I have documents with the following structure:
{field: ["id1", "id3"]},
{field: ["id2", "id1"]}
To query the documents I use
aggregate({$match: {'field' : { $in: ['id1'] }}})
I get the documents with this query but I would like only
{field: ["id2"]},
{field: ["id3"]}
I.e., I want to remove "id1" from the array in the aggregation step only, and not from the actual document (via an update with $pull or something similar).
Say we have following documents in a collection named collection:
db.collection.insert({field: ["id1", "id3"]})
db.collection.insert({field: ["id2", "id1"]})
Then below aggregation pipeline would do the trick:
db.collection.aggregate([
{
$match: {field: "id1"}
},
{
$project: {
field: {
$filter: {
input: "$field",
as: "item",
cond: {
$ne: ["$$item", "id1"]
}
}
}
}
}
])
The output from mongo shell is:
{ "field" : [ "id3" ] }
{ "field" : [ "id2" ] }
An alternative way is to $unwind the field and then $group it back:
db.collection.aggregate([
{
$match: {field: "id1"}
},
{
$unwind: "$field"
},
{
$group: {
_id: "$_id",
field: {
$push: {
$cond: {
if: { $eq: [ "$field", "id1" ] },
then: "$$REMOVE",
else: "$field"
}
}
}
}
},
{
$project: {
_id: 0
}
}
])
