Data Annotation Updates in .NET 8

In .NET 8, we were given some new data annotation options for validating our properties. Let's look at these new options and how to use them in this 10-minute training video.
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[@KarmCraft]

Tim you need to show what happens if you enter an invalid value. Is it design time or runtime? What does it throw?

[@chris_cole]

Love these quick and simple videos. I didn't even realize until now that they had added these.

[@dmytroshchotkin2939]

Thanks, Tim. It would have been nicer if you had shown one use-case scenario. Are the attributes applicable when we deserialize using System.Text serializer only?

[@andergarcia1115]

Thanks, Master. You're amazing as always.

[@anandvgchennai1974]

Thanks for explaining these new cool features. Next time I think MS should come with LengthAfterTrim (5, 25). Most of the time we check the length of string after trimming the values entered.

[@Vsd13]

It would be interesting to know what to do with the project after its development, how to upload your project and database to the server. For example, so that I can send a link to the site I created. Maybe you already have a video that indirectly explains this topic?

[@shadmansudipto7287]

What? You need to watch a beginner aspnet tutorial. There are many on KZbin. Why ask him to make yet another? It doesn't add any value to do what is already done.

[@user-fqlt]

Thanks very useful.

[@aslamsayyedsayyed2885]

Lots of love and respect from India. Thanks for your efforts.

[@IAmTimCorey]

You are welcome.

[@benjaminshinar9509]

seems nice, but I could really use a demo of those. are they checked at runtime or compile time? do they throw exceptions?

[@Anton-Os]

Tim, thanks!

[@IAmTimCorey]

You are welcome.

[@marcusreinicke7352]

Thx Tim, can combined the allowed and denied values with RegEx matching?

[@queenstownswords]

Hello Tim. Great video. Would you need to check for consistency in the database table, in the class definition annotation (this video) and in a UI text attributes? Is there an annotation for keeping DeniedValues - like something that is not UTF-8 - out of the input?

[@IAmTimCorey]

I always check the data whenever a user has access to create/change it. Never trust the user. Data integrity in the database is a whole different topic and not one you would typically address with these types of rules. As for a non-UTF-8 check, that would probably need to be a custom rule.

[@BrentHollett]

Do any of these flow to EF and remove the need for some Entity Configuration steps?

[@kvelez]

Cool excellent man.

[@IAmTimCorey]

Thanks!

[@scdecade]

Hmmm now I'm curious to see the error messages generated by these validations

[@FernandoZamudioC]

Thanks for this wonderful videos ! I hace a question...i usually i used a partial class to define this data annotatios but ModelMetadataType in the Microsoft.aspnetCore.mvc is deprecated ! can you helpme ?

[@IAmTimCorey]

I believe you just need to use the Core version of the library: learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.mvc.modelmetadatatypeattribute?view=aspnetcore-8.0

[@cissemy]

Thanks

[@IAmTimCorey]

You are welcome.

[@dotnetdevni]

i wish they allowed dyanmic annotations so could come from the db

[@Don-ii4vm]

4:38 Is it possible to dynamically set AllowedValues from a table?

[@ajdin3511]

If its data that is a lookup table(values that dont change often), perhaps a table that stores types of roles user can have, I believe you can just create an enum and use its values in data annotation as allowed values and it should work fine, making it dynamic is an issue i dont think this solves.

[@Don-ii4vm]

@@ajdin3511 The values dont change often, but they do change and it would be useful if the software didnt need to be recompiled each time.

[@anandvgchennai1974]

I also had the same question in my mind.

[@Don-ii4vm]

@@anandvgchennai1974 As Luke says, it woiuld be best to write a custom validator in that case.

[@anandvgchennai1974]

@@Don-ii4vm Yes. Thats a good option.

[@DDDD-rr6uo]

Hello IAmTimCorey! I wont you to tell your students when its good to use ai or copilot for coding or how much is it allowed to do so as a new c sharp students who are following your master course

[@IAmTimCorey]

I would recommend avoiding it when you are learning. Copilot is great, but it isn't always right. Learn how to do things right before you get led astray by code that looks right but actually isn't.

[@Maykon861]

Can I validate that there are no duplicate objects in a list?

[@IAmTimCorey]

That would need to be a custom validator. Either that or you could use a specific list type that did not allow duplicates like HashSet.

[@swordblaster2596]

But what's it FOR?

[@IAmTimCorey]

Data validation. So if you have a user fill out a form, you can check to see if the data is valid according to your rules.

[@holger_p]

@@IAmTimCorey So is there a package like EF or Dabber, processing these annotations, or do I have to do it myself, if you say "you can check" ? If I have to do it myself, I can always define the Annotations myself and the entire thing would be useless - if nobody else is processing it. When I just query a remote database into these annotated classes, does the execution fail, if incoming data are invalid.

[@IAmTimCorey]

When the user submits a form, the validations can be automatically checked before the submit button is processed (client-side) and once the data is sent to the server (server-side). It isn't something you need to do manually.

[@holger_p]

@@IAmTimCorey OK, the question came up, cause Entity Framework is building a SQL-structure from such kind of annotations, translating MinLength, MaxLength into Datatype NVarChar(min, max) The term "Data annotations" is not unique to validation.

[@E_G_]

Waiting for BlackFriday Dsicounts :)