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：
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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：
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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();
}
static int FunWithNoPara() { return 10; }
static int FunWithPara(int i) { return i; }
static bool FunWithMultiPara(int i,string s) { return i.ToString().Equals(s) ? true : false; } } } |
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
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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
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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; }
public int Age { get; set; }
public int Sex { get; set; }
public string Email { get; set; } } } |
3、定义数据库访问方法接口
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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;
List<T> QueryAll<T>() where T : BaseModel;
int Insert<T>(T t) where T : BaseModel;
int Update<T>(T t) where T : BaseModel;
int Delete<T>(int id) where T : BaseModel; } } |
4、定义属性帮助类
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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
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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; }
private string _Name = null; public string GetColumnName() { return this._Name; } } } |
6、定义数据库方法接口实现类
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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;
using (SqlConnection conn = new SqlConnection(strConn)) { string strSQL = "delete from Student where Id=@Id"; SqlParameter para = new SqlParameter("Id", id); SqlCommand command = new SqlCommand(strSQL, conn); command.Parameters.Add(para); conn.Open(); result = command.ExecuteNonQuery(); } return result; }
public int Insert<T>(T t) where T : BaseModel { int result = 0; using (SqlConnection conn = new SqlConnection(strConn)) { Type type = typeof(T); var propArray = type.GetProperties().Where(p => p.Name != "Id"); string strSQL = "insert into Student Values (@Name,@Age,@Sex,@Email) "; SqlCommand command = new SqlCommand(strSQL, conn); var parameters = propArray.Select(p => new SqlParameter($"@{p.GetColumnName()}", p.GetValue(t) ?? DBNull.Value)).ToArray(); command.Parameters.AddRange(parameters); conn.Open(); result = command.ExecuteNonQuery(); } return result; }
public T Query<T>(int id) where T : BaseModel { Type type = typeof(T); string columnString = string.Join(",", type.GetProperties().Select(p => $"[{p.GetColumnName()}]")); string sql = $"SELECT {columnString} FROM [{type.Name}] WHERE Id={id}"; T t = null;// (T)Activator.CreateInstance(type);
using (SqlConnection conn = new SqlConnection(strConn)) { SqlCommand command = new SqlCommand(sql, conn); conn.Open(); SqlDataReader reader = command.ExecuteReader(); List<T> list = this.ReaderToList<T>(reader); t = list.FirstOrDefault(); } return t; }
public List<T> QueryAll<T>() where T : BaseModel { Type type = typeof(T); string columnString = string.Join(",", type.GetProperties().Select(p => $"[{p.GetColumnName()}]")); string sql = $"SELECT {columnString} FROM [{type.Name}] "; List<T> list = new List<T>(); using (SqlConnection conn = new SqlConnection(strConn)) { SqlCommand command = new SqlCommand(sql, conn); conn.Open(); SqlDataReader reader = command.ExecuteReader(); list = this.ReaderToList<T>(reader); } return list; }
public int Update<T>(T t) where T : BaseModel { int result = 0; using (SqlConnection conn = new SqlConnection(strConn)) { Type type = typeof(T); var propArray = type.GetProperties().Where(p => p.Name != "Id"); string columnString = string.Join(",", propArray.Select(p => $"[{p.GetColumnName()}]=@{p.GetColumnName()}")); var parameters = propArray.Select(p => new SqlParameter($"@{p.GetColumnName()}", p.GetValue(t) ?? DBNull.Value)).ToArray(); //必须参数化 否则引号？ 或者值里面还有引号 string strSQL = $"UPDATE [{type.Name}] SET {columnString} WHERE Id={t.Id}"; SqlCommand command = new SqlCommand(strSQL, conn); command.Parameters.AddRange(parameters); conn.Open(); result = command.ExecuteNonQuery(); } return result; }
