Custom Validation of a Computed Property

Question

Hi I have searched this, but can't find a solution :(  Please help!

Ok so my problem is that I can't get the validation rule to fire!  The calculation of the number of SatelliteFarmers works...but my validation never fires.  Basically I just need to call the validate method after everytime the NumberSatFarmers_Compute() method is called...but i have no idea of how to do that :(

here the code is;

public partial class Mentor
    {
       public Int32 count;
        partial void NumberSatFarmers_Compute(ref int result)
        {

            count = (from farmer in SatelliteFarmers
                     where farmer.Mentor.Id == this.Id
                     select farmer).Count();
            result = count;
        }

        partial void NumberSatFarmers_Validate(EntityValidationResultsBuilder results)
        {
            if (this.NumberSatFarmers>3)
            results.AddPropertyError("<Error-Message>");

        }
}


     

Answer 1

I Don't Know will it work or not as i had not tried but you can try this thing,

You can call the Validate Sub Routine after assigning the value for NumberSatFarmer i.e after result = count.

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Sharad Soni

Answer 2

yes, but how do I call it in C# code in lightswitch? Cause the method is looking for the parameter (EntityValidationResultsBuilder results) so i dont know how I am meant to call it....

Answer 3

It seems that your app doesn't have a callback subscribed to your method.

Can I suggest renaming your method to Mentor_Validate() instead?  This means that the validation will be at the record level rather than the field level, but I think from memory that the validators in LightSwitch are record level by default.

Happy to be told I'm wrong of course. :)

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Jeremy Huppatz
Managing Consultant
Solitaire Systems

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Answer 4

Hey Jeremy,

Unfortunately it didn't work...the validation still does not fire.

Here a screenshot is;

Answer 5

Hey I8aNoob (nice nickname, didn't get it at first but really funny :-))

The reason why your validation doesn't fire is because validation only is triggered if a property on the actual entity (Mentor) changes.  In your case, Mentor doesn't change in itself, but the number of child entities change (SatFarmers).

I found a small workaround which works with a couple of glitches but does what you need.  You can add a random property on your Mentor ("RandomBool").  Whenever the NumberSatFarmers_Computer method is called, change the value of this random property if a validation error should be thrown.  This will trigger a re-validation (because you changed something on the Mentor-entity) and your validation error will be shown...

In code (sample, adjust to your needs)

        partial void Tab2ItemsLength_Compute(ref int result)
        {
            // Set result to the desired field value
            result = this.Table2Items.Count();
            if(!this.isValid())
                this.SomeRandomBool = !this.SomeRandomBool;
        }
        partial void Tab2ItemsLength_Validate(EntityValidationResultsBuilder results)
        {
            if(!this.isValid())
            {
                results.AddPropertyError("Whoa momma, too many farmers!");
            }
        }
        private bool isValid() {
            return (this.Tab2ItemsLength <= 2);
        }

However...

I'm not really agreeing with your design here.  In your setup, (after modifications above) I can't add a more than 5 sattelite farmers to a mentor because of the validation on your computed property.  However, I can create and add as many sattelite farmers to one mentor from the Satelite farmers list-detail screen.  IMHO, it would be best to move the business logic about the maximum number of sattelite farmers per mentor, to the sattelite farmer entity instead.  (SatteliteFarmer_Created / _Edited / ... methods).  

Keep rocking LS!

Jan

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It's your story - time to switch on the innovation. || About me || LightSwitch blog

Answer 6

Thanks Jan,

Used ur advice and made the validation in SattelliteFarmer and it works now.  I understand how the validation rules work now.  Thanks :)

Answer 7

Ur welcome...

Once again, great nickname! :D

Keep rocking LS!

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It's your story - time to switch on the innovation. || About me || LightSwitch blog