本文主要结合测试案例介绍了Lucene下的各种查询语句以及它们的简化方法.
通过本文你将了解Lucene的基本查询语句,并通过学习相关的测试代码以加强了解.
具体的查询语句
在了解了SQL后, 你是否想了解一下查询语法树?在这里简要介绍一些能被Lucene直接使用的查询语句.
1. TermQuery
查询某个特定的词,在文章开始的例子中已有介绍.常用于查询关键字.
public void Keyword()
{
IndexSearcher searcher = new IndexSearcher(directory);
Term t = new Term("isbn", "1930110995");
Query query = new TermQuery(t);
Hits hits = searcher.Search(query);
Assert.AreEqual(1, hits.Length(), "JUnit in Action");
}
注意Lucene中的关键字,是需要用户去保证唯一性的.
TermQuery和QueryParse只要在QueryParse的Parse方法中只有一个word,就会自动转换成TermQuery.
2. RangeQuery
用于查询范围,通常用于时间,还是来看例子:
{
public class RangeQueryTest : LiaTestCase
{
private Term begin, end;
[SetUp]
protected override void Init()
{
begin = new Term("pubmonth", "200004");
end = new Term("pubmonth", "200206");
base.Init();
}
[Test]
public void Inclusive()
{
RangeQuery query = new RangeQuery(begin, end, true);
IndexSearcher searcher = new IndexSearcher(directory);
Assert.AreEqual(1, hits.Length());
}
[Test]
public void Exclusive()
{
RangeQuery query = new RangeQuery(begin, end, false);
IndexSearcher searcher = new IndexSearcher(directory);
Hits hits = searcher.Search(query);
Assert.AreEqual(0, hits.Length());
}
}
}
RangeQuery的第三个参数用于表示是否包含该起止日期.
RangeQuery和QueryParse
[Test]public void TestQueryParser()
{
Query query = QueryParser.Parse("pubmonth:[200004 TO 200206]", "subject", new SimpleAnalyzer());
Assert.IsTrue(query is RangeQuery);
IndexSearcher searcher = new IndexSearcher(directory);
Hits hits = searcher.Search(query);
query = QueryParser.Parse("{200004 TO 200206}", "pubmonth", new SimpleAnalyzer());
hits = searcher.Search(query);
Assert.AreEqual(0, hits.Length(), "JDwA in 200206");
}
Lucene用[] 和{}分别表示包含和不包含.
3. PrefixQuery
用于搜索是否包含某个特定前缀,常用于Catalog的检索.
[Test]public void TestPrefixQuery()
{
PrefixQuery query = new PrefixQuery(new Term("category", "/Computers"));
IndexSearcher searcher = new IndexSearcher(directory);
Hits hits = searcher.Search(query);
Assert.AreEqual(2, hits.Length());
query = new PrefixQuery(new Term("category", "/Computers/JUnit"));
hits = searcher.Search(query);
Assert.AreEqual(1, hits.Length(), "JUnit in Action");
}
PrefixQuery和QueryParse
[Test]
public void TestQueryParser()
{
QueryParser qp = new QueryParser("category", new SimpleAnalyzer());
qp.SetLowercaseWildcardTerms(false);
Query query =qp.Parse("/Computers*");
Console.Out.WriteLine("query = {0}", query.ToString());
IndexSearcher searcher = new IndexSearcher(directory);
Hits hits = searcher.Search(query);
Assert.AreEqual(2, hits.Length());
query =qp.Parse("/Computers/JUnit*");
hits = searcher.Search(query);
Assert.AreEqual(1, hits.Length(), "JUnit in Action");
}
这里需要注意的是我们使用了QueryParser对象,而不是QueryParser类. 原因在于使用对象可以对QueryParser的一些默认属性进行修改.比如在上面的例子中我们的category是大写的,而QueryParser默认会把所有的含*的查询字符串变成小写/computer*. 这样我们就会查不到原文中的/Computers* ,所以我们需要通过设置QueryParser的默认属性来改变这一默认选项.即qp.SetLowercaseWildcardTerms(false)所做的工作.
4. BooleanQuery
用于测试满足多个条件.
下面两个例子用于分别测试了满足与条件和或条件的情况.
