一、什么是Func委托
Func委托代表有返回类型的委托

二、Func委托定义
查看Func的定义：
`using System.Runtime.CompilerServices;

namespace System
{
//
// 摘要:
// 封装一个方法，该方法具有两个参数，并返回由 TResult 参数指定的类型的值。
//
// 参数:
// arg1:
// 此委托封装的方法的第一个参数。
//
// arg2:
// 此委托封装的方法的第二个参数。
//
// 类型参数:
// T1:
// 此委托封装的方法的第一个参数的类型。
//
// T2:
// 此委托封装的方法的第二个参数的类型。
//
// TResult:
// 此委托封装的方法的返回值类型。
//
// 返回结果:
// 此委托封装的方法的返回值。
[TypeForwardedFrom(“System.Core, Version=3.5.0.0, Culture=Neutral, PublicKeyToken=b77a5c561934e089”)]
public delegate TResult Func<in T1, in T2, out TResult>(T1 arg1, T2 arg2);
}`
你会发现，Func其实就是有多个输出参数并且有返回值的delegate。

3、示例
Func至少0个输入参数，至多16个输入参数，根据返回值泛型返回。必须有返回值，不可void。

Func<int> 表示没有输入参参，返回值为int类型的委托。

Func<object,string,int> 表示传入参数为object, string ，返回值为int类型的委托。

Func<object,string,int> 表示传入参数为object, string， 返回值为int类型的委托。

Func<T1,T2,,T3,int> 表示传入参数为T1,T2,,T3(泛型)，返回值为int类型的委托。

代码示例如下：
`using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FunDemo
{
class Program
{
static void Main(string[] args)
{
// 无参数，只要返回值
Func<int> fun1 = new Func<int>(FunWithNoPara);
int result1= fun1();
Console.WriteLine(result1);
Console.WriteLine(“——————————————“);
Func<int> fun2 = delegate { return 19; };
int result2 = fun2();
Console.WriteLine(result2);
Console.WriteLine(“——————————————“);
Func<int> fun3 = () => { return 3; };
int result3 = fun3();
Console.WriteLine(result3);
Console.WriteLine(“——————————————“);
//有一个参数，一个返回值
Func<int, int> fun4 = new Func<int, int>(FunWithPara);
int result4 = fun4(4);
Console.WriteLine($”这里是一个参数一个返回值的方法，返回值是：{result4}”);
Console.WriteLine(“——————————————“);
// 使用委托
Func<int, string> fun5 = delegate (int i) { return i.ToString(); };
string result5 = fun5(5);
Console.WriteLine($”这里是一个参数一个返回值的委托，返回值是：{result5}”);
Console.WriteLine(“——————————————“);
// 使用匿名委托
Func<int, string> fun6 = (int i) =>
{
return i.ToString();
};
string result6 = fun6(6);
Console.WriteLine($”这里是一个参数一个返回值的匿名委托，返回值是：{result6}”);
Console.WriteLine(“——————————————“);
// 多个输入参数
Func<int, string, bool> fun7 = new Func<int, string, bool>(FunWithMultiPara);
bool result7 = fun7(2, “2”);
Console.WriteLine($”这里是有多个输入参数的方法，返回值是：{result7}”);
Console.WriteLine(“——————————————“);
// 使用委托
Func<int, string, bool> fun8 = delegate (int i, string s)
{
return i.ToString().Equals(s) ? true : false;
};
bool result8 = fun8(2, “abc”);
Console.WriteLine($”这里是有多个输入参数的委托，返回值是：{result8}”);
Console.WriteLine(“——————————————“);
// 使用匿名委托
Func<int, string, bool> fun9 = (int i, string s) =>
{
return i.ToString().Equals(s) ? true : false;
};
bool result9 = fun9(45, “ert”);
Console.WriteLine($”这里是有多个输入参数的匿名委托，返回值是：{result9}”);
Console.ReadKey();

  1.     }
  3.     static int FunWithNoPara()
  4.     {
  5.         return 10;
  6.     }
  8.     static int FunWithPara(int i)
  9.     {
  10.         return i;
  11.     }
  13.     static bool FunWithMultiPara(int i,string s)
  14.     {
  15.         return i.ToString().Equals(s) ? true : false;
  16.     }
  17. }

