermQuery(new Term("studentfirstname", "james"));
    SpanQuery q2  = new SpanTermQuery(new Term("studentsurname", "jones"));
    SpanQuery q2m = new FieldMaskingSpanQuery(q2, "studentfirstname");
    Query q = new SpanNearQuery(new SpanQuery[] { q1, q2m }, -1, false);
to search for 'studentfirstname:james studentsurname:jones' and find teacherid 1 without matching teacherid 2 (which has a 'james' in position 0 and 'jones' in position 1).

Note: as Field returns the masked field, scoring will be done using the Similarity and collection statistics of the field name supplied, but with the term statistics of the real field. This may lead to exceptions, poor performance, and unexpected scoring behavior.

Inheritance
System.Object
Query
SpanQuery
FieldMaskingSpanQuery
Inherited Members
Namespace: Lucene.Net.Search.Spans
Assembly: Lucene.Net.dll
Syntax
public class FieldMaskingSpanQuery : SpanQuery

Constructors

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FieldMaskingSpanQuery(SpanQuery, String)

Declaration
public FieldMaskingSpanQuery(SpanQuery maskedQuery, string maskedField)
Parameters
Type Name Description
SpanQuery maskedQuery
System.String maskedField

Properties

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Field

Declaration
public override string Field { get; }
Property Value
Type Description
System.String
Overrides
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MaskedQuery

Declaration
public virtual SpanQuery MaskedQuery { get; }
Property Value
Type Description
SpanQuery

Methods

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CreateWeight(IndexSearcher)

Declaration
public override Weight CreateWeight(IndexSearcher searcher)
Parameters
Type Name Description
IndexSearcher searcher
Returns
Type Description
Weight
Overrides
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Equals(Object)

Declaration
public override bool Equals(object o)
Parameters
Type Name Description
System.Object o
Returns
Type Description
System.Boolean
Overrides
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ExtractTerms(ISet<Term>)

Declaration
public override void ExtractTerms(ISet<Term> terms)
Parameters
Type Name Description
ISet<Term> terms
Overrides
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GetHashCode()

Declaration
public override int GetHashCode()
Returns
Type Description
System.Int32
Overrides
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GetSpans(AtomicReaderContext, IBits, IDictionary<Term, TermContext>)

Declaration
public override Spans GetSpans(AtomicReaderContext context, IBits acceptDocs, IDictionary<Term, TermContext> termContexts)
Parameters
Type Name Description
AtomicReaderContext context
IBits acceptDocs
IDictionary<Term, TermContext> termContexts
Returns
Type Description
Spans
Overrides
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Rewrite(IndexReader)

Declaration
public override Query Rewrite(IndexReader reader)
Parameters
Type Name Description
IndexReader reader
Returns
Type Description
Query
Overrides
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ToString(String)

Declaration
public override string ToString(string field)
Parameters
Type Name Description
System.String field
Returns
Type Description
System.String
Overrides