es - elasticsearch mapping - field data type - 8

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 ：nested field type有什么特点？
答 ：

1. 为数组元素建立嵌套索引
2. 使用nested搜索
3. 使用nested聚合和reverse_nested聚合进行分析
4. 使用nested sorting排序
5. 使用netsted inner hits实现检索和高亮
6. 消耗大

问 ：nested field type防止mappings explosion的settings有哪些？
答 ：

1. index.mapping.nested_fields.limit : 
    每个索引nested类型的field的最大数量，默认50
2. index.mapping.nested_objects.limit :
    每个文档可以包含的nested对象的最大数量，默认10000

问 ：nested field type如何使用？
答 ：

# nested
# 配置项 ：
#   1. dynamic
#   2. properties
#   3. include_in_parent
#   4. include_in_root

PUT /netsted_test
{
  "mappings" : {
    "properties" : {
      "user1" : {
        "type" : "nested"
      }, "user2" : {
        "type" : "flattened"
      }
    }
  }
}

POST /netsted_test/_doc
{
  "user1" : [
    {"first" : "hello", "last" : "good"},
    {"first" : "me", "last" : "kik"}
  ],
  "user2" : [
    {"first" : "hello", "last" : "good"},
    {"first" : "me", "last" : "kik"}
  ]
}

# 不使用netsted，搜索结果为空
GET /netsted_test/_search
{
  "query" : {
    "bool" : {
      "must" : [
        {"match" : {"user1.first" : "hello"}},
        {"match" : {"user1.last"  : "good"}}
      ]
    }
  }
}

# 结果
{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 0,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  }
}

# flattened匹配数组内的任何元素节点，也可以交叉匹配
GET /netsted_test/_search
{
  "query" : {
    "bool" : {
      "must" : [
        {"match" : {"user2.first" : "hello"}},
        {"match" : {"user2.last"  : "kik"}}
      ]
    }
  }
}

# 结果
{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 0.83003354,
    "hits" : [
      {
        "_index" : "netsted_test",
        "_type" : "_doc",
        "_id" : "42vD9XcBnJvha9PMe4w_",
        "_score" : 0.83003354,
        "_source" : {
          "user1" : [
            {
              "first" : "hello",
              "last" : "good"
            },
            {
              "first" : "me",
              "last" : "kik"
            }
          ],
          "user2" : [
            {
              "first" : "hello",
              "last" : "good"
            },
            {
              "first" : "me",
              "last" : "kik"
            }
          ]
        }
      }
    ]
  }
}

# nested只针对数组内某个元素匹配
GET /netsted_test/_search
{
  "query" : {
    "nested" : {
      "path"  : "user1",
      "query" : {
        "bool" : {
          "must" : [
            {"match" : {"user1.first" : "hello"}},
            {"match" : {"user1.last"  : "good"}}
          ]
        }
      },
      "inner_hits" : {
        "highlight" : {
          "fields" : {"user1.first": {}}
        }
      }
    }
  }
}

# 结果
{
  "took" : 62,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 1.3862942,
    "hits" : [
      {
        "_index" : "netsted_test",
        "_type" : "_doc",
        "_id" : "42vD9XcBnJvha9PMe4w_",
        "_score" : 1.3862942,
        "_source" : {
          "user1" : [
            {
              "first" : "hello",
              "last" : "good"
            },
            {
              "first" : "me",
              "last" : "kik"
            }
          ],
          "user2" : [
            {
              "first" : "hello",
              "last" : "good"
            },
            {
              "first" : "me",
              "last" : "kik"
            }
          ]
        },
        "inner_hits" : {
          "user1" : {
            "hits" : {
              "total" : {
                "value" : 1,
                "relation" : "eq"
              },
              "max_score" : 1.3862942,
              "hits" : [
                {
                  "_index" : "netsted_test",
                  "_type" : "_doc",
                  "_id" : "42vD9XcBnJvha9PMe4w_",
                  "_nested" : {
                    "field" : "user1",
                    "offset" : 0
                  },
                  "_score" : 1.3862942,
                  "_source" : {
                    "last" : "good",
                    "first" : "hello"
                  },
                  "highlight" : {
                    "user1.first" : [
                      "<em>hello</em>"
                    ]
                  }
                }
              ]
            }
          }
        }
      }
    ]
  }
}