分层开发之MySchool

No.1实现登陆功能，验证用户名和密码。从数据库里进行匹配，看是否有符合要求的数据。

在DAL层编写代码，返回值为布尔类型。方法参数为（student实体类对象），使用参数化SqlParameter类型防止SQL注入。

 1 public bool IsLogin(Student stu)
 2        {
 3            bool flag = false;
 4            SqlConnection con = new SqlConnection(SqlHelper.str);
 5
 6            string sql = "select count(1) from student where studentNo=@StudentName  and LoginPwd=@LoginPwd";
 7            //02 将sql语句交给SQL服务器执行
 8            SqlParameter para1 = new SqlParameter("@StudentName", stu.StudentNo);
 9            SqlParameter para2 = new SqlParameter("@LoginPwd", stu.LoginPwd);
10            SqlCommand cmd = new SqlCommand(sql,con);
11            cmd.Parameters.Add(para1);
12            cmd.Parameters.Add(para2);
13            try
14            {
15                con.Open();
16                int count = Convert.ToInt32(cmd.ExecuteScalar());
17                if (count > 0)
18                {
19                    flag = true;
20                }
21            }
22            catch (Exception ex)
23            {
24
25                throw ex;
26            }
27            finally
28            {
29                con.Close();
30            }
31            return flag;
32        }

在BLL层创建DAL层的对象，调用DAL层的login方法，返回值和参数和DAL层login方法一致，return dal.login(stu)

1  public bool IsLogin(Student stu)
2        {
3            return dal.IsLogin(stu);
4        }

在UI层调用BLL层的方法，并在UI层创建实体类对象，给实体类对象的属性赋值后将对象放入调用的BLL层的方法中。判断登陆是否成功！

 1 StudentBLL bll = new StudentBLL();
 2             Student stu = new Student();
 3             stu.StudentNo = Convert.ToInt32(txtName.Text);
 4             stu.LoginPwd = txtPwd.Text;
 5             bool flag = bll.IsLogin(stu);
 6             if (flag)
 7             {
 8                 MessageBox.Show("登陆成功");
 9                 frmlist list = new frmlist();
10                 list.Show();
11             }
12             else
13             {
14                 MessageBox.Show("登陆失败");
15             }

No.2展示学生信息

在DAL层编写方法返回值是泛型集合，无方法参数，使用工具类（SqlHelper类）将DataTable类型转换为泛型

 1  public List<Student> Select()
 2        {
 3            SqlConnection con = new SqlConnection(SqlHelper.str);
 4            string sql = "select * from student";
 5            DataTable dt = SqlHelper.ExecuteDataTable(sql);
 6            My_Tool tool = new My_Tool();
 7            List<Student> list = tool.DataTableToList<Student>(dt);
 8            return list;
 9
10        }

在BLL层编写方法与DAL层同理

1  public List<Student> Select()
2        {
3            return dal.Select();
4        }

在UI层的初始化Select方法（）将数据绑定到datagridView中！

 1  private void frmlist_Load(object sender, EventArgs e)
 2         {
 3             Initial();
 4         }
 5         public  List<Student> list = new List<Student>();
 6         public void Initial()
 7         {
 8             StudentBLL bll = new StudentBLL();
 9             list= bll.Select();
10             this.dgvlist.DataSource = list;
11
12         }

No.3实现添加学生信息

Insert语句插入数据的参数较多，所以我们可以声明一个SqlParaMeters类型的数组，节约代码，方法返回值依然是bool类型，方法参数是Student类型的对象。注意！在给Command对象添加参数的时候

