Elasticsearch(036)：es中批量操作之mget(批量查询)

分手后的思念是犯贱 2022-12-17 05:27 513阅读 0赞

# mget(批量查询) #

## 一、介绍 ##

`mget`是`es`提供的一种批量的读取操作的API。

`mget` API允许根据索引，`类型（可选）`和`id（以及可能的路由）`获取多个文档。响应包括一个`docs数组`。该数组具有与原始多重获取请求相对应的所有提取文档（如果特定的get失败，则在响应中包含包含此错误的对象）。成功获取的结构与get API提供的文档的结构相似。

## 二、示例用法 ##

### 2.1 测试数据准备 ###

**示例索引结构如下**

PUT example
    
    PUT example/docs/_mapping
    { 
      "properties": { 
        "id": { "type": "long"},
        "name": { "type": "text"},
        "counter": { "type": "integer"},
        "tags": { "type": "text"}
      }
    }
    
    PUT example/docs/1
    { 
        "id": 1,
        "name": "admin",
        "counter": 1,
        "tags": ["gray"]
    }
    PUT example/docs/2
    { 
        "id": 2,
        "name": "zhangsan",
        "counter": 1,
        "tags": ["black"]
    }
    PUT example/docs/3
    { 
        "id": 3,
        "name": "lisi",
        "counter": 1,
        "tags": ["purple"]
    }
    PUT example_test
    
    PUT example_test/docs/_mapping
    { 
      "properties": { 
        "id": { "type": "long"},
        "name": { "type": "text"},
        "counter": { "type": "integer"},
        "tags": { "type": "text"}
      }
    }
    
    PUT example_test/docs/1
    { 
        "id": 1,
        "name": "test-admin",
        "counter": 1,
        "tags": ["gray"]
    }
    PUT example_test/docs/2
    { 
        "id": 2,
        "name": "test-zhangsan",
        "counter": 1,
        "tags": ["black"]
    }
    PUT example_test/docs/3
    { 
        "id": 3,
        "name": "test-lisi",
        "counter": 1,
        "tags": ["purple"]
    }
    
    
    #查询example所有数据
    GET example/docs/_search
    { 
      "query": { 
        "match_all": { }
      }
    }
    
    #查询example_test所有数据
    GET example_test/docs/_search
    { 
      "query": { 
        "match_all": { }
      }
    }

### 2.2 传统的单条查询，在面对需要查询多个时，需要一次次发送请求到es ###

**示例查询**

GET example/docs/1
    GET example/docs/2
    
    GET example_test/docs/1
    GET example_test/docs/2

这样其实局限性，多次的网络请求很容易造成*资源浪费*和*降低性能*。

### 2.3 mget之查询（index不同） ###

**示例如下**

GET _mget
    { 
        "docs": [
            { 
                "_index": "example",
                "_type": "docs",
                "_id": "1"
            },
            { 
                "_index": "example",
                "_type": "docs",
                "_id": "2"
            },
            { 
                "_index": "example_test",
                "_type": "docs",
                "_id": "1"
            },
            { 
                "_index": "example_test",
                "_type": "docs",
                "_id": "2"
            }
        ]
    }

**返回数据如下**

{ 
      "docs": [
        { 
          "_index": "example",
          "_type": "docs",
          "_id": "1",
          "_version": 1,
          "found": true,
          "_source": { 
            "id": 1,
            "name": "admin",
            "counter": 1,
            "tags": [
              "gray"
            ]
          }
        },
        { 
          "_index": "example",
          "_type": "docs",
          "_id": "2",
          "_version": 1,
          "found": true,
          "_source": { 
            "id": 2,
            "name": "zhangsan",
            "counter": 1,
            "tags": [
              "black"
            ]
          }
        },
        { 
          "_index": "example_test",
          "_type": "docs",
          "_id": "1",
          "_version": 1,
          "found": true,
          "_source": { 
            "id": 1,
            "name": "test-admin",
            "counter": 1,
            "tags": [
              "gray"
            ]
          }
        },
        { 
          "_index": "example_test",
          "_type": "docs",
          "_id": "2",
          "_version": 1,
          "found": true,
          "_source": { 
            "id": 2,
            "name": "test-zhangsan",
            "counter": 1,
            "tags": [
              "black"
            ]
          }
        }
      ]
    }

### 2.4 mget之查询（index相同，type不同） ###

不建议掌握，type有可能在后续的版本废除。这里只做一下简单示例。

GET _mget
    { 
        "docs": [
            { 
                "_index": "example",
                "_type": "docs1",
                "_id": "1"
            },
            { 
                "_index": "example",
                "_type": "docs2",
                "_id": "1"
            },
        ]

### 2.5 mget之查询（index相同，type相同）。 ###

**示例如下**

GET _mget
    { 
        "docs": [
            { 
                "_index": "example",
                "_type": "docs",
                "_id": "1"
            },
            { 
                "_index": "example",
                "_type": "docs",
                "_id": "2"
            },
            { 
                "_index": "example",
                "_type": "docs",
                "_id": "3"
            }
        ]
    }
    
    #index和type相同的话可以简化成如下
    GET example/docs/_mget
    { 
        "docs": [
            { 
                "_id": "1"
            },
            { 
                "_id": "2"
            },
            { 
                "_id": "3"
            }
        ]
    }

**返回结果**

{ 
      "docs": [
        { 
          "_index": "example",
          "_type": "docs",
          "_id": "1",
          "_version": 1,
          "found": true,
          "_source": { 
            "id": 1,
            "name": "admin",
            "counter": 1,
            "tags": [
              "gray"
            ]
          }
        },
        { 
          "_index": "example",
          "_type": "docs",
          "_id": "2",
          "_version": 1,
          "found": true,
          "_source": { 
            "id": 2,
            "name": "zhangsan",
            "counter": 1,
            "tags": [
              "black"
            ]
          }
        },
        { 
          "_index": "example",
          "_type": "docs",
          "_id": "3",
          "_version": 1,
          "found": true,
          "_source": { 
            "id": 3,
            "name": "lisi",
            "counter": 1,
            "tags": [
              "purple"
            ]
          }
        }
      ]
    }

**`mget`是很重要的，一般来说，进行查询的时候，如果一次性查询多条数据的话，那么一定要用`batch`批量操作的api，尽可能减少网络开销次数，可以将性能大幅度提升。**