$pull

Remove All Items That Equal a Specified Value删除所有等于指定值的项

Create the stores collection:创建stores集合：

db.stores.insertMany( [
   {
      _id: 1,
      fruits: [ "apples", "pears", "oranges", "grapes", "bananas" ],
      vegetables: [ "carrots", "celery", "squash", "carrots" ]
   },
   {
      _id: 2,
      fruits: [ "plums", "kiwis", "oranges", "bananas", "apples" ],
      vegetables: [ "broccoli", "zucchini", "carrots", "onions" ]
   }
] )

The following operation removes以下操作将删除

• "apples" and "oranges" from the fruits arrayfruits数组中的"apples"和"oranges"
• "carrots" from the vegetables arrayvegetables数组中的"carrots"

db.stores.updateMany(
    { },
    { $pull: { fruits: { $in: [ "apples", "oranges" ] }, vegetables: "carrots" } }
)

Confirm the result with db.collection.find():使用db.collection.find()确认结果：

{
  _id: 1,
  fruits: [ 'pears', 'grapes', 'bananas' ],
  vegetables: [ 'celery', 'squash' ]
},
{
  _id: 2,
  fruits: [ 'plums', 'kiwis', 'bananas' ],
  vegetables: [ 'broccoli', 'zucchini', 'onions' ]
}

Remove All Items That Match a Specified $pull Condition删除所有符合指定$pull条件的项目

Create the profiles collection:创建profiles集合：

db.profiles.insertOne( { _id: 1, votes: [ 3, 5, 6, 7, 7, 8 ] } )

The following operation will remove all items from the votes array that are greater than or equal to ( $gte ) 6:以下操作将从votes数组中删除所有大于或等于（$gte）6的项目：

db.profiles.updateOne( { _id: 1 }, { $pull: { votes: { $gte: 6 } } } )

After the update operation, the document only has values less than 6:更新操作后，文档的值仅小于6:

{ _id: 1, votes: [  3,  5 ] }

Remove All Items That Match a Specified $pull Condition With bulkWrite()使用bulkWrite()删除与指定$pull条件匹配的所有项

The following db.collection.bulkWrite() operation:以下db.collection.bulkWrite()操作：

• Creates the profilesBulkWrite collection.创建profilesBulkWrite集合。
• Removes all items from the votes array that are greater than or equal to ( $gte ) 6.从votes数组中删除所有大于或等于（$gte）6的项目。
• Removes all items from the votes array that are less than or equal to ( $lte ) 3.从votes数组中删除所有小于或等于（$lte）3的项目。

try {
   db.profilesBulkWrite.bulkWrite( [
      {
         insertOne: {
            "document": { _id: 1, votes: [ 3, 5, 6, 7, 7, 8 ] }
         }
      },
      {
         updateOne: {
            "filter": { _id: 1 },
            "update": { $pull: { votes: { $gte: 6 } } }
         }
      },
      {
         updateOne: {
            "filter": {_id: 1},
            "update": { $pull: { votes: { $lte: 3 } } }
         }
      }
   ] );
} catch (e) {
   print(e);
}

After the db.collection.bulkWrite() operation, you can confirm the document only has values less than 6 and greater than 3 using the following operation:在执行db.collection.bulkWrite()操作后，可以使用以下操作确认文档的值仅小于6且大于3：

db.profilesBulkWrite.find()

The operation returns the following:该操作返回以下内容：

[ { _id: 1, votes: [ 5 ] } ]

Remove Items from an Array of Documents从文档数组中删除项目

Create the survey collection:创建survey集合：

db.survey.insertMany([
   {
      _id: 1,
      results: [
         { item: "A", score: 5 },
         { item: "B", score: 8 }
      ]
   },
   {
      _id: 2,
      results: [
         { item: "C", score: 8 },
         { item: "B", score: 4 }
      ]
   }
] )

The following operation removes all elements from the results array that contain both a score field equal to 8 and an item field equal to "B":以下操作将从results数组中删除同时包含等于8的score字段和等于"B"的item字段的所有元素：

db.survey.updateMany(
  { },
  { $pull: { results: { score: 8 , item: "B" } } }
)

The $pull expression applies the condition to each element of the results array as though it were a top-level document.$pull表达式将条件应用于results数组的每个元素，就好像它是顶级文档一样。

After the operation, the results array contains no documents that contain both a score field equal to 8 and an item field equal to "B".操作后，results数组中不包含同时包含等于8的score字段和等于"B"的item字段的文档。

{ _id: 1, results: [ { item: 'A', score: 5 } ] },
{
  _id: 2,
  results: [ { item: 'C', score: 8 }, { item: 'B', score: 4 } ]
}

The $pull operator treats each element as a top-level object. $pull运算符将每个元素视为顶级对象。The query is applied to each element. 查询将应用于每个元素。The expression does not need to use $elemMatch to specify match conditions.表达式不需要使用$elemMatch来指定匹配条件。

On the contrary, the following operation does not $pull any elements from the original collection:相反，以下操作不会$pull原始集合中的任何元素：

db.survey.updateMany(
  { },
  { $pull: { results: { $elemMatch: { score: 8 , item: "B" } } } }
)

Remove Documents from Nested Arrays从嵌套数组中删除文档

Create a new survey collection with documents that are embedded in nested arrays.使用嵌套数组中嵌入的文档创建新的survey集合。

db.survey.drop()

db.survey.insertMany( [
   {
      _id: 1,
      results: [
         {
            item: "A",
            score: 5,
            answers: [ { q: 1, a: 4 }, { q: 2, a: 6 } ]
         },
         {
            item: "B",
            score: 8,
            answers: [ { q: 1, a: 8 }, { q: 2, a: 9 } ]
         }
      ]
   },
   {
      _id: 2,
      results: [
         {
            item: "C",
            score: 8,
            answers: [ { q: 1, a: 8 }, { q: 2, a: 7 } ]
         },
         {
            item: "B",
            score: 4,
            answers: [ { q: 1, a: 0 }, { q: 2, a: 8 } ]
         }
      ]
   }
] )

Then you can specify multiple conditions on the elements of the answers array with $elemMatch:然后，您可以使用$elemMatch在answers数组的元素上指定多个条件：

db.survey.updateMany(
  { },
  {
     $pull:
        {
           results:
              {
                 answers: { $elemMatch: { q: 2, a: { $gte: 8 } } }
              }
        }
  }
)

The operation updated the results array in each document it matched. 该操作更新了与其匹配的每个文档中的results数组。db.collection.updateMany() removed documents from results when an element of the embedded answers array matched the selection conditions in the highlighted line.当嵌入answers数组的元素与突出显示的行中的选择条件匹配时，从results中删除文档。

{
  _id: 1,
  results: [
    {
      item: 'A',
      score: 5,
      answers: [ { q: 1, a: 4 }, { q: 2, a: 6 } ]
    }
  ]
},
{
  _id: 2,
  results: [
    {
      item: 'C',
      score: 8,
      answers: [ { q: 1, a: 8 }, { q: 2, a: 7 } ]
    }
  ]
}