db.users.aggregate([
{$project:{
"field_count": {$size: {$objectToArray:"$$ROOT"}}
}},
{$group:{
"_id": {field_count: "$field_count"},
"document_count": {$sum: NumberInt(1)},
}},
{$project:{
"field_count": "$_id.field_count"
, "document_count": 1
, "_id": 0
}},
{$sort: {
"field_count": -1
}}
]);
PS. In other words, how many documents exist for each field count (e.g. "78 documents have 5 fields").
db.COLLECTION_NAME.aggregate([
{$project:{
"arr": {$objectToArray:"$$ROOT"},
}},
{$unwind: "$arr"},
{$project: {
"_id": 0,
"k": "$arr.k",
}},
{$group: {
"_id": { "k": "$k" },
"f": {$sum: NumberInt(1)},
}},
{$project: {
"_id": 0,
"k": "$_id.k",
"f": 1,
}},
{$sort: {
"f": -1,
"k": 1,
}},
]);
db.COLLECTION_NAME.aggregate([
{$unwind: {
"path": "$FIELD_NAME",
"preserveNullAndEmptyArrays": true
}}
]);
db.COLLECTION.update(
{
"any_field": "any_value"
}
, {$set: {
"parent.$[x].child.$[xx].grandchild": "any_value"
}}
, {
arrayFilters: [
{"x.any_matching_field": "any_value"}
, {"xx.any_matching_field": "any_value"}
]
, multi: true
, upsert: false
}
);
let str = 'abc def SOMETHING_TO_LOOK_FOR 12';
str = str.replace(
/(.*)SOMETHING_TO_LOOK_FOR ([0-9]{1,})(.*)/
, "$1 ANY_OTHER_TEXT $2 $3"
);
console.log(str);
let re = /{([^}]+)}/;
let matches = re.exec(str);
console.log(matches[1]);
db.COLLECTION.aggregate([
{$match: {
$expr: {
$eq: ["$field1", "$field2.subfield3"]
}
}}
]);