Mongodb update array $pull modifier

1. $pull modifier deletes qualifying elements from the array in the following format:

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

2. Specify a value to delete all lists

Give a document under a stores collection

{
   _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" ]
}
Update the "apples" and "oranges" of all documents in the collection stores in the array fruits and delete the "carrots" in the array vegetables as follows
db.stores.update(
    { },
    { $pull: { fruits: { $in: [ "apples", "oranges" ] }, vegetables: "carrots" } },
    { multi: true }
)

The result of the operation is:

{
  "_id" : 1,
  "fruits" : [ "pears", "grapes", "bananas" ],
  "vegetables" : [ "celery", "squash" ]
}
{
  "_id" : 2,
  "fruits" : [ "plums", "kiwis", "bananas" ],
  "vegetables" : [ "broccoli", "zucchini", "onions" ]
}
3. $pull deletes all eligible elements

Collection documents based on collection profiles

{ _id: 1, votes: [ 3, 5, 6, 7, 7, 8 ] }

The following deletes elements in the votes array that have elements greater than or equal to 6

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

All elements in the array after the operation are less than 6

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

4. Remove elements from an array nested document

A survey collection contains the following documents

{
   _id: 1,
   results: [
      { item: "A", score: 5 },
      { item: "B", score: 8, comment: "Strongly agree" }
   ]
}
{
   _id: 2,
   results: [
      { item: "C", score: 8, comment: "Strongly agree" },
      { item: "B", score: 4 }
   ]
}

Document collections with element item equal to B and element score equal to 8 in array results will be deleted as follows

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

The result of the operation is:

{
   "_id" : 1,
   "results" : [ { "item" : "A", "score" : 5 } ]
}
{
  "_id" : 2,
  "results" : [
      { "item" : "C", "score" : 8, "comment" : "Strongly agree" },
      { "item" : "B", "score" : 4 }
   ]
}

5. The following set document is the array set array type

{
   _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 } ] }
   ]
}

You can use $elemMatch to match multiple conditions

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

The result of the operation is:

{
   "_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 } ] }
   ]
}

Tags: Celery less

Posted on Mon, 20 Jul 2020 10:53:53 -0400 by maniac1aw