}`
运行结果：

4、真实示例
在下面的示例中，利用Func委托封装数据库通用访问类。

1、定义BaseModel基类
`using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FunApplication.Model
{
public class BaseModel
{
public int Id { get; set; }
}
}2、定义Student类继承自BaseModel基类using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FunApplication.Model
{
public class Student : BaseModel
{
public string Name { get; set; }

  1.     public int Age { get; set; }
  3.     public int Sex { get; set; }
  5.     public string Email { get; set; }
  6. }

}3、定义数据库访问方法接口using FunApplication.Model;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FunApplication.IDAL
{
public interface IBaseDAL
{
T Query<T>(int id) where T : BaseModel;

  1.     List<T> QueryAll<T>() where T : BaseModel;
  3.     int Insert<T>(T t) where T : BaseModel;
  5.     int Update<T>(T t) where T : BaseModel;
  7.     int Delete<T>(int id) where T : BaseModel;
  8. }

}4、定义属性帮助类using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace FunApplication.AttributeExtend
{
public static class AttributeHelper
{
public static string GetColumnName(this PropertyInfo prop)
{
if (prop.IsDefined(typeof(ColumnAttribute), true))
{
ColumnAttribute attribute = (ColumnAttribute)prop.GetCustomAttribute(typeof(ColumnAttribute), true);
return attribute.GetColumnName();
}
else
{
return prop.Name;
}
}
}
}5、定义ColumnAttribute类using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FunApplication.AttributeExtend
{
[AttributeUsage(AttributeTargets.Property)]
public class ColumnAttribute : Attribute
{
public ColumnAttribute(string name)
{
this._Name = name;
}

  1.     private string _Name = null;
  2.     public string GetColumnName()
  3.     {
  4.         return this._Name;
  5.     }
  6. }

}6、定义数据库方法接口实现类using FunApplication.IDAL;
using FunApplication.Model;
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Reflection;
using FunApplication.AttributeExtend;

namespace FunApplication.DAL
{
public class BaseDAL : IBaseDAL
{
// 数据库链接字符串
private static string strConn = ConfigurationManager.ConnectionStrings[“DbConnection”].ConnectionString;
public int Delete<T>(int id) where T : BaseModel
{
int result = 0;

