赋值给Nullable<使用FastMember
本文关键字:使用 FastMember Nullable 赋值 | 更新日期: 2023-09-27 18:15:27
我已经成功地使用这个函数为属性和嵌套属性赋值
private static void AssignValueToProperty(ObjectAccessor accessor, object value, string propertyLambdaString)
{
var index = propertyLambdaString.IndexOf('.');
if (index == -1)
{
accessor[propertyLambdaString] = value;
// problem above: throws Exception if assigning value to Nullable<T>
}
else
{
var property = propertyLambdaString.Substring(0, index);
accessor = ObjectAccessor.Create(accessor[property]);
AssignValueToProperty(accessor, value, propertyLambdaString.Substring(index + 1));
}
}
然而,赋值会抛出InvalidCastException异常。如何分配空值,而不是使用FastMember?例如public class A
{
public double? SomeValue {get; set;}
}
...
var a = new A();
var accessor = ObjectAccessor.Create(a);
accessor["SomeValue"] = 100; // throws Exception, when assigning 100.0 it works???
FastMember与它的工具箱内的类型转换无关,所以这是我提出的解决方案,作为FastMember ObjectAccessor
的扩展方法:
public static class FastMemberExtensions
{
public static void AssignValueToProperty(this ObjectAccessor accessor, string propertyName, object value)
{
var index = propertyName.IndexOf('.');
if (index == -1)
{
var targetType = Expression.Parameter(accessor.Target.GetType());
var property = Expression.Property(targetType, propertyName);
var type = property.Type;
type = Nullable.GetUnderlyingType(type) ?? type;
value = value == null ? GetDefault(type) : Convert.ChangeType(value, type);
accessor[propertyName] = value;
}
else
{
accessor = ObjectAccessor.Create(accessor[propertyName.Substring(0, index)]);
AssignValueToProperty(accessor, propertyName.Substring(index + 1), value);
}
}
private static object GetDefault(Type type)
{
return type.IsValueType ? Activator.CreateInstance(type) : null;
}
}
可以这样调用:
var accessor = ObjectAccessor.Create(t); // t is instance of SomeType
accessor.AssignValueToProperty("Nested.Property", value); // t.Nested.Property = value
FastMember不会为您转换类型。100是int字面值,但目标属性是decimal?类型。没有从整型到十进制的隐式转换?(或小数)。100.0是隐式转换为十进制的Double字面值。,因此赋值将成功。
public class A
{
public double? SomeValue { get; set; }
}
public static class Sample
{
public static void Go()
{
var a = new A();
var accessor = ObjectAccessor.Create(a);
accessor["SomeValue"] = 100.0; // succeeds
accessor["SomeValue"] = 100M; // succeeds
accessor["SomeValue"] = null; // succeeds
accessor["SomeValue"] = 100; // throws, can't convert from int to decimal?
}
}
如果没有隐式转换,则必须在代码中执行必要的转换。
隐式转换:https://msdn.microsoft.com/en-us/library/y5b434w4.aspx
显式转换:https://msdn.microsoft.com/en-us/library/yht2cx7b.aspx