“user may do X is user owns object Y”: Implement logic in Model Validation or Controller logic?
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30-04-2021 - |
Pregunta
Consider, for example's sake, the logic "A user may only edit or delete a comment that the user has authored".
My Controller Actions will repeat the logic of checking whether the currently logged in user can affect the comment. Example
[Authorize]
public ActionResult DeleteComment(int comment_id)
{
var comment = CommentsRepository.getCommentById(comment_id);
if(comment == null)
// Cannot find comment, return bad input
return new HttpStatusCodeResult(400);
if(comment.author != User.Identity.Name)
// User not allowed to delete this comment, return Forbidden
return new HttpStatusCodeResult(403);
// Error checking passed, continue with delete action
return new HttpStatusCodeResult(200);
}
Of course, I can bundle that logic up in a method so that I'm not copy / pasting that snippet; however, taking that code out of the controller and putting it in a ValidationAttribute keeps my Action smaller and easier to write tests for. Example
public class MustBeCommentAuthorAttribute : ValidationAttribute
{
// Import attribute for Dependency Injection
[Import]
ICommentRepository CommentRepository { get; set; }
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
int comment_id = (int)value;
var comment = CommentsRepository.getCommentById(comment_id);
if(comment == null)
return new ValidationResult("No comment with that ID");
if(comment.author != HttpContext.Current.User.Identity.Name)
return new ValidationResult("Cannot edit this comment");
// No errors
return ValidationResult.Success;
}
}
public class DeleteCommentModel
{
[MustBeCommentAuthor]
public int comment_id { get; set; }
}
Is Model Validation the right tool for this job? I like taking that concern out of the controller Action; but in this case, it may complicate things further. This is especially true when you consider that this Action is part of a RESTful API and needs to return a different HTTP Status Code depending on the Validation errors in the ModelState.
Is there "best practice" in this case?
Solución
Personally, I think that it looks nice, but you are getting carried away with annotations. I think that this does not belong in your presentation layer and it should be handled by your service layer.
I would have something on the lines of:
[Authorize]
public ActionResult DeleteComment(int comment_id)
{
try
{
var result = CommentsService.GetComment(comment_id, Auth.Username);
// Show success to the user
}
catch(Exception e)
{
// Handle by displaying relevant message to the user
}
}