Elasticsearch search api and DSL

Why am I writing this shit, beacause the official documentation really really sucks, though you might find this article about es search api and query dsl sucks more.

Elasticsearch可以通过search api提供对文档的精细检索。Elasticsearch的search api对文档的精细检索主要靠Elasticsearch的DSL检索语言实现，它通过自身的query参数指定具体的DSL查询语句。

• search api
  • 具体语法见https://www.elastic.co/guide/en/elasticsearch/reference/current/search-search.html#search-multi-index-type。
  • 主要关注带request body的api调用形式，因为DSL必须在这种形式下才可以使用。

    curl -XGET 'http://host:port/index/doc/_search' -d ' {   # request body
        ... 
        "query": {DSL_QUERY_CLAUSE}                          # query 参数
        ...
    }'

• DSL语法

    DSL_QUERY_CLAUSE: 
    {
        QUERY_NAME: 
        {
            FIELD_NAME: 
            {
                ARGUMENT: VALUE,
                ARGUMENT: VALUE
               ...
            }
        }
    }

• DSL 上下文

  • query context(按匹配程度筛选结果)
    • A query clause used in query context answers the question “How well does this document match this query clause?”
  • filter context(类似精确匹配)
    • In filter context, a query clause answers the question “Does this document match this query clause?”

• Query clause 类型

  • leave clause
  • compound clause
    • wrap other leaf or compound queries and used to combine multiple queries in a logical fashion(quote from official documentation).

• compound queries

  • 比较重要，因为需要使用复合查询的场景可能比较多
  • 通过复合查询，可以指定子查询是query context还是filter context
  • https://www.elastic.co/guide/en/elasticsearch/reference/current/compound-queries.html
  • eg
    • bool query https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-bool-query.html