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 using System;
  17 using IndexReader = Lucene.Net.Index.IndexReader;
  18 using Term = Lucene.Net.Index.Term;
  19 using TermEnum = Lucene.Net.Index.TermEnum;
  20 namespace Lucene.Net.Search
  21 {
  22
  23         /// <summary>A Query that matches documents containing terms with a specified prefix. </summary>
  24         [Serializable]
  25         public class PrefixQuery:Query
  26         {
  27                 private Term prefix;
  28
  29                 /// <summary>Constructs a query for terms starting with <code>prefix</code>. </summary>
  30                 public PrefixQuery(Term prefix)
  31                 {
  32                         this.prefix = prefix;
  33                 }
  34
  35                 /// <summary>Returns the prefix of this query. </summary>
  36                 public virtual Term GetPrefix()
  37                 {
  38                         return prefix;
  39                 }
  40
  41                 public override Query Rewrite(IndexReader reader)
  42                 {
  43                         BooleanQuery query = new BooleanQuery(true);
  44                         TermEnum enumerator = reader.Terms(prefix);
  45                         try
  46                         {
  47                                 System.String prefixText = prefix.Text();
  48                                 System.String prefixField = prefix.Field();
  49                                 do
  50                                 {
  51                                         Term term = enumerator.Term();
  52                                         if (term != null && term.Text().StartsWith(prefixText) && (System.Object) term.Field() == (System.Object) prefixField)
  53                                         {
  54                                                 TermQuery tq = new TermQuery(term); // found a match
  55                                                 tq.SetBoost(GetBoost()); // set the boost
  56                                                 query.Add(tq, BooleanClause.Occur.SHOULD); // add to query
  57                                                 //System.out.println("added " + term);
  58                                         }
  59                                         else
  60                                         {
  61                                                 break;
  62                                         }
  63                                 }
  64                                 while (enumerator.Next());
  65                         }
  66                         finally
  67                         {
  68                                 enumerator.Close();
  69                         }
  70                         return query;
  71                 }
  72
  73                 public override Query Combine(Query[] queries)
  74                 {
  75                         return Query.MergeBooleanQueries(queries);
  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                         if (GetBoost() != 1.0f)
  90                         {
  91                 System.Globalization.NumberFormatInfo nfi = new System.Globalization.CultureInfo("en-US", false).NumberFormat;
  92                 nfi.NumberDecimalDigits = 1;
  93
  94                                 buffer.Append("^");
  95                                 buffer.Append(GetBoost().ToString("N", nfi));
  96                         }
  97                         return buffer.ToString();
  98                 }
  99                 override public System.Object Clone()
 100                 {
 101                         return null;
 102                 }
 103         }
 104 }