  1.         using (SqlConnection conn = new SqlConnection(strConn))
  2.         {
  3.             string strSQL = "delete from Student where Id=@Id";
  4.             SqlParameter para = new SqlParameter("Id", id);
  5.             SqlCommand command = new SqlCommand(strSQL, conn);
  6.             command.Parameters.Add(para);
  7.             conn.Open();
  8.             result = command.ExecuteNonQuery();
  9.         }
  10.         return result;
  11.     }
  13.     public int Insert<T>(T t) where T : BaseModel
  14.     {
  15.         int result = 0;
  16.         using (SqlConnection conn = new SqlConnection(strConn))
  17.         {
  18.             Type type = typeof(T);
  19.             var propArray = type.GetProperties().Where(p => p.Name != "Id");
  20.             string strSQL = "insert into Student Values (@Name,@Age,@Sex,@Email) ";
  21.             SqlCommand command = new SqlCommand(strSQL, conn);
  22.             var parameters = propArray.Select(p => new SqlParameter($"@{p.GetColumnName()}", p.GetValue(t) ?? DBNull.Value)).ToArray();
  23.             command.Parameters.AddRange(parameters);
  24.             conn.Open();
  25.             result = command.ExecuteNonQuery();
  26.         }
  27.             return result;
  28.     }
  30.     public T Query<T>(int id) where T : BaseModel
  31.     {
  32.         Type type = typeof(T);
  33.         string columnString = string.Join(",", type.GetProperties().Select(p => $"[{p.GetColumnName()}]"));
  34.         string sql = $"SELECT {columnString} FROM [{type.Name}] WHERE Id={id}";
  35.         T t = null;// (T)Activator.CreateInstance(type);
  37.         using (SqlConnection conn = new SqlConnection(strConn))
  38.         {
  39.             SqlCommand command = new SqlCommand(sql, conn);
  40.             conn.Open();
  41.             SqlDataReader reader = command.ExecuteReader();
  42.             List<T> list = this.ReaderToList<T>(reader);
  43.             t = list.FirstOrDefault();          
  44.         }
  45.         return t;
  46.     }
  48.     public List<T> QueryAll<T>() where T : BaseModel
  49.     {
  50.         Type type = typeof(T);
  51.         string columnString = string.Join(",", type.GetProperties().Select(p => $"[{p.GetColumnName()}]"));
  52.         string sql = $"SELECT {columnString} FROM [{type.Name}] ";
  53.         List<T> list = new List<T>();
  54.         using (SqlConnection conn = new SqlConnection(strConn))
  55.         {
  56.             SqlCommand command = new SqlCommand(sql, conn);
  57.             conn.Open();
  58.             SqlDataReader reader = command.ExecuteReader();
  59.             list = this.ReaderToList<T>(reader);
  60.         }
  61.         return list;
  62.     }
  64.     public int Update<T>(T t) where T : BaseModel
  65.     {
  66.         int result = 0;
  67.         using (SqlConnection conn = new SqlConnection(strConn))
  68.         {
  69.             Type type = typeof(T);
  70.             var propArray = type.GetProperties().Where(p => p.Name != "Id");
  71.             string columnString = string.Join(",", propArray.Select(p => $"[{p.GetColumnName()}]=@{p.GetColumnName()}"));
