findAndModify

lastErrorObject

The lastErrorObject embedded document contains the following fields:

value

For remove operations, value contains the removed document if the query matches a document. If the query does not match a document to remove, value contains null.

For update operations, the value embedded document contains the following:

• If the new parameter is not set or is false:

  • the pre-modification document if the query matches a document;

  • otherwise, null.

• If new is true:

  • the updated document if the query returns a match;

  • the inserted document if upsert: true and no document matches the query;

  • otherwise, null.

使用唯一索引进行 upsert

除非有唯一索引来防止重复，否则 upsert 可能会创建重复的文档。

以某一情况为例，其中不存在名为 Andy 的文档，且多个客户端大致会在同一时间发出以下命令：

db.runCommand(
   {
     findAndModify: "people",
     query: { name: "Andy" },
     update: { $inc: { score: 1 } },
     upsert: true
   }
)

如果所有 findAndModify 操作在任何客户端成功插入数据之前完成了查询阶段，且 name 字段上没有唯一索引，则每个 findAndModify 操作都可能导致插入，从而使用 name: Andy 创建多个文档。

name 字段上的唯一索引可确保仅创建一个文档。通过此唯一索引，多个 findAndModify 操作此时便有如下行为：

• 只需执行一次 findAndModify 操作就能成功插入一个新文档。

• 其他 findAndModify 操作要么更新新插入的文档，要么由于唯一键冲突而失败。

  为了让其他 findAndModify 操作更新新插入的文档，必须满足以下所有条件：

  • 目标collection具有会导致重复键错误的唯一索引。

  • 更新操作不是updateMany或multi是false 。

  • 更新匹配条件为：

    • 单个相等谓词。例如 { "fieldA" : "valueA" }

    • 等式谓词的逻辑 AND。例如 { "fieldA" : "valueA", "fieldB" : "valueB" }

  • 相等谓词中的字段与唯一索引键模式中的字段匹配。

  • 更新操作不会修改唯一索引键模式中的任何字段。

下表显示了upsert操作的示例，当发生键冲突时，这些操作要么导致更新，要么失败。

{ name : 1 }

db.people.updateOne(
   { name: "Andy" },
   { $inc: { score: 1 } },
   { upsert: true }
)

{ name : 1 }

db.people.updateOne(
   { name: { $ne: "Joe" } },
   { $set: { name: "Andy" } },
   { upsert: true }
 )

{ name : 1 }

db.people.updateOne(
  { name: "Andy", email: "andy@xyz.com" },
  { $set: { active: false } },
  { upsert: true }
)

分片集合

要在分片集合上使用 findAndModify：

• If you only target one shard, you can use a partial shard key in the query field or,

• You can provide an equality condition on a full shard key in the query field.

• 从版本 7.1 开始，您不需要在查询规范中提供分片键 或 _id 字段。

分片集合中的文档可能缺少分片键字段。要定位缺失分片键的文档，可将 null 等值匹配与其他过滤条件（例如针对 _id 字段）结合使用。例如：

{ _id: <value>, <shardkeyfield>: null } // _id of the document missing shard key

模式验证

findAndModify 命令新增了对 bypassDocumentValidation 选项的支持，从而允许您在附带验证规则的集合中插入或更新文档时绕过模式验证。

Comparisons with the update Method

When updating a document, findAndModify and the updateOne() method operate differently:

• If multiple documents match the update criteria, for findAndModify, you can specify a sort to provide some measure of control on which document to update.

  updateOne() updates the first document that matches.

• By default, findAndModify returns an object that contains the pre-modified version of the document, as well as the status of the operation. To obtain the updated document, use the new option.

  The updateOne() method returns a WriteResult() object that contains the status of the operation.

  To return the updated document, use the find() method. However, other updates may have modified the document between your update and the document retrieval. Also, if the update modified only a single document but multiple documents matched, you will need to use additional logic to identify the updated document.

When modifying a single document, both findAndModify and the updateOne() method atomically update the document. See 原子性和事务 for more details about interactions and order of operations of these methods.