要使用AddRange()方法！

 1  public bool Insert(Student stu)
 2        {
 3            bool flag = false;
 4            SqlConnection con = new SqlConnection(SqlHelper.str);
 5            string sql = "insert into student values(@LoginPwd,@StudentName,@Gender,@GradeId,@Phone,@Address,@Birthday,@Email,@MyTT)";
 6            SqlParameter[] para =
 7            {
 8                new SqlParameter("@LoginPwd", stu.LoginPwd),
 9                new SqlParameter("@StudentName", stu.StudentName),
10                new SqlParameter("@Gender", stu.Gender),
11                new SqlParameter("@GradeId", stu.GradeId),
12                new SqlParameter("@Phone", stu.Phone),
13                new SqlParameter("@Address", stu.Address),
14                new SqlParameter("@Birthday", stu.Birthday),
15                new SqlParameter("@Email", stu.Email),
16                new SqlParameter("@MyTT", stu.MyTT)
17            };
18            SqlCommand cmd = new SqlCommand(sql,con);
19            cmd.Parameters.AddRange(para);
20
21            try
22            {
23                con.Open();
24                int count = Convert.ToInt32(cmd.ExecuteScalar());
25                if (count > 0)
26                {
27                    flag = true;
28                }
29
30            }
31            catch (Exception ex)
32            {
33
34                throw ex;
35            }
36            finally
37            {
38                con.Close();
39            }
40            return flag;
41        }

在BLL层同样实现了方法调用！

1  public bool Insert(Student stu)
2        {
3            return dal.Insert(stu);
4        }

在UI层调用BLL层的方法，给Student类的属性赋值，判断是否添加学生信息成功！

 1 StudentBLL bll = new StudentBLL();
 2             Student stu = new Student();
 3
 4             stu.LoginPwd = txtPwd.Text;
 5             stu.StudentName = txtName.Text;
 6             if (rbtnFemale.Checked)
 7             {
 8                 stu.Gender = "0";
 9             }
10             else if (rbtnMan.Checked)
11             {
12                 stu.Gender = "1";
13             }
14             if (cboGrade.SelectedItem.ToString() == "S1")
15             {
16                 stu.GradeId = 0;
17             }
18             else if (cboGrade.SelectedItem.ToString() == "S2")
19             {
20                 stu.GradeId = 1;
21             }
22             stu.Phone = txtPhone.Text;
23             stu.Address = txtAddress.Text;
24             stu.Birthday = dpBirthday.Value;
25             stu.Email = txtEmail.Text;
26             this.listnew.Add(stu);
27             bool flag= bll.Insert(stu);
28             frm.dgvlist.DataSource = new BindingList<Student>(this.listnew);
29             this.Close();

No.4实现comboBox的两级联动，当选中下拉框中的一项时，另一个下拉框会自动匹配，并且以筛选条件来查询！

在GradeDAL层编写读取所有年级下拉框的方法，返回值为泛型集合，无方法参数

 1  public List<Grade> GetGradenew()
 2        {
 3            List<Grade> list = new List<Grade>();
 4            using (SqlConnection con = new SqlConnection(SqlHelper.str))
 5            {
 6                string sql = "select * from Grade";
 7                SqlCommand cmd = new SqlCommand(sql,con);
 8                con.Open();
 9                using (SqlDataReader dr = cmd.ExecuteReader())
10                {
11                    while (dr.Read())
12                    {
13                        Grade ga = new Grade();
14                        ga.GradeId = Convert.ToInt32(dr["GradeId"]);
15                        ga.GradeName = dr["GradeName"].ToString();
16                        list.Add(ga);
17
18                    }
19                }
20
21            }
22            return list;
23        }

在BLL层调用该方法！

1  public List<Grade> GetGradenew()
2        {
3            return dal.GetGradenew();
4        }

在UI 层中调用此方法，comboBox的disPalyMember属性为“gradename”，valuemember属性设置为“gradeid”，将comboBox的DropDownHeight属性设置为106，避免下拉框冗余

1 this.comboBox2.DropDownHeight = 106;
2             this.comboBox1.DataSource = bll.GetGradenew();
3             this.comboBox1.ValueMember = "GradeId";
4             this.comboBox1.DisplayMember = "GradeName";

