Updates with Aggregation Pipeline使用聚合管道进行更新

Example 实例1

Create an example students collection (if the collection does not currently exist, insert operations will create the collection):创建示例students集合（如果该集合当前不存在，则插入操作将创建该集合）：

db.students.insertMany( [
   { _id: 1, test1: 95, test2: 92, test3: 90, modified: new Date("01/05/2020") },
   { _id: 2, test1: 98, test2: 100, test3: 102, modified: new Date("01/05/2020") },
   { _id: 3, test1: 95, test2: 110, modified: new Date("01/04/2020") }
] )

To verify, query the collection:若要验证，请查询集合：

db.students.find()

The following db.collection.updateOne() operation uses an aggregation pipeline to update the document with _id: 3:以下db.collection.updateOne()操作使用聚合管道更新_id为3的文档：

db.students.updateOne( { _id: 3 }, [ { $set: { "test3": 98, modified: "$$NOW"} } ] )

Specifically, the pipeline consists of a $set stage which adds the test3 field (and sets its value to 98) to the document and sets the modified field to the current datetime. The operation uses the aggregation variable NOW for the current datetime. To access the variable, prefix with $$ and enclose in quotes.具体来说，管道由一个$set阶段组成，它将test3字段（并将其值设置为98）添加到文档中，并将modified字段设置为当前日期时间。该操作将聚合变量NOW用于当前日期时间。若要访问该变量，请在前缀前加上$$并用引号括起来。

To verify the update, you can query the collection:若要验证更新，可以查询集合：

db.students.find().pretty()

Example 实例2

Create an example students2 collection (if the collection does not currently exist, insert operations will create the collection):创建一个示例students2集合（如果该集合当前不存在，则插入操作将创建该集合）：

db.students2.insertMany( [
   { "_id" : 1, quiz1: 8, test2: 100, quiz2: 9, modified: new Date("01/05/2020") },
   { "_id" : 2, quiz2: 5, test1: 80, test2: 89, modified: new Date("01/05/2020") },
] )

To verify, query the collection:若要验证更新，可以查询集合：

db.students2.find()

The following db.collection.updateMany() operation uses an aggregation pipeline to standardize the fields for the documents (i.e. documents in the collection should have the same fields) and update the modified field:以下db.collection.updateMany()操作使用聚合管道来标准化文档的字段（即集合中的文档应该具有相同的字段）并更新modified字段：

db.students2.updateMany( {},
  [
    { $replaceRoot: { newRoot:
       { $mergeObjects: [ { quiz1: 0, quiz2: 0, test1: 0, test2: 0 }, "$$ROOT" ] }
    } },
    { $set: { modified: "$$NOW"}  }
  ]
)

Specifically, the pipeline consists of:具体而言，管道包括：

• a $replaceRoot stage with a $mergeObjects expression to set default values for the quiz1, quiz2, test1 and test2 fields. 带有$mergeObjects表达式的$replaceRoot阶段，用于设置quiz1、quiz2、test1和test2字段的默认值。The aggregation variable ROOT refers to the current document being modified. 聚合变量ROOT是指正在修改的当前文档。To access the variable, prefix with $$ and enclose in quotes. The current document fields will override the default values.若要访问该变量，请在前缀前加上$$并用引号括起来。当前文档字段将覆盖默认值。
• a $set stage to update the modified field to the current datetime. 一个$set阶段，用于将modified字段更新为当前日期时间。The operation uses the aggregation variable NOW for the current datetime. To access the variable, prefix with $$ and enclose in quotes.该操作将聚合变量NOW用于当前日期时间。若要访问该变量，请在前缀前加上$$并用引号括起来。

To verify the update, you can query the collection:若要验证更新，可以查询集合：

db.students2.find()

Example 实例3

Create an example students3 collection (if the collection does not currently exist, insert operations will create the collection):创建一个示例students3集合（如果该集合当前不存在，则插入操作将创建该集合）：

db.students3.insertMany( [
   { "_id" : 1, "tests" : [ 95, 92, 90 ], "modified" : ISODate("2019-01-01T00:00:00Z") },
   { "_id" : 2, "tests" : [ 94, 88, 90 ], "modified" : ISODate("2019-01-01T00:00:00Z") },
   { "_id" : 3, "tests" : [ 70, 75, 82 ], "modified" : ISODate("2019-01-01T00:00:00Z") }
] );

To verify, query the collection:若要验证，可以查询集合：

db.students3.find()

