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Array Update Operators

$pull

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  • Behavior
  • Examples
$pull

The $pull operator removes from an existing array all instances of a value or values that match a specified condition.

The $pull operator has the form:

{ $pull: { <field1>: <value|condition>, <field2>: <value|condition>, ... } }

To specify a <field> in an embedded document or in an array, use dot notation.

Behavior

Starting in MongoDB 5.0, update operators process document fields with string-based names in lexicographic order. Fields with numeric names are processed in numeric order. See Update Operators Behavior for details.

If you specify a <condition> and the array elements are embedded documents, $pull operator applies the <condition> as if each array element were a document in a collection. See Remove All Items That Match a Specified $pull Condition With bulkWrite() for an example.

If the specified <value> to remove is an array, $pull removes only the elements in the array that match the specified <value> exactly, including order.

If the specified <value> to remove is a document, $pull removes only the elements in the array that have the exact same fields and values. The ordering of the fields can differ.

Starting in MongoDB 5.0, mongod no longer raises an error when you use an update operator like $pull with an empty operand expression ( { } ). An empty update results in no changes and no oplog entry is created (meaning that the operation is a no-op).

Examples

Remove All Items That Equal a Specified Value

Create the stores collection:

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

  • "apples" and "oranges" from the fruits array

  • "carrots" from the vegetables array

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

Confirm the result with db.collection.find():

{
  _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

Create the profiles collection:

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:

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

After the update operation, the document only has values less than 6:

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

Remove All Items That Match a Specified $pull Condition With bulkWrite()

The following db.collection.bulkWrite() operation:

  • Creates the profilesBulkWrite collection.

  • Removes all items from the votes array that are greater than or equal to ( $gte ) 6.

  • Removes all items from the votes array that are less than or equal to ( $lte ) 3.

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);
}

Note

bulkWrite()

The db.collection.bulkWrite() method executes multiple write operations listed in an array. In this example, the db.collection.bulkWrite() performs multiple operations on the profiles collection.

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:

db.profilesBulkWrite.find()

The operation returns the following:

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

Remove Items from an Array of Documents

Create the survey collection:

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":

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.

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".

{ _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. The query is applied to each element. The expression does not need to use $elemMatch to specify match conditions.

On the contrary, the following operation does not $pull any elements from the original collection:

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

Note

Drop the survey collection with:

Then recreate it to run this example.

Remove Documents from Nested Arrays

Create a new survey collection with documents that are embedded in nested arrays.

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:

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

The operation updated the results array in each document it matched. db.collection.updateMany() removed documents from results when an element of the embedded answers array matched the selection conditions in the highlighted line.

{
  _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 } ]
    }
  ]
}

Tip

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