Elasticsearch 7：动态映射

#Elasticsearch

dynamic用来配置处理新出现字段的行为，有true，false，strict 三种。
true 是默认值，会自动在 mapping 中添加字段，并在文档中保存新字段的值。
false 代表不会在 mapping 中添加字段，但会将数据存起来。
strict 代表既不会新增字段，也不会保存新字段的内容，遇到新字段直接报错。 另外，对于嵌套类型的字段，可以单独设置。

默认情况下，我们向索引中写入数据，如果有些字段之前未定义过，ES会自动猜测其类型，然后在mapping中生成。

举个例子：

PUT student
{
  "mappings": {
    "properties": {
      "name": {
        "type": "keyword",
        "doc_values": false
      }
    }
  },
  "settings": {
    "number_of_shards": "8",
    "number_of_replicas": "2"
  }
}

使用 bulk 插入数据:

POST _bulk
{ "index" : { "_index" : "student", "_id" : "1" } }
{ "name" : "张三", "age": 12 }

查询：

GET student/_search

# 查询结果
{
  "took" : 18,
  "timed_out" : false,
  "_shards" : {
    "total" : 8,
    "successful" : 8,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "student",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 1.0,
        "_source" : {
          "name" : "张三",
          "age" : 12
        }
      }
    ]
  }
}

查询结果有 age。

查看 mapping:

GET student/_mapping

# 查询结果
{
  "student" : {
    "mappings" : {
      "dynamic" : "true",
      "properties" : {
        "age" : {
          "type" : "long"
        },
        "name" : {
          "type" : "keyword",
          "doc_values" : false
        }
      }
    }
  }
}

age 出现在了 mapping 中，且自动判断为 long 类型。

有时，自动判断的类型可能是不符合我们的预期的，但是呢，类型一旦确定，又是不能更改的。所以我们要谨慎对待这种特性。

dynamic 可以用来配置相关行为。

测试: dynamic 使用默认值 true 时

当我们没有配置 dynamic 时，用的默认值 true。也就是，下面两个方式效果是相同的：

方式1:

PUT student
{
  "mappings": {
    "properties": {
      "name": {
        "type": "keyword",
        "doc_values": false
      }
    }
  },
  "settings": {
    "number_of_shards": "8",
    "number_of_replicas": "2"
  }
}

方式2:

PUT student
{
  "mappings": {
    "dynamic": "true",
    "properties": {
      "name": {
        "type": "keyword",
        "doc_values": false
      }
    }
  },
  "settings": {
    "number_of_shards": "8",
    "number_of_replicas": "2"
  }
}

测试: dynamic 为 false 时

PUT student
{
  "mappings": {
    "dynamic": "false",
    "properties": {
      "name": {
        "type": "keyword",
        "doc_values": false
      }
    }
  },
  "settings": {
    "number_of_shards": "8",
    "number_of_replicas": "2"
  }
}

插入数据：

POST _bulk
{ "index" : { "_index" : "student", "_id" : "1" } }
{ "name" : "张三", "age": 12 }

查询：

GET student/_search

# 查询结果
{
  "took" : 2,
  "timed_out" : false,
  "_shards" : {
    "total" : 8,
    "successful" : 8,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "student",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 1.0,
        "_source" : {
          "name" : "张三",
          "age" : 12
        }
      }
    ]
  }
}

查看 mapping:

GET student/_mapping

# 查询结果
{
  "student" : {
    "mappings" : {
      "dynamic" : "false",
      "properties" : {
        "name" : {
          "type" : "keyword",
          "doc_values" : false
        }
      }
    }
  }
}

age 没有出现在 mapping 中。

测试: dynamic 为 strict 时

PUT student
{
  "mappings": {
    "dynamic": "strict",
    "properties": {
      "name": {
        "type": "keyword",
        "doc_values": false
      }
    }
  },
  "settings": {
    "number_of_shards": "8",
    "number_of_replicas": "2"
  }
}

插入数据：

POST _bulk
{ "index" : { "_index" : "student", "_id" : "1" } }
{ "name" : "张三", "age": 12 }

会报错：

{
  "took" : 29,
  "errors" : true,
  "items" : [
    {
      "index" : {
        "_index" : "student",
        "_type" : "_doc",
        "_id" : "1",
        "status" : 400,
        "error" : {
          "type" : "strict_dynamic_mapping_exception",
          "reason" : "mapping set to strict, dynamic introduction of [age] within [_doc] is not allowed"
        }
      }
    }
  ]
}

查询：

GET student/_search

# 查询结果为空

查看 mapping:

GET student/_mapping

# 查询结果
{
  "student" : {
    "mappings" : {
      "dynamic" : "strict",
      "properties" : {
        "name" : {
          "type" : "keyword",
          "doc_values" : false
        }
      }
    }
  }
}

单独设置嵌套类型字段

可参考 这篇文章.

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