c# - 在泛型类 C# 中调用类型参数的函数

Question

我们如何调用在泛型基类中定义为抽象的函数。

我有一个通用的

class Class1<T> where T : class, new()

以及从它派生的多个类

Class2: Class1<Class2> 
Class3: Class1<Class3>

泛型类有3个函数

1->接受一个动态对象，并将所有值放入派生对象中的相应属性

2->接受ID，在数据库中查找对应的行，将动态对象传递给func1并返回结果

3-> 一个返回表中所有行的 listall 函数

这是通用代码

public abstract partial class Class1<T> where T : class, new()
{
    public static EntityLayout EntityLayout { get; protected set; }

    [TypeAttributes(TypeAttributes.Options.IsPrimary, TypeAttributes.Options.IsAutoIncrement)]
    /// <summary> Automatically Incremented 64 bit Integer Primary Key
    /// represents the Unique ID of each row in Table </summary>
    public long ID { get; set; }
    /// <summary> Converts the row returned from Database to Object </summary>
    /// <param name="row"></param>
    /// <returns></returns>
    public abstract T GetDetails(dynamic row);
    public static T GetDetails(long ID)
    {
        var row = Shared.SessionWrapper.Current.globaldbcon.QuerySingle("SELECT * FROM [" 
            + EntityLayout.ContainerName + "].["
            + EntityLayout.TableName + "] WHERE ID=@0", ID);
        if (row != null) return GetDetails(row);
        return new T();
    }
    public static List<T> ListAll()
    {
        List<T> result = new List<T>();
        foreach (var row in Shared.SessionWrapper.Current.globaldbcon.Query("SELECT * FROM [" 
            + EntityLayout.ContainerName + "].["
            + EntityLayout.TableName + "]")) result.Add(GetDetails(row));
        return result;
    }
}

一个示例类实现

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using Arinsys.Database;

namespace WebApplication1.Models
{
    [EntityAttributes(EntityAttributes.Options.TestingEnabled)]
    public class Class3 : Class1<Class3>
    {
        static Class3()
        {
            EntityLayout.DisplayName = "Users";
        }
        /// <summary> User ID of the User </summary>
        public long UID { get; set; }
        /// <summary> User ID of the User if defined in Universal Data Store  </summary>
        public long UDSID { get; set; }
        /// <summary> Login ID of User </summary>
        public string LoginID { get; set; }
        /// <summary> Registered email of the user. If not set will be set same as LoginID </summary>
        public string Registeredemail { get; set; }
        [TypeAttributes(TypeAttributes.Options.IsPassword)]
        /// <summary> Password of user </summary>
        public string Password { get; set; }
        /// <summary> A Unique Security Stamp used for activation/deactivation of account or similar intense tasks </summary>
        public string SecurityStamp { get; set; }
        /// <summary> Timezone ID of the Default Timezone of User </summary>
        public string DefaultTimezone { get; set; }
        /// <summary> Current Status of User </summary>
        public string CurrentStatus { get; set; }
        /// <summary> Discriminator which defines the type of user in multi-user heirarchy scenario </summary>
        public string UserType { get; set; }
        /// <summary> Number of failed login attempts in total or same session depending upon configuration. Resets after Successful Login </summary>
        public short FailedAttempts { get; set; }
        /// <summary> Date Time of Last Failed Login Attempt in UTC </summary>
        public DateTime LastFailedAttempt { get; set; }
        /// <summary> Date Time of Last Successful Login in UTC </summary>
        public DateTime LastLogin { get; set; }
        /// <summary> Creation Date of User Account in UTC </summary>
        public DateTime CreationDate { get; set; }
        public override Class3 GetDetails(dynamic row)
        {
            Class3 result = new Class3();
            if (row != null)
            {
                result.ID = Convert.ToInt64(row.ID);
                result.UID = Convert.ToInt64(row.UID);
                result.UDSID = Convert.ToInt64(row.UDSID);
                result.UserType = row.UserType;
                result.LoginID = row.LoginID;
                result.Password = row.Password;
                result.Registeredemail = row.Registeredemail;
                result.SecurityStamp = row.SecurityStamp;
                result.DefaultTimezone = row.DefaultTimezone;
                result.CurrentStatus = row.CurrentStatus;
                result.FailedAttempts = Convert.ToInt16(row.FailedAttempts);
                result.LastFailedAttempt = Convert.ToDateTime(row.LastFailedAttempt);
                result.LastLogin = Convert.ToDateTime(row.LastLogin);
                result.CreationDate = Convert.ToDateTime(row.CreationDate);
            }
            return result;
        }
    }
}

发帖前到处找答案已经两周了，没找到解决办法。

我想要的只是 ListAll 函数应该调用第一个函数。因为它是抽象定义的，所以我确信派生类必须有一个实现(即使它可能只是抛出 NotImplementException，但实现是有保证的)

我首先通过反射在泛型类本身中定义了第一个函数的实现。虽然这行得通，但速度非常慢，通过在 Controller Action 开始/结束时启动/停止秒表来进行性能基准测试，仅 100 行就花费了大约 35 秒，因此它肯定不适合生产使用。

注意事项

• 静态不能定义为抽象
• 无法从静态上下文访问实例成员
• 由于性能问题不能使用反射

我想可能的解决方案最接近(但我无法理解如何在我的案例中使用它们)

• 将所有方法转换为实例方法并使用单例
• 使用接口(interface)
• 在派生类中定义一个静态方法并假设它会存在于所有类中，如果我这样做那么在这种情况下如何访问 T 上的静态方法

我想要实现的是 ListAll 函数应该调用接受动态对象的第一个函数。

一些非常接近的问题是这些，但没有一个能解决我的查询。

Stack Overflow Q1 Stack Overflow Q2 Stack Overflow Q3

Answer 1

看起来设计应该是这样的

public abstract partial class Class1<T> where T : Class1<T>, new()
{
    protected abstract void Load(dynamic row);

    private static T GetItem(dynamic row)
    {
        var item = new T();
        if (row != null)
            item.Load(row);
        return item;        
    }

    public static T GetDetails(long ID)
    {
        var row = Shared.SessionWrapper.Current.globaldbcon.QuerySingle("SELECT * FROM [" 
            + EntityLayout.ContainerName + "].["
            + EntityLayout.TableName + "] WHERE ID=@0", ID);
        return GetItem(row);
    }

    public static List<T> ListAll()
    {
        List<T> result = new List<T>();
        foreach (var row in Shared.SessionWrapper.Current.globaldbcon.Query("SELECT * FROM [" 
            + EntityLayout.ContainerName + "].["
            + EntityLayout.TableName + "]")) result.Add(GetItem(row));
        return result;
    }
}

和示例实现

public class Class3 : Class1<Class3>    {
{
    // ...
    protected override void Load(dynamic row)
    {
        // No need to check for null, it is enforced by the base class
        ID = Convert.ToInt64(row.ID);
        UID = Convert.ToInt64(row.UID);
        // ...
    }
}

基本上你探索Curiously recurring template pattern .NET 泛型类约束 (T : Class1<T>) 支持以确保派生类包含抽象 Load方法，而 new T()部分由 new() 强制执行约束条件。