Is this a bug in binding an ASP.NET model?

Question

I have a simple form in ASP.NET MVC. I am trying to publish these results for a controller action and I am getting weird behavior.

view is a simple HTML table:

View image http://img502.imageshack.us/img502/7271/survey.png

Here is part of the HTML form. View:

  <form action="/Applications/UpdateSurvey" method="post"><table id=questionsTable class=questionsTable border=1> <thead><tr><td>Name</td><td>Answer</td><td>Name Attribute(for debugging)</td></tr> </thead><tbody> <tr> <td>Question 0:</td> <td><input type='checkbox' class='checkboxes' name='updater.questions[0].responseIds' value=1 >1&nbsp;&nbsp;<input type='checkbox' class='checkboxes' name='updater.questions[0].responseIds' value=2 >2&nbsp;&nbsp;<input type='checkbox' class='checkboxes' name='updater.questions[0].responseIds' value=3 >3&nbsp;&nbsp;<input type='checkbox' class='checkboxes' name='updater.questions[0].responseIds' value=4 >4&nbsp;&nbsp;<input type='checkbox' class='checkboxes' name='updater.questions[0].responseIds' value=5 >5&nbsp;&nbsp;</td> <td>updater.questions[0].responseIds</td> </tr> <tr> <td>Question 1:</td> <td><input type='checkbox' class='checkboxes' name='updater.questions[1].responseIds' value=1 >1&nbsp;&nbsp;<input type='checkbox' class='checkboxes' name='updater.questions[1].responseIds' value=2 >2&nbsp;&nbsp;<input type='checkbox' class='checkboxes' name='updater.questions[1].responseIds' value=3 >3&nbsp;&nbsp;<input type='checkbox' class='checkboxes' name='updater.questions[1].responseIds' value=4 >4&nbsp;&nbsp;<input type='checkbox' class='checkboxes' name='updater.questions[1].responseIds' value=5 >5&nbsp;&nbsp;</td> <td>updater.questions[1].responseIds</td> </tr> </tbody></table> <input type="submit" value="Save" /> </form> 

Binding Object:

 public class SurveyUpdater { public Question[] questions { get; set; } } public class Question { public int[] responseIds { get; set; } } 

Controller Action Code:

  public ActionResult UpdateSurvey(SurveyUpdater updater) { if (updater.questions == null) { //I dont understand why this is getting hit } if (updater.questions.Length != 5) { //I dont understand why this is getting hit } return View("TestSurvey"); } 

After testing, here are my observations:

• If I have at least one CheckBox selected for each of the questions, this also works fine in my controller updater.questions.Length == 5 , and the data is perfectly connected.

• If I don’t answer one of the questions at all, I get only an array with the number that I missed: -1 . So if I did not answer question No. 3, I get the array in my control action 2.

• Using logic # 2, if I don't answer the first question, I just get null for updater.questions

What I want to get (and what I expected) is the following:

I would always get questions with a length of 5 , and in cases where I did not answer one of the questions, I would just get an array of size 0 for this responseIds index.

Is this a bug in binding the ASP.NET MVC model? If not, is there something that I don’t see or in any way to get the desired behavior I'm looking for?

Answer 1

The problem, I think, is that when no selections are selected, the inputs do not even return to the query parameters. One way to do this would be to set a hidden flag by default containing a known value that you could filter out initially for each question (the “did not answer” flag if you want). This ensures that you get a selection for each question and that a query parameter exists for each element of the array.

Think about it in terms of what will be sent back. Only those elements that have values, have names and are not disabled, are published. If not all questions matter, how many array elements need to be created? In the best case, it can be assumed that the last element selected should be the size of the array, but what values ​​should it use for any elements between them? The structure cannot read your mind, and perhaps should not, although providing a default value for the type may be reasonable. IMO, it would be better to just omit the value and thus force the developer to provide a default if necessary. This is similar to what is happening.