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How to request only documents with the last timestamp from a group?

In the MongoDB collection that I request, each document represents an element at a specific time. When updating a document, a new document is created with the same element identifier and new time stamp. All elements have unique element identifiers.

To illustrate this, consider this example. Let's start with one revision of an element:

{
    _id: x,
    itemId: 123,
    createdOn: ISODate("2013-01-30T11:16:20.102Z"),
    field1: "foo",
    field2: "bar
}

After the update, we have two revisions of the item with the same itemId and different timestamps.

[{
  _id: x,
  itemId: 123,
  createdOn: ISODate("2013-01-30T11:16:20.102Z"),
  field1: "foo",
  field2: "bar"
},
{
  _id: y,
  itemId: 123,
  createdOn: ISODate("2014-02-09T14:26:20.102Z"),
  field1: "baz",
  field2: "fiz"
}]

How to find all the elements that in their latest edition satisfy a specific query?

() , , , itemId :

ItemModel.aggregate({ $match: { field1: "foo"} }).sort({createdOn: -1}).group(
    {
        _id: '$itemId', // grouping key
        createdOn: {$first: '$createdOn'},
        field1: {$first: '$field1'},
        field2: {$first: '$field2'}
    }).exec(...);

, . . "123", - .

0
2

, . , :

db.collection.aggregate([
    {$sort: { createdOn: -1 }},
    {$group: { _id: "$itemId", 
        createdOn: {$first: "$createdOn"},
        field1: {$first: "$field1" },
        field2: {$first: "$field2" }
    }},
    {$match: { field1: "foo" }}
])

, . itemId ( $first), $match, . .

+1

, , . ; :

{
    _id: x,
    itemId: 123,
    createdOn: ISODate("2014-02-09T14:26:20.102Z"),
    field1: "baz",
    field2: "fiz,
    revisions: [
        {createdOn: ISODate("2013-01-30T11:16:20.102Z"), field1: "foo", field2: "bar"},
        {createdOn: ISODate("2014-02-09T14:26:20.102Z"), field1: "baz", field2: "fiz"}
    ]
}

, MongoDB 16 ; . : db.collection.find({field1: "foo" })

...

+1

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