  72.             var parameters = propArray.Select(p => new SqlParameter($"@{p.GetColumnName()}", p.GetValue(t) ?? DBNull.Value)).ToArray();                
  73.             //必须参数化  否则引号？  或者值里面还有引号
  74.             string strSQL = $"UPDATE [{type.Name}] SET {columnString} WHERE Id={t.Id}";
  75.             SqlCommand command = new SqlCommand(strSQL, conn);
  76.             command.Parameters.AddRange(parameters);
  77.             conn.Open();
  78.             result = command.ExecuteNonQuery();            
  79.         }
  80.         return result;
  81.     }
  83.     private List<T> ReaderToList<T>(SqlDataReader reader) where T : BaseModel
  84.     {
  85.         Type type = typeof(T);
  86.         List<T> list = new List<T>();
  87.         while (reader.Read())//表示有数据  开始读
  88.         {
  89.             T t = (T)Activator.CreateInstance(type);
  90.             foreach (var prop in type.GetProperties())
  91.             {
  92.                 object oValue = reader[prop.GetColumnName()];
  93.                 if (oValue is DBNull)
  94.                     oValue = null;
  95.                 prop.SetValue(t, oValue);//除了guid和枚举
  96.             }
  97.             list.Add(t);
  98.         }
  99.         return list;
  100.     }
  101. }

}7、在Main()方法中调用using FunApplication.DAL;
using FunApplication.Model;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FunApplication
{
class Program
{
static void Main(string[] args)
{

  1.         #region MyRegion
  2.         BaseDAL dal = new BaseDAL();
  3.         // 查询
  4.         Student student = dal.Query<Student>(2);
  5.         Console.WriteLine($"姓名：{student.Name},年龄：{student.Age},Email地址：{student.Email}");
  6.         Console.WriteLine("----------------------------");
  7.         // 查询所有
  8.         List<Student> list = dal.QueryAll<Student>();
  9.         Console.WriteLine($"集合个数：{list.Count}");
  10.         Console.WriteLine("----------------------------");
  11.         // 插入
  12.         Student studentIns = new Student()
  13.         {
  14.             Name = "小明",
  15.             Age = 20,
  16.             Sex = 2,
  17.             Email = "xiaoming@qq.com"
  18.         };
  19.         bool resultIns = dal.Insert<Student>(studentIns) > 0 ? true : false;
  20.         Console.WriteLine($"插入执行结果：{resultIns}");
  21.         Console.WriteLine("----------------------------");
  22.         // 更新
  23.         Student studentUpd = new Student()
  24.         {
  25.             Id = 1,
  26.             Name = "zhangsan1234",
  27.             Age = 20,
  28.             Sex = 2,
  29.             Email = "zhangsan1234@qq.com"
  30.         };
  31.         bool resultUpd = dal.Update<Student>(studentUpd) > 0 ? true : false;
  32.         Console.WriteLine($"更新执行结果：{resultUpd}");
  33.         Console.WriteLine("----------------------------");
  34.         // 删除
  35.         bool resultDel = dal.Delete<Student>(3) > 0 ? true : false;
  36.         Console.WriteLine($"删除执行结果：{resultDel}");
  37.         #endregion
  38.         Console.ReadKey();
  39.     }
  40. }

