https://mongodb.github.io/mongo-csharp-driver/2.14/apidocs/html/M_MongoDB_Driver_ProjectionDefinitionBuilder_1_As__1.htm
ProjectionDefinitionBuilder(TSource).As(TProjection) Method
Creates a client side projection that is implemented solely by using a different serializer.
method
https://mongodb.github.io/mongo-csharp-driver/2.14/apidocs/html/M_MongoDB_Driver_ProjectionDefinitionBuilder_1_Include_1.htm
ProjectionDefinitionBuilder(TSource).Include Method (Expression(Func(TSource, Object)))
Creates a projection that includes a field.
includemethodexpressionfuncobject
https://mongodb.github.io/mongo-csharp-driver/2.5/apidocs/html/M_MongoDB_Driver_ProjectionDefinitionBuilder_1_Combine.htm
ProjectionDefinitionBuilder(TSource).Combine Method (ProjectionDefinition(TSource)[])
Combines the specified projections.
combinemethod