edismax支持boost函数与score相乘作为,而dismax只能使用bf作用效果是相加,所以在处理多个维度排序时,score其实也应该是其中一个维度 ,用相加的方式处理调整麻烦。
而dismax的实现代码逻辑比较简单,看起来比较易理解,edismax是它的加强版,其实是改变了不少。。比如在以下:
先看看dismax的解析主要实现思路:
首先取出搜索字段名qf
将最终解析成一个BooleanQuery
先解析主mainQuery:
- 用户主要是搜索串的解析
- altQuery解析处理,看是否使用用户定义的后备搜索串
- PhraseQuery解析组装
再解析bq查询,主要是额外加分的查询,不会影响搜索结果数,只会影响排序
再则是bf解析,函数搜索最后会以加的方式作用于文档评分
看主要代码更清晰:
- @Override
- public Query parse() throws ParseException {
- SolrParams solrParams = SolrParams.wrapDefaults(localParams, params);
- queryFields = SolrPluginUtils.parseFieldBoosts(solrParams.getParams(DisMaxParams.QF));
- if (0 == queryFields.size()) {
- queryFields.put(req.getSchema().getDefaultSearchFieldName(), 1.0f);
- }
- /* the main query we will execute. we disable the coord because
- * this query is an artificial construct
- */
- BooleanQuery query = new BooleanQuery(true);
- boolean notBlank = addMainQuery(query, solrParams);
- if (!notBlank)
- return null;
- addBoostQuery(query, solrParams);
- addBoostFunctions(query, solrParams);
- return query;
- }
edismax的主要实现思路跟dismax差不多,以下是一些主要差别之处:
edismax解析含有+,OR,NOT,-语法时,就会忽略掉使用MM。
以下是主要代码实现:
统计搜索串中+,OR ,NOT,-语法元个数
- // defer escaping and only do if lucene parsing fails, or we need phrases
- // parsing fails. Need to sloppy phrase queries anyway though.
- List<Clause> clauses = null;
- int numPluses = 0;
- int numMinuses = 0;
- int numOR = 0;
- int numNOT = 0;
- clauses = splitIntoClauses(userQuery, false);
- for (Clause clause : clauses) {
- if (clause.must == ‘+’) numPluses++;
- if (clause.must == ‘-‘) numMinuses++;
- if (clause.isBareWord()) {
- String s = clause.val;
- if (“OR”.equals(s)) {
- numOR++;
- } else if (“NOT”.equals(s)) {
- numNOT++;
- } else if (lowercaseOperators && “or”.equals(s)) {
- numOR++;
- }
- }
- }
/////当搜索串里包含有+,OR ,NOT,-这四种时候,mm就会失效
- boolean doMinMatched = (numOR + numNOT + numPluses + numMinuses) == 0;
- (parsedUserQuery != null && doMinMatched) {
- String minShouldMatch = solrParams.get(DisMaxParams.MM, “100%”);
- if (parsedUserQuery instanceof BooleanQuery) {
- SolrPluginUtils.setMinShouldMatch((BooleanQuery)parsedUserQuery, minShouldMatch);
- }
- }
短语查询,先找出普通的查询,原来就是短语查询的、或者属于“OR”,“AND”,“NOT”,’TO‘类型的都不要。由于edismax支持解析符合lucene语法的搜索串,所以不像dismax那样,只需要简单的将搜索串去掉\“,然后加个“”括起来就行
// find non-field clauses
List<Clause>normalClauses =new ArrayList<Clause>(clauses.size());
for (Clauseclause :clauses) {
if (clause.field !=null ||clause.isPhrase)continue;
// check for keywords “AND,OR,TO”
if (clause.isBareWord()) {
String s =clause.val.toString();
// avoid putting explict operators in the phrase query
if (“OR”.equals(s) ||”AND”.equals(s) ||”NOT”.equals(s) || “TO”.equals(s))continue;
}
normalClauses.add(clause);
}
// full phrase…
addShingledPhraseQueries(query, normalClauses, phraseFields, 0,
tiebreaker,pslop);
// shingles…
addShingledPhraseQueries(query, normalClauses, phraseFields2, 2,
