Datagrid FluentValidationHandler support unavailable or undocumented

[dsmiller95]

Describe the bug
The datagrid ValidationsHandlerType does not appear to be respected when set to FluentValidationHandler. The validation handler type defined on a DataGrid is not used when validating columns during edit/create flows. Specifically this prevents the use of FluentValidationHandler on the top-level datagrid.

To Reproduce

minimal code example:
https://github.com/dsmiller95/data-grid-fluent-validation-example/blob/fe93ed4ac1a4211a3ab490f1f4d8946a789a801f/DataGridFluentValidation/Pages/DataGridPage.razor

Steps to reproduce the behavior:

1. Follow setup steps for Blazorise.FluentValidation : https://blazorise.com/docs/extensions/fluent-validation
2. Copy example for DataGrid validation : https://blazorise.com/docs/extensions/datagrid/validations
3. Set ValidationsHandlerType="typeof(FluentValidationHandler)"
4. Implement EmployeeValidator : AbstractValidator<Employee>
5. Run the app, edit the Employee row
6. Observe that the validations are not applied

Expected behavior
The validations in EmployeeValidator are checked over the data before saving, or while editing.

Screenshots
Data grid allows saving an employee with no name, when a FluentValidator is defined to explicitly deny this:

Additional context
I believe the ValidationsHandlerType is completely ignored in this use case. In this revision of the code , we set ValidationsHandlerType="typeof(TestValidationHandler)". TestValidationHandler throws an exception on all methods, but no exceptions are thrown when running the app. And a breakpoint set in TestValidationHandler will not be hit.

This may be intentional, but the documentation implies it is not, as I have not overriden the HandlerType anywhere else in the code:

Attributes
DataGrid

Name	Description
ValidationsHandlerType	Defines the default handler