es - elasticsearch mapping - field data type - 5

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 ：alias field type有什么特点？
答 :

1. alias是field的别名
2. alias只用于搜索（查询、聚合、排序）
3. 一个alias不能映射多个fields
4. 一个field可以有多个alias
5. 不能用alias获取文档field的值
6. alias不在_source中显示
7. alias可以修改为指向另一个field

问 ：alias field type如何使用？
答 ：

1. 基本使用

# alias
# 配置项 :
#   1. path : field名

PUT /alias_test
{
  "mappings" : {
    "properties" : {
      "my_name"  : {"type" : "keyword"},
      "my_alias" : {
        "type" : "alias",
        "path" : "my_name"
      }
    }
  }
}

POST /alias_test/_doc
{
  "my_name" : "hello"
}

POST /alias_test/_doc
{
  "my_name" : "good"
}

# 用别名搜索
GET /alias_test/_search
{
  "query" : {
    "match" : {
      "my_alias": "good"
    }
  }
}

# 结果
{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 0.6931471,
    "hits" : [
      {
        "_index" : "alias_test",
        "_type" : "_doc",
        "_id" : "32uy1ncBnJvha9PMQIwX",
        "_score" : 0.6931471,
        "_source" : {
          "my_name" : "good"
        }
      }
    ]
  }
}


# 通配符查找别名
GET /alias_test/_field_caps?fields=my*

# 结果
{
  "indices" : [
    "alias_test"
  ],
  "fields" : {
    "my_name" : {
      "keyword" : {
        "type" : "keyword",
        "searchable" : true,
        "aggregatable" : true
      }
    },
    "my_alias" : {
      "keyword" : {
        "type" : "keyword",
        "searchable" : true,
        "aggregatable" : true
      }
    }
  }
}

2. 多个别名

# 一个field可以有多个alias
PUT /alias_test2
{
  "mappings" : {
    "properties" : {
      "my_name"  : {"type" : "keyword"},
      "my_alias" : {
        "type" : "alias",
        "path" : "my_name"
      },
      "my_alias2" : {
        "type" : "alias",
        "path" : "my_name"
      }
    }
  }
}

# 通配符查找别名
GET /alias_test2/_field_caps?fields=my*

# 结果
{
  "indices" : [
    "alias_test2"
  ],
  "fields" : {
    "my_name" : {
      "keyword" : {
        "type" : "keyword",
        "searchable" : true,
        "aggregatable" : true
      }
    },
    "my_alias" : {
      "keyword" : {
        "type" : "keyword",
        "searchable" : true,
        "aggregatable" : true
      }
    },
    "my_alias2" : {
      "keyword" : {
        "type" : "keyword",
        "searchable" : true,
        "aggregatable" : true
      }
    }
  }
}

3. 修改指向

PUT /alias_test3
{
  "mappings" : {
    "properties" : {
      "my_name"  : {"type" : "keyword"},
      "my_alias" : {
        "type" : "alias",
        "path" : "my_name"
      },
      "my_alias2" : {
        "type" : "alias",
        "path" : "my_name"
      },
      "my_addr" : {"type" : "text"}
    }
  }
}

GET /alias_test3/_mapping

# 结果
{
  "alias_test3" : {
    "mappings" : {
      "properties" : {
        "my_addr" : {
          "type" : "text"
        },
        "my_alias" : {
          "type" : "alias",
          "path" : "my_name"
        },
        "my_alias2" : {
          "type" : "alias",
          "path" : "my_name"
        },
        "my_name" : {
          "type" : "keyword"
        }
      }
    }
  }
}


# 修改别名指向
PUT /alias_test3/_mapping
{
  "properties" : {
    "my_alias2" : {
      "type" : "alias",
      "path" : "my_addr"
    }
  }
}

GET /alias_test3/_mapping

# 结果
{
  "alias_test3" : {
    "mappings" : {
      "properties" : {
        "my_addr" : {
          "type" : "text"
        },
        "my_alias" : {
          "type" : "alias",
          "path" : "my_name"
        },
        "my_alias2" : {
          "type" : "alias",
          "path" : "my_addr"
        },
        "my_name" : {
          "type" : "keyword"
        }
      }
    }
  }
}