从Entity Framework中的db列生成的属性。 为什么在列的情况下属性设置器中不存在if条件，则允许NULL

Question

If column allow does not allow NULL in db then a condition in setter of generated property in Entity Framework is if (_ColumnName != value )

What is the use of this?

Why this condition is missing in setter generated from columns which allow NULL?

[EdmScalarPropertyAttribute(EntityKeyProperty=true, IsNullable=false)]
[DataMemberAttribute()]
public global::System.String Address1
{
    get
    {
    return _Address1;
    }
    set
    {
    if (_Address1 != value) // This condition is only for columns which are not null in db. Why this is not needed for nullable columns.
    {
        OnAddress1Changing(value);
        ReportPropertyChanging("Address1");
        _Address1 = StructuralObject.SetValidValue(value, false);
        ReportPropertyChanged("Address1");
        OnAddress1Changed();
    }
    }
}
private global::System.String _Address1;

[EdmScalarPropertyAttribute(EntityKeyProperty=false, IsNullable=true)]
[DataMemberAttribute()]
public global::System.String Address2
{
    get
    {
    return _Address2;
    }
    set
    {
        // NO IF CONDITION HERE LIKE IT IS IN PROPERTY WHICH DON'T ALLOW NULL (ABOVE PROPERTY ADDRESS1)
        OnAddress2Changing(value);
    ReportPropertyChanging("Address2");
    _Address2 = StructuralObject.SetValidValue(value, true);
    ReportPropertyChanged("Address2");
    OnAddress2Changed();
    }
}
private global::System.String _Address2;

Answer 1

No, that if condition has nothing to do with whether or not the property is Nullable. It will be generated only when the property is EntityKey .

Digging into the ADO.NET EntityObject Generator T4 templte (which is the default code generation tool and is the one that VS 2010 uses to generate Entity Objects) reveals this:

if (ef.IsKey(primitiveProperty))
            {
                if (ef.ClrType(primitiveProperty.TypeUsage) == typeof(byte[]))
                {
#>
            if (!StructuralObject.BinaryEquals(<#=code.FieldName(primitiveProperty)#>, value))
<#+
                }
                else
                {
#>
            // Here it inject the if condition:
            if (<#=code.FieldName(primitiveProperty)#> != value )
<#+
                }
#>
            {
<#+
        PushIndent(CodeRegion.GetIndent(1));
            }
#>
            <#=ChangingMethodName(primitiveProperty)#>(value);
            ReportPropertyChanging("<#=primitiveProperty.Name#>");
            <#=code.FieldName(primitiveProperty)#> = StructuralObject.SetValidValue(value<#=OptionalNullableParameterForSetValidValue(primitiveProperty, code)#>);
            ReportPropertyChanged("<#=primitiveProperty.Name#>");
            <#=ChangedMethodName(primitiveProperty)#>();
<#+
        if (ef.IsKey(primitiveProperty))
            {
        PopIndent();
#>
            }
<#+
            }
#>
        }