MongoDB C＃列出子文档中所有条目的最新条目

Question

Is it possible to list all the restaurants and their latest grade, if grades is a an array within a restaurant?

{
    "_id" : ObjectId("56bf7957b5e096fd06b755b2"),
    "grades" : [ 
        {
            "date" : ISODate("2014-11-15T00:00:00.000Z"),
            "grade" : "Z",
            "score" : 38
        }, 
        {
            "date" : ISODate("2014-05-02T00:00:00.000Z"),
            "grade" : "A",
            "score" : 10
        }, 
        {
            "date" : ISODate("2013-03-02T00:00:00.000Z"),
            "grade" : "A",
            "score" : 7
        }, 
        {
            "date" : ISODate("2012-02-10T00:00:00.000Z"),
            "grade" : "A",
            "score" : 13
        }
    ],
    "name" : "Brunos On The Boulevard",
}

I would want to get:

{
    "_id" : ObjectId("56bf7957b5e096fd06b755b2"),
    "grades" : [ 
        {
            "date" : ISODate("2014-11-15T00:00:00.000Z"),
            "grade" : "Z",
            "score" : 38
        }
    ],
    "name" : "Brunos On The Boulevard",
}

Explanation

The answer below uses the unwind operator . There's a really simple explanation of it on this answer , should anyone be confused by it as I was.

Answer 1

An option could be doing an aggregate with two operations, an Unwind which deconstructs your array field from the input documents to output a document for each element, and later a sort operation by date in descending order. This way you can get the result you are expected selecting the first element from the aggregate result:

 var result = collection.Aggregate()
                        .Unwind(e => e["grades"])
                        .SortByDescending(e=>e["grades.date"])
                        .FirstOrDefault();