找到DBUpdateException的原因

Question

在调用时DbContext.SaveChanges,我得到一个DbUpdateException:

EntityFramework.dll中发生了未处理的"System.Data.Entity.Infrastructure.DbUpdateException"类型异常.附加信息:更新条目时发生错误.有关详细信息,请参阅内部异常

不幸的是,没有内在的例外(至少,不是我能看到的).有没有办法确切地知道为什么SaveChanges抛出异常？至少,看看SaveChanges在发生错误时尝试更新的表格会很有帮助.

Answer 1

这是我对SaveChanges的重写.它给了我一个放置断点的有用位置:

    public override int SaveChanges()
    {
        try
        {
            return base.SaveChanges();
        }
        catch (DbEntityValidationException e)
        {
            foreach (var eve in e.EntityValidationErrors)
            {
                Debug.WriteLine(@"Entity of type ""{0}"" in state ""{1}"" 
                   has the following validation errors:",
                    eve.Entry.Entity.GetType().Name, 
                    eve.Entry.State);
                foreach (var ve in eve.ValidationErrors)
                {
                    Debug.WriteLine(@"- Property: ""{0}"", Error: ""{1}""",
                        ve.PropertyName, ve.ErrorMessage);
                }
            }
            throw;
        }
        catch(DbUpdateException e)
        {
           //Add your code to inspect the inner exception and/or
           //e.Entries here.
           //Or just use the debugger.
           //Added this catch (after the comments below) to make it more obvious 
           //how this code might help this specific problem
        }
        catch (Exception e)
        {
            Debug.WriteLine(e.Message);
            throw;
        }
    }

参考:

一个或多个实体的验证失败.有关详细信息,请参阅"EntityValidationErrors"属性

Answer 2

这是我对SaveChanges的重写,显示了处理DbUpdateException的其他代码(根据问题).

    public override int SaveChanges()
    {
        try
        {
            return base.SaveChanges();
        }
        catch (DbEntityValidationException vex)
        {
            var exception = HandleDbEntityValidationException(vex);
            throw exception;
        }
        catch(DbUpdateException dbu)
        {
            var exception = HandleDbUpdateException(dbu);
            throw exception;
        }
    }

    private Exception HandleDbUpdateException(DbUpdateException dbu)
    {
        var builder = new StringBuilder("A DbUpdateException was caught while saving changes. ");

        try
        {
            foreach (var result in dbu.Entries)
            {
                builder.AppendFormat("Type: {0} was part of the problem. ", result.Entity.GetType().Name);
            }
        }
        catch (Exception e)
        {
            builder.Append("Error parsing DbUpdateException: " + e.ToString());
        }

        string message = builder.ToString();
        return new Exception(message, dbu);
    }

我没有使日志代码非常具体,但它改进了类似的标准错误消息:

The conversion of a datetime2 data type to a datetime data type resulted in an out-of-range value.

这样,至少我可以看到哪个实体有问题,而这通常足以解决问题.

Answer 3

根据Colin的回答,可以提供有关EF持久性故障的完整详细信息,如下所示:

public bool SaveChangesEx()
{
    try
    {
        SaveChanges();
        return true;
    }
    catch (DbEntityValidationException exc)
    {
        // just to ease debugging
        foreach (var error in exc.EntityValidationErrors)
        {
            foreach (var errorMsg in error.ValidationErrors)
            {
                // logging service based on NLog
                Logger.Log(LogLevel.Error, $"Error trying to save EF changes - {errorMsg.ErrorMessage}");
            }
        }

        throw;
    }
    catch (DbUpdateException e)
    {
        var sb = new StringBuilder();
        sb.AppendLine($"DbUpdateException error details - {e?.InnerException?.InnerException?.Message}");

        foreach (var eve in e.Entries)
        {
            sb.AppendLine($"Entity of type {eve.Entity.GetType().Name} in state {eve.State} could not be updated");
        }

        Logger.Log(LogLevel.Error, e, sb.ToString());

        throw;
    }
}

除了验证错误,更新异常将输出一般错误和上下文信息.

注意:此代码需要C#6.0才能工作,因为它使用空传播和字符串插值.

对于.NET Core,代码稍有更改,因为可能引发的异常具有不同的结构/填充不同:

    public void SaveChangesEx()
    {
        try
        {
            // this triggers defined validations such as required
            Context.Validate();
            // actual save of changes
            Context.SaveChangesInner();
        }
        catch (ValidationException exc)
        {
            Logger.LogError(exc, $"{nameof(SaveChanges)} validation exception: {exc?.Message}");
            throw;
        }
        catch (DbUpdateException exc)
        {
            Logger.LogError(exc, $"{nameof(SaveChanges)} db update error: {exc?.InnerException?.Message}");
            throw;
        }
        catch (Exception exc)
        {
            // should never reach here. If it does, handle the more specific exception
            Logger.LogError(exc, $"{nameof(SaveChanges)} generic error: {exc.Message}");
            throw;
        }
    }

如果不立即处理相同的上下文,则可以增强上下文以自动拒绝失败时的更改:

public void RejectChanges()
{
    foreach (var entry in ChangeTracker.Entries().Where(e => e.Entity != null).ToList())
    {
        switch (entry.State)
        {
            case EntityState.Modified:
            case EntityState.Deleted:
                entry.State = EntityState.Modified; //Revert changes made to deleted entity.
                entry.State = EntityState.Unchanged;
                break;
            case EntityState.Added:
                entry.State = EntityState.Detached;
                break;
        }
    }
}

public bool SaveChangesInner()
{
    try
    {
        SaveChanges();
        return true;
    }
    catch (Exception)
    {
        RejectChanges();
        throw;
    }
}

Answer 4

当真正的异常似乎在某处丢失时，最好的办法是打破每个异常。无论它是在某个地方被抓住还是被吞下，在你够不着的地方，调试器都会崩溃，让你看看发生了什么。

有关更多信息，请参阅此 MSDN 链接：

如何：在抛出异常时中断