Update Array Elements in a Document with MQL Positional Operators使用MQL位置运算符更新文档中的数组元素

Use the $ Operator to Update the First Match in an Array使用$运算符更新数组中的第一个匹配项

To update only the first match within an array, use the $ operator. 要仅更新数组中的第一个匹配项，请使用$运算符。The $ operator acts as a placeholder to update the first element matched.$运算符充当占位符，用于更新匹配的第一个元素。

The following example uses the updateOne() method with the $ and $set operators to update the first email that has the value missingEmail in the engineering array to alice@mail.com.以下示例使用带有$和$set运算符的updateOne()方法将engineering数组中具有missingEmail值的第一封电子邮件更新为alice@mail.com。

db.employees.updateOne(
   { "engineering.email": "missingEmail" },
   { "$set": { "engineering.$.email": "alice@mail.com" } }
);

Use the find() method to confirm the update to Alice's email.使用find()方法确认对Alice电子邮件的更新。

   db.employees.find()

[
   {
      _id: 'SF',
      engineering: [
         { name: 'Alice', email: 'alice@mail.com', salary: 100000 },
         { name: 'Bob', email: 'missingEmail', salary: 75000 }
      ],
      sales: [
         { name: 'Charlie', email: 'charlie@mail.com', salary: 90000, bonus: 1000 }
      ]
   },
   {
      _id: 'NYC',
      engineering: [
         { name: 'Dave', email: 'dave@mail.com', salary: 55000 }
      ],
      sales: [
         { name: 'Ed', email: 'ed@mail.com', salary: 99000, bonus: 2000 },
         { name: 'Fran', email: 'fran@mail.com', salary: 50000, bonus: 10000 }
      ]
   }
]

As shown in the example above, after you filter for documents that have an array element with the engineering.email field set to missingEmail, the $ operator only updates the first occurrence that matches the filter.如上例所示，在筛选出具有engineering.email字段设置为missingEmail的数组元素的文档后，$运算符仅更新与筛选器匹配的第一个匹配项。

Use the $ Operator with $elemMatch to Update a Specific Element使用$运算符和$elemMatch来更新特定元素

To update a particular element, you can use the $elemMatch operator.要更新特定元素，可以使用$elemMatch运算符。

The following example uses the $elemMatch operator and the $ operator to update Bob's email to "bob@mail.com".以下示例使用$elemMatch运算符和$运算符将Bob的email更新为"bob@mail.com"。

db.employees.updateOne(
   { engineering: { $elemMatch: { name: "Bob", email: "missingEmail" } } },
   { $set: { "engineering.$.email": "bob@mail.com" } }
);

Use the find() method to confirm the update to Bob's email.使用find()方法确认对Bob电子邮件的更新。

db.employees.find(
   { "engineering": { $elemMatch: { name: "Bob" } } },
   { "engineering.$": 1, _id: 0 }
);

[
   {
      engineering: [ { name: 'Bob', email: 'bob@mail.com', salary: 75000 } ]
   }
]

Use the $[] Operator to Update All Array Elements Within a Document使用$[]运算符更新文档中的所有数组元素

To update every element of an array with a single operation, use the $[] operator.要使用单个操作更新数组的每个元素，请使用$[]运算符。

Consider a case where you want to give an additional bonus of $2,000 to your sales employees in NYC. You can use the updateMany() method with the $[] operator and the $inc operator to increase all bonus fields within the sales array in the NYC document by 2000.考虑一个案例，你想给纽约市的销售员工额外发放2000美元的奖金。您可以将updateMany()方法配合$[]运算符和$inc运算符一起使用，以将NYC文档中sales数组中的所有bonus（奖金）字段增加2000。

db.employees.updateMany(
   { "_id": "NYC" },
   { "$inc": { "sales.$[].bonus": 2000 } }
);

Use the find() method to confirm the update to the bonus fields for the employees on NYC's sales team.使用find()方法确认对NYC销售团队员工bonus字段的更新。

db.employees.find(
   { _id: "NYC" },
   { sales: 1, _id: 0 }
);

[
   {
      sales: [
         { name: 'Ed', email: 'ed@mail.com', salary: 99000, bonus: 4000 },
         { name: 'Fran', email: 'fran@mail.com', salary: 50000, bonus: 12000 }
      ]
   }
]

Use the $[<identifier>] Operator to Update Elements that Match a Filter Condition使用$[<identifier>]运算符更新与筛选条件匹配的元素

To update several array elements in a single operation without excessive client-side code paired with a replace operation, use the $[<identifier>] operator. 要在单个操作中更新多个数组元素，而不需要与替换操作配对过多的客户端代码，请使用$[<identifier>]运算符。The $[<identifier>] operator acts as a placeholder to update all elements that match an arrayFilters condition.$[<identifier>]运算符充当占位符，用于更新与arrayFilters条件匹配的所有元素。

Consider a case where you want to update specific employees' salaries if they meet a number of conditions. You can use the updateMany() method with the $[<identifier>] operator to accomplish this task.考虑一个案例，如果特定员工满足一些条件，你想更新他们的工资。您可以使用updateMany()方法配合$[<identifier>]运算符来完成此任务。

db.employees.updateMany(
   {},
   {
      "$set": {
            "engineering.$[elemX].salary": 95000,
             "sales.$[elemY].salary": 75000
      }
   },
   {
      "arrayFilters": [
            { "elemX.name": "Bob", "elemX.salary": 75000 },
            { "elemY.name": "Ed", "elemY.salary": 50000, }
      ]
   }
);

In the above example, the first parameter is an empty match, to evaluate all documents in the collection.在上面的示例中，第一个参数是空匹配，用于计算集合中的所有文档。

elemX and elemY represent two different arrayFilters:elemX和elemY表示两个不同的arrayFilters：

• To match elemX, an array object must have a name field of Bob and a salary of 75000.为了匹配elemX，数组对象必须具有name字段为Bob和75000字段为salary。
• To match elemY, an array object must have a name field of Ed and a salary of 50000.为了匹配elemY，数组对象必须具有name字段为Ed和salary字段为50000。

If an array item in the document matches the elemX filter, then updateMany() sets the salary field for the object to 95000. 如果文档中的数组项与elemX筛选器匹配，则updateMany()将对象的工资字段设置为95000。If an array item matches the elemY filter, then updateMany() sets the salary field for the object to 75000. 如果数组项与elemY筛选器匹配，则updateMany()将对象的salary字段设置为75000。If a filter doesn't match, the corresponding $set operation doesn't trigger.如果筛选器不匹配，则相应的$set操作不会触发。

Use the find() method to confirm the update to Bob's salary because he meets both elemX's conditions.使用find()方法确认Bob的工资更新，因为他满足elemX的两个条件。

db.employees.find(
   { "engineering.name": "Bob" },
   { engineering: { $elemMatch: { name: "Bob" } }, _id: 0 }
);

[
   {
      engineering: [
         { name: "Bob", email: "bob@mail.com", salary: 95000 }
      ]
   }
]

Use the find() method to confirm the update to Ed's salary did not succeed because he does not meet either elemX or elemY's conditions.使用find()方法确认Ed的工资更新没有成功，因为他不符合elemX或elemY的条件。

db.employees.find(
   { "sales.name": "Ed" },
   { sales: { $elemMatch: { name: "Ed" } }, _id: 0 }
);

[
   {
      sales: [
         { name: "Ed", email: "ed@mail.com", salary: 99000, bonus: 4000 }
      ]
   }
]