[Test]public void And()
{
TermQuery searchingBooks =
new TermQuery(new Term("subject", "junit"));
RangeQuery currentBooks =
new RangeQuery(new Term("pubmonth", "200301"),
new Term("pubmonth", "200312"),
true);
BooleanQuery currentSearchingBooks = new BooleanQuery();
currentSearchingBooks.Add(searchingBooks, true, false);
currentSearchingBooks.Add(currentBooks, true, false);
IndexSearcher searcher = new IndexSearcher(directory);
Hits hits = searcher.Search(currentSearchingBooks);
AssertHitsIncludeTitle(hits, "JUnit in Action");
}
[Test]
public void Or()
{
TermQuery methodologyBooks = new TermQuery(
new Term("category",
"/Computers/JUnit"));
TermQuery easternPhilosophyBooks = new TermQuery(
new Term("category",
"/Computers/Ant"));
BooleanQuery enlightenmentBooks = new BooleanQuery();
enlightenmentBooks.Add(methodologyBooks, false, false);
enlightenmentBooks.Add(easternPhilosophyBooks, false, false);
IndexSearcher searcher = new IndexSearcher(directory);
Hits hits = searcher.Search(enlightenmentBooks);
Console.Out.WriteLine("or = " + enlightenmentBooks);
AssertHitsIncludeTitle(hits, "Java Development with Ant");
AssertHitsIncludeTitle(hits, "JUnit in Action");
}
什么时候是与什么时候又是或? 关键在于BooleanQuery对象的Add方法的参数.
参数一是待添加的查询条件.
参数二Required表示这个条件必须满足吗? True表示必须满足, False表示可以不满足该条件.
参数三Prohibited表示这个条件必须拒绝吗? True表示这么满足这个条件的结果要排除, False表示可以满足该条件.
这样会有三种组合情况,如下表所示:
BooleanQuery和QueryParse
[Test]public void TestQueryParser()
{
Query query = QueryParser.Parse("pubmonth:[200301 TO 200312] AND junit", "subject", new SimpleAnalyzer());
IndexSearcher searcher = new IndexSearcher(directory);
Hits hits = searcher.Search(query);
Assert.AreEqual(1, hits.Length());
query = QueryParser.Parse("/Computers/JUnit OR /Computers/Ant", "category", new WhitespaceAnalyzer());
hits = searcher.Search(query);
Assert.AreEqual(2, hits.Length());
}
注意AND和OR的大小 如果想要Ａ与非B 就用 A AND –B 表示, +A –B也可以.
默认的情况下QueryParser会把空格认为是或关系,就象google一样.但是你可以通过QueryParser对象修改这一属性.
[Test]
public void TestQueryParserDefaultAND()
{
QueryParser qp = new QueryParser("subject", new SimpleAnalyzer());
qp.SetOperator(QueryParser.DEFAULT_OPERATOR_AND );
Query query = qp.Parse("pubmonth:[200301 TO 200312] junit");
IndexSearcher searcher = new IndexSearcher(directory);
Hits hits = searcher.Search(query);
Assert.AreEqual(1, hits.Length());
}
5. PhraseQuery
查询短语,这里面主要有一个slop的概念, 也就是各个词之间的位移偏差, 这个值会影响到结果的评分.如果slop为0,当然最匹配.看看下面的例子就比较容易明白了,有关slop的计算用户就不需要理解了,不过slop太大的时候对查询效率是有影响的,所以在实际使用中要把该值设小一点. PhraseQuery对于短语的顺序是不管的,这点在查询时除了提高命中率外,也会对性能产生很大的影响, 利用SpanNearQuery可以对短语的顺序进行控制,提高性能.
