C#LINQ

LINQ：语言集成查询

帮我们干了两件事：1.帮我们造了实体对象出来；

2.提供了很多便捷的增删改查询方法，将数据库的T-sql挪了过来。

右键添加LINQ类之后，右击服务器资源管理器中的数据连接，添加链接，选择数据库，完成连接。

将资源管理器中的表格拖进类文件里就可以创建表格的实体对象，以后可以直接使用

private void Form1_Load(object sender, EventArgs e)
        {
            DataClasses1DataContext context = new DataClasses1DataContext();

          List<Car >list=context.Car.ToList();
          dataGridView1.DataSource = list;
        }

运行结果

//Func<string, string> fc = delegate(string a)
            //{
            //    a += "你好";
            //    return a;
            //};
            //MessageBox.Show(fc("5").ToString());
            DataClasses1DataContext context = new DataClasses1DataContext();
            //List<bread> list = context.bread.Where(r => Convert.ToDecimal(r.breadprice.ToString()) < 15).ToList();
            var list2 = from quary in context.bread where Convert.ToDecimal(quary.breadprice.ToString()) < 15 select quary;
            dataGridView1.AutoGenerateColumns = true;
            dataGridView1.DataSource = list2;
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
public class studentDA
 
    {
        private DataClasses1DataContext _context;
        public studentDA()
        {
            _context = new DataClasses1DataContext();
        }
        //添加数据
        public void insert(Student data)
        {
            _context.Student.InsertOnSubmit(data);
            _context.SubmitChanges();
        }
        //修改数据
        public void update(Student  data)
        {
            Student sdata =_context.Student.Single(r => r.Sno == data.Sno);
            if (sdata != null)
            {
                sdata.Sno = data.Sno;
                sdata.Sname = data.Sname;
                sdata.Ssex = data.Ssex;
                sdata.Sbirthday = data.Sbirthday;
                _context.SubmitChanges();
            }
 
        }
        //删除数据
        public void delete(Student data)
        {
            Student sdata = _context.Student.Single(r=>r.Sno==data.Sno);
            _context.Student.DeleteOnSubmit(sdata);
            _context.SubmitChanges();
        }
         ////////根据学生编号删除
        public void delete(string sno)
        {
            Student data = _context.Student.Single(r => r.Sno == sno);
            if (data != null)
            {
                _context.Student.DeleteOnSubmit(data);
                _context.SubmitChanges();
            }
        }
       ///////////查询所有学生数据
        public List<Student> select()
        {
            return _context.Student.ToList().Count>0? _context.Student.ToList():null;
        }
///////////////根据学生编号查询
        public Student select(string sno)
        {
            return _context.Student.Where(r => r.Sno == sno).First();
        }
/////////////根据学生姓名查询
        public List<Student> selectbyname(string sname)
        {
           List <Student> list=   _context.Student.Where(r => r.Sname.Contains(sname)).ToList();
           return list.Count>0? list:null;
        }
    }
}
//////////////////////////////////////////////////////////////////////////////////////////////////////////////
往数据库中添加数据
 Student data = new Student
            {
               Sno=textBox1.Text,
               Sname=textBox2.Text,
               Ssex=radioButton1.Checked?"男":"女",
               Sbirthday=dateTimePicker1.Value,
               Class=textBox3.Text,
                              
            };
            new studentDA().insert(data);
 
 
/////////////用linq的方法从数据库中查询数据
 private void Form3_Load(object sender, EventArgs e)
        {
            List<Student> list = new studentDA().select();
            if (list != null)
            {
                dataGridView1.AutoGenerateColumns = true;
                dataGridView1.DataSource = list;
            }
        }
 
//////////用linq的方法从数据库中根据姓名查询
        private void button1_Click(object sender, EventArgs e)
        {
            List<Student> list = new studentDA().selectbyname(textBox1.Text);
            if (list != null)
            {
                dataGridView1.AutoGenerateColumns = true;
                dataGridView1.DataSource = list;
            }
        }
 
/////////用linq的方法从数据库中删除数据
        private void button2_Click(object sender, EventArgs e)
        {
            if (dataGridView1.SelectedRows.Count > 0)
            {
                Student data = (Student)dataGridView1.SelectedRows[0].DataBoundItem;
                new studentDA().delete(data);
            }
            dataGridView1.AutoGenerateColumns = true;
            dataGridView1.DataSource = new studentDA().select();
        }
 
        private void button3_Click(object sender, EventArgs e)
        {
            if (dataGridView1.SelectedRows.Count > 0)
            {
                Form4 f = new Form4((Student)dataGridView1.SelectedRows[0].DataBoundItem);
                f.Show();
            }
        }
 
 
 
 
 
 
 
 
 private Student sdata;////将选择的信息传到相应的地方构造函数
        public Form4(Student data)
        {
            InitializeComponent();
            sdata = data;
 
        }
 
        private void Form4_Load(object sender, EventArgs e)
        {
            textBox1.Text = sdata.Sno;
            textBox2.Text = sdata.Sname;
            textBox3.Text = sdata.Class;
            if (sdata.Ssex == "男")
            {
                radioButton1.Checked = true;
            }
            else
            {
                radioButton2.Checked = true;
            }
            dateTimePicker1.Value = DateTime.Parse(sdata.Sbirthday.ToString());
        }
/////////////////////////////////////////////////////////////////
 
 
 
///////将传回的信息修改后传回数据库
        private void button1_Click(object sender, EventArgs e)
        {
            Student sdata = new Student();
            sdata.Sno = textBox1.Text;
            sdata.Sname = textBox2.Text;
            sdata.Class = textBox3.Text;
            sdata.Ssex = radioButton1.Checked ? "男" : "女";
            sdata.Sbirthday = dateTimePicker1.Value;
            new studentDA().update(sdata);
            this.Close();
        }