在DAL层编写两个方法，返回值都是泛型，一个方法有返回值，另一个没有，一个方法是为了查询所有科目，另一个是根据年级编号查询科目

public List<Subject> GetSubjectName()
       {
           List<Subject> list = new List<Subject>();
           using (SqlConnection con = new SqlConnection(SqlHelper.str))
           {
               string sql = "select * from Subject";
               SqlCommand cmd = new SqlCommand(sql, con);
               con.Open();
               using (SqlDataReader dr = cmd.ExecuteReader())
               {
                   while (dr.Read())
                   {
                       Subject sub = new Subject();
                       sub.SubjectId = Convert.ToInt32(dr["SubjectId"]);
                       sub.SubjectName = dr["SubjectName"].ToString();
                       sub.GradeId = Convert.ToInt32(dr["GradeId"]);
                       sub.ClassHour = Convert.ToInt32(dr["ClassHour"]);
                       list.Add(sub);
                   }
               }
           }
           return list;
       }
       public List<Subject> GetSubjectByGrade(int gradeid)
       {
           List<Subject> list = new List<Subject>();
           using (SqlConnection con = new SqlConnection(SqlHelper.str))
           {
               string sql = "select * from Subject where gradeId='" + gradeid + "'";
               SqlCommand cmd = new SqlCommand(sql, con);
               con.Open();
               using (SqlDataReader dr = cmd.ExecuteReader())
               {
                   while (dr.Read())
                   {
                       Subject sub = new Subject();
                       sub.SubjectId = Convert.ToInt32(dr["SubjectId"]);
                       sub.SubjectName = dr["SubjectName"].ToString();
                       sub.GradeId = Convert.ToInt32(dr["GradeId"]);
                       sub.ClassHour = Convert.ToInt32(dr["ClassHour"]);
                       list.Add(sub);
                   }
               }
           }
           return list;

       }

在BLL层调用方法

 1  SubjectDAL dal = new SubjectDAL();
 2        public List<Subject> GetSubjectName()
 3        {
 4            return dal.GetSubjectName();
 5        }
 6        public List<Subject> GetSubjectByGrade(int gradeid)
 7        {
 8            return dal.GetSubjectByGrade(gradeid);
 9        }
10        public List<Subject> GetSubjectById(int subjectid)
11        {
12            return dal.GetSubjectById(subjectid);
13        }

在UI层编写代码，注意如果其他事件触发的顺序在窗体load事件之前，使用bool类型变量来调整先后顺序，执行完load事件后flag的值为ture，如果为True，执行其他的事件，在科目下拉框再加入一个请选择，用泛型的Insert方法将其加到下标为0的位置上！

 1  private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
 2         {
 3             if (flag)
 4             {
 5             int num = Convert.ToInt32(this.comboBox1.SelectedValue);
 6
 7             List < Subject > list= sub.GetSubjectByGrade(num);
 8             Subject ject = new Subject();
 9             ject.SubjectId = -1;
10             ject.SubjectName = "请选择";
11             list.Insert(0, ject);
12             this.comboBox2.ValueMember = "SubjectId";
13             this.comboBox2.DisplayMember = "SubjectName";
14             this.comboBox2.DataSource = list;
15             }
16         }

在DAL层编写方法，作为条件查询学生成绩的方法，根据查询条件来设置方法参数和SQL语句，实现多种条件下的模糊查询

 1 public DataTable GetList(string name, int id)
 2        {
 3            using (SqlConnection con = new SqlConnection(SqlHelper.str))
 4            {
 5                string sql = "select StudentName,subjectName,studentresult,examdate from student,result,Subject,grade where subject.gradeid=grade.GradeId and result.studentNo=student.studentNo and result.subjectid=subject.subjectid";
 6                if (id != -1)
 7                {
 8                    sql += " and Subject.Subjectid='" + id + "'";
 9                }
10                if (!string.IsNullOrEmpty(name))
11                {
12                    sql += " and StudentName='" + name + "'";
13                }
14                SqlDataAdapter da = new SqlDataAdapter(sql, con);
15                DataSet ds = new DataSet();
16                da.Fill(ds, "ss");
17                return ds.Tables["ss"];
18            }
19        }

在BLL层调用该方法！

1    public DataTable GetList(string name, int id)
2        {
3            return dal.GetList(name, id);
4        }

在UI层调用该方法，给方法参数赋值，实体类的属性赋值

1  private void button1_Click(object sender, EventArgs e)
2         {
3             string name = textBox1.Text;
4             int subjectid = Convert.ToInt32(comboBox2.SelectedValue);
5             DataTable dt = re.GetList(name, subjectid);
6             this.dataGridView1.DataSource = dt;
7         }