使用MongoDb C#驱动程序的Sample()遇到困难 [英] Having Difficulty Using MongoDb C# Driver's Sample()

问题描述

我正在尝试使用 Sample( )方法.我将驱动程序更新为最新版本，并从链接的示例中复制了using语句.但是，有些事情不起作用，我希望这是我的一些简单错误.所有相关信息在下图中:

I am trying to get some random items from the database using the Sample() method. I updated to the latest version of the driver and copied the using statements from the linked example. However, something isn't working, and I am hoping it's some simple mistake on my part. All the relevant information is in the image below:

Greg，我在此处和原始数据库阅读了聚合文档方法此处的文档，但我仍然不明白.最后两行是我的尝试，我之前从未使用过聚合:

Greg, I read the aggregation docs here and the raw db method doc here, but I still don't get it. Last two lines are my attempts, I have never used aggregation before:

            var mongoCollection = GetMongoCollection<BsonDocument>(collectionName);
            long[] locationIds = new long[] { 1, 2, 3, 4, 5 };
            var locationsArray = new BsonArray();
            foreach (long l in locationIds) { locationsArray.Add(l); };
            FilterDefinition<BsonDocument> sampleFilter = Builders<BsonDocument>.Filter.In("LocationId", locationsArray);
            var findSomething = mongoCollection.Find(sampleFilter); //this works, the two attempts below don't.
            var aggregateSomething = mongoCollection.Aggregate(sampleFilter).Sample(25);
            var aggregateSomething2 = mongoCollection.Aggregate().Match(sampleFilter).Sample(25);

推荐答案

样本仅可用于聚合.您需要从聚合"而不是查找"开始.我相信Linq也可以提供它.

Sample is only available from an aggregation. You need to start with Aggregate, not Find. I believe it's also available in Linq.

更新: 看来我们没有专门的方法.但是，您可以使用AppendStage方法.

UPDATE: Looks like we don't have a method for it specifically. However, you can use the AppendStage method.

mongoCollection.Aggregate(sampleFilter)
               .AppendStage<BsonDocument>("{ $sample: { size: 3 } }");

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