C#学习笔记10：数据库编程（二）

SQLServer

System.Data.SqlClient

Access

 System.Data.OleClient

SQLConnection,SQLCommand,SQLDataReader

SQLCommand属性：Connection

                  CommandText

                  CommandType

            函数：ExecuteReader()    select语句

                  ExecuteNonQuery()  insert,update,delete语句

                  ExecuteScalar()  执行返回唯一值SQL语句

eg:   string sql=”select count(*) fromstudent”; //记录个数

string sql=”select max(sage) fromstudent”;

string sql=”select min(sage) fromstudent”;

string sql=”select avg(sage) fromstudent”;

string sql=”select sum(sage) fromstudent”;

3、带参数SQL语句

stringsql = "delete fromcustomers where customerid='" + cid + "'";
stringsql = "delete from customers where customerid='1001'";
string sql = "insertinto customers values('"+cid+"','"+cname+"','"+cphone+"')";
string sql = "insertinto customers values(@cid,@cname,@cphone)";
@参数名   SQLParameter：参数名称、参数类型（数据库）、参数大小、参数值、参数方向。

eg:

public static string connstr = @"DataSource=.\zpsqlserver;Initial Catalog=mydb;User ID=sa;Password=4846";
       static void addCustomer(string cid, string cname, string cphone)
       {
           string sql = "insert into customersvalues(@cid,@cname,@cphone)";
           SqlConnection conn = new SqlConnection(connstr);
           conn.Open();//打开连接
          SqlCommand cmd = new SqlCommand();
 
           cmd.Connection = conn;//命令对象Connection属性
           cmd.CommandText = sql;//命令文本SQL
 
           SqlParameter p1 = new SqlParameter();
p1.ParameterName = "@cid";
           p1.SqlDbType = SqlDbType.Char;
           p1.Size = 20;
           p1.Value = cid;
           cmd.Parameters.Add(p1);//向命令对象参数集合中添加参数
 
           SqlParameter p2 = new SqlParameter();
           p2.ParameterName = "@cname";
           p2.SqlDbType = SqlDbType.Char;
           p2.Size = 30;
           p2.Value = cname;
           cmd.Parameters.Add(p2);//向命令对象参数集合中添加参数
 
           SqlParameter p3 = new SqlParameter();
           p3.ParameterName = "@cphone";
           p3.SqlDbType = SqlDbType.Char;
           p3.Size = 30;
           p3.Value = cphone;
           cmd.Parameters.Add(p3);//向命令对象参数集合中添加参数
           //执行insert,delete,update命令
           cmd.ExecuteNonQuery();
           conn.Close();
       }
       static void deleteCustomer(string cid)
       {
           SqlConnection conn = new SqlConnection(connstr);
           conn.Open();//打开连接
           string sql = "delete from customers wherecustomerid='" + cid + "'";
           SqlCommand cmd = new SqlCommand();
 
           cmd.Connection = conn;//命令对象Connection属性
           cmd.CommandText = sql;//命令文本SQL
           //执行insert,delete,update命令
           cmd.ExecuteNonQuery();
           conn.Close();
       }
        static void Main(string[] args)
        {
            addCustomer("1006","zhou","010-1212");
            Console.ReadLine();
        }

使用string.Format函数

public static string connstr = @"DataSource=.\zpsqlserver;Initial Catalog=mydb;User ID=sa;Password=4846";
       static void addCustomer(string cid, string cname, string cphone)
       {
           //string sql = "insert into customersvalues(@cid,@cname,@cphone)";
           string sql = "insert into customers values('{0}','{1}','{2}')";
           sql = string.Format(sql,cid, cname, cphone);
           SqlConnection conn = new SqlConnection(connstr);
           conn.Open();//打开连接
          SqlCommand cmd = new SqlCommand();
 
           cmd.Connection = conn;//命令对象Connection属性
           cmd.CommandText = sql;//命令文本SQL
          

           cmd.ExecuteNonQuery();
           conn.Close();
       }

4、数据库分层访问技术

1)数据库访问基础类（工具类）
   class SQLHelper
    {
        private static string connstr = @"Data Source=.\zpsqlserver;InitialCatalog=mydb;User ID=sa;Password=4846";
        private static SqlConnectionconn = new SqlConnection(connstr);
        private static SqlCommandcmd = new SqlCommand("", conn);
        /*执行查询语句，返回DataReader*/
        public static SqlDataReaderExecuteQuery(string sql)
        {
            if(conn.State==ConnectionState.Closed)
            conn.Open();
            cmd.CommandText = sql;
            SqlDataReaderdr=cmd.ExecuteReader();
            return dr;
        }
        /*执行insert,update,delete语句*/
        public static int ExecuteUpdate(string sql)
        {
            if (conn.State == ConnectionState.Closed)
                conn.Open();
            cmd.CommandText = sql;
           int x=cmd.ExecuteNonQuery();
           conn.Close();
           return x;
        }
        /*关闭连接对象*/
        public static void CloseConnection()
        {
            if (conn != null && conn.State!= ConnectionState.Closed)
                conn.Close();
        }
}

测试类：

   class Ex1_1
    {
       static void addCustomer(string cid, string cname, string cphone)
       {
           string sql = "insert into customersvalues('{0}','{1}','{2}')";
           sql = string.Format(sql, cid,cname, cphone);
           SQLHelper.ExecuteUpdate(sql);
       }
       static void deleteCustomer(string cid)
       {
           string sql = "delete from customers wherecustomerid='"+cid+"'";
           SQLHelper.ExecuteUpdate(sql);
       }
       static void dispCustomers()
       {
           string sql = "select * from customers";
           SqlDataReader dr= SQLHelper.ExecuteQuery(sql);
           while (dr.Read())
           {
               Console.WriteLine("{0},{1},{2}",dr[0],dr[1],dr[2]);
           }
           SQLHelper.CloseConnection();
       }
        static void Main(string[] args)
        {
            dispCustomers();
            Console.ReadLine();
        }
   }

2) 编写一个实体类，映射数据库中表结构
   class Customer
    {
        private string cid, cname, cphone;
        public Customer() { }
        public Customer(string cid, string cname, string cphone)
        {
            this.cid = cid; this.cname = cname; this.cphone= cphone;
        }
        /*属性访问器*/
    }

3) 编写一个实体操作类，封装对实体操作。
   class CustomerDao
    {
        public void addCustomer(Customercus)
        {
            string sql = "insert into customers values('{0}','{1}','{2}')";
            sql = string.Format(sql, cus.Cid,cus.Cname, cus.Cphone);
            SQLHelper.ExecuteUpdate(sql);
        }
        public void deleteCustomer(string cid)
        {
            string sql = "delete from customers wherecustomerid='" + cid + "'";
            SQLHelper.ExecuteUpdate(sql);
        }
        public List<Customer> queryAllCustomers()
        {
            List<Customer> clist = newList<Customer>();
            string sql = "select * from customers";
            SqlDataReader dr = SQLHelper.ExecuteQuery(sql);
            while (dr.Read())
            {
                Customer cus = new Customer(dr[0],dr[1],dr[2]);
                clist.Add(cus);
            }
            SQLHelper.CloseConnection();
            return clist;
        }
    }

三层架构下的测试函数

   class Ex1_1
    {
    

        static void Main(string[] args)
        {
            CustomerDao dao = new CustomerDao();
            List<Customer> clist = dao.queryAllCustomers();
            Console.WriteLine(clist.Count);
            Console.ReadLine();
        }
    }

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