https://lucene.apache.org/lucene-parent/lucene-core: Apache Lucene Java Core (The Apache Software Foundation) 
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 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
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 *
 *     http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.lucene.search;


import java.io.IOException;
import java.util.Objects;

import org.apache.lucene.index.FilteredTermsEnum; // javadocs
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.SingleTermsEnum;   // javadocs
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermStates;
import org.apache.lucene.index.Terms;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.search.BooleanQuery.Builder;
import org.apache.lucene.util.AttributeSource;


An abstract Query that matches documents containing a subset of terms provided by a FilteredTermsEnum enumeration. 
This query cannot be used directly; you must subclass it and define getTermsEnum(Terms, AttributeSource) to provide a FilteredTermsEnum that iterates through the terms to be matched. 
NOTE: if setRewriteMethod is either CONSTANT_SCORE_BOOLEAN_REWRITE or SCORING_BOOLEAN_REWRITE, you may encounter a TooManyClauses exception during searching, which happens when the number of terms to be searched exceeds BooleanQuery.getMaxClauseCount(). Setting setRewriteMethod to CONSTANT_SCORE_REWRITE prevents this. 
The recommended rewrite method is CONSTANT_SCORE_REWRITE: it doesn't spend CPU computing unhelpful scores, and is the most performant rewrite method given the query. If you need scoring (like FuzzyQuery, use TopTermsScoringBooleanQueryRewrite which uses a priority queue to only collect competitive terms and not hit this limitation. Note that org.apache.lucene.queryparser.classic.QueryParser produces MultiTermQueries using CONSTANT_SCORE_REWRITE by default. 
/**
 * An abstract {@link Query} that matches documents
 * containing a subset of terms provided by a {@link
 * FilteredTermsEnum} enumeration.
 *
 * <p>This query cannot be used directly; you must subclass
 * it and define {@link #getTermsEnum(Terms,AttributeSource)} to provide a {@link
 * FilteredTermsEnum} that iterates through the terms to be
 * matched.
 *
 * <p><b>NOTE</b>: if {@link #setRewriteMethod} is either
 * {@link #CONSTANT_SCORE_BOOLEAN_REWRITE} or {@link
 * #SCORING_BOOLEAN_REWRITE}, you may encounter a
 * {@link BooleanQuery.TooManyClauses} exception during
 * searching, which happens when the number of terms to be
 * searched exceeds {@link
 * BooleanQuery#getMaxClauseCount()}.  Setting {@link
 * #setRewriteMethod} to {@link #CONSTANT_SCORE_REWRITE}
 * prevents this.
 *
 * <p>The recommended rewrite method is {@link
 * #CONSTANT_SCORE_REWRITE}: it doesn't spend CPU
 * computing unhelpful scores, and is the most
 * performant rewrite method given the query. If you
 * need scoring (like {@link FuzzyQuery}, use
 * {@link TopTermsScoringBooleanQueryRewrite} which uses
 * a priority queue to only collect competitive terms
 * and not hit this limitation.
 *
 * Note that org.apache.lucene.queryparser.classic.QueryParser produces
 * MultiTermQueries using {@link #CONSTANT_SCORE_REWRITE}
 * by default.
 */
public abstract class MultiTermQuery extends Query {
  protected final String field;
  protected RewriteMethod rewriteMethod = CONSTANT_SCORE_REWRITE;

  
Abstract class that defines how the query is rewritten. 
/** Abstract class that defines how the query is rewritten. */
  public static abstract class RewriteMethod {
    public abstract Query rewrite(IndexReader reader, MultiTermQuery query) throws IOException;
    
See Also:
/**
     * Returns the {@link MultiTermQuery}s {@link TermsEnum}
     * @see MultiTermQuery#getTermsEnum(Terms, AttributeSource)
     */
    protected TermsEnum getTermsEnum(MultiTermQuery query, Terms terms, AttributeSource atts) throws IOException {
      return query.getTermsEnum(terms, atts); // allow RewriteMethod subclasses to pull a TermsEnum from the MTQ 
    }
  }

  
A rewrite method that first creates a private Filter,
 by visiting each term in sequence and marking all docs
 for that term.  Matching documents are assigned a
 constant score equal to the query's boost.
 
