When to use .Value with variable name in C#-CodePudding

The output of stringVar.Value and stringVar in second statement are same. I just want to know when to use stringVar.Value and stringVar.

var stringVar= dbContext.tbl.FirstOrDefault(x => x.id == id)?.ColumnName;
return stringVar!= null ? stringVar.Value : 0;

CodePudding user response：

.Value is a property of Nullable data type. When there is class member defined with Nullable data type, then to get actual value, you should use .Value property.

In your case, you used FirstOrDefault() with Null propagation operator, which will propagate null if there is no value found for specific id.

In next line you checked if the stringVar is not null then to get actual value you used .Value property otherwise return 0

CodePudding user response：

Just refer to the declaration of Nullable<T>, Value is read-only and gives the actual value.

[Serializable]
[NonVersionable] // This only applies to field layout
[System.Runtime.CompilerServices.TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
public partial struct Nullable<T> where T : struct
{
    private readonly bool hasValue; // Do not rename (binary serialization)
    internal T value; // Do not rename (binary serialization) or make readonly (can be mutated in ToString, etc.)

    [NonVersionable]
    public Nullable(T value)
    {
        this.value = value;
        hasValue = true;
    }

    public readonly bool HasValue
    {
        [NonVersionable]
        get => hasValue;
    }

    public readonly T Value
    {
        get
        {
            if (!hasValue)
            {
                ThrowHelper.ThrowInvalidOperationException_InvalidOperation_NoValue();
            }
            return value;
        }
    }