beagled/Lucene.Net/Search/PrefixQuery.cs

   1 /*
   2  * Copyright 2004 The Apache Software Foundation
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  * http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 using System;
  18 using IndexReader = Lucene.Net.Index.IndexReader;
  19 using Term = Lucene.Net.Index.Term;
  20 using TermEnum = Lucene.Net.Index.TermEnum;
  21 using ToStringUtils = Lucene.Net.Util.ToStringUtils;
  22
  23 namespace Lucene.Net.Search
  24 {
  25
  26         /// <summary>A Query that matches documents containing terms with a specified prefix. A PrefixQuery
  27         /// is built by QueryParser for input like <code>app*</code>.
  28         /// </summary>
  29         [Serializable]
  30         public class PrefixQuery : Query
  31         {
  32                 private Term prefix;
  33
  34                 /// <summary>Constructs a query for terms starting with <code>prefix</code>. </summary>
  35                 public PrefixQuery(Term prefix)
  36                 {
  37                         this.prefix = prefix;
  38                 }
  39
  40                 /// <summary>Returns the prefix of this query. </summary>
  41                 public virtual Term GetPrefix()
  42                 {
  43                         return prefix;
  44                 }
  45
  46                 public override Query Rewrite(IndexReader reader)
  47                 {
  48                         BooleanQuery query = new BooleanQuery(true);
  49                         TermEnum enumerator = reader.Terms(prefix);
  50                         try
  51                         {
  52                                 System.String prefixText = prefix.Text();
  53                                 System.String prefixField = prefix.Field();
  54                                 do
  55                                 {
  56                                         Term term = enumerator.Term();
  57                                         if (term != null && term.Text().StartsWith(prefixText) && term.Field() == prefixField)
  58                                         {
  59                                                 TermQuery tq = new TermQuery(term); // found a match
  60                                                 tq.SetBoost(GetBoost()); // set the boost
  61                                                 query.Add(tq, BooleanClause.Occur.SHOULD); // add to query
  62                                                 //System.out.println("added " + term);
  63                                         }
  64                                         else
  65                                         {
  66                                                 break;
  67                                         }
  68                                 }
  69                                 while (enumerator.Next());
  70                         }
  71                         finally
  72                         {
  73                                 enumerator.Close();
  74                         }
  75                         return query;
  76                 }
  77
  78                 /// <summary>Prints a user-readable version of this query. </summary>
  79                 public override System.String ToString(System.String field)
  80                 {
  81                         System.Text.StringBuilder buffer = new System.Text.StringBuilder();
  82                         if (!prefix.Field().Equals(field))
  83                         {
  84                                 buffer.Append(prefix.Field());
  85                                 buffer.Append(":");
  86                         }
  87                         buffer.Append(prefix.Text());
  88                         buffer.Append('*');
  89                         buffer.Append(ToStringUtils.Boost(GetBoost()));
  90                         return buffer.ToString();
  91                 }
  92
  93                 /// <summary>Returns true iff <code>o</code> is equal to this. </summary>
  94                 public  override bool Equals(System.Object o)
  95                 {
  96                         if (!(o is PrefixQuery))
  97                                 return false;
  98                         PrefixQuery other = (PrefixQuery) o;
  99                         return (this.GetBoost() == other.GetBoost()) && this.prefix.Equals(other.prefix);
 100                 }
 101
 102                 /// <summary>Returns a hash code value for this object.</summary>
 103                 public override int GetHashCode()
 104                 {
 105                         return BitConverter.ToInt32(BitConverter.GetBytes(GetBoost()), 0) ^ prefix.GetHashCode();
 106                 }
 107         }
 108 }