}8、结果![](https://img.php.cn/upload/image/780/909/496/1647168486223716.jpg)9、优化仔细观察上面步骤7中的代码，你会发现在每个方法中都有重复的代码，打开链接，执行SqlCommand命令，那么这些重复的代码能不能提取到一个公共的方法中进行调用呢？答案是可以的，那就是利用Func委托，看下面优化后的代码：using FunApplication.AttributeExtend;
using FunApplication.IDAL;
using FunApplication.Model;
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace FunApplication.DAL
{
public class FunBaseDAL : IBaseDAL
{
// 数据库链接字符串
private static string strConn = ConfigurationManager.ConnectionStrings[“DbConnection”].ConnectionString;

  1.     public int Delete<T>(int id) where T : BaseModel
  2.     {
  3.         Type type = typeof(T);
  4.         string sql = $"delete from {type.Name} where Id=@Id";
  5.         Func<SqlCommand, int> func = (SqlCommand command) => 
  6.         {               
  7.             SqlParameter para = new SqlParameter("Id", id);
  8.             command.Parameters.Add(para);
  9.             return command.ExecuteNonQuery();
  10.         };
  12.         return ExcuteSql<int>(sql, func);
  13.     }
  15.     public int Insert<T>(T t) where T : BaseModel
  16.     {
  17.         int result = 0;
  18.         Type type = typeof(T);
  19.         var propArray = type.GetProperties().Where(p => p.Name != "Id");
  20.         string strSQL = "insert into Student Values (@Name,@Age,@Sex,@Email) ";
  21.         var parameters = propArray.Select(p => new SqlParameter($"@{p.GetColumnName()}", p.GetValue(t) ?? DBNull.Value)).ToArray();
  22.         Func<SqlCommand, int> func = (SqlCommand command) => 
  23.         {
  24.             command.Parameters.AddRange(parameters);
  25.             return command.ExecuteNonQuery();
  26.         };
  27.         result = ExcuteSql<int>(strSQL, func);
  28.         return result;
  29.     }
  31.     public T Query<T>(int id) where T : BaseModel
  32.     {
  33.         Type type = typeof(T);
  34.         string columnString = string.Join(",", type.GetProperties().Select(p => $"[{p.GetColumnName()}]"));
  35.         string sql = $"SELECT {columnString} FROM [{type.Name}] WHERE Id=@Id";
  36.         T t = null;
  37.         DataTable dt = new DataTable();
  39.         Func<SqlCommand, T> func = (SqlCommand command) => 
  40.         {
  41.             SqlParameter para = new SqlParameter("@Id", id);
  42.             command.Parameters.Add(para);
  43.             SqlDataAdapter adapter = new SqlDataAdapter(command);
  44.             //SqlDataReader reader = command.ExecuteReader();
  45.             //List<T> list = this.ReaderToList<T>(reader);
  46.             adapter.Fill(dt);
  47.             List<T> list = ConvertToList<T>(dt);
  48.             T tResult = list.FirstOrDefault();
  49.             return tResult;
  50.         };
  51.         t = ExcuteSql<T>(sql, func);
  52.         return t;
  53.     }
  55.     public List<T> QueryAll<T>() where T : BaseModel
  56.     {
  57.         Type type = typeof(T);
  58.         string columnString = string.Join(",", type.GetProperties().Select(p => $"[{p.GetColumnName()}]"));
  59.         string sql = $"SELECT {columnString} FROM [{type.Name}] ";
  60.         T t = null;
  62.         Func<SqlCommand, List<T>> func = (SqlCommand command) =>
  63.         {
  64.             SqlDataReader reader = command.ExecuteReader();
  65.             List<T> list = this.ReaderToList<T>(reader);
  66.             return list;
  67.         };
  68.         return ExcuteSql<List<T>>(sql, func);
  69.     }
  71.     public int Update<T>(T t) where T : BaseModel
  72.     {
  73.         int result = 0;
  74.         Type type = typeof(T);
  75.         var propArray = type.GetProperties().Where(p => p.Name != "Id");
  76.         string columnString = string.Join(",", propArray.Select(p => $"[{p.GetColumnName()}]=@{p.GetColumnName()}"));
  77.         var parameters = propArray.Select(p => new SqlParameter($"@{p.GetColumnName()}", p.GetValue(t) ?? DBNull.Value)).ToArray();
  78.         //必须参数化  否则引号？  或者值里面还有引号
  79.         string strSQL = $"UPDATE [{type.Name}] SET {columnString} WHERE Id={t.Id}";
  80.         Func<SqlCommand, int> func = (SqlCommand command) => 
  81.         {
  82.             command.Parameters.AddRange(parameters);
  83.             return command.ExecuteNonQuery();
  84.         };
  85.         result = ExcuteSql<int>(strSQL, func);
  86.         return result;
  87.     }
  90.     //多个方法里面重复对数据库的访问  想通过委托解耦，去掉重复代码
  91.     private T ExcuteSql<T>(string sql, Func<SqlCommand, T> func)
  92.     {
  93.         using (SqlConnection conn = new SqlConnection(strConn))
  94.         {
  95.             using (SqlCommand command = new SqlCommand(sql, conn))
  96.             {
  97.                 conn.Open();
  98.                 SqlTransaction sqlTransaction = conn.BeginTransaction();
  99.                 try
  100.                 {
  101.                     command.Transaction = sqlTransaction;
  102.                     T tResult = func.Invoke(command);
  103.                     sqlTransaction.Commit();
  104.                     return tResult;
  105.                 }
  106.                 catch (Exception ex)
  107.                 {
  108.                     sqlTransaction.Rollback();
  109.                     throw;
  110.                 }
  111.             }
  112.         }
  113.     }
  115.     private List<T> ReaderToList<T>(SqlDataReader reader) where T : BaseModel
  116.     {
  117.         Type type = typeof(T);
  118.         List<T> list = new List<T>();
  119.         while (reader.Read())//表示有数据  开始读
  120.         {
  121.             T t = (T)Activator.CreateInstance(type);
  122.             foreach (var prop in type.GetProperties())
  123.             {
  124.                 object oValue = reader[prop.GetColumnName()];
  125.                 if (oValue is DBNull)
  126.                     oValue = null;
  127.                 prop.SetValue(t, oValue);//除了guid和枚举
  128.             }
  129.             list.Add(t);
  130.         }
  131.         reader.Close();
  132.         return list;
  133.     }
  134. }