 This method is faster than the BooleanQuery rewrite methods when the number of matched terms or matched documents is non-trivial. Also, it will never hit an errant TooManyClauses exception. @see #setRewriteMethod 
/** A rewrite method that first creates a private Filter,
   *  by visiting each term in sequence and marking all docs
   *  for that term.  Matching documents are assigned a
   *  constant score equal to the query's boost.
   * 
   *  <p> This method is faster than the BooleanQuery
   *  rewrite methods when the number of matched terms or
   *  matched documents is non-trivial. Also, it will never
   *  hit an errant {@link BooleanQuery.TooManyClauses}
   *  exception.
   *
   *  @see #setRewriteMethod */
  public static final RewriteMethod CONSTANT_SCORE_REWRITE = new RewriteMethod() {
    @Override
    public Query rewrite(IndexReader reader, MultiTermQuery query) {
      return new MultiTermQueryConstantScoreWrapper<>(query);
    }
  };

  
A rewrite method that first translates each term into Occur.SHOULD clause in a BooleanQuery, and keeps the scores as computed by the query. Note that typically such scores are meaningless to the user, and require non-trivial CPU to compute, so it's almost always better to use CONSTANT_SCORE_REWRITE instead. 
NOTE: This rewrite method will hit TooManyClauses if the number of terms exceeds BooleanQuery.getMaxClauseCount. @see #setRewriteMethod 
/** A rewrite method that first translates each term into
   *  {@link BooleanClause.Occur#SHOULD} clause in a
   *  BooleanQuery, and keeps the scores as computed by the
   *  query.  Note that typically such scores are
   *  meaningless to the user, and require non-trivial CPU
   *  to compute, so it's almost always better to use {@link
   *  #CONSTANT_SCORE_REWRITE} instead.
   *
   *  <p><b>NOTE</b>: This rewrite method will hit {@link
   *  BooleanQuery.TooManyClauses} if the number of terms
   *  exceeds {@link BooleanQuery#getMaxClauseCount}.
   *
   *  @see #setRewriteMethod */
  public final static RewriteMethod SCORING_BOOLEAN_REWRITE = ScoringRewrite.SCORING_BOOLEAN_REWRITE;

  
Like SCORING_BOOLEAN_REWRITE except scores are not computed. Instead, each matching document receives a constant score equal to the query's boost. 
NOTE: This rewrite method will hit TooManyClauses if the number of terms exceeds BooleanQuery.getMaxClauseCount. @see #setRewriteMethod 
/** Like {@link #SCORING_BOOLEAN_REWRITE} except
   *  scores are not computed.  Instead, each matching
   *  document receives a constant score equal to the
   *  query's boost.
   * 
   *  <p><b>NOTE</b>: This rewrite method will hit {@link
   *  BooleanQuery.TooManyClauses} if the number of terms
   *  exceeds {@link BooleanQuery#getMaxClauseCount}.
   *
   *  @see #setRewriteMethod */
  public final static RewriteMethod CONSTANT_SCORE_BOOLEAN_REWRITE = ScoringRewrite.CONSTANT_SCORE_BOOLEAN_REWRITE;

  
A rewrite method that first translates each term into Occur.SHOULD clause in a BooleanQuery, and keeps the scores as computed by the query. 
 This rewrite method only uses the top scoring terms so it will not overflow the boolean max clause count. It is the default rewrite method for FuzzyQuery. 
See Also:
  • setRewriteMethod
/**
   * A rewrite method that first translates each term into
   * {@link BooleanClause.Occur#SHOULD} clause in a BooleanQuery, and keeps the
   * scores as computed by the query.
   * 
   * <p>
   * This rewrite method only uses the top scoring terms so it will not overflow
   * the boolean max clause count. It is the default rewrite method for
   * {@link FuzzyQuery}.
   * 
   * @see #setRewriteMethod
   */
  public static final class TopTermsScoringBooleanQueryRewrite extends TopTermsRewrite<BooleanQuery.Builder> {

    
Create a TopTermsScoringBooleanQueryRewrite for 
at most size terms.

 NOTE: if BooleanQuery.getMaxClauseCount is smaller than size, then it will be used instead. 