事务

findAndModify 可以在分布式事务中使用。

Update and Return

The following command updates an existing document in the people collection where the document matches the query criteria:

db.runCommand(
   {
     findAndModify: "people",
     query: { name: "Tom", state: "active", rating: { $gt: 10 } },
     sort: { rating: 1 },
     update: { $inc: { score: 1 } }
   }
)

This command performs the following actions:

1. The query finds a document in the people collection where the name field has the value Tom, the state field has the value active and the rating field has a value greater than 10.

2. The sort orders the results of the query in ascending order. If multiple documents meet the query condition, the command will select for modification the first document as ordered by this sort.

3. The update increments the value of the score field by 1.

4. 此命令将返回一个包含以下字段的文档：

   • The lastErrorObject field that contains the details of the command, including the field updatedExisting which is true, and

   • The value field that contains the original (i.e. pre-modification) document selected for this update:

     {
       "lastErrorObject" : {
          "connectionId" : 1,
          "updatedExisting" : true,
          "n" : 1,
          "syncMillis" : 0,
          "writtenTo" : null,
          "err" : null,
          "ok" : 1
       },
       value" : {
         "_id" : ObjectId("54f62d2885e4be1f982b9c9c"),
         "name" : "Tom",
         "state" : "active",
         "rating" : 100,
         "score" : 5
       },
       "ok" : 1
     }

To return the updated document in the value field, add the new:true option to the command.

If no document match the query condition, the command returns a document that contains null in the value field:

{ "value" : null, "ok" : 1 }

mongosh and many drivers provide a findAndModify() helper method. Using the shell helper, this previous operation can take the following form:

db.people.findAndModify( {
   query: { name: "Tom", state: "active", rating: { $gt: 10 } },
   sort: { rating: 1 },
   update: { $inc: { score: 1 } }
} );

However, the findAndModify() shell helper method returns only the unmodified document, or if new is true, the updated document.

{
   "_id" : ObjectId("54f62d2885e4be1f982b9c9c"),
   "name" : "Tom",
   "state" : "active",
   "rating" : 100,
   "score" : 5
}

upsert: true

The following findAndModify command includes the upsert: true option for the update operation to either update a matching document or, if no matching document exists, create a new document:

db.runCommand(
               {
                 findAndModify: "people",
                 query: { name: "Gus", state: "active", rating: 100 },
                 sort: { rating: 1 },
                 update: { $inc: { score: 1 } },
                 upsert: true
               }
             )

If the command finds a matching document, the command performs an update.

If the command does not find a matching document, the update with upsert: true operation results in an insertion and returns a document with the following fields:

• The lastErrorObject field that contains the details of the command, including the field upserted that contains the _id value of the newly inserted document, and

• The value field containing null.

{
  "value" : null,
  "lastErrorObject" : {
     "updatedExisting" : false,
     "n" : 1,
     "upserted" : ObjectId("54f62c8bc85d4472eadea26f")
  },
  "ok" : 1
}

Return New Document

The following findAndModify command includes both upsert: true option and the new:true option. The command either updates a matching document and returns the updated document or, if no matching document exists, inserts a document and returns the newly inserted document in the value field.

In the following example, no document in the people collection matches the query condition:

db.runCommand(
   {
     findAndModify: "people",
     query: { name: "Pascal", state: "active", rating: 25 },
     sort: { rating: 1 },
     update: { $inc: { score: 1 } },
     upsert: true,
     new: true
   }
)

The command returns the newly inserted document in the value field:

{
  "lastErrorObject" : {
     "connectionId" : 1,
     "updatedExisting" : false,
     "upserted" : ObjectId("54f62bbfc85d4472eadea26d"),
     "n" : 1,
     "syncMillis" : 0,
     "writtenTo" : null,
     "err" : null,
     "ok" : 1
  },
  "value" : {
     "_id" : ObjectId("54f62bbfc85d4472eadea26d"),
     "name" : "Pascal",
     "rating" : 25,
     "state" : "active",
     "score" : 1
  },
  "ok" : 1
}

