LinQ和ADO.Net增删改查 备忘

是否些倦了 SqlConnection conn=new SqlConnection();一系列繁冗的代码? 来试试Linq吧

查:

using System.Data.SqlClient;

namespace obj
{
    public class StudentDA
    {
        SqlConnection conn;
        SqlCommand cmd;
        public StudentDA()
        {
            conn = new SqlConnection("server=.;database=aaaaa;user=sa;pwd=123");
            cmd = conn.CreateCommand();
        }
        public List<type> Search()
    {
        List<type> data = null;
        cmd.CommandText = "select Student.sno,sname,Course.Cno,cname,tname,degree from Score join  Student on student.sno=score.sno join  course  on course.Cno=score.Cno join teacher  on teacher.tno=course.tno";
        cmd.Parameters.Clear();
        conn.Open();
        SqlDataReader dr = cmd.ExecuteReader();
        if (dr.HasRows)
        {
            data = new List<type>();
            while (dr.Read())
            {
                type a = new type();
                a.Sno = dr["Sno"].ToString();
                a.Sname = dr["Sname"].ToString();
                a.Cno = dr["Cno"].ToString();
                a.Cname = dr["Cname"].ToString();
                a.Tname = dr["Tname"].ToString();
                a.Degree = dr["Degree"].ToString();
                data.Add(a);
            }
        }
        cmd.Dispose();
        conn.Close();
        return data;
    }

 public type Ss(string id,string od)  //两个参数值,数出 type类型结果
        {
            type Ss = null;
            cmd.CommandText = "select Student.sno,sname,Course.Cno,cname,tname,degree from Score join  Student on student.sno=score.sno join  course  on course.Cno=score.Cno join teacher  on teacher.tno=course.tno where course.cno=@Cno and student.sno=@Sno";
            cmd.Parameters.Clear();
            cmd.Parameters.Add("@Cno", od);
            cmd.Parameters.Add("@Sno", id);
            conn.Open();
            SqlDataReader dr =cmd.ExecuteReader();
            if(dr.Read())
            {
                Ss = new type();
                Ss.Sno = dr["Sno"].ToString();
                Ss.Sname = dr["Sname"].ToString();
                Ss.Cno = dr["Cno"].ToString();
                Ss.Cname = dr["Cname"].ToString();
                Ss.Tname = dr["Tname"].ToString();
                Ss.Degree = dr["Degree"].ToString();
            }
            cmd.Dispose();
            conn.Close();
            return Ss;
        }

LinQ:

需要先建一个 LinQ to SQL类,在服务器资源管理器中建立新的连接 然后设置数据库地址和登录设置,然后选取数据库

确定建好类文件 .dbml 选择数据空中的表拖入,系统自动会生成以列名相同的类,

然后见一个类 来写方法

 public class InfoBF
    {
        private MyDBDataContext _Context = new MyDBDataContext();
        public List<Info> Select()  //查询info类型的所有
        {
            return _Context.Info.ToList();
        }
        public Info Select(string code) //一个输入参数返回 info类型
        {
            var query = _Context.Info.Where(p=>p.Code == code);  //lambda表达式
            if (query.Count() > )
            {
                return query.First();   //取第一条
            }
            return null;
        }

增:

 public void Insert(Student stu)
        {
            cmd.CommandText = "insert into student values(@Sno,@Sname,@Ssex,@Sbirthday,@Class)";
            cmd.Parameters.Clear();
            cmd.Parameters.Add("@Sno", stu.Sno);
            cmd.Parameters.Add("@Sname", stu.Sname);
            cmd.Parameters.Add("@Ssex", stu.Ssex);
            cmd.Parameters.Add("@Sbirthday", stu.Sbirthday);
            cmd.Parameters.Add("@Class", stu.Class);
            conn.Open();
            cmd.ExecuteNonQuery();
            conn.Close();
        }

LinQ:

   public void Insert(string code, string name, bool sex, string nation, DateTime birthday)
        {
            Info data = new Info
            {
                Code = code,
                Name = name,
                Sex = sex,
                Nation = nation,
                Birthday = birthday
            };
            _Context.Info.InsertOnSubmit(data);
            _Context.SubmitChanges();
        }
 

 public void Insert(Info data)
        {
            _Context.Info.InsertOnSubmit(data);
            _Context.SubmitChanges();
        }

改:

 public void Update(type data)
        {
            cmd.CommandText = "update student set sname=@Sname where sno=@Sno;update score set degree=@Degree where cno=@Cno and sno=@Sno;update course set cname=@Cname where cno=@Cno;update teacher set tname=@Tname where tno =(select tno from course where cno=@Cno)";
            cmd.Parameters.Add("@Sno", data.Sno);
            cmd.Parameters.Add("@Sname", data.Sname);
            cmd.Parameters.Add("@Cno", data.Cno);
            cmd.Parameters.Add("@Cname", data.Cname);
            cmd.Parameters.Add("@Tname", data.Tname);
            cmd.Parameters.Add("@Degree", data.Degree);
            conn.Open();
            cmd.ExecuteNonQuery();
            conn.Close();
        }

LinQ:

 public void Update(string code, string name, bool sex, string nation, DateTime birthday)
        {
            var query = _Context.Info.Where(p => p.Code == code);
            if (query.Count() > )
            {
                Info data = query.First();
                data.Name = name;
                data.Sex = sex;
                data.Nation = nation;
                data.Birthday = birthday;
                _Context.SubmitChanges();
            }
        }

删:

 public void Delete(string id)
        {
            cmd.CommandText = "";
            cmd.Parameters.Clear();
            cmd.Parameters.Add("@id", id);
            conn.Open();
            cmd.ExecuteNonQuery();
            conn.Close();
        }

LinQ:

 public void Delete(string code)
        {
            var query = _Context.Info.Where(p=>p.Code == code);
            if (query.Count() > )
            {
                Info data = query.First();
                _Context.Info.DeleteOnSubmit(data);
                _Context.SubmitChanges();
            }
        }