你没有向我们展示很多代码，但我会给你一个很好的例子来说明我如何处理程序和 SQL 数据库之间的通信。
首先我为每个对象创建类。在你的例子中，我看到你有Employee，所以我会创建一个关于我的每个员工和我想为他们拥有的功能的信息（变量）很少的类。所以类看起来像这样：
public class Employee
{
static string databaseString = "";
public int Id { get { return _Id; } } //This is property
public string Name { get { return _Name; } set { _Name = value; } } //This is property
private int _Id; //This is private variable used by property
private string _Name; //This is private variable used by property
public Employee()
{
//Constructor used to create empty object
}
public Employee(int Id)
{
try
{
using (SqlConnection con = new SqlConnection(databaseString))
{
con.Open();
using (SqlCommand cmd = new SqlCommand("SELECT NAME FROM Employee WHERE ID = @ID", con))
{
cmd.Parameters.AddWithValue("@ID", Id);
SqlDataReader dr = cmd.ExecuteReader();
//I am usin IF(dr.Read()) instead of WHILE(dr.Read()) since i want to read only first row.
if (dr.Read())
{
this._Id = Id;
this._Name = dr[0].ToString();
}
else
{
System.Windows.Forms.MessageBox.Show("There was no Employee with that ID in database!");
}
}
}
}
catch(SqlException ex)
{
System.Windows.Forms.MessageBox.Show(ex.ToString());
}
}
public void Save(bool showMessage)
{
using (SqlConnection con = new SqlConnection(databaseString))
{
con.Open();
using (SqlCommand cmd = new SqlCommand("UPDATE Employee SET NAME = @N WHERE ID = @ID", con))
{
cmd.Parameters.AddWithValue("@N", this._Name);
cmd.Parameters.AddWithValue("@ID", this._Id);
cmd.ExecuteNonQuery();
if (showMessage)
System.Windows.Forms.MessageBox.Show("Employee saved!");
}
}
}
public static void Create(string Name, bool showMessage = true)
{
using (SqlConnection con = new SqlConnection(databaseString))
{
con.Open();
using (SqlCommand cmd = new SqlCommand("INSERT INTO Employee (ID, NAME) VALUES (COALESCE(MAX(ID), 1), @NAME)", con))
{
cmd.ExecuteNonQuery();
if (showMessage)
System.Windows.Forms.MessageBox.Show("New Employee created!");
}
}
}
}
现在当我上课时，我可以用两种方式称呼它：
Employee emp = new Employee(); //This will create empty employee object
Employee emp1 = new Employee(1); //This will create employee object and will load employees data from database where employees id == 1
我还能做的是：
Employee.Create("SomeName"); //Calling public static method from Employee class. Doesn't require you to create object for static methods
或者如果我加载了员工并想更改其名称然后保存，我会这样做：
Employee emp2 = new Employee(1); //Created and loaded emp from database
emp2.Name = "Changed Name";
emp2.Save(); //Called public method.
所以现在，如果您有显示一名员工的表单，它将如下所示：
public partial class Form1 : Form
{
private Employee emp;
public Form(int EmployeeID)
{
InitializeComponents();
//Creating new object of Employee but with constructor that will automatically load variables into it.
emp = new Employee(EmployeeID);
//Checking to see if employee is loaded since if there was no employee with given ID it would return null
if(emp.Id == null || < 1)
{
DialogResult dr = MessageBox.Show("Employee doesn't exist. Do you want to create new one?", "Confirm", MessageBoxButtons.YesNo);
if(dr == DialogResult.No)
{
//User doesn't want to create new employee but since there is no employee loaded we close form
this.Close();
}
else
{
Employee.Create("New Employee");
MessageBox.Show("New employee created");
//Here we need to load this employee with code like emp = new Employee(newEmployeeId);
//To get new employee id you have 2 options. First is to create function inside Employee class that will Select MAX(ID) from Employee and return it. (bad solution)
//Second solution is to return value upon creating new employee so instead function `public static void Create()` you need to have `public static int Create()` so it returns newly created ID of new row in SQL database. I won't explain it since you are new and it will be too much information for now. You will easily improve code later. For now you can use Select Max(id) method
}
}
textBox1.Text = emp.Id;
textBox2.Text = emp.Name;
}
private void OnButton_Save_Click(object sender, EventArgs e)
{
DialogResult dr = MessageBox.Show("Do you really want to save changes?", "Save", MessageBoxButtons.YesNo);
if(dr == DialogResult.Yes)
{
emp.Save();
}
else
{
//Here create private Reload function inside form that will do emp = Employee(emp.Id) and then set UI again.
}
}
private void OnButton_CreateNewEmployee_Click(object sender, EventArgs e)
{
Employee.Create("New Employee");
int newEmpID = something; //As i said up create method to select MAX ID or update SQL inside Create function to return newly created ID
//I am using using since after form closes it automatically disposes it
using(Form1 f = new Form1(newEmpID))
{
f.showDialog()
}
this.Close();
}
}