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I have collection users where each contains property gyms e.g.:
{
"_id" : ObjectId("aaaaa"),
"firstName" : "first",
"lastName" : "second",
"email" : "aaa@aaaa",
"password" : "aaaaa",
"gyms" : [
{
"name" : "aaaaaa",
"address" : "aaaaaaaaaaaaa"
}
]
}
However when I run db.users.aggregate(..) I get:
exception: Value at end of $unwind field path '$gyms' must be an Array, but is a Object
It seems that some of the users documents contain gym:{} or no gym at all rather than array. I need to find these documents, how would I do that?
EDIT:
Aggregate command I run:
db.users.aggregate({ $unwind: "$gyms" }, { $match: { "gyms.address": { $exists: true } } } )
281
Filter MongoDB Array Element Using $Filter Operator This operator uses three variables: input – This represents the array that we want to extract. cond – This represents the set of conditions that must be met. as – This optional field contains a name for the variable that represent each element of the input array.
Use $match With $eq to Find Matching Documents in an Array in MongoDB. Use $match With $all to Find Matching Documents in an Array in MongoDB.
You can use $setDifference to compare min with max array and return if there are elements in the min array which are not in max array. Use $expr with $setDifference . $expr allows use of aggregation expressions in the regular find query. You can also look at here to return when there is matching elements in arrays.
Using {$type: "object"} gives you results containing documents with arrays too. So, to check for pure objects, just add an extra check to ensure that arrays are discarded, viz., obj.0.key: {$exists: false}.
In your case,
db.users.find({"gyms": {$type: "object"}, "gyms.0.name": {$exists: false}}).map(function(u) {
// modify u.gyms to your satisfaction
db.conversations.save(c);
})
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