Sort and Remove

By including a sort specification on the rating field, the following example removes from the people collection a single document with the state value of active and the lowest rating among the matching documents:

db.runCommand(
   {
     findAndModify: "people",
     query: { state: "active" },
     sort: { rating: 1 },
     remove: true
   }
)

The command returns the deleted document:

{
  "lastErrorObject" : {
     "connectionId" : 1,
     "n" : 1,
     "syncMillis" : 0,
     "writtenTo" : null,
     "err" : null,
     "ok" : 1
  },
  "value" : {
     "_id" : ObjectId("54f62a6785e4be1f982b9c9b"),
     "name" : "XYZ123",
     "score" : 1,
     "state" : "active",
     "rating" : 3
  },
  "ok" : 1
}

指定排序规则。

排序规则允许用户为字符串比较指定特定于语言的规则，例如字母大小写和重音符号规则。

集合 myColl 包含以下文档：

{ _id: 1, category: "café", status: "A" }
{ _id: 2, category: "cafe", status: "a" }
{ _id: 3, category: "cafE", status: "a" }

以下操作包括排序规则选项：

db.runCommand(
   {
     findAndModify: "myColl",
     query: { category: "cafe", status: "a" },
     sort: { category: 1 },
     update: { $set: { status: "Updated" } },
     collation: { locale: "fr", strength: 1 }
   }
)

该操作将返回以下文档：

{
   "lastErrorObject" : {
      "updatedExisting" : true,
      "n" : 1
   },
   "value" : {
      "_id" : 1,
      "category" : "café",
      "status" : "A"
   },
   "ok" : 1
}

使用 arrayFilters 执行数组更新操作

更新数组字段时，您可以指定 arrayFilters 确定要更新哪些数组元素。

db.students.insertMany( [
   { "_id" : 1, "grades" : [ 95, 92, 90 ] },
   { "_id" : 2, "grades" : [ 98, 100, 102 ] },
   { "_id" : 3, "grades" : [ 95, 110, 100 ] }
] )

db.runCommand(
   {
     findAndModify: "students",
     query: { grades: { $gte: 100 } },
     update:  { $set: { "grades.$[element]" : 100 } },
     arrayFilters: [ { "element": { $gte: 100 } } ]
   }
)

{ "_id" : 1, "grades" : [ 95, 92, 90 ] }
{ "_id" : 2, "grades" : [ 98, 100, 100 ] }
{ "_id" : 3, "grades" : [ 95, 110, 100 ] }

db.students2.insertMany( [
   {
      "_id" : 1,
      "grades" : [
         { "grade" : 80, "mean" : 75, "std" : 6 },
         { "grade" : 85, "mean" : 90, "std" : 4 },
         { "grade" : 85, "mean" : 85, "std" : 6 }
      ]
   },
   {
      "_id" : 2,
      "grades" : [
         { "grade" : 90, "mean" : 75, "std" : 6 },
         { "grade" : 87, "mean" : 90, "std" : 3 },
         { "grade" : 85, "mean" : 85, "std" : 4 }
      ]
   }
] )

db.runCommand(
   {
     findAndModify: "students2",
     query: { _id : 1 },
     update: { $set: { "grades.$[elem].mean" : 100 } },
     arrayFilters: [ { "elem.grade": { $gte: 85 } } ]
   }
)

{
   "_id" : 1,
   "grades" : [
      { "grade" : 80, "mean" : 75, "std" : 6 },
      { "grade" : 85, "mean" : 100, "std" : 4 },
      { "grade" : 85, "mean" : 100, "std" : 6 }
    ]
}
{
   "_id" : 2,
   "grades" : [
      { "grade" : 90, "mean" : 75, "std" : 6 },
      { "grade" : 87, "mean" : 90, "std" : 3 },
      { "grade" : 85, "mean" : 85, "std" : 4 }
   ]
}

使用聚合管道进行更新

findAndModify can accept an aggregation pipeline for the update. The pipeline can consist of the following stages:

