Class DisjunctionMaxQuery

A query that generates the union of documents produced by its subqueries, and that scores each document with the maximum score for that document as produced by any subquery, plus a tie breaking increment for any additional matching subqueries. This is useful when searching for a word in multiple fields with different boost factors (so that the fields cannot be combined equivalently into a single search field). We want the primary score to be the one associated with the highest boost, not the sum of the field scores (as BooleanQuery would give).

If the query is "albino elephant" this ensures that "albino" matching one field and "elephant" matching another gets a higher score than "albino" matching both fields.

To get this result, use both BooleanQuery and DisjunctionMaxQuery: for each term a DisjunctionMaxQuery searches for it in each field, while the set of these DisjunctionMaxQuery's is combined into a BooleanQuery. The tie breaker capability allows results that include the same term in multiple fields to be judged better than results that include this term in only the best of those multiple fields, without confusing this with the better case of two different terms in the multiple fields.

Collection initializer note: To create and populate a DisjunctionMaxQuery in a single statement, you can use the following example as a guide:

var disjunctionMaxQuery = new DisjunctionMaxQuery(0.1f) {
    new TermQuery(new Term("field1", "albino")), 
    new TermQuery(new Term("field2", "elephant"))
};

Inheritance

System.Object

Query

DisjunctionMaxQuery

Implements

IEnumerable<Query>

Inherited Members

Query.Boost

Query.ToString()

Namespace: Lucene.Net.Search

Assembly: Lucene.Net.dll

Syntax

public class DisjunctionMaxQuery : Query, IEnumerable<Query>

Constructors

DisjunctionMaxQuery(ICollection<Query>, Single)

Creates a new DisjunctionMaxQuery

Declaration

public DisjunctionMaxQuery(ICollection<Query> disjuncts, float tieBreakerMultiplier)

Parameters

Type	Name	Description
ICollection<Query>	disjuncts	A ICollection{Query} of all the disjuncts to add
System.Single	tieBreakerMultiplier	The weight to give to each matching non-maximum disjunct

DisjunctionMaxQuery(Single)

Creates a new empty DisjunctionMaxQuery. Use Add(Query) to add the subqueries.

Declaration

public DisjunctionMaxQuery(float tieBreakerMultiplier)

Parameters

Type	Name	Description
System.Single	tieBreakerMultiplier	The score of each non-maximum disjunct for a document is multiplied by this weight and added into the final score. If non-zero, the value should be small, on the order of 0.1, which says that 10 occurrences of word in a lower-scored field that is also in a higher scored field is just as good as a unique word in the lower scored field (i.e., one that is not in any higher scored field).

Properties

Disjuncts

Declaration

public virtual IList<Query> Disjuncts { get; }

Property Value

Type	Description
IList<Query>	The disjuncts.

TieBreakerMultiplier

Declaration

public virtual float TieBreakerMultiplier { get; }

Property Value

Type	Description
System.Single	Tie breaker value for multiple matches.

Methods

Add(ICollection<Query>)

Add a collection of disjuncts to this disjunction via IEnumerable{Query}

Declaration

public virtual void Add(ICollection<Query> disjuncts)

Parameters

Type	Name	Description
ICollection<Query>	disjuncts	A collection of queries to add as disjuncts.

Add(Query)

Add a subquery to this disjunction

Declaration

public virtual void Add(Query query)

Parameters

Type	Name	Description
Query	query	The disjunct added

Clone()

Create a shallow copy of us -- used in rewriting if necessary

Declaration

public override object Clone()

Returns

Type	Description
System.Object	A copy of us (but reuse, don't copy, our subqueries)

Overrides

Query.Clone()

CreateWeight(IndexSearcher)

Create the Weight used to score us

Declaration

public override Weight CreateWeight(IndexSearcher searcher)

Parameters

Type	Name	Description
IndexSearcher	searcher

Returns

Type	Description
Weight

Overrides

Query.CreateWeight(IndexSearcher)

Equals(Object)

Return true if we represent the same query as o

Declaration

public override bool Equals(object o)

Parameters

Type	Name	Description
System.Object	o	Another object

Returns

Type	Description
System.Boolean	true if o is a DisjunctionMaxQuery with the same boost and the same subqueries, in the same order, as us

Overrides

Query.Equals(Object)

ExtractTerms(ISet<Term>)

Expert: adds all terms occurring in this query to the terms set. Only works if this query is in its rewritten (Rewrite(IndexReader)) form.

Declaration

public override void ExtractTerms(ISet<Term> terms)

Parameters

Type	Name	Description
ISet<Term>	terms

Overrides

Query.ExtractTerms(ISet<Term>)

GetEnumerator()

Declaration

public virtual IEnumerator<Query> GetEnumerator()

Returns

Type	Description
IEnumerator<Query>	An IEnumerator{Query} over the disjuncts

GetHashCode()

Compute a hash code for hashing us

Declaration

public override int GetHashCode()

Returns

Type	Description
System.Int32	the hash code

Overrides

Query.GetHashCode()

Rewrite(IndexReader)

Optimize our representation and our subqueries representations

Declaration

public override Query Rewrite(IndexReader reader)

Parameters

Type	Name	Description
IndexReader	reader	The IndexReader we query

Returns

Type	Description
Query	An optimized copy of us (which may not be a copy if there is nothing to optimize)

Overrides

Query.Rewrite(IndexReader)

ToString(String)

Prettyprint us.

Declaration

public override string ToString(string field)

Parameters

Type	Name	Description
System.String	field	The field to which we are applied

Returns

Type	Description
System.String	A string that shows what we do, of the form "(disjunct1 | disjunct2 | ... | disjunctn)^boost"

Overrides

Query.ToString(String)

Implements

IEnumerable<>