将SetFields与MongoDB C#驱动程序2.0结合使用 [英] Using SetFields with MongoDB C# driver 2.0

问题描述

使用旧驱动程序，我可以指定要从查询中返回的字段，如下所示:

With the old driver I could specify the fields I wanted to return from a query as follows:

var cursor = Collection.Find(query).
  SetFields(Fields<MealPlan>.Exclude (plan => plan.Meals));

如何使用2.0驱动程序来完成此操作?

How do I accomplish this with the 2.0 driver?

推荐答案

您需要在IFindFluent上使用Projection方法(这是Find和Projection返回的内容):

You need to use the Projection method on IFindFluent (which is what Find and Projection return):

var findFluent = Collection.Find(query).Projection(Fields<MealPlan>.Exclude (plan => plan.Meals))

现在，这最终将生成一个BsonDocument s的游标，因为它不知道投影的外观.您可以调用通用Projection来添加该类型:

Now, this would eventually generate a cursor of BsonDocuments since it doesn't know how the projection looks. You can call the generic Projection instead to add that type:

var findFluent = Collection.Find(query).Projection<MealPlan>(Fields<MealPlan>.Exclude (plan => plan.Meals))

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从更一般的意义上讲(使用Exclude时不那么相关)，您还可以使用lambda表达式指定字段:

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In a more general sense (which is less relevant when using Exclude), you could also specify fields using a lambda expression:

var findFluent = Collection.Find(query).Projection(plan => plan.Meals)

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