• $addFields 及其别名 $set

• $project 及其别名 $unset

• $replaceRoot 及其别名 $replaceWith

使用聚合分析管道可以进行更具表现力的更新声明，例如基于当前字段值的Express条件更新或使用另一个字段的值更新一个字段。

例如，使用以下文档创建名为 students2 的集合：

db.students2.insertMany( [
   {
      "_id" : 1,
      "grades" : [
         { "grade" : 80, "mean" : 75, "std" : 6 },
         { "grade" : 85, "mean" : 90, "std" : 4 },
         { "grade" : 85, "mean" : 85, "std" : 6 }
      ]
   },
   {
      "_id" : 2,
      "grades" : [
         { "grade" : 90, "mean" : 75, "std" : 6 },
         { "grade" : 87, "mean" : 90, "std" : 3 },
         { "grade" : 85, "mean" : 85, "std" : 4 }
      ]
   }
] )

以下操作查找 _id 字段等于 1 的文档，并使用聚合管道根据 grades 字段计算新字段 total 的值：

db.runCommand(
   {
     findAndModify: "students2",
     query: {  "_id" : 1 },
     update: [ { $set: { "total" : { $sum: "$grades.grade" } } } ],
     new: true
   }
)

操作完成后，集合有以下文档：

{
  "_id" : 1,
  "grades" : [ { "grade" : 80, "mean" : 75, "std" : 6 }, { "grade" : 85, "mean" : 90, "std" : 4 }, { "grade" : 85, "mean" :85, "std" : 6 } ],
  "total" : 250
}
{
   "_id" : 2,
   "grades" : [ { "grade" : 90, "mean" : 75, "std" : 6 }, { "grade" : 87, "mean" : 90, "std" : 3 }, { "grade" : 85, "mean" : 85,"std" : 4 } ]
}

Specify hint for findAndModify Operations

在 mongosh 中，创建一个 members 集合，其中包含以下文档：

db.members.insertMany( [
   { "_id" : 1, "member" : "abc123", "status" : "P", "points" :  0,  "misc1" : null, "misc2" : null },
   { "_id" : 2, "member" : "xyz123", "status" : "A", "points" : 60,  "misc1" : "reminder: ping me at 100pts", "misc2" : "Some random comment" },
   { "_id" : 3, "member" : "lmn123", "status" : "P", "points" :  0,  "misc1" : null, "misc2" : null },
   { "_id" : 4, "member" : "pqr123", "status" : "D", "points" : 20,  "misc1" : "Deactivated", "misc2" : null },
   { "_id" : 5, "member" : "ijk123", "status" : "P", "points" :  0,  "misc1" : null, "misc2" : null },
   { "_id" : 6, "member" : "cde123", "status" : "A", "points" : 86,  "misc1" : "reminder: ping me at 100pts", "misc2" : "Some random comment" }
] )

在集合上创建以下索引：

db.members.createIndex( { status: 1 } )
db.members.createIndex( { points: 1 } )

The following operation explicitly hints to use the index { status: 1 }:

db.runCommand({
   findAndModify: "members",
   query: { "points": { $lte: 20 }, "status": "P" },
   remove: true,
   hint: { status: 1 }
})

要查看使用的索引，请对操作运行 explain：

db.runCommand(
   {
     explain: {
       findAndModify: "members",
       query: { "points": { $lte: 20 }, "status": "P" },
       remove: true,
       hint: { status: 1 }
     },
     verbosity: "queryPlanner"
   }
)

在 let 中使用变量

要定义可在命令中其他位置访问的变量，请使用 let 选项。

创建集合 cakeFlavors：

db.cakeFlavors.insertMany( [
   { _id: 1, flavor: "chocolate" },
   { _id: 2, flavor: "strawberry" },
   { _id: 3, flavor: "cherry" }
] )

The following example defines a targetFlavor variable in let and uses the variable to change the cake flavor from cherry to orange:

db.cakeFlavors.runCommand( {
   findAndModify: db.cakeFlavors.getName(),
   query: { $expr: { $eq: [ "$flavor", "$$targetFlavor" ] } },
   update: { flavor: "orange" },
   let: { targetFlavor: "cherry" }
} )