tiebreaker,pslop);
addShingledPhraseQueries(query, normalClauses, phraseFields3, 3,
tiebreaker,pslop);
////下面是dismax获取短语查询的作法:
- protected Query getPhraseQuery(String userQuery, SolrPluginUtils.DisjunctionMaxQueryParser pp) throws ParseException {
- String userPhraseQuery = userQuery.replace(“\””, “”);
- return pp.parse(“\”” + userPhraseQuery + “\””);
- }
下面是edismax的作法:
- private void addShingledPhraseQueries(final BooleanQuery mainQuery,
- final List<Clause> clauses,
- final Map<String,Float> fields,
- int shingleSize,
- final float tiebreaker,
- final int slop)
- throws ParseException {
- if (null == fields || fields.isEmpty() ||
- null == clauses || clauses.size() <= shingleSize )
- return;
- if (0 == shingleSize) shingleSize = clauses.size();
- final int goat = shingleSize-1; // :TODO: better name for var?
- StringBuilder userPhraseQuery = new StringBuilder();
- for (int i=0; i < clauses.size() – goat; i++) {
- userPhraseQuery.append(‘”‘);
- for (int j=0; j <= goat; j++) {
- userPhraseQuery.append(clauses.get(i + j).val);
- userPhraseQuery.append(‘ ‘);
- }
- userPhraseQuery.append(‘”‘);
- userPhraseQuery.append(‘ ‘);
- }
- ExtendedSolrQueryParser pp =
- new ExtendedSolrQueryParser(this, IMPOSSIBLE_FIELD_NAME);
- pp.addAlias(IMPOSSIBLE_FIELD_NAME, tiebreaker, fields);
- pp.setPhraseSlop(slop);
- pp.setRemoveStopFilter(true); // remove stop filter and keep stopwords
- pp.makeDismax = true;
- pp.minClauseSize = 2;
- Query phrase = pp.parse(userPhraseQuery.toString());
- if (phrase != null) {
- mainQuery.add(phrase, BooleanClause.Occur.SHOULD);
- }
- }
edismax技术另一个重要的boost查询,
boost查询也是不会影响搜索结果数,但是影响排序,主要作用是将最后得分以相乘的方式作用于score,函数的解析跟bf差不多。
- //
- // create a boosted query (scores multiplied by boosts)
- //
- Query topQuery = query;
- multBoosts = solrParams.getParams(“boost”);
- if (multBoosts!=null && multBoosts.length>0) {
- List<ValueSource> boosts = new ArrayList<ValueSource>();
- for (String boostStr : multBoosts) {
- if (boostStr==null || boostStr.length()==0) continue;
- Query boost = subQuery(boostStr, FunctionQParserPlugin.NAME).getQuery();
- ValueSource vs;
- if (boost instanceof FunctionQuery) {
- vs = ((FunctionQuery)boost).getValueSource();
- } else {
- vs = new QueryValueSource(boost, 1.0f);
- }
- boosts.add(vs);
- }
- if (boosts.size()>1) {
- ValueSource prod = new ProductFloatFunction(boosts.toArray(new ValueSource[boosts.size()]));
- topQuery = new BoostedQuery(query, prod);
- } else if (boosts.size() == 1) {
- topQuery = new BoostedQuery(query, boosts.get(0));
- }
- }
可以看到最后不是一个BooleanQuery,而是一个BoostedQuery。
它就是简单处理子查询的分值再与函数查询的分值相乘返回 :主要的score方法如下:
- public float score() throws IOException {
- float score = qWeight * scorer.score() * vals.floatVal(scorer.docID());
- return score>Float.NEGATIVE_INFINITY ? score : -Float.MAX_VALUE;
- }