ADO.NET基本操作（CRUD、Procedure、Transaction）

模型沿用上篇博客所提到的学生、教师、课程，以详细的代码进行演示。

增删改查

添加学生、教师、课程

using System.Data.SqlClient;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.ConnectionString = "server=.;database=school;uid=sa;pwd=123456;";
                conn.Open();

                string insertStudent = "insert into 学生表(studentname,gender,birthday) values('张三','" + (int)Gender.Male + "','" + DateTime.Parse("1989-6-1") + "')";
                SqlCommand cmd = new SqlCommand(insertStudent, conn);
                cmd.ExecuteNonQuery();
                Console.WriteLine("添加学生成功");

                string insertTeacher = "insert into 教师表(teachername,gender,birthday) values('教师1','" + (int)Gender.Female + "','" + DateTime.Parse("1974-8-1") + "')";
                cmd = new SqlCommand(insertTeacher, conn);
                cmd.ExecuteNonQuery();
                Console.WriteLine("添加教师成功");

                string[] insertSubjects = new string[]
                {
                    "insert into 课程表(subjectname) values('语文')",
                    "insert into 课程表(subjectname) values('数学')",
                    "insert into 课程表(subjectname) values('英语')",
                };

                for (int i = 0; i < insertSubjects.Length; i++)
                {
                    cmd = new SqlCommand(insertSubjects[i], conn);
                    cmd.ExecuteNonQuery();
                }

                Console.WriteLine("添加课程成功");
            }
        }
    }

    public enum Gender
    {
        Female, Male
    }
}

修改学生、教师

using System.Data.SqlClient;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.ConnectionString = "server=.;database=school;uid=sa;pwd=123456;";
                conn.Open();

                string modifyStudent = "update 学生表 set birthday='" + DateTime.Parse("1989-01-01") + "' where studentname = '张三'";
                SqlCommand cmd = new SqlCommand(modifyStudent, conn);
                cmd.ExecuteNonQuery();
                Console.WriteLine("修改学生成功");

                string modifyTeacher = "update 教师表 set teachername = '教师' where teachername = '教师1'";
                cmd = new SqlCommand(modifyTeacher, conn);
                cmd.ExecuteNonQuery();
                Console.WriteLine("修改教师成功");
            }
        }
    }
}

删除学生、教师

using System.Data.SqlClient;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.ConnectionString = "server=.;database=school;uid=sa;pwd=123456;";
                conn.Open();

                string deleteStudent = "delete from 学生表 where studentname = '张三'";
                SqlCommand cmd = new SqlCommand(deleteStudent, conn);
                cmd.ExecuteNonQuery();
                Console.WriteLine("删除学生成功");

                string deleteTeacher = "delete from 教师表 where teachername = '教师'";
                cmd = new SqlCommand(deleteTeacher, conn);
                cmd.ExecuteNonQuery();
                Console.WriteLine("删除教师成功");
            }
        }
    }
}

添加教师授课信息

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.ConnectionString = "server=.;database=school;uid=sa;pwd=123456;";
                conn.Open();

                string teachername = "教师1", subjectname = "英语";
                string insert = @"declare @teacherid int,@subjectid int
set @teacherid = (select teacherid from 教师表 where teachername = '" + teachername + "')"
+ "set @subjectid = (select subjectid from 课程表 where subjectname = '" + subjectname + "')"
+ "insert into 教师课程表(teacherid, subjectid)"
+ "values(@teacherid, @subjectid)";
                SqlCommand cmd = new SqlCommand(insert, conn);
                cmd.ExecuteNonQuery();
                Console.WriteLine("添加教师课程成功");
            }
        }
    }

    public enum Gender
    {
        Female, Male
    }
}

可以看到，代码中应用了嵌入T-SQL的方式，实现了给教师1添加英语教课的信息。

如果想查看教师教哪些课程，可以使用如下代码：

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.ConnectionString = "server=.;database=school;uid=sa;pwd=123456;";
                conn.Open();

                string query = @"select b.teachername,c.subjectname from 教师课程表 a 
inner join 教师表 b on a.teacherid = b.teacherid
inner join 课程表 c on a.subjectid = c.subjectid";
                SqlCommand cmd = new SqlCommand(query, conn);
                SqlDataAdapter sda = new SqlDataAdapter(cmd);
                DataSet ds = new DataSet();
                sda.Fill(ds);

                if (ds != null && ds.Tables.Count > 0)
                {
                    foreach (DataRow dr in ds.Tables[0].Rows)
                    {
                        Console.WriteLine("{0}授课课程名：{1}",dr["teachername"],dr["subjectname"]);
                    }
                }
            }
        }
    }
}