[SetUp]
protected void Init()
{
// set up sample document
RAMDirectory directory = new RAMDirectory();
IndexWriter writer = new IndexWriter(directory,
new WhitespaceAnalyzer(), true);
Document doc = new Document();
doc.Add(Field.Text("field",
"the quick brown fox jumped over the lazy dog"));
writer.AddDocument(doc);
writer.Close();
searcher = new IndexSearcher(directory);
}
private bool matched(String[] phrase, int slop)
{
PhraseQuery query = new PhraseQuery();
query.SetSlop(slop);
for (int i = 0; i < phrase.Length; i++)
{
query.Add(new Term("field", phrase[i]));
}
Hits hits = searcher.Search(query);
return hits.Length() > 0;
}
[Test]
public void SlopComparison()
{
String[] phrase = new String[]{"quick", "fox"};
Assert.IsFalse(matched(phrase, 0), "exact phrase not found");
Assert.IsTrue(matched(phrase, 1), "close enough");
}
[Test]
public void Reverse()
{
String[] phrase = new String[] {"fox", "quick"};
Assert.IsFalse(matched(phrase, 2), "exact phrase not found");
Assert.IsTrue(matched(phrase, 3), "close enough");
}
[Test]
public void Multiple()-
{
Assert.IsFalse(matched(new String[] {"quick", "jumped", "lazy"}, 3), "not close enough");
Assert.IsTrue(matched(new String[] {"quick", "jumped", "lazy"}, 4), "just enough");
Assert.IsFalse(matched(new String[] {"lazy", "jumped", "quick"}, 7), "almost but not quite");
Assert.IsTrue(matched(new String[] {"lazy", "jumped", "quick"}, 8), "bingo");
}
PhraseQuery和QueryParse
利用QueryParse进行短语查询的时候要先设定slop的值,有两种方式如下所示
[Test]public void TestQueryParser()
{
Query q1 = QueryParser.Parse(""quick fox"",
"field", new SimpleAnalyzer());
Hits hits1 = searcher.Search(q1);
Assert.AreEqual(hits1.Length(), 0);
Query q2 = QueryParser.Parse(""quick fox"~1", //第一种方式
"field", new SimpleAnalyzer());
Hits hits2 = searcher.Search(q2);
Assert.AreEqual(hits2.Length(), 1);
qp.SetPhraseSlop(1); //第二种方式
Query q3=qp.Parse(""quick fox"");
Assert.AreEqual(""quick fox"~1", q3.ToString("field"),"sloppy, implicitly");
Hits hits3 = searcher.Search(q2);
Assert.AreEqual(hits3.Length(), 1);
}
6. WildcardQuery
通配符搜索,需要注意的是child, mildew的分值是一样的.
[Test]
public void Wildcard()
{
IndexSingleFieldDocs(new Field[]
{
Field.Text("contents", "wild"),
Field.Text("contents", "child"),
Field.Text("contents", "mild"),
Field.Text("contents", "mildew")
});
IndexSearcher searcher = new IndexSearcher(directory);
Query query = new WildcardQuery(
new Term("contents", "?ild*"));
Hits hits = searcher.Search(query);
Assert.AreEqual(3, hits.Length(), "child no match");
Assert.AreEqual(hits.Score(0), hits.Score(1), 0.0, "score the same");
Assert.AreEqual(hits.Score(1), hits.Score(2), 0.0, "score the same");
}
WildcardQuery和QueryParse
需要注意的是出于性能的考虑使用QueryParse的时候,不允许在开头就使用就使用通配符.
同样处于性能考虑会将只在末尾含有*的查询词转换为PrefixQuery.
[Test, ExpectedException(typeof (ParseException))]
public void TestQueryParserException()
{
Query query = QueryParser.Parse("?ild*", "contents", new WhitespaceAnalyzer());
}
[Test]
public void TestQueryParserTailAsterrisk()
{
Query query = QueryParser.Parse("mild*", "contents", new WhitespaceAnalyzer());
Assert.IsTrue(query is PrefixQuery);
Assert.IsFalse(query is WildcardQuery);
}
[Test]
public void TestQueryParser()
{
Query query = QueryParser.Parse("mi?d*", "contents", new WhitespaceAnalyzer());
Hits hits = searcher.Search(query);
Assert.AreEqual(2, hits.Length());
}
7. FuzzyQuery
模糊查询, 需要注意的是两个匹配项的分值是不同的,这点和WildcardQuery是不同的
[Test]
public void Fuzzy()
{
Query query = new FuzzyQuery(new Term("contents", "wuzza"));
Hits hits = searcher.Search(query);
Assert.AreEqual( 2, hits.Length(),"both close enough");
Assert.IsTrue(hits.Score(0) != hits.Score(1),"wuzzy closer than fuzzy");
Assert.AreEqual("wuzzy", hits.Doc(0).Get("contents"),"wuzza bear");
}
FuzzyQuery和QueryParse
注意和PhraseQuery中表示slop的区别,前者~后要跟数字.
[Test]
public void TestQueryParser()
{
Query query =QueryParser.Parse("wuzza~","contents",new SimpleAnalyzer());
Hits hits = searcher.Search(query);
Assert.AreEqual( 2, hits.Length(),"both close enough");
}
