Validation is a necessary part of any application. There may be many inbuilt validations in an application. If you want to use a custom validation to ensure useful data in an application then you can do that. There may be many custom validations that can be created in LightSwitch, but here we will discuss some custom validations which are as follows.

Step 1 : Open Visual Studio->Click on create new table.

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Step 2 : Create a table, such as employees.

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Step 3 : Go to properties of FirstName->Mark IsRequired checkbox and maximum length(255)->Click on custom validation->Write the code.

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Code

partial void FirstName_Validate(EntityValidationResultsBuilder results)
{
// results.AddPropertyError("<Error-Message>");
 if (this.FirstName != null && !System.Text.RegularExpressions.Regex.IsMatch(this.FirstName, @"^[a-zA-Z]+$"))
{
results.AddPropertyError("Invalid characters, Only alphabets allowed.");
}
}

Step 4 : Go to properties of LastName->Mark IsRequired checkbox and maximum length(255)->Click on custom validation->Write the code.

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Code

partial void LastName_Validate(EntityValidationResultsBuilder results)
{
// results.AddPropertyError("<Error-Message>");
 if (this.LastName != null && !System.Text.RegularExpressions.Regex.IsMatch(this.LastName, @"^[a-zA-Z]+$"))
{
results.AddPropertyError("Invalid characters, Only alphabets allowed.");
}
}

Step 5 : Go to DateOfBirth properties->Click on custom validation.

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Code

partial void DateOfBirth_Validate(EntityValidationResultsBuilder results)
{
// results.AddPropertyError("<Error-Message>");
 if (this.DateOfBirth.CompareTo(this.JoiningDate) > 0)
{
results.AddPropertyError("DateOfBirth should be earlier than joining date");
}
}

or

partial void JoiningDate_Validate(EntityValidationResultsBuilder results)
{
// results.AddPropertyError("<Error-Message>");
 if (this.DateOfBirth.CompareTo(this.JoiningDate) > 0)
{
results.AddPropertyError("Joining date should be after DateOfBirth");
}
}

Step 6 : Now go to InTime properties->Write maximum and minimum value->Click on custom validation->Write the code.

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Code

partial void InTime_Validate(EntityValidationResultsBuilder results)
{
// results.AddPropertyError("<Error-Message>");
 if (InTime > OutTime)
{
results.AddPropertyError("InTime must be before OutTime");
}
}

or

partial void OutTime_Validate(EntityValidationResultsBuilder results)
{
// results.AddPropertyError("<Error-Message>");
 if (OutTime < InTime)
{
results.AddPropertyError("OutTime must be after InTime");
}
}

Step 7 : Now we will add a screen. Right click on screens->Add screen.

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Step 8 : Select editable grid screen->Select screen data (employees)->Ok.

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Step 9 : Run theapplication (F5). If you clear the FirstName column then an error will occur; it will be "A value is required".

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Step 10 : If you entered an integer value in the FirstName column then an error will occur; it will be "Invalid character, Only alphabet allowed".

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Step 11 : If you enter a DateOfBirth that is after the joining date then an error will occur; it will be "DateOfBirth should be earlier than joining date".

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Step 12 : If you enter an InTime that is after the OutTime then an error will occur; it will be "InTime must be before OutTime".

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Conclusion

So custom validation is a validation which is created manually. Validation is required to prevent invalid data and ensure useful data in the application.. So validation is very necessary for an application.

Some helpful resources