添加学生选课信息

原理与添加教师授课信息一样，代码不再重复。不过这里稍微讲述一下原理。

ADO.NET执行的就是SQL，这个SQL可以是T-SQL，也可以是普通的SQL语句。添加教师授课信息执行的就是T-SQL。实际上，我们在实际开发当中，一般都会先在SQL Server

Management Studio开发工具中执行一下T-SQL，执行通过后再复制到ADO.NET程序中。

declare @studentid int,@subjectid int
set @studentid = (select studentid from 学生表 where studentname = '张三')
set @subjectid = (select subjectid from 课程表 where subjectname = '数学')
insert into 学生课程表(subjectid, studentid) values(@subjectid,@studentid)

存储过程

存储过程的优点至少有下面两点：

1、  安全性高

相比C#后台代码被反编译，甚至浏览器端完全暴露的JS代码来说，数据库存储过程代码在数据库中，不容易被SQL注入（除非本身存储过程代码写的有问题），安全性高。

2、  执行效率高

首先节约了网络传输的时间（传输的是存储过程名，而不是长长的SQL语句）。其次存储过程代码都是经过数据库预编译的，节约了数据库编译SQL代码的时间，直接执行存储过程。

示例：通过存储过程来添加课程信息

if exists (select * from sysobjects where name = 'add_subjects')
drop procedure add_subjects
go
create procedure add_subjects
@subjectname varchar(20),--输入参数
@flag int output --输出参数
as
begin
    insert into 课程表(subjectname) values(@subjectname);
    select @flag=@@ROWCOUNT --输出参数的值
    return @flag--存储过程返回值
end

需要说明的是，这个存储过程add_subjects有两个参数，分别为输入参数subjectname、输出参数flag。最后存储过程还有一个return @flag，也就是存储过程本身有一个返回值。

然后在C#代码中调用这个存储过程：

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.ConnectionString = "server=.;database=school;uid=sa;pwd=123456;";
                conn.Open();

                SqlCommand cmd = new SqlCommand("add_subjects", conn);

                SqlParameter[] parameters = new SqlParameter[]
                {
                    new SqlParameter() { ParameterName="@subjectname", Value="历史", Size=20, Direction = ParameterDirection.Input },
                    new SqlParameter() { ParameterName="@flag", Size = 4, Direction = ParameterDirection.Output }
                };
                cmd.Parameters.AddRange(parameters);
                cmd.CommandType = CommandType.StoredProcedure;
                int effectRows = cmd.ExecuteNonQuery();
                if (effectRows > 0)
                    Console.WriteLine("课程添加成功，输出参数结果：" + parameters[1].Value);
            }
        }
    }
}

Parameters[1].Value对应存储过程输出参数@flag的值，effectRows对应存储过程的返回值。

事务

如果在执行数据库SQL操作时，不能保证多条SQL语句要么一起执行，要么不一起执行，就会造成数据不一致的情况。典型的例子就是银行转账，A转账给B，如果A少了100元钱，但这时程序发生了错误，导致B并没有收到100元钱，显然这时候就需要一种机制保证这个转账的操作是一个整体。数据库提出了事务这一概念来解决这一问题。

示例：一次性添加多门课程以及教师的信息

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.ConnectionString = "server=.;database=school;uid=sa;pwd=123456;";
                conn.Open();

                using (SqlCommand cmd = new SqlCommand() { Connection = conn })
                {
                    using (SqlTransaction trans = conn.BeginTransaction())
                    {
                        cmd.Transaction = trans;
                        try
                        {
                            string[] strs = new string[]
                            {
                                "insert into 课程表(subjectname) values('C#')",
                                "insert into 课程表(subjectname) values('.NET')",
                                "insert into 课程表(subjectname) values('ADO.NET')",
                                "insert into 教师表(teachername,gender,birthday) values('教师2','"+(int)Gender.Male+"','"+DateTime.Parse("1978-4-12")+"')",
                            };
                            foreach (string str in strs)
                            {
                                cmd.CommandText = str;
                                cmd.ExecuteNonQuery();
                            }
                            trans.Commit();
                            Console.WriteLine("事务执行成功");
                        }
                        catch (Exception ex)
                        {
                            trans.Rollback();
                            Console.WriteLine("事务执行失败，错误信息：" + ex.Message);
                        }
                    }
                }
            }
        }
    }
    public enum Gender { Female, Male }
}