/** 
     * Create a TopTermsScoringBooleanQueryRewrite for 
     * at most <code>size</code> terms.
     * <p>
     * NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than 
     * <code>size</code>, then it will be used instead. 
     */
    public TopTermsScoringBooleanQueryRewrite(int size) {
      super(size);
    }
    
    @Override
    protected int getMaxSize() {
      return BooleanQuery.getMaxClauseCount();
    }
    
    @Override
    protected BooleanQuery.Builder getTopLevelBuilder() {
      return new BooleanQuery.Builder();
    }
    
    @Override
    protected Query build(Builder builder) {
      return builder.build();
    }
    
    @Override
    protected void addClause(BooleanQuery.Builder topLevel, Term term, int docCount, float boost, TermStates states) {
      final TermQuery tq = new TermQuery(term, states);
      topLevel.add(new BoostQuery(tq, boost), BooleanClause.Occur.SHOULD);
    }
  }
  
  
A rewrite method that first translates each term into Occur.SHOULD clause in a BooleanQuery, but adjusts the frequencies used for scoring to be blended across the terms, otherwise the rarest term typically ranks highest (often not useful eg in the set of expanded terms in a FuzzyQuery). 

This rewrite method only uses the top scoring terms so it will not overflow
the boolean max clause count.

See Also:
  • setRewriteMethod
/**
   * A rewrite method that first translates each term into
   * {@link BooleanClause.Occur#SHOULD} clause in a BooleanQuery, but adjusts
   * the frequencies used for scoring to be blended across the terms, otherwise
   * the rarest term typically ranks highest (often not useful eg in the set of
   * expanded terms in a FuzzyQuery).
   * 
   * <p>
   * This rewrite method only uses the top scoring terms so it will not overflow
   * the boolean max clause count.
   * 
   * @see #setRewriteMethod
   */
  public static final class TopTermsBlendedFreqScoringRewrite extends
      TopTermsRewrite<BlendedTermQuery.Builder> {

    
Create a TopTermsBlendedScoringBooleanQueryRewrite for at most
size terms.

 NOTE: if BooleanQuery.getMaxClauseCount is smaller than size, then it will be used instead.

/**
     * Create a TopTermsBlendedScoringBooleanQueryRewrite for at most
     * <code>size</code> terms.
     * <p>
     * NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than
     * <code>size</code>, then it will be used instead.
     */
    public TopTermsBlendedFreqScoringRewrite(int size) {
      super(size);
    }

    @Override
    protected int getMaxSize() {
      return BooleanQuery.getMaxClauseCount();
    }

    @Override
    protected BlendedTermQuery.Builder getTopLevelBuilder() {
      BlendedTermQuery.Builder builder = new BlendedTermQuery.Builder();
      builder.setRewriteMethod(BlendedTermQuery.BOOLEAN_REWRITE);
      return builder;
    }

    @Override
    protected Query build(BlendedTermQuery.Builder builder) {
      return builder.build();
    }

    @Override
    protected void addClause(BlendedTermQuery.Builder topLevel, Term term, int docCount,
        float boost, TermStates states) {
      topLevel.add(term, boost, states);
    }
  }

  
A rewrite method that first translates each term into Occur.SHOULD clause in a BooleanQuery, but the scores are only computed as the boost. 

This rewrite method only uses the top scoring terms so it will not overflow
the boolean max clause count.

See Also:
  • setRewriteMethod
/**
   * A rewrite method that first translates each term into
   * {@link BooleanClause.Occur#SHOULD} clause in a BooleanQuery, but the scores
   * are only computed as the boost.
   * <p>
   * This rewrite method only uses the top scoring terms so it will not overflow
   * the boolean max clause count.
   * 
   * @see #setRewriteMethod
   */
  public static final class TopTermsBoostOnlyBooleanQueryRewrite extends TopTermsRewrite<BooleanQuery.Builder> {
    
    
Create a TopTermsBoostOnlyBooleanQueryRewrite for 
at most size terms.

 NOTE: if BooleanQuery.getMaxClauseCount is smaller than size, then it will be used instead. 

