Removing a value from existing array using $pull
Suppose we have the following documents in the users collection:
{<br>"_id": 1,<br>"user_name": "sujaykundu",<br>"email": "sujaykundu777@gmail.com",<br>"sports": ["cricket", "football", "swimming"]<br>},<br>{<br>"_id": 2,<br>"user_name": "johndoe",<br>"email": "johndoe@gmail.com,<br>"sports" ["webdev", "swimming"]<br>}Now, if I want to delete swimming from the document where the user_name is “sujaykundu”
we can do is :
db.users.update(
{ "user_name": "sujaykundu" },
{
$pull: {
sports: {
$in : ["swimming", "football" ]
}
},
{
multi: true
}
)Now, the result will be:
{
"_id": 1,
"user_name": "sujaykundu",
"email": "sujaykundu777@gmail.com",
"sports": ["cricket"]
},
{
"_id": 2,
"user_name": "johndoe",
"email": "johndoe@gmail.com,
"sports" ["webdev", "swimming"]
}### Remove Items from an Array of embedded documents
Now suppose we had the documents which has array of embedded documents,
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 }
]
}Now if we want to remove documents that have score as 8 and item field as B,
we can do the following :
db.users.update(
{ "user_name": "sujaykundu" },
{
$pull : {
"results": { score: 8, item: "B" }
},
{
multi :true
}
}
)then the result will be like this:
{<br>"_id" : 1,<br>"results" : [ { "item" : "A", "score" : 5 } ]<br>}<br>{<br>"_id" : 2,<br>"results" : [<br>{ "item" : "C", "score" : 8, "comment" : "Strongly agree" },<br>{ "item" : "B", "score" : 4 }<br>]<br>}### Remove Items from an Array of embedded documents that also contains arrays
suppose we have this :
{
_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.update(
{ },
{ $pull: { results: { answers: { $elemMatch: { q: 2, a: { $gte: 8 } } } } } },
{ multi: true }
)The operation removed from the results array those embedded documents with an answers field that contained at least one element with q equal to 2 and a greater than or equal to 8:
{
"_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 } ] }
]
}So that was $pull in mongodb aggregation