private List<T> ReaderToList<T>(SqlDataReader reader) where T : BaseModel { Type type = typeof(T); List<T> list = new List<T>(); while (reader.Read())//表示有数据 开始读 { T t = (T)Activator.CreateInstance(type); foreach (var prop in type.GetProperties()) { object oValue = reader[prop.GetColumnName()]; if (oValue is DBNull) oValue = null; prop.SetValue(t, oValue);//除了guid和枚举 } list.Add(t); } return list; } } } |
7、在Main()方法中调用
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using FunApplication.DAL; using FunApplication.Model; using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;
namespace FunApplication { class Program { static void Main(string[] args) { #region MyRegion BaseDAL dal = new BaseDAL(); // 查询 Student student = dal.Query<Student>(2); Console.WriteLine($"姓名：{student.Name},年龄：{student.Age},Email地址：{student.Email}"); Console.WriteLine("----------------------------"); // 查询所有 List<Student> list = dal.QueryAll<Student>(); Console.WriteLine($"集合个数：{list.Count}"); Console.WriteLine("----------------------------"); // 插入 Student studentIns = new Student() { Name = "小明", Age = 20, Sex = 2, Email = "xiaoming@qq.com" }; bool resultIns = dal.Insert<Student>(studentIns) > 0 ? true : false; Console.WriteLine($"插入执行结果：{resultIns}"); Console.WriteLine("----------------------------"); // 更新 Student studentUpd = new Student() { Id = 1, Name = "zhangsan1234", Age = 20, Sex = 2, Email = "zhangsan1234@qq.com" }; bool resultUpd = dal.Update<Student>(studentUpd) > 0 ? true : false; Console.WriteLine($"更新执行结果：{resultUpd}"); Console.WriteLine("----------------------------"); // 删除 bool resultDel = dal.Delete<Student>(3) > 0 ? true : false; Console.WriteLine($"删除执行结果：{resultDel}"); #endregion Console.ReadKey(); } } } |
8、结果
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：
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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;
public int Delete<T>(int id) where T : BaseModel { Type type = typeof(T); string sql = $"delete from {type.Name} where Id=@Id"; Func<SqlCommand, int> func = (SqlCommand command) => { SqlParameter para = new SqlParameter("Id", id); command.Parameters.Add(para); return command.ExecuteNonQuery(); };
return ExcuteSql<int>(sql, func); }
public int Insert<T>(T t) where T : BaseModel { int result = 0; Type type = typeof(T); var propArray = type.GetProperties().Where(p => p.Name != "Id"); string strSQL = "insert into Student Values (@Name,@Age,@Sex,@Email) "; var parameters = propArray.Select(p => new SqlParameter($"@{p.GetColumnName()}", p.GetValue(t) ?? DBNull.Value)).ToArray(); Func<SqlCommand, int> func = (SqlCommand command) => { command.Parameters.AddRange(parameters); return command.ExecuteNonQuery(); }; result = ExcuteSql<int>(strSQL, func); return result; }
public T Query<T>(int id) where T : BaseModel { Type type = typeof(T); string columnString = string.Join(",", type.GetProperties().Select(p => $"[{p.GetColumnName()}]")); string sql = $"SELECT {columnString} FROM [{type.Name}] WHERE Id=@Id"; T t = null; DataTable dt = new DataTable();
Func<SqlCommand, T> func = (SqlCommand command) => { SqlParameter para = new SqlParameter("@Id", id); command.Parameters.Add(para); SqlDataAdapter adapter = new SqlDataAdapter(command); //SqlDataReader reader = command.ExecuteReader(); //List<T> list = this.ReaderToList<T>(reader); adapter.Fill(dt); List<T> list = ConvertToList<T>(dt); T tResult = list.FirstOrDefault(); return tResult; }; t = ExcuteSql<T>(sql, func); return t; }
public List<T> QueryAll<T>() where T : BaseModel { Type type = typeof(T); string columnString = string.Join(",", type.GetProperties().Select(p => $"[{p.GetColumnName()}]")); string sql = $"SELECT {columnString} FROM [{type.Name}] "; T t = null;
Func<SqlCommand, List<T>> func = (SqlCommand command) => { SqlDataReader reader = command.ExecuteReader(); List<T> list = this.ReaderToList<T>(reader); return list; }; return ExcuteSql<List<T>>(sql, func); }
public int Update<T>(T t) where T : BaseModel { int result = 0; Type type = typeof(T); var propArray = type.GetProperties().Where(p => p.Name != "Id"); string columnString = string.Join(",", propArray.Select(p => $"[{p.GetColumnName()}]=@{p.GetColumnName()}")); var parameters = propArray.Select(p => new SqlParameter($"@{p.GetColumnName()}", p.GetValue(t) ?? DBNull.Value)).ToArray(); //必须参数化 否则引号？ 或者值里面还有引号 string strSQL = $"UPDATE [{type.Name}] SET {columnString} WHERE Id={t.Id}"; Func<SqlCommand, int> func = (SqlCommand command) => { command.Parameters.AddRange(parameters); return command.ExecuteNonQuery(); }; result = ExcuteSql<int>(strSQL, func); return result; }
