elasticsearch 更改已有字段的数据类型

【问题背景】：
在elasticsearch中，如果你没有指定字段映射，那么，elasticsearch将对为指定数据类型的字段做动态映射。
例如，当入库的前期数据字段result为数值型时，elasticsearch将其映射为long类型；当入库的后期数据字段result为字符串时，会报数据类型错误。

更改索引blog中的动态映射字段priority数据类型：由long更改为keyword

一：查看原有字段动态映射类型

查看mapping
命令：GET http://localhost:9002/index[索引名]/_mapping

只能创建index时手动建立mapping，或者新增field mapping，但是不能update field mapping

{
	"blog": {
		"mappings": {
			"article": {
				"properties": {
					"content": {
						"type": "text",
						"fields": {
							"keyword": {
								"type": "keyword",
								"ignore_above": 256
							}
						}
					},
					"counter": {
						"type": "long"
					},
					"id": {
						"type": "text",
						"fields": {
							"keyword": {
								"type": "keyword",
								"ignore_above": 256
							}
						}
					},
					"priority": {
						"type": "long"
					},
					"tags": {
						"type": "text",
						"fields": {
							"keyword": {
								"type": "keyword",
								"ignore_above": 256
							}
						}
					},
					"title": {
						"type": "text",
						"fields": {
							"keyword": {
								"type": "keyword",
								"ignore_above": 256
							}
						}
					}
				}
			}
		}
	}
}

二：更改指定字段类型，新建索引blog_new

命令：PUT http://localhost:9002/blog_new

{
	"mappings": {
		"article": {
			"properties": {
				"content": {
					"type": "text",
					"fields": {
						"keyword": {
							"type": "keyword",
							"ignore_above": 256
						}
					}
				},
				"counter": {
					"type": "long"
				},
				"id": {
					"type": "text",
					"fields": {
						"keyword": {
							"type": "keyword",
							"ignore_above": 256
						}
					}
				},
				"priority": {
					"type": "keyword"
				},
				"tags": {
					"type": "text",
					"fields": {
						"keyword": {
							"type": "keyword",
							"ignore_above": 256
						}
					}
				},
				"title": {
					"type": "text",
					"fields": {
						"keyword": {
							"type": "keyword",
							"ignore_above": 256
						}
					}
				}
			}
		}
	}
}

三：将blog数据reindex到blog_new

命令：POST http://localhost:9002/_reindex

{
  "source": {
    "index": "blog"
  },
  "dest": {
    "index": "blog_new"
  }
}

四：删除索引blog

命令：DELETE http://localhost:9002/blog

五：将blog_new数据reindex到blog

命令：POST http://localhost:9002/_reindex

{
  "source": {
    "index": "blog_new"
  },
  "dest": {
    "index": "blog"
  }
}

六：删除索引blog_new

命令：DELETE http://localhost:9002/blog_new