[英]Using c# Mongodb driver 2.2, how to find max record when grouped by on a particular field
我有一個“ UserRecords”集合。 其結構如下
{
"_id" : "ee654ce6-e50d-4243-8738-35c087a85e67",
"_t" : "Animals",
"ClickedOn" : NumberLong(1452600122),
"Category" : "Nature",
"UserId" : "a1",
}
{
"_id" : "ee654ce6-e50d-4243-8738-35c087a85e67",
"_t" : "Abstract",
"ClickedOn" : NumberLong(1247634566),
"Category" : "Modern",
"UserId" : "a1",
}
{
"_id" : "ee654ce6-e50d-4243-8738-35c087a85e67",
"_t" : "Abstract",
"ClickedOn" : NumberLong(1247634440),
"Category" : "Modern",
"UserId" : "a1",
}
和更多...
現在我想為每個類別點擊“ Max”。 使用最新的Mongo C#驅動程序類似
select Max(clicked) from table group by Category in SQL.
可以使用MongoDB 聚合框架有效地處理此類查詢。 但是,查詢是用JSON編寫的,因此使其難以閱讀。
var dataCollection = Database.GetCollection("UserRecords");
var AggArgs = new AggregateArgs {
Pipeline =
new[] {BsonDocument.Parse(@"{$group : {_id : '$Category', ClickedOn : {$max : '$ClickedOn'}}}")}
};
foreach (var result in dataCollection.Aggregate(AggArgs))
{
Console.WriteLine($"Category: {result["_id"]} Clicked: {result["ClickedOn"]}");
}
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