Although object-relational mapping is relatively simple and basic, it is the foundation of the persistence layer framework, so it still needs to be recorded.
When inserting, there is a problem of garbled characters. I have never encountered it before. This time I also write a summary. I will not put it here for the time being. I am afraid it will be too long.
Insert an object into the database
package ORM;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
/**
*
* Insert an object into the database
* @author zhuang
*
*/
public class TestJdbcInsert {
static void add(User user) {
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace ();
}
// use precompiled sql
String sql = "insert into user values(?,?,?)";
try (
Connection c = DriverManager.getConnection(
"jdbc:mysql://127.0.0.1:3306/jdbc?characterEncoding=UTF-8",
"root",
"123");
PreparedStatement ps = c.prepareStatement(sql);
)
{
ps.setInt(1, user.id);
ps.setString(2, user.name);
ps.setInt(3, user.age);
// Use execute or executeUpdate here
ps.executeUpdate();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace ();
}
}
public static void main(String[] args) {
User user = new User(3, "DZ", 23);
add(user);
}
}
Delete the data corresponding to this User object
package ORM;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
/**
* Delete the data corresponding to this User object
*
* @author zhuang
*
*/
public class TestJdbcDelete {
static void delete(User user) {
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace ();
}
// use precompiled sql
String sql = "delete from user where id=?";
try (
Connection c = DriverManager.getConnection(
"jdbc:mysql://127.0.0.1:3306/jdbc?characterEncoding=UTF-8",
"root",
"123");
PreparedStatement ps = c.prepareStatement(sql);
)
{
ps.setInt(1, user.id);
// Use execute or executeUpdate here
ps.execute();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace ();
}
}
public static void main(String[] args) {
User user = new User(2, "凌志玲", 33);
delete(user);
}
}
Update this User object
package ORM;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
/**
* Update this User object
*
* @author zhuang
*
*/
public class TestJdbcUpdate {
static void update(User user) {
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace ();
}
// use precompiled sql
String sql = "update user set name=?,age=? where id=?";
try (
Connection c = DriverManager.getConnection(
"jdbc:mysql://127.0.0.1:3306/jdbc?characterEncoding=UTF-8",
"root",
"123");
PreparedStatement ps = c.prepareStatement(sql);
)
{
ps.setString(1, user.name);
ps.setInt(2, user.age);
ps.setInt(3, user.id);
// Use execute or executeUpdate here
ps.execute();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace ();
}
}
public static void main(String[] args) {
User user = new User(1, "Chen Guanxi", 37);
update(user);
}
}
//Get a user object based on the id value
package ORM;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
/**
* //Get a user object according to the id value
*
* @author zhuang
*
*/
public class TestJdbcGetById {
static User user;
/**
* How to get the user object
*
* @param id
* @return
*/
static User getUser(int id) {
try {
// open the driver
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace ();
}
try (
// Get the connection through the driver
Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/jdbc", "root", "123");
Statement s = c.createStatement();) {
String sql = "select * from user where id=" + id;
ResultSet rs = s.executeQuery(sql);
if (rs.next()) {
String name = rs.getString("name");
int age = rs.getInt("age");
user = new User(id, name, age);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace ();
}
return user;
}
public static void main(String[] args) {
User u = getUser(1);
System.out.println(u.name);
}
}
Query all User data, convert it to User object, and put it back in a collection
package ORM;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
/**
* Query all User data, convert it to User object, and return it in a collection
* @author zhuang
*
*/
public class TestJdbcList {
static List<User> getList(User user) {
// prepare a collection
List<User> userList = new ArrayList<>();
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace ();
}
// use precompiled sql
String sql = "select * from user";
try (
Connection c = DriverManager.getConnection(
"jdbc:mysql://127.0.0.1:3306/jdbc?characterEncoding=UTF-8",
"root",
"123");
PreparedStatement ps = c.prepareStatement(sql);
)
{
ps.execute();
ResultSet rs = ps.getResultSet();
//get the collection
while(rs.next()) {
// Load the fields into the User object
user = new User(rs.getInt("id"), rs.getString("name"), rs.getInt("age"));
// put the user object into the list
userList.add(user);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace ();
}
return userList;
}
public static void main(String[] args) {
User user = new User(1, "", 1);
List<User> listUser = getList(user);
System.out.println(listUser);
}
}