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

如果column allow不允许db中的NULL，则Entity Framework中生成的属性的setter中的条件为if (_ColumnName != value ）

有什么用？

为什么从允许NULL的列生成的setter中缺少此条件？

[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

不，如果条件与该属性是否为Nullable无关。 仅当属性为EntityKey时才会生成它。

深入研究ADO.NET EntityObject Generator T4模板 （这是默认的代码生成工具，它是VS 2010用于生成实体对象的工具）揭示了这一点：

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();
#>
            }
<#+
            }
#>
        }