如何轉換 Linq 表達式<func<object,object,bool> &gt; 表達<func<t1,t2,bool> &gt; </func<t1,t2,bool></func<object,object,bool>

Question

我正在嘗試將 ORM 的所有關聯/連接存儲在列表中

public class OrmJoin{
  public Type Type1 { get; set;}
  public Type Type2 { get; set;}
  public bool IsRequired { get; set;}
  public Expression<Func<object, object, bool>> Predicate { get; set;}
}

然后我可以循環遍歷此列表並將 Predicate 屬性轉換為Expression<Func<T1,T2,bool>>通過使用typeof(Type1)和typeof(Type2)以某種方式將前 2 個對象表達式參數轉換為類型化參數嗎？

Answer 1

以下是您的操作方法：

public class OrmJoin
{
    // ...

    public Expression AsTyped()
    {
        var parameters = new[] { Type1, Type2 }
            .Select(Expression.Parameter)
            .ToArray();
        var castedParameters = parameters
            .Select(x => Expression.Convert(x, typeof(object)))
            .ToArray();
        var invocation = Expression.Invoke(Predicate, castedParameters);

        return Expression.Lambda(invocation, parameters);
    }
    public Expression<Func<T1, T2, bool>> AsTyped<T1, T2>() => (Expression<Func<T1, T2, bool>>)AsTyped();
}

---

void Main()
{
    var test = new OrmJoin { Type1 = typeof(string), Type2 = typeof(int), Predicate = (a,b) => Test(a,b) };
    var compiled = test.AsTyped<string, int>().Compile();

    Console.WriteLine(compiled.Invoke("asd", 312));
}
bool Test(object a, object b)
{
    Console.WriteLine(a);
    Console.WriteLine(b);
    return true;
}