/** 
     * Create a TopTermsBoostOnlyBooleanQueryRewrite for 
     * at most <code>size</code> terms.
     * <p>
     * NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than 
     * <code>size</code>, then it will be used instead. 
     */
    public TopTermsBoostOnlyBooleanQueryRewrite(int size) {
      super(size);
    }
    
    @Override
    protected int getMaxSize() {
      return BooleanQuery.getMaxClauseCount();
    }
    
    @Override
    protected BooleanQuery.Builder getTopLevelBuilder() {
      return new BooleanQuery.Builder();
    }
    
    @Override
    protected Query build(BooleanQuery.Builder builder) {
      return builder.build();
    }
    
    @Override
    protected void addClause(BooleanQuery.Builder topLevel, Term term, int docFreq, float boost, TermStates states) {
      final Query q = new ConstantScoreQuery(new TermQuery(term, states));
      topLevel.add(new BoostQuery(q, boost), BooleanClause.Occur.SHOULD);
    }
  }

  
Constructs a query matching terms that cannot be represented with a single
Term.

/**
   * Constructs a query matching terms that cannot be represented with a single
   * Term.
   */
  public MultiTermQuery(final String field) {
    this.field = Objects.requireNonNull(field, "field must not be null");
  }

  
Returns the field name for this query 
/** Returns the field name for this query */
  public final String getField() { return field; }

  
Construct the enumeration to be used, expanding the pattern term. This method should only be called if the field exists (ie, implementations can assume the field does exist). This method should not return null (should instead return TermsEnum.EMPTY if no terms match). The TermsEnum must already be positioned to the first matching term. The given AttributeSource is passed by the RewriteMethod to share information between segments, for example TopTermsRewrite uses it to share maximum competitive boosts 
/** Construct the enumeration to be used, expanding the
   *  pattern term.  This method should only be called if
   *  the field exists (ie, implementations can assume the
   *  field does exist).  This method should not return null
   *  (should instead return {@link TermsEnum#EMPTY} if no
   *  terms match).  The TermsEnum must already be
   *  positioned to the first matching term.
   *  The given {@link AttributeSource} is passed by the {@link RewriteMethod} to
   *  share information between segments, for example {@link TopTermsRewrite} uses
   *  it to share maximum competitive boosts
   */
  protected abstract TermsEnum getTermsEnum(Terms terms, AttributeSource atts) throws IOException;

  
Constructs an enumeration that expands the pattern term.
This method should only be called if the field exists (ie,
implementations can assume the field does exist).
This method never returns null.
The returned TermsEnum is positioned to the first matching term.

/**
   * Constructs an enumeration that expands the pattern term.
   * This method should only be called if the field exists (ie,
   * implementations can assume the field does exist).
   * This method never returns null.
   * The returned TermsEnum is positioned to the first matching term.
   */
  public final TermsEnum getTermsEnum(Terms terms) throws IOException {
    return getTermsEnum(terms, new AttributeSource());
  }

  
To rewrite to a simpler form, instead return a simpler enum from getTermsEnum(Terms, AttributeSource). For example, to rewrite to a single term, return a SingleTermsEnum 
/**
   * To rewrite to a simpler form, instead return a simpler
   * enum from {@link #getTermsEnum(Terms, AttributeSource)}.  For example,
   * to rewrite to a single term, return a {@link SingleTermsEnum}
   */
  @Override
  public final Query rewrite(IndexReader reader) throws IOException {
    return rewriteMethod.rewrite(reader, this);
  }

  
See Also:
  • setRewriteMethod
/**
   * @see #setRewriteMethod
   */
  public RewriteMethod getRewriteMethod() {
    return rewriteMethod;
  }

  
Sets the rewrite method to be used when executing the query. You can use one of the four core methods, or implement your own subclass of RewriteMethod. 
/**
   * Sets the rewrite method to be used when executing the
   * query.  You can use one of the four core methods, or
   * implement your own subclass of {@link RewriteMethod}. */
  public void setRewriteMethod(RewriteMethod method) {
    rewriteMethod = method;
  }

  @Override
  public int hashCode() {
    final int prime = 31;
    int result = classHash();
    result = prime * result + rewriteMethod.hashCode();
    result = prime * result + field.hashCode();
    return result;
  }

  @Override
  public boolean equals(Object other) {
    return sameClassAs(other) &&
           equalsTo(getClass().cast(other));
  }

  private boolean equalsTo(MultiTermQuery other) {
    return rewriteMethod.equals(other.rewriteMethod) && 
           field.equals(other.field);
  }
}