Elasticsearch源码分析六--调用Lucene查询接口之前缀查询(Prefix)

简介

查询语法

源码分析

简介

前缀查询在配置方面来说跟词条查询类似。前缀查询能让我们匹配这样的文档：它们的特定

字段以给定的前缀开始。。

查询语法

例：查找所有title字段以cri开始的文档：

{

“query” : {

“prefix” : {

“title” : {

“value” : “cri”,

“boost” : 3.0

}}}}

源码分析

'''(1)Elasticsearch code'''
public class PrefixQueryParser implements QueryParser {
public static final String NAME = "prefix";
@Override
public Query parse(QueryParseContext parseContext) throws IOException, QueryParsingException {
XContentParser parser = parseContext.parser();

XContentParser.Token token = parser.nextToken();
if (token != XContentParser.Token.FIELD_NAME) {
throw new QueryParsingException(parseContext.index(), "[prefix] query malformed, no field");
}
String fieldName = parser.currentName();
String rewriteMethod = null;

Object value = null;
float boost = 1.0f;
token = parser.nextToken();
if (token == XContentParser.Token.START_OBJECT) {
String currentFieldName = null;
while ((token = parser.nextToken()) != XContentParser.Token.END_OBJECT) {
if (token == XContentParser.Token.FIELD_NAME) {
currentFieldName = parser.currentName();
} else if (token.isValue()) {
if ("prefix".equals(currentFieldName)) {
value = parser.objectBytes();
} else if ("value".equals(currentFieldName)) {
value = parser.text();
} else if ("boost".equals(currentFieldName)) {
boost = parser.floatValue();
} else if ("rewrite".equals(currentFieldName)) {
rewriteMethod = parser.textOrNull();
}
} else {
throw new QueryParsingException(parseContext.index(), "[prefix] query does not support [" + currentFieldName + "]");
}
}
parser.nextToken();
} else {
value = parser.text();
parser.nextToken();
}

if (value == null) {
throw new QueryParsingException(parseContext.index(), "No value specified for prefix query");
}

MultiTermQuery.RewriteMethod method = QueryParsers.parseRewriteMethod(rewriteMethod, null);

Query query = null;
MapperService.SmartNameFieldMappers smartNameFieldMappers = parseContext.smartFieldMappers(fieldName);
if (smartNameFieldMappers != null && smartNameFieldMappers.hasMapper()) {
if (smartNameFieldMappers.explicitTypeInNameWithDocMapper()) {
String[] previousTypes = QueryParseContext.setTypesWithPrevious(new String[]{smartNameFieldMappers.docMapper().type()});
try {
query = smartNameFieldMappers.mapper().prefixQuery(value, method, parseContext);
} finally {
QueryParseContext.setTypes(previousTypes);
}
} else {
query = smartNameFieldMappers.mapper().prefixQuery(value, method, parseContext);
}
}
if (query == null) {
'''构造Lucene的PrefixQuery对象(Term("title","cri"))'''
PrefixQuery prefixQuery = new PrefixQuery(new Term(fieldName, BytesRefs.toBytesRef(value)));
'''设置重写方法，将cri重写为索引中以cri开始的词，这些词以或的关系组织'''
if (method != null) {
prefixQuery.setRewriteMethod(method);
}
query = prefixQuery;
}
query.setBoost(boost);
return wrapSmartNameQuery(query, smartNameFieldMappers, parseContext);
}
}

'''(2)Lucene code'''
public class PrefixQuery extends AutomatonQuery {
....
}
public class AutomatonQuery extends MultiTermQuery {
....
}
public abstract class MultiTermQuery extends Query {
....
@Override
'''PrefixQuery是MultiTermQuery的子类，调用父类的rewrite方法'''
public final Query rewrite(IndexReader reader) throws IOException {
return rewriteMethod.rewrite(reader, this);
}
}

'''(3)Lucene 常用词查询举例'''
public void testPrefixQuery() throws Exception {
Directory directory = newDirectory();

String[] categories = new String[] {"/Computers",
"/Computers/Mac",
"/Computers/Windows"};
RandomIndexWriter writer = new RandomIndexWriter(random(), directory);
for (int i = 0; i < categories.length; i++) {
Document doc = new Document();
doc.add(newStringField("category", categories[i], Field.Store.YES));
writer.addDocument(doc);
}
IndexReader reader = writer.getReader();

'''查找category字段中以"/Computers"开始的文档'''
PrefixQuery query = new PrefixQuery(new Term("cat
bf86
egory", "/Computers"));
IndexSearcher searcher = newSearcher(reader);
ScoreDoc[] hits = searcher.search(query, 1000).scoreDocs;
assertEquals("All documents in /Computers category and below", 3, hits.length);

'''查找category字段中以"/Computers/Mac"开始的文档'''
query = new PrefixQuery(new Term("category", "/Computers/Mac"));
hits = searcher.search(query, 1000).scoreDocs;
assertEquals("One in /Computers/Mac", 1, hits.length);

'''查找category字段中以任何字符串开始的文档即所有文档'''
query = new PrefixQuery(new Term("category", ""));
hits = searcher.search(query, 1000).scoreDocs;
assertEquals("everything", 3, hits.length);
writer.close();
reader.close();
directory.close();
}