i:nill="true" appears in response - entity-framework

Question

I have a model -
public class EmployeeModel
{
public int Id { get; set; }
public string Name { get; set; }
public string Designation { get; set; }
public double? Salary { get; set; }
}
and a LINQ method syntax like -
public List<EmployeeModel> GetEmployees()
{
using (var DbCon = new OfficeEntities())
{
var result = DbCon.Employee.Select(x => new EmployeeModel()
{
Id = x.Id,
Name = x.Name
//Salary = x.Salary,
//Designation = x.Designation
})
.ToList();
return result;
}
}
I have commented out salary and designation but even though it prints with
key : salary and for value i:null="true" why
result comes like this
<EmployeeModel>
<Designation i:nil="true"/>
<Id>1</Id>
<Name>Sulochana </Name>
<Salary i:nil="true"/>
</EmployeeModel>
Even though commented/removed the parameters in the query, why it is appearing in the result. Kindly help

Answer 1

Because you didn't include those properties in the projection.
This has a special meaning for the client to interpret, it's not that these fields have a null value, these fields we're not included in the projection, so their values are indeterminate.
If the client has requesting a projection with $select=Id,Name then these fields would not have been included at all, but because the client is expecting all the fields this is how the API expresses to the client that the fields we're deliberately omitted, but to satisfy the return contract the fields must be provided in some form.
This answer is assuming OP is writing an OData service, but the same concept applies with Linq to Entities in general. If the Linq expression is projecting into a model type, but not including certain fields, then those fields will have an uninitialized value on the model instances that are projected out.

Answer 2

You are creating an EmployeeModel object in the Select projection. Hence, Salary and Designation are being initialized with their default values, even though you didn't set values for them. Then after serializing all properties are present in the result.
If you are expecting only Id and Name in the output/result, then define a type in that shape -
public class EmployeeInfo
{
public int Id { get; set; }
public string Name { get; set; }
}
and create an object of that type in the projection -
var result = DbCon.Employee.Select(x => new EmployeeInfo()
{
Id = x.Id,
Name = x.Name
})
.ToList();