通过反射检查是否计算了属性

Question

请想象在一个类中有以下两个属性:

public string Category { get; set; }
public string DisplayCategory => "SomeCategory"

现在我只想收集所有没有计算属性的PropertyInfo对象

var properties = type.GetProperties();
var serializables = properties.Where(p => p.CanRead, true));

我如何通过Reflection发现如果一个属性是一个计算的，所以我可以忽略它?

我想这样做的原因是因为我使用Expression Trees来自动创建通过Entity Framework 6处理的查询。实体框架仅为非计算属性创建列，因此无法查询计算属性。

参见本文

Answer 1

下面的方法对我很有效。

我试着看看我是否能找到计算属性和没有Set方法的属性之间的区别:

public int Computed => 2;
public int NoSet { get; }

PropertyInfo.SetMethod返回null

查看get方法生成的IL，在NoSet属性上有CompilerGeneratedAttribute，但在Computed属性上没有:

.method public hidebysig specialname instance int32
  get_Computed() cil managed
{
  .maxstack 8
  // [215 32 - 215 33]
  IL_0000: ldc.i4.2
  IL_0001: ret
}
.method public hidebysig specialname instance int32
  get_NoSet() cil managed
{
  .custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor()
    = (01 00 00 00 )
  .maxstack 8
  // [217 28 - 217 32]
  IL_0000: ldarg.0      // this
  IL_0001: ldfld        int32 TestNamespace.TestClass::'<NoSet>k__BackingField'
  IL_0006: ret
}

检查变成:

if (property.SetMethod == null && property.GetMethod.GetCustomAttribute(typeof(CompilerGeneratedAttribute)) == null)
    return "Computed Property";

Answer 2

我使用delegatedecomcompiler，目前我必须手动将每个计算属性名称添加到自定义配置中。

如果下面的ShouldDecompile方法能自动确定哪些属性应该反编译就好了:

  public class CustomDelegateDecompilerConfiguration : Configuration {
    public static CustomDelegateDecompilerConfiguration Instance { get; } = new CustomDelegateDecompilerConfiguration();
    public static void Enable() => Configuration.Configure(Instance);
    public CustomDelegateDecompilerConfiguration() {
      RegisterDecompileableMember<Person, string>(x => x.Name);
      RegisterDecompileableMembers(typeof(string), nameof(string.IsNullOrWhiteSpace));
      RegisterDecompileableMembers(typeof(CustomComputedMethods), new[] {
        nameof(CustomComputedMethods.PersonName),
        nameof(CustomComputedMethods.MonthInteger),
        nameof(CustomComputedMethods.WholeMonthsBetween),
        nameof(CustomComputedMethods.WholeYearsBetween)
      });
    }
    public HashSet<MemberInfo> DecompileableMembers { get; } = new HashSet<MemberInfo>();
    public override bool ShouldDecompile(MemberInfo memberInfo) => memberInfo.GetCustomAttributes(typeof(DecompileAttribute), true).Length > 0
      || memberInfo.GetCustomAttributes(typeof(ComputedAttribute), true).Length > 0
      || memberInfo.GetCustomAttributes(typeof(CompilerGeneratedAttribute), true).Length > 0
      || DecompileableMembers.Contains(memberInfo)
      //***  Would be nice if auto detection was possible with non-existing methods below ***
      //|| memberInfo.AutoProperty      (One with a backing field automatically generated by the compiler)
      //|| memberInfo.HasExpressionBody (One implemented using the => (lambda) syntax)
      //|| memberInfo.HasFunctionBody   (One implemented using the normal {...} syntax)
      ;
    public override void RegisterDecompileableMember(MemberInfo prop) => DecompileableMembers.Add(prop);
    public void RegisterDecompileableMember<T, TResult>(Expression<Func<T, TResult>> expression) where T : class => RegisterDecompileableMember(expression.Body.GetMemberInfo());
    public void RegisterDecompileableMembers(Type type, params string[] memberNames) {
      foreach(var tmi in type.GetMembers().Where(mi => memberNames.Contains(mi.Name))) {
        DecompileableMembers.Add(tmi);
      }
    }
    public void RegisterDecompileableMembers<T>(params string[] memberNames) where T : class => RegisterDecompileableMembers(typeof(T), memberNames);
  }

一个示例类:

  public class Person {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string AlternativeFirstName { get; set; }
    public string Name => string.Concat(AlternativeFirstName == string.Empty ? FirstName : AlternativeFirstName, " ", LastName);
  }

一些示例扩展方法:

  public static class CustomComputedMethods {
    public static string PersonName(string firstName, string lastName, string knownAs) => (knownAs ?? firstName).Trim() + " " + lastName.Trim();
    public static long MonthInteger(this DateTime d) => checked(d.Year * 12 + d.Month);
    public static int WholeMonthsBetween(this DateTime d, DateTime maxDate) => (int)(maxDate.MonthInteger() - d.MonthInteger() - (d.Day > maxDate.Day ? 1 : 0));
    public static int WholeYearsBetween(this DateTime d, DateTime maxDate) => d.WholeMonthsBetween(maxDate) / 12;
  }