世界上并没有完美的程序，但是我们并不因此而沮丧，因为写程序就是一个不断追求完美的过程。

问 ：_routing有什么特点？
答 ：

问 ：_routing如何使用？
答 ：

# _routing
PUT /routing_test
{
  "mappings" : {
    "_routing"   : {
      "required" : true
    }, 
    "properties" : {
      "name" : {"type" : "text"}
    }
  }
}


# 索引
POST /routing_test/_doc/1?routing=hello
{
  "name" : "hello good"
}

# 索引，当_routing设置为required=true时，没有routing则报错
POST /routing_test/_doc/2
{
  "name" : "tea"
}

# 结果
{
  "error" : {
    "root_cause" : [
      {
        "type" : "routing_missing_exception",
        "reason" : "routing is required for [routing_test]/[_doc]/[2]",
        "index_uuid" : "_na_",
        "index" : "routing_test"
      }
    ],
    "type" : "routing_missing_exception",
    "reason" : "routing is required for [routing_test]/[_doc]/[2]",
    "index_uuid" : "_na_",
    "index" : "routing_test"
  },
  "status" : 400
}

# 搜索
GET /routing_test/_search
{
  "query" : {
    "terms" : {
      "_routing" : ["hello"]
    }
  }
}

# 结果
{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "routing_test",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 1.0,
        "_routing" : "hello",
        "_source" : {
          "name" : "hello good"
        }
      }
    ]
  }
}