{"id":539,"date":"2003-11-16T00:22:30","date_gmt":"2003-11-16T04:22:30","guid":{"rendered":"http:\/\/wordpress.cephas.net\/?p=539"},"modified":"2003-11-16T00:22:30","modified_gmt":"2003-11-16T04:22:30","slug":"queryparser-in-nlucene","status":"publish","type":"post","link":"https:\/\/cephas.net\/blog\/2003\/11\/16\/queryparser-in-nlucene\/","title":{"rendered":"QueryParser … in NLucene"},"content":{"rendered":"

Misleading title. I implemented the first of the examples that Erik Hatcher used in his
\narticle about the Lucene QueryParser<\/a>, only I used NLucene<\/a>. Lucene and NLucene are very similar, so if anything, it’s interesting only because it highlights a couple of the differences between C# and Java. <\/p>\n

First, here’s the Java example taken directly from Erik’s article:
\n
\npublic static void search(File indexDir, String q) {
\n  Directory fsDir = FSDirectory.getDirectory(indexDir, false);
\n  IndexSearcher is = new IndexSearcher(fsDir);
\n  Query query = QueryParser.parse(q, \"contents\", new StandardAnalyzer());
\n  Hits hits = is.search(query);
\n  System.out.println(\"Found \" hits.length() +
\n    \" document(s) that matched query '\" q \"':\");
\n  for (int i = 0; i
\nThe NLucene version looks eerily similar:
\n
\npublic static void Search(DirectoryInfo indexDir, string q) {
\n  DotnetPark.NLucene.Store.Directory fsDir = FsDirectory.GetDirectory(indexDir, false);
\n  IndexSearcher searcher = new IndexSearcher(fsDir);
\n  Query query = QueryParser.Parse(q, \"contents\", new StandardAnalyzer());
\n  Hits hits = searcher.Search(query);
\n  Console.WriteLine(\"Found \" + hits.Length +
\n    \" document(s) that matched query '\" + q + \"':\");
\n  for (int i = 0; i
\nThe differences are mainly syntax. <\/p>\n

First, Erik used the variable name 'is' for his IndexSearcher. In C# 'is' is a keyword<\/a>, so I switched the variable name to 'searcher'. If you're really geeky, you might want to brush up on all the Java keywords<\/a> and the C# keywords<\/a>.<\/p>\n

Second, while Java uses the File<\/a> class to describe directories and files, the .NET Framework uses the DirectoryInfo<\/a> class. <\/p>\n

Third, Java programmers are encouraged to capitalize class names<\/a> and use camel Case notation for method and variable names<\/a> while C# programmers are encouraged to Pascal notation for methods and camel Case for variables<\/a>, so I switched the static method name from 'search' to 'Search'. <\/p>\n

Next, 'Directory<\/a>' is a system class, so the reference to the NLucene directory needed to be fully qualified:
\n
\nDotnetPark.NLucene.Store.Directory fsDir = FsDirectory.GetDirectory(indexDir, false);
\n<\/code>
\nrather than this:
\n
\nDirectory fsDir = FsDirectory.GetDirectory(indexDir, false);
\n<\/code>
\nFinally, the Hits class contains a couple differences. Java programmers use the length() method on a variety of classes, so it made sense for the Java version to use a length() method as well. C# introduced the idea of a property<\/a>, which is nothing more than syntactic sweetness that allows the API developer to encapsulate the implementation of a variable, but allow access to it as if it were a public field. The end result is that instead of writing:
\n
\nfor (int i = 0; i
\nin Java, you'd use this in C#:
\n
\nfor (int i = 0; i
\nThe authors of Lucene also decided to use the C# indexer<\/a> functionality (which I wrote about a couple days ago<\/a>) so that an instance of the Hits class can be accessed as if it were an array:
\n
\nDocument doc = hits[i].Document;
\n<\/code>
\nI put together a complete sample that you can download and compile yourself if you're interested in using NLucene. Download it here<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

Misleading title. I implemented the first of the examples that Erik Hatcher used in his article about the Lucene QueryParser, only I used NLucene. Lucene and NLucene are very similar, so if anything, it’s interesting only because it highlights a couple of the differences between C# and Java. First, here’s the Java example taken directly … Continue reading QueryParser … in NLucene<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[17,3,19,2],"tags":[],"_links":{"self":[{"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/posts\/539"}],"collection":[{"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/comments?post=539"}],"version-history":[{"count":0,"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/posts\/539\/revisions"}],"wp:attachment":[{"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/media?parent=539"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/categories?post=539"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/tags?post=539"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}