}10、在Main()方法中调用using FunApplication.DAL;
using FunApplication.Model;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FunApplication
{
class Program
{
static void Main(string[] args)
{

  1.         #region 传统实现
  2.         //BaseDAL dal = new BaseDAL();
  3.         //// 查询
  4.         //Student student = dal.Query<Student>(2);
  5.         //Console.WriteLine($"姓名：{student.Name},年龄：{student.Age},Email地址：{student.Email}");
  6.         //Console.WriteLine("----------------------------");
  7.         //// 查询所有
  8.         //List<Student> list = dal.QueryAll<Student>();
  9.         //Console.WriteLine($"集合个数：{list.Count}");
  10.         //Console.WriteLine("----------------------------");
  11.         //// 插入
  12.         //Student studentIns = new Student()
  13.         //{
  14.         //    Name = "小明",
  15.         //    Age = 20,
  16.         //    Sex = 2,
  17.         //    Email = "xiaoming@qq.com"
  18.         //};
  19.         //bool resultIns = dal.Insert<Student>(studentIns) > 0 ? true : false;
  20.         //Console.WriteLine($"插入执行结果：{resultIns}");
  21.         //Console.WriteLine("----------------------------");
  22.         //// 更新
  23.         //Student studentUpd = new Student()
  24.         //{
  25.         //    Id = 1,
  26.         //    Name = "zhangsan1234",
  27.         //    Age = 20,
  28.         //    Sex = 2,
  29.         //    Email = "zhangsan1234@qq.com"
  30.         //};
  31.         //bool resultUpd = dal.Update<Student>(studentUpd) > 1 ? true : false;
  32.         //Console.WriteLine($"更新执行结果：{resultUpd}");
  33.         //Console.WriteLine("----------------------------");
  34.         //// 删除
  35.         //bool resultDel = dal.Delete<Student>(5) > 1 ? true : false;
  36.         //Console.WriteLine($"删除执行结果：{resultDel}");
  37.         #endregion
  39.         #region 利用委托
  40.         // 查询
  41.         FunBaseDAL dal = new FunBaseDAL();
  42.         Student student = dal.Query<Student>(1);
  43.         Console.WriteLine($"姓名：{student.Name},年龄：{student.Age},Email地址：{student.Email}");
  44.         Console.WriteLine("----------------------------");
  45.         // 查询所有
  46.         List<Student> list = dal.QueryAll<Student>();
  47.         Console.WriteLine($"集合个数：{list.Count}");
  48.         Console.WriteLine("----------------------------");
  49.         // 插入
  50.         Student studentIns = new Student()
  51.         {
  52.             Name = "tom",
  53.             Age = 19,
  54.             Sex = 1,
  55.             Email = "tom@163.com"
  56.         };
  57.         bool resultIns = dal.Insert<Student>(studentIns) > 0 ? true : false;
  58.         Console.WriteLine($"插入执行结果：{resultIns}");
  59.         Console.WriteLine("----------------------------");
  60.         List<Student> list1 = dal.QueryAll<Student>();
  61.         Console.WriteLine($"插入后集合个数：{list1.Count}");
  62.         Console.WriteLine("----------------------------");
  63.         // 更新
  64.         Student studentUpd = new Student()
  65.         {
  66.             Id = 2,
  67.             Name = "马六123",
  68.             Age = 20,
  69.             Sex = 2,
  70.             Email = "maliu1234@qq.com"
  71.         };
  72.         bool resultUpd = dal.Update<Student>(studentUpd) > 0 ? true : false;
  73.         Console.WriteLine($"更新执行结果：{resultUpd}");
  74.         Console.WriteLine("----------------------------");
  75.         // 删除
  76.         bool resultDel = dal.Delete<Student>(8) > 0 ? true : false;
  77.         Console.WriteLine($"删除执行结果：{resultDel}");
  78.         List<Student> list2 = dal.QueryAll<Student>();
  79.         Console.WriteLine($"删除后集合个数：{list2.Count}");
  80.         Console.WriteLine("----------------------------");
  81.         #endregion
  82.         Console.ReadKey();
  83.     }
  84. }

}`
11、结果

注意
在使用SqlDataReader的时候有时会报错：“已有打开的与此Command相关联的DataReader，必须先将它关闭”。

同时打开两个或循环多个sqldatareader会出现以上错误。因为用的是sqldatareader做数据库的数据读取，sqlconnection开启没有关闭。

一个SqlConnection只能执行一次事务，没用一次必须关闭然后再开启。上面我只用了一次没有关闭，直接开启所以会报错。解决方案有如下两种：

1、其实不用多次打开在开启，那样实现起来很麻烦。直接在连接字符串的后面加上MultipleActiveResultSets=true即可。 配置文件定义如下：
`<?xml version=”1.0” encoding=”utf-8” ?>

<configuration>
<connectionStrings>
<!--<add name="DbConnection" connectionString="Server=.;Initial Catalog=MyDb;User ID=sa;Password=123456;MultipleActiveResultSets=True"/>-->
<!--配置文件里面添加MultipleActiveResultSets=True-->
<add name="DbConnection" connectionString="Server=.;Initial Catalog=MyDb;User ID=sa;Password=123456;MultipleActiveResultSets=True"/>
</connectionStrings>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
</startup>
</configuration>2、使用DataTable在上面是使用的SqlDataReader读取数据，然后转换成List<T>，可以用DataTable代替SqlDataReader，这样就不会报错了，代码如下：/// <summary>
/// 将DataTable转换成List
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="dt"></param>
/// <returns></returns>
private List<T> ConvertToList<T>(DataTable dt) where T:BaseModel
{
Type type = typeof(T);
List<T> list = new List<T>();
foreach(DataRow dr in dt.Rows)
{
T t = (T)Activator.CreateInstance(type);
foreach(PropertyInfo prop in type.GetProperties())
{
object value = dr[prop.GetColumnName()];
if(value is DBNull)
{
value = null;
}
prop.SetValue(t, value);
}
list.Add(t);
}
return list;
}`

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