对 IQueryable OfType<> 的反思

Question

我的 Entity Framework 上下文中有一个 Employees DbSet，可以查询为：

IQueryable employees = _context.Employees;

想法是使用反射执行以下方法：

var result= _context.Employees.OfType<PaidEmployee>()

我扩展了 Employee 对象以创建一个 PaidEmployee class。我想使用 REFLECTION 查询 PaidEmployee 的上下文。

Assembly asm = Assembly.LoadFrom("MyModel.dll");
Type t = asm.GetType("PaidEmployee");

var ofType = typeof(Queryable).GetMethod("OfType",
                     BindingFlags.Static | BindingFlags.Public);

var methodinfo = ofType.MakeGenericMethod(t);

var obj = methodinfo.Invoke(employees , null);

当我执行上面的代码时，出现错误：

System.Reflection.TargetParameterCountException was unhandled by user code HResult=-2147352562 Message=Parameter count mismatch.
Source=mscorlib StackTrace: at System.Reflection.RuntimeMethodInfo.InvokeArgumentsCheck(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters) at Tests.test_dynamic.TestMethod2() in e:\Projects\Tests\test_dynamic.cs:line 54 InnerException:

Answer 1

尝试

var obj = methodinfo.Invoke(null, new[] { employees });

OfType是静态的，所以nullobj（[=14=的第一个参数]，即方法使用对象的实例）！

对 IQueryable OfType<> 的反思

Reflection on IQueryable OfType<>

c#

generics

reflection

entity-framework