Question

我对实体框架有疑问。在我的程序中，我首先用数据填充了我的DbContext。然后，我需要从数据库表中删除所有数据，但前提是要保存新数据。如果db.Savechanges（）抛出异常，我需要我的旧数据仍然在表中。

我的代码是：

static void Main(string[] args)
        {
            PdmContext db = new PdmContext();

            FillDbContext();

            try
            {

                if (db.SaveChanges() > 0)
                {
                    using (var del = new PdmContext())
                    {
                        DeleteModel.deleteFromAllTables();
                    }
                    db.SaveChanges();
                }
            }
            catch (Exception exp)
            {
                Logger.Log("Exception (global catch));
            }
        }

我似乎无法弄清楚。有人可以帮忙吗？：）

Answer 1

您可以使用select g.groupname, m.membername, su.* from (select groupid, memberid, max(subscribed) as subscribed, max(sdate) as sdate, max(unsubscribed) as unsubscribed, max(udate) as udate from ((select groupid, memberid, 1 as subscribed, date as sdate, 0 as unsubscribed, null as udate from subscribed s ) union all (select groupid, memberid, 0 as subscribed, null as sdate, 1 as unsubscribed, date as udate from subscribed s ) ) su group by groupid, memberid ) join groups g on g.groupid = su.groupid join member m on m.memberid = su.memberid;，如果在某个阶段操作失败，它将确保恢复在其范围内完成的操作：

Transaction

现在，对数据库的更改将是原子性的，因此它将仅保留所有更改或根本不保留所有更改。为了简单起见，我没有包括异常处理代码，但是由于任何原因，如果未执行using (var scope = new TransactionScope(TransactionScopeOption.Required)) { using (var del = new PdmContext()) { DeleteModel.deleteFromAllTables(); } db.SaveChanges(); scope.Complete(); // commits the transaction }并且控件存在事务块而未执行，则该事务将被回滚。

Answer 2

您需要使用交易。

查看如何使用它：

    using (var dbContextTransaction = PdmContext.Database.BeginTransaction())
            {
                try
                {
                   // HERE your operation insert etc.

                    PdmContext.SaveChanges();

                    dbContextTransaction.Commit(); // here, apply your operation
                }
                catch (Exception)
                {
                    dbContextTransaction.Rollback(); // here, undo your operations
                }
            }

Answer 3

您可以通过事务管理来处理这种情况。

有两种处理方法。

1）您可以对所有操作使用单个dbcontext，而不是对单个操作创建多个dbcontext。

using (var context = new SchoolContext())
{

    try
    {


        context.Students.Add(new Student()
        {
            FirstName = "Rama2",
            StandardId = standard.StandardId
        });


        context.Courses.Add(new Course() { CourseName = "Computer Science" });
        context.SaveChanges();

        transaction.Commit();
    }
    catch (Exception ex)
    {
        transaction.Rollback();
        Console.WriteLine("Error occurred.");
    }
}

2）使用单个DbContextTransaction对象：

using (var context = new SchoolContext())
{
context.Database.Log = Console.Write;

using (DbContextTransaction transaction = context.Database.BeginTransaction())
{
    try
    {
          context.Students.Add(new Student()
        {
            FirstName = "Rama2",
            StandardId = standard.StandardId
        });


        context.SaveChanges();

        context.Courses.Add(new Course() { CourseName = "Computer Science" });
        context.SaveChanges();

        transaction.Commit();
    }
    catch (Exception ex)
    {
        transaction.Rollback();
        Console.WriteLine("Error occurred.");
    }
}
}

我希望它对您有用。

数据库上下文保存（如果有效）

3 个答案: