Error 500 on Post new entity with TableController and AzureMobileApps

问题

I'm experiencing a problem using TableController on AzureMobileApps. I've created a new Azure Mobile App TableController in visual studio using scaffolding. In post I modified the resulting code adding an attach on the dbContext to avoid creating referenced item during insert on the child table. That's the resulting code:

 public async Task<IHttpActionResult> PostLocation(Location item)
    {
        _context.Accounts.Attach(item.LocationAccount);
        _context.Categories.Attach(item.PrimaryCategory);

        Location current = await InsertAsync(item);
        return CreatedAtRoute("Tables", new { id = current.Id }, current);
    }

The problem is that each time I invoke the post method I get a 500 internal server error on the "CreatedAtRoute" event even if the entity has been correctly inserted.

Any idea on what is the problem ?!

UPDATE: Entity Model

public class Account : EntityData
{
    public Account()
    {
        this.Locations = new HashSet<Location>();
    }

    [Required]
    public string Username { get; set; }

    [Required]
    public string FirstName { get; set; }

    [Required]
    public string LastName { get; set; }

    public virtual ICollection<Location> Locations { get; private set; }
}

public class Location : EntityData
{
    [Required]
    public Account LocationAccount { get; set; }

    ........
}   

Thanks everyone.

回答1:

AFAIK, before you adding Attach related code, if the LocationAccount,PrimaryCategory are the new items, then they would be created automatically. If any of them (LocationAccount,PrimaryCategory) exists in the database table, then you would retrieve the 409 status code.

Based on my test, after added Attach related code, if LocationAccount and PrimaryCategory exist, then you could create new Location item successfully. But if any of them does not exist, then you may get the error as follows:

Per my understanding, you need to check if the navigation properties of Location exist. For the existing navigation property item you could use the DbSet.Attach method to stop the attached entity from inserting, while the new navigation property item, you need to use DbSet.Add or do nothing.

Moreover, you could add the following code in the ConfigureMobileApp method of your Startup.MobileApp.cs file for including error details and return to your client side.

config.IncludeErrorDetailPolicy = IncludeErrorDetailPolicy.Always;

UPDATE:

By default, the referenced Entities (LocationAccount,PrimaryCategory) would be inserted, if any entity exists, then you would receive the 409 as follows:

After added _context.Accounts.Attach(item.LocationAccount);, you could create the Location entity which has relationships with the existing referenced Entities (LocationAccount,PrimaryCategory), if the referenced Entities (LocationAccount,PrimaryCategory) do not exist, you would receive the following error:

For your scenario, you post the existing referenced Entities (LocationAccount,PrimaryCategory) for location. Even though the location item could be successfully created, based on your entity models, you may encounter the 500 error as follows:

You may mark the Locations property in Account entity model as JsonIgnore. Or you need to modify your entity model to ignore the reference Loops when handling serialization.

Moreover, you could leverage the following code snippet instead of CreatedAtRoute.

return Json(current, new JsonSerializerSettings()
{
    ReferenceLoopHandling = ReferenceLoopHandling.Ignore
});

I also tried to set the global setting for SerializerSettings under Startup.MobileApp.cs as follows, but it does not work as expected.

config.Formatters.JsonFormatter.SerializerSettings.Re‌​ferenceLoopHandling = ReferenceLoopHandling.Ignore;

Additionally, you could follow Loop Reference handling in Web API for more detailed approaches.

来源：https://stackoverflow.com/questions/48891640/error-500-on-post-new-entity-with-tablecontroller-and-azuremobileapps