本文属于机器翻译版本。若本译文内容与英语原文存在差异，则一律以英文原文为准。

# \$1mergeObjects
<a name="mergeObjects"></a>

Amazon DocumentDB 中的`$mergeObjects`运算符用于将多个文档或对象合并为一个文档。当您需要合并两个或多个文档或对象的内容时，此运算符特别有用，这可能会将一个对象的值与另一个对象的值覆盖。

**参数**
+ `expression1`: 第一个要合并的对象。
+ `expression2`:（可选）要合并的第二个对象。
+ `expression3`:（可选）要合并的其他对象。

## 示例（MongoDB 外壳）
<a name="mergeObjects-examples"></a>

以下示例演示如何使用`$mergeObjects`运算符组合两个对象。

**创建示例文档**

```
db.collection.insertMany([
  { "_id": 1, "name": "John", "address": { "city": "New York", "state": "NY" } },
  { "_id": 2, "name": "Jane", "address": { "city": "Los Angeles", "state": "CA" } }
]);
```

**查询示例**

```
db.collection.aggregate([
  {
    $project: {
      "combinedAddress": {
        $mergeObjects: ["$address", { "country": "USA" }]
      }
    }
  }
])
```

**输出**

```
[
  {
    "_id": 1,
    "combinedAddress": {
      "city": "New York",
      "state": "NY",
      "country": "USA"
    }
  },
  {
    "_id": 2,
    "combinedAddress": {
      "city": "Los Angeles",
      "state": "CA",
      "country": "USA"
    }
  }
]
```

## 代码示例
<a name="mergeObjects-code"></a>

要查看使用该`$mergeObjects`命令的代码示例，请选择要使用的语言的选项卡：

------
#### [ Node.js ]

```
const { MongoClient } = require('mongodb');

async function example() {
  const client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
  const db = client.db('test');
  const collection = db.collection('collection');

  const result = await collection.aggregate([
    {
      $project: {
        "combinedAddress": {
          $mergeObjects: ["$address", { "country": "USA" }]
        }
      }
    }
  ]).toArray();

  console.log(result);
  await client.close();
}

example();
```

------
#### [ Python ]

```
from pymongo import MongoClient

def example():
    client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
    db = client['test']
    collection = db['collection']

    result = list(collection.aggregate([
        {
            '$project': {
                "combinedAddress": {
                    "$mergeObjects": ["$address", { "country": "USA" }]
                }
            }
        }
    ]))

    print(result)
    client.close()

example()
```

------