Question

in web application, i am trying to declare property, i found in some of blogs that they declare property like this :

 public System.Nullable<DateTime> LoginDateTime { get; set; }

what is the meaning of the above property.

Answer 1

This is called an auto-implemented property.

In C# 3.0 and later, auto-implemented properties make
property-declaration more concise when no additional logic is required
in the property accessors. They also enable client code to create
objects. When you declare a property as shown in the following
example, the compiler creates a private, anonymous backing field that
can only be accessed through the property’s get and set accessors.

The compiler will transform this code into something like:

private System.Nullable<DateTime> xxx;
public System.Nullable<DateTime> LoginDateTime
{ 
    get
    {
        return xxx;
    }
    set
    {
        xxx = value;
    }
}

The “generated” code is then called a property:

A property is a member that provides a flexible mechanism to read,
write, or compute the value of a private field. Properties can be used
as if they are public data members, but they are actually special
methods called accessors. This enables data to be accessed easily and
still helps promote the safety and flexibility of methods.

---

About System.Nullable<>

Value type cannot have a null value (compared to reference types). The use of System.Nullable<> allows representing the correct range of values for its underlying value type, plus an additional null value.

Another notation to System.Nullable<DateTime> is DateTime?

Nullable Types (C# Programming Guide)