/// <summary>
/// 按courseId删除Seminar.
/// @author zhouzhongjun
/// </summary>
/// 先根据CourseId获得所有的seminar的信息，然后根据seminar信息删除相关topic的记录，然后再根据SeminarId删除SeminarGroup表记录,最后再将seminar的信息删除
/// <param name="courseId">课程Id</param>
/// <returns>true删除成功 false删除失败</returns>
/// <seealso cref="M:Xmu.Crms.Shared.Service.ISeminarService.ListSeminarByCourseIdAsync(System.Int64)" />
/// <seealso cref="M:Xmu.Crms.Shared.Service.ITopicService.DeleteTopicBySeminarIdAsync(System.Int64)" />
/// <seealso cref="M:Xmu.Crms.Shared.Service.ISeminarGroupService.DeleteSeminarGroupBySeminarIdAsync(System.Int64)" />
/// <exception cref="ArgumentException">格式错误时抛出</exception>
/// <exception cref="CourseNotFoundException">该课程不存在时抛出</exception>
public async Task DeleteSeminarByCourseIdAsync(long courseId)
{
if (courseId < 0)
{
throw new ArgumentException();
}
var seminars = await _db.Seminar.Where(_seminar => _seminar.Course.Id == courseId).ToListAsync();
if (seminars == null)
{
throw new SeminarNotFoundException();
}
for (var i = 0; i <= seminars.Count; i++)
{
_db.Seminar.Remove(seminars[i]);
}
await _db.SaveChangesAsync();
}