a different object with the same identifier value was already associated with the session:

编程时遇到的一个经典错误。

a different object with the same identifier value was already associated with the session: [com.tarena.oa.pojo.Department#15]

经过排查，原来是代码保存时的错误。

public String edit() throws Exception{Department department=departmentService.getById(model.getId());department.setDescription(model.getDescription());department.setName(model.getName());department.setParent(departmentService.getById(parentId)); // 上级部门departmentService.update(model);return "toList";}

在departmentService.update(model)时错误

应该是

departmentService.update(department);