//多个方法里面重复对数据库的访问 想通过委托解耦，去掉重复代码 private T ExcuteSql<T>(string sql, Func<SqlCommand, T> func) { using (SqlConnection conn = new SqlConnection(strConn)) { using (SqlCommand command = new SqlCommand(sql, conn)) { conn.Open(); SqlTransaction sqlTransaction = conn.BeginTransaction(); try { command.Transaction = sqlTransaction; T tResult = func.Invoke(command); sqlTransaction.Commit(); return tResult; } catch (Exception ex) { sqlTransaction.Rollback(); throw; } } } }
private List<T> ReaderToList<T>(SqlDataReader reader) where T : BaseModel { Type type = typeof(T); List<T> list = new List<T>(); while (reader.Read())//表示有数据 开始读 { T t = (T)Activator.CreateInstance(type); foreach (var prop in type.GetProperties()) { object oValue = reader[prop.GetColumnName()]; if (oValue is DBNull) oValue = null; prop.SetValue(t, oValue);//除了guid和枚举 } list.Add(t); } reader.Close(); return list; } } } |
10、在Main()方法中调用
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using FunApplication.DAL; using FunApplication.Model; using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;
namespace FunApplication { class Program { static void Main(string[] args) { #region 传统实现 //BaseDAL dal = new BaseDAL(); //// 查询 //Student student = dal.Query<Student>(2); //Console.WriteLine($"姓名：{student.Name},年龄：{student.Age},Email地址：{student.Email}"); //Console.WriteLine("----------------------------"); //// 查询所有 //List<Student> list = dal.QueryAll<Student>(); //Console.WriteLine($"集合个数：{list.Count}"); //Console.WriteLine("----------------------------"); //// 插入 //Student studentIns = new Student() //{ // Name = "小明", // Age = 20, // Sex = 2, // Email = "xiaoming@qq.com" //}; //bool resultIns = dal.Insert<Student>(studentIns) > 0 ? true : false; //Console.WriteLine($"插入执行结果：{resultIns}"); //Console.WriteLine("----------------------------"); //// 更新 //Student studentUpd = new Student() //{ // Id = 1, // Name = "zhangsan1234", // Age = 20, // Sex = 2, // Email = "zhangsan1234@qq.com" //}; //bool resultUpd = dal.Update<Student>(studentUpd) > 1 ? true : false; //Console.WriteLine($"更新执行结果：{resultUpd}"); //Console.WriteLine("----------------------------"); //// 删除 //bool resultDel = dal.Delete<Student>(5) > 1 ? true : false; //Console.WriteLine($"删除执行结果：{resultDel}"); #endregion
#region 利用委托 // 查询 FunBaseDAL dal = new FunBaseDAL(); Student student = dal.Query<Student>(1); Console.WriteLine($"姓名：{student.Name},年龄：{student.Age},Email地址：{student.Email}"); Console.WriteLine("----------------------------"); // 查询所有 List<Student> list = dal.QueryAll<Student>(); Console.WriteLine($"集合个数：{list.Count}"); Console.WriteLine("----------------------------"); // 插入 Student studentIns = new Student() { Name = "tom", Age = 19, Sex = 1, Email = "tom@163.com" }; bool resultIns = dal.Insert<Student>(studentIns) > 0 ? true : false; Console.WriteLine($"插入执行结果：{resultIns}"); Console.WriteLine("----------------------------"); List<Student> list1 = dal.QueryAll<Student>(); Console.WriteLine($"插入后集合个数：{list1.Count}"); Console.WriteLine("----------------------------"); // 更新 Student studentUpd = new Student() { Id = 2, Name = "马六123", Age = 20, Sex = 2, Email = "maliu1234@qq.com" }; bool resultUpd = dal.Update<Student>(studentUpd) > 0 ? true : false; Console.WriteLine($"更新执行结果：{resultUpd}"); Console.WriteLine("----------------------------"); // 删除 bool resultDel = dal.Delete<Student>(8) > 0 ? true : false; Console.WriteLine($"删除执行结果：{resultDel}"); List<Student> list2 = dal.QueryAll<Student>(); Console.WriteLine($"删除后集合个数：{list2.Count}"); Console.WriteLine("----------------------------"); #endregion Console.ReadKey(); } } } |
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：
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<?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：
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/// <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; } |