The following db.collection.updateMany() operation uses an aggregation pipeline to update the documents with the calculated grade average and letter grade.下面的db.collection.updateMany()操作使用聚合管道来更新具有计算出的平均成绩和字母成绩的文档。

db.students3.updateMany(
   { },
   [
     { $set: { average : { $trunc: [ { $avg: "$tests" }, 0 ] }, modified: "$$NOW" } },
     { $set: { grade: { $switch: {
                           branches: [
                               { case: { $gte: [ "$average", 90 ] }, then: "A" },
                               { case: { $gte: [ "$average", 80 ] }, then: "B" },
                               { case: { $gte: [ "$average", 70 ] }, then: "C" },
                               { case: { $gte: [ "$average", 60 ] }, then: "D" }
                           ],
                           default: "F"
     } } } }
   ]
)

Specifically, the pipeline consists of:具体而言，管道包括：

• a $set stage to calculate the truncated average value of the tests array elements and to update the modified field to the current datetime. $set阶段，用于计算tests数组元素的截断平均值，并将modified字段更新为当前日期时间。To calculate the truncated average, the stage uses the $avg and $trunc expressions. The operation uses the aggregation variable NOW for the current datetime. To access the variable, prefix with $$ and enclose in quotes.为了计算截断的平均值，该阶段使用$avg和$trunc表达式。该操作将聚合变量NOW用于当前日期时间。若要访问该变量，请在前缀前加上$$并用引号括起来。
• a $set stage to add the grade field based on the average using the $switch expression.一个$set阶段，用于使用$switch表达式根据average添加grade字段。

To verify the update, you can query the collection:若要验证更新，可以查询集合：

db.students3.find()

Example 实例4

Create an example students4 collection (if the collection does not currently exist, insert operations will create the collection):创建一个示例students4集合（如果该集合当前不存在，则插入操作将创建该集合）：

db.students4.insertMany( [
  { "_id" : 1, "quizzes" : [ 4, 6, 7 ] },
  { "_id" : 2, "quizzes" : [ 5 ] },
  { "_id" : 3, "quizzes" : [ 10, 10, 10 ] }
] )

To verify, query the collection:若要验证，可以查询集合：

db.students4.find()

The following db.collection.updateOne() operation uses an aggregation pipeline to add quiz scores to the document with _id: 2:以下db.collection.updateOne()操作使用聚合管道将测验分数添加到_id为2的文档中：

db.students4.updateOne( { _id: 2 },
  [ { $set: { quizzes: { $concatArrays: [ "$quizzes", [ 8, 6 ]  ] } } } ]
)

To verify the update, query the collection:若要验证更新，可以查询集合：

db.students4.find()

Example 实例5

Create an example temperatures collection that contains temperatures in Celsius (if the collection does not currently exist, insert operations will create the collection):创建包含以摄氏度为单位的温度的示例temperatures集合（如果该集合当前不存在，则插入操作将创建该集合）：

db.temperatures.insertMany( [
  { "_id" : 1, "date" : ISODate("2019-06-23"), "tempsC" : [ 4, 12, 17 ] },
  { "_id" : 2, "date" : ISODate("2019-07-07"), "tempsC" : [ 14, 24, 11 ] },
  { "_id" : 3, "date" : ISODate("2019-10-30"), "tempsC" : [ 18, 6, 8 ] }
] )

To verify, query the collection:若要验证，可以查询集合：

db.temperatures.find()

The following db.collection.updateMany() operation uses an aggregation pipeline to update the documents with the corresponding temperatures in Fahrenheit:以下db.collection.updateMany()操作使用聚合管道来更新文档，使其具有以华氏度为单位的相应温度：

db.temperatures.updateMany( { },
  [
    { $addFields: { "tempsF": {
          $map: {
             input: "$tempsC",
             as: "celsius",
             in: { $add: [ { $multiply: ["$$celsius", 9/5 ] }, 32 ] }
          }
    } } }
  ]
)

Specifically, the pipeline consists of an $addFields stage to add a new array field tempsF that contains the temperatures in Fahrenheit. 具体来说，管道由$addFields阶段组成，用于添加新的数组字段tempsF，该字段包含以华氏度为单位的温度。To convert each celsius temperature in the tempsC array to Fahrenheit, the stage uses the $map expression with $add and $multiply expressions.要将tempsC数组中的每个摄氏度温度转换为华氏度，该阶段将$map表达式与$add和$multiply表达式一起使用。

To verify the update, you can query the collection:若要验证更新，可以查询集合：

db.temperatures.find()

Additional Examples其他示例

See also the various update method pages for additional examples:有关其他示例，请参阅各种更新方法页面：

• db.collection.updateOne
• db.collection.updateMany
• db.collection.findOneAndUpdate()
• db.collection.findAndModify()
• Bulk.find.update()
• Bulk.find.updateOne()
• Bulk.find.upsert()