Using Linq and grouping by variable parameter

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    • Type: New Feature
    • Resolution: Won't Do
    • Priority: Minor - P4
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    • Affects Version/s: 2.4.4
    • Component/s: LINQ
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    • Environment:
      net.core 1.1
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      1. What would you like to communicate to the user about this feature?
      2. Would you like the user to see examples of the syntax and/or executable code and its output?
      3. Which versions of the driver/connector does this apply to?

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      1. What would you like to communicate to the user about this feature? 2. Would you like the user to see examples of the syntax and/or executable code and its output? 3. Which versions of the driver/connector does this apply to?
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      var result = await Events.AsQueryable()
            .Where(_ => _.Date >= from.Date && _.Date <= to.Date)
            .GroupBy(_ => _.SomeProp)
            .Select(n => new { n.Key, Count = n.Count() })
            .ToListAsync();

      works like charm. But lets say that I want to aggregate by custom field - received in aggregateBy string parameter. So I try:

      var propertyToGroupBy = typeof(DiagnosticEvent).GetProperties()
              .First(x => x.Name.ToLowerInvariant() == aggregateBy);

      And then:

      var result = await Events.AsQueryable()
            .Where(_ => _.Date >= from.Date && _.Date <= to.Date)
            .GroupBy(p => propertyToGroupBy.GetValue(p))
            .Select(n => new { n.Key, Count = n.Count() })
            .ToListAsync();

      Which ends up in exception:
      GetValue of type System.Reflection.PropertyInfo is not supported in the expression tree System.String Type.GetValue(document)

      Any idea how to do it while sticking to LINQ? I know that i can use Fluent API with:

      var group = new BsonDocument { { "_id", $"${aggregateBy}"}, { "Count", new BsonDocument("$sum", 1) } };

      But I want to be consistent with LINQ approach.

      Full stack trace: https://pastebin.com/RNzXi1kj

            Assignee:
            Unassigned
            Reporter:
            Lucacs Peplinski
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              Created:
              Updated:
              Resolved: