Invalid Values and ModelState

Let's face it, life isn't perfect, and 0:00 neither will our form field values be perfect, far from it. 0:03 Our app needs to be able to handle invalid values. 0:07 Press F5 to start the app and browse to the Add Entry page. 0:10 What happens when we supply an invalid value for the date field? 0:15 I'll enter ASDF, and save the form. 0:20 Here in the Locals window, we can see that the day parameter is null. 0:24 This makes sense though the MPC model binder 0:33 wasn't able to convert the text ASDF to a date time value. 0:36 Ideally, we display a message back to the user asking, 0:41 asking them to provide a valid value for the date field. 0:44 We'll see how to do this in the later video. 0:48 For now, let's figure out how to redisplay the invalid value back to the user. 0:50 If we look at the request form value, we can see the value that we provided. 0:56 So, we could use the request form property to get the provided value when it's 1:01 invalid but, just like the last time we considered using the request object, 1:06 NVC provides a better way, the controller's model state property. 1:11 The model state contains a collection of the name value pairs that were posted 1:15 to the server along with a collection of error messages for each value submitted. 1:19 Here is a collection of the keys that together represent our model, 1:24 and here's a collection of the values. 1:28 Each key is defined by the intersection of our action methods parameter names and 1:37 the posted form field names. 1:43 We can add a key to ModelState by adding a parameter to our action methods parameter 1:45 list, provided that the posted form data also contains a field with the same name. 1:50 Removing a key from ModelState is as simple as removing the parameter 1:56 from the action method parameter list, or removing the field from the view. 1:59 Each value is actually a ModelState object that contains errors in value properties. 2:04 The errors property is a collection allowing each value to have one or 2:10 more errors. 2:15 We can see that the first element, which is the value for 2:16 the date field, has one error. 2:19 The parameter conversion from type system string to type system date time failed. 2:21 If we expand the value property, we can see that it in turn 2:27 contains an AttemptedValue property that contains our invalid value. 2:31 We can use the AttemptedValue properties instead of our parameters for 2:35 the values that we flow back to the form. 2:39 ModelState[''] .value.AttemptedValue, 2:47 then copy and paste this code down to 2:54 each of our view bag properties. 2:59 Then go back and fill in the ModelState keys. 3:16 Date. 3:23 Activity ID. 3:24 Duration. 3:29 Intensity. 3:32 Exclude. 3:36 And notes. 3:41 Let's test our form again. 3:44 If I enter 1/1/2016 for the date, and save the form 3:50 We can see in the Locals window, that the date parameter has the correct day 3:57 time value, and the view bag date property has the original form field value. 4:02 So far so good. 4:08 Now let's enter ASDF, and save the form. 4:09 The day parameter value is now null, but 4:16 the view bag day property still contains the original form field value. 4:19 Success. 4:25 Go ahead and stop the app. 4:27 If you're using GitHub, let's commit our changes. 4:30 [Blank Audio] Enter a commit message of, 4:33 Updated the EntriesController Add 4:40 method to handle invalid values, and click the Commit All button. 4:46 So while we came up with a solution for handling invalid form field values, 4:56 we're having to do a lot of manual lifting, which is not ideal. 5:01 We don't want to write all of this code if we don't have to. 5:05 Right? 5:09 In the next video, we'll see how NVC can help. 5:10