Elasticsearch源码分析一--调用Lucene查询接口之match_all查询

简介

查询语法

源码分析

简介

match_all查询是Elasticsearch中最简单的查询之一。它使我们能够匹配索引中的所有文件。

可以在查询中包含加权值，它将赋给所有跟它匹配的文档

查询语法

例1：得到索引中的所有文档，可以发送以下查询：

{

“query” : {

“match_all” : {}

}

例2：在match_all查询中给所有文档加上2.0的加权，可以发送以下查询：

{

“query” : {

“match_all” : {

“boost” : 2.0

} } }

源码分析

'''(1)Elasticsearch code'''
public class MatchAllQueryParser implements QueryParser {

public static final String NAME = "match_all";

@Override
public Query parse(QueryParseContext parseContext) throws IOException, QueryParsingException {
XContentParser parser = parseContext.parser();

float boost = 1.0f;
String normsField = null;
String currentFieldName = null;

XContentParser.Token token;
while (((token = parser.nextToken()) != XContentParser.Token.END_OBJECT && token != XContentParser.Token.END_ARRAY)) {
if (token == XContentParser.Token.FIELD_NAME) {
currentFieldName = parser.currentName();
} else if (token.isValue()) {
'''解析加权值'''
if ("boost".equals(currentFieldName)) {
boost = parser.floatValue();
} else if ("norms_field".equals(currentFieldName) || "normsField".equals(currentFieldName)) {
normsField = parseContext.indexName(parser.text());
} else {
throw new QueryParsingException(parseContext.index(), "[match_all] query does not support [" + currentFieldName + "]");
}
}
}
'''未设置加权值时，直接返回XConstantScoreQuery对象，We do not use MatchAllDocsQuery, its slower than the one below '''
if (boost == 1.0f && normsField == null) {
return Queries.MATCH_ALL_QUERY;
}

'''构造Lucene的MatchAllDocsQuery并返回'''
MatchAllDocsQuery query = new MatchAllDocsQuery();
query.setBoost(boost);
return query;
}
}
'''(2)Lucene code'''
public final class MatchAllDocsQuery extends Query {

@Override
'''创建Weight对象树'''
public Weight createWeight(IndexSearcher searcher, boolean needsScores) {
return new RandomAccessWeight(this) {
@Override
protected Bits getMatchingDocs(LeafReaderContext context) throws IOException {
'''返回所有文档，Lucene中查询结果是以bit数组方式返回，每一个bit位对应一个DocID，bit值为1表示该DocID对应的文档matched'''
return new Bits.MatchAllBits(context.reader().maxDoc());
}
};
}