C# – Project on multiple fields in C# MongoDB 2.0

cmongodbmongodb-.net-drivermongodb-csharp-2.0net

How do you project on fields in the new MongoDB C# drivers when the fields are given in the form of a String array ?.
I could find ways to project on a single field by doing

collection.find(filter).Project(Builders<Category>.Projection.Include(fieldName)

How do I extend this to take an array of fields ?.

Best Answer

There is also extension method Include

var projection = Builders<Category>.Projection.Include(fieldList.First());
foreach (var field in fieldList.Skip(1))
{
    projection = projection.Include(field);
}
var result = await collection.Find(filter).Project(projection).ToListAsync();

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Catch System.Exception and switch on the types

catch (Exception ex)            
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C# – How would you count occurrences of a string (actually a char) within a string

If you're using .NET 3.5 you can do this in a one-liner with LINQ:

int count = source.Count(f => f == '/');

If you don't want to use LINQ you can do it with:

int count = source.Split('/').Length - 1;

You might be surprised to learn that your original technique seems to be about 30% faster than either of these! I've just done a quick benchmark with "/once/upon/a/time/" and the results are as follows:

Your original = 12s
source.Count = 19s
source.Split = 17s
foreach (from bobwienholt's answer) = 10s

(The times are for 50,000,000 iterations so you're unlikely to notice much difference in the real world.)

Best Answer

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