LINQ中的数据冲突

以下是查看冲突所在位置的方法(这是一个MSDN示例,因此您需要进行大量自定义):

try
{
    db.SubmitChanges(ConflictMode.ContinueOnConflict);
}
catch (ChangeConflictException e)
{
    Console.WriteLine("Optimistic concurrency error.");
    Console.WriteLine(e.Message);
    Console.ReadLine();
    foreach (ObjectChangeConflict occ in db.ChangeConflicts)
    {
        MetaTable metatable = db.Mapping.GetTable(occ.Object.GetType());
        Customer entityInConflict = (Customer)occ.Object;
        Console.WriteLine("Table name: {0}", metatable.TableName);
        Console.Write("Customer ID: ");
        Console.WriteLine(entityInConflict.CustomerID);
        foreach (MemberChangeConflict mcc in occ.MemberConflicts)
        {
            object currVal = mcc.CurrentValue;
            object origVal = mcc.OriginalValue;
            object databaseVal = mcc.DatabaseValue;
            MemberInfo mi = mcc.Member;
            Console.WriteLine("Member: {0}", mi.Name);
            Console.WriteLine("current value: {0}", currVal);
            Console.WriteLine("original value: {0}", origVal);
            Console.WriteLine("database value: {0}", databaseVal);
        }
    }
}

要使其忽略问题并无论如何提交,请执行以下操作:

db.SubmitChanges(ConflictMode.ContinueOnConflict);

这些(您可以将其添加到datacontext的分部类中)可能有助于您了解其工作原理:

public void SubmitKeepChanges()
{
    try
    {
        this.SubmitChanges(ConflictMode.ContinueOnConflict);
    }
    catch (ChangeConflictException e)
    {
        foreach (ObjectChangeConflict occ in this.ChangeConflicts)
        {
            //Keep current values that have changed, 
//updates other values with database values

            occ.Resolve(RefreshMode.KeepChanges);
        }
    }
}

public void SubmitOverwrite()
{
    try
    {
        this.SubmitChanges(ConflictMode.ContinueOnConflict);
    }
    catch (ChangeConflictException e)
    {
        foreach (ObjectChangeConflict occ in this.ChangeConflicts)
        {
            // All database values overwrite current values with 
//values from database

            occ.Resolve(RefreshMode.OverwriteCurrentValues);
        }
    }
}

public void SubmitKeepCurrent()
{
    try
    {
        this.SubmitChanges(ConflictMode.ContinueOnConflict);
    }
    catch (ChangeConflictException e)
    {
        foreach (ObjectChangeConflict occ in this.ChangeConflicts)
        {
            //Swap the original values with the values retrieved from the database. No current value is modified
            occ.Resolve(RefreshMode.KeepCurrentValues);
        }
    }
}

我所做的是通过一个DataContext加载一个LINQ对象,然后尝试通过另一个DataContext为该对象提交changes(),给出了完全相同的错误。

值得一看,特别是如果你认为根本不应该有任何冲突。

当O/R-Designer中的列或类型与SQL数据库中的列不匹配时,有时也会出现错误“Row not found or changed”(行未找到或更改),尤其是当一列在SQL中可为null,但在O/R-Designer中不可为null时。

因此,请检查O/R-Designer中的表映射是否与SQL数据库匹配!

感谢@vzczc。我发现您给出的示例非常有用,但我需要在解析后再次调用SubmitChanges。这里是我修改过的方法-希望它能帮助别人。

    /// <summary>
    /// Submits changes and, if there are any conflicts, the database changes are auto-merged for 
    /// members that client has not modified (client wins, but database changes are preserved if possible)
    /// </summary>
    public void SubmitKeepChanges()
    {
        this.Submit(RefreshMode.KeepChanges);
    }

    /// <summary>
    /// Submits changes and, if there are any conflicts, simply overwrites what is in the database (client wins).
    /// </summary>
    public void SubmitOverwriteDatabase()
    {
        this.Submit(RefreshMode.KeepCurrentValues);
    }

    /// <summary>
    /// Submits changes and, if there are any conflicts, all database values overwrite
    /// current values (client loses).
    /// </summary>
    public void SubmitUseDatabase()
    {
        this.Submit(RefreshMode.OverwriteCurrentValues);
    }

    /// <summary>
    /// Submits the changes using the specified refresh mode.
    /// </summary>
    /// <param name="refreshMode">The refresh mode.</param>
    private void Submit(RefreshMode refreshMode)
    {
        bool moreToSubmit = true;
        do
        {
            try
            {
                this.SubmitChanges(ConflictMode.ContinueOnConflict);
                moreToSubmit = false;
            }
            catch (ChangeConflictException)
            {
                foreach (ObjectChangeConflict occ in this.ChangeConflicts)
                {
                    occ.Resolve(refreshMode);
                }
            }
        }
        while (moreToSubmit);

    }

未找到或未更改行在大多数情况下是并发问题

如果其他用户正在更改同一条记录,则会弹出这些错误,因为该记录已被其他用户更改。因此,当您想要消除这些错误时,您应该在应用程序中处理并发性。如果处理好并发性,就不会再出现这些错误。上面的代码示例是处理并发错误的一种方法。缺少的是,在并发错误的情况下,您应该将 refresh 这些方法中的变量,因此 是 true 更新后需要在屏幕上刷新数据,以便您也可以看到其他用户所做的更新。

    /// <remarks>
    ///     linq has optimistic concurrency, so objects can be changed by other users, while
    ///     submitted keep database changes but make sure users changes are also submitted
    ///     and refreshed with the changes already made by other users.
    /// </remarks>
    /// <returns>return if a refresh is needed.</returns>
    public bool SubmitKeepChanges()
    {
        // try to submit changes to the database.
        bool refresh = false;
        try
        {
            base.SubmitChanges(ConflictMode.ContinueOnConflict);
        }

        /* 
         * assume a "row not found or changed" exception, if thats the case:
         * - keep the database changes already made by other users and make sure
         * - this users changes are also written to the database
         */
        catch (ChangeConflictException)
        {
            // show where the conflicts are in debug mode
            ShowConflicts();

            // get database values and combine with user changes 
            base.ChangeConflicts.ResolveAll(RefreshMode.KeepChanges);

            // submit those combined changes again to the database.
            base.SubmitChanges();

            // a refresh is needed
            refresh = true;
        }

        // return if a refresh is needed.
        return refresh;
    }

您可以将实体上的“更新检查”属性设置为“从不”,以停止该字段用于乐观并发检查。

您还可以使用:

db.SubmitChanges(ConflictMode.ContinueOnConflict)