我有一个数据库设计问题,我面临着我的一个项目.我试图实现一个服务,而这个服务的一部分是一个db层.它的设置是这样的,我有一个帮助类,执行get / update方法到数据库和它们之上的层,作为一个看门人.例如：
public class GetStudentDBHelper {
public List<Student> get(List<Integer> ids) {
Conn getConnection...
// run sql query and construct returning Student objects
}
public List<Student> get(List<Classroom> byClassroom) {
// get all students in passed in classrooms
// run sql query and construct returning Student objects
}
}
public class StudentJanitor {
public GetStudentDBHelper getStudentDBHelper;
public UpdateStudentDBHelper updateStudentDBHelper;
public UpdateClassroomDBHelper updateClassroomDBHelper;
public List<Student> getStudents(List<Integer> ids) {
return getStudentDBHelper.get(ids);
}
public void saveStudents(List<Students> students,int classRoomid) {
Connection conn = Pool.getConnection(); // assume this gives a jdbc
conn.autocommit(false);
try {
try
{
updateStudentDBHelper.saveForClassroom(students,classRoomid,conn);
updateClassroomDBHelper.markUpdated(classRoomid,conn);
conn.commit();
}
catch
{
throw new MyCustomException(ErrorCode.Student);
}
}
catch (sqlException c)
{
conn.rollback();
}
finally {
conn.close();
}
}
public class ClassroomJanitor{
public void saveClassRoon(List<Classrooms> classrooms) {
Connection conn = Pool.getConnection()// assume this gives a jdbc
conn.autocommit(false);
try {
try {
updateClassroomDBHelper.save(classrooms,conn);
updateStudentDBHelper.save(classrooms.stream().map(Classroom::getStudents).collect(Collections.toList()),conn);
conn.commit();
}
catch {
throw new MyCustomException(ErrorCode.ClassRoom);
}
}
catch (sqlException c)
{
conn.rollback();
}
finally {
conn.close();
}
}...
public class GetClassroomDBHelper{}...
public class UpdateClassroomDBHelper{}...
更新db类都会组成多个其他更新程序,以防他们需要更新其他表中的值(即保存学生意味着我必须触摸学生所属的课堂表,以更新其上次更新的时间).
我遇到的问题是更新db类,如果我正在触摸多个表,以便拥有交易和回滚功能,我必须从我的Janitor类传递一个连接.看到上面我的意思.有没有更好的方法来做到这一点？这种类型的try,catch,传入conn到db helpers,必须为我的管理器中的任何多事务操作完成.
Connection conn = Pool.getConnection()// assume this gives a jdbc
conn.autocommit(false);
try {
try {
//do some business logic requiring Connection conn
}
catch {
throw new MyCustomException(ErrorCode);
}
}
catch (sqlException c)
{
conn.rollback();
}
finally {
conn.close();
}
解决方法
每当你有一个代码序列是重复的,但它只在一些部分不同,你可以使用一个
template method.
在你的情况下,我将介绍一个TransactionTemplate类,并为不同的部分使用回调接口.例如.
public class TransactionTemplate {
private DataSource dataSource;
public TransactionTemplate(DataSource dataSource) {
this.dataSource = Objects.requireNonNull(dataSource);
}
public <T> T execute(TransactionCallback<T> transactionCallback) throws Exception {
Connection conn = dataSource.getConnection();// assume this gives a jdbc
try {
conn.setAutoCommit(false);
T result = transactionCallback.doInTransaction(conn);
conn.commit();
return result;
} catch (Exception e) {
conn.rollback();
throw e;
} finally {
conn.close();
}
}
}
回调界面看起来像这样
public interface TransactionCallback<T> {
public T doInTransaction(Connection conn) throws Exception;
}
正如您可以看到TransactionTemplate管理事务,而TransactionCallback实现了在一个事务中必须完成的逻辑.
那么你的客户端代码就会这样
public class StudentJanitor {
private TransactionTemplate transactionTemplate;
StudentJanitor(DataSource dataSource) {
transactionTemplate = new TransactionTemplate(dataSource);
}
public void saveStudents(List<Students> students,int classRoomid) {
SaveStudentsTransaction saveStudentsTransaction = new SaveStudentsTransaction(students,classRoomid);
transactionTemplate.execute(saveStudentsTransaction);
}
}
逻辑放在TransactionCallback中
public class SaveStudentsTransaction implements TransactionCallback<Void> {
public GetStudentDBHelper getStudentDBHelper;
public UpdateStudentDBHelper updateStudentDBHelper;
public UpdateClassroomDBHelper updateClassroomDBHelper;
private List<Students> students;
private int classRoomid;
public SaveStudentsTransaction(List<Students> students,int classRoomid) {
this.students = students;
this.classRoomid = classRoomid;
}
@Override
public Void doInTransaction(Connection conn) throws Exception {
try
{
updateStudentDBHelper.saveForClassroom(students,conn);
updateClassroomDBHelper.markUpdated(classRoomid,conn);
conn.commit();
}
catch
{
throw new MyCustomException(ErrorCode.Student);
}
return null;
}
}
