实体框架-重复处理

Question

I am using Entity Framework 6, C#, and MySQL InnoDB as our db engine.

I have the following code to "insert on duplicate update" a record:

public async Task AddHostIdToGroup(HostsToGroup hostToGroup)
{
    using (var context = new MaintDbContext())
    {
        HostsToGroup htg = context.HostsToGroup.SingleOrDefault(hs => hs.HostId == hostToGroup.HostId);

        if (htg != null)
        {
            htg.GroupId = hostToGroup.GroupId;
            await context.SaveChangesAsync();
        }

        else
        {
            context.HostsToGroup.Add(hostToGroup);
            await context.SaveChangesAsync();
        }
    }
}

The code itself looks fine for insert on duplicate update .

Still, on our production server I occasionally see duplicate errors .

My initial thought was that it's a race condition issue.

What can I do to prevent these errors, or how should I handle them?

Answer 1

Your problem is not necessarily the code but what triggers that code. Say the code is triggered by an ASP.net app button, if a user double clicks on the button then it could shoot off two simultaneous requests that results in double entity creation.

So either fix your front end/entry point to eliminate the double create scenario, push everything into a synchronous service/queue that will allow you to deduplicate or use Where instead of Single and handle the duplication in code.