反射性能 - 使用条件参数创建委托（C# 属性）

Question

我正在使用问题的解决方案：Reflection Performance - Create Delegate (Properties C#)

我有以下代码：

private static Action<object, object> BuildSetAccessor(string name, MethodInfo method)
{
    if (method == null) return null;
    if (method.DeclaringType == null) return null;
    var obj = Expression.Parameter(typeof(object), name);
    var value = Expression.Parameter(typeof(object));
    var expr = Expression.Lambda<Action<object, object>>(Expression.Call(Expression.Convert(obj, method.DeclaringType), method, Expression.Convert(value, method.GetParameters()[0].ParameterType)), obj, value);
    return expr.Compile();
}

private static Func<object, object> BuildGetAccessor(string name, MethodInfo method)
{
    if (method.DeclaringType == null) return null;
    var obj = Expression.Parameter(typeof(object), name);
    var expr = Expression.Lambda<Func<object, object>>(Expression.Convert(Expression.Call(Expression.Convert(obj, method.DeclaringType), method), typeof(object)), obj);
    return expr.Compile();
}

正在使用的代码...

var cacheProperty = new CacheForReflectionClassProperty()
                {
                    Name = p.Name,
                    SetValue = BuildSetAccessor(p.Name, p.GetSetMethod()),
                    GetValue = BuildGetAccessor(p.Name, p.GetGetMethod())
                };
if (Attribute.IsDefined(p, typeof(IsIdentityColumn)))
{
    // TODO: Instead of just getting the old value, 
    // I need to verify if the value is NULL
    // in that case I need to create a new value of ID type....
    // and at the end I need to use the SetValue() method as well
    GetValue = .... // TODO: 
}
else if (Attribute.IsDefined(p, typeof(IsCreatedOnColumn)))
                {
    // TODO: Instead of just getting the old value, 
    // I need to verify if the value is NULL
    // in that case I need to create a new value with DateTime.UtcNow
    // and at the end I need to use the SetValue() method as well
    GetValue = .... // TODO:
                }

我知道我需要创建以下方法：

private static Func<object, object> BuildGetAccessorForIdentityColumn(string name, MethodInfo method)

private static Func<object, object> BuildGetAccessorForCreatedOnColumn(string name, MethodInfo method)

我曾尝试学习如何使用表达式树，但我还没有找到一种方法，我的 BuildGetAccessor 不仅可以获取值，还可以将结果与某些东西进行比较，如果需要还需要使用 BuildSetAccessor。

我该怎么做？

Answer 1

您这样做是因为反射会影响性能。但是在你完成反射部分之后——你不再需要使用编译表达式——只需使用常规代码：

    var getAccessor = BuildGetAccessor(p.Name, p.GetGetMethod());
    var setAccessor = BuildSetAccessor(p.Name, p.GetSetMethod());
    // if IsCreatedOnColumn
    cacheProperty.GetValue = (instance) =>
    {
        var value = getAccessor(instance);
        if (value == null)
        {
            value = DateTime.UtcNow;
            setAccessor(instance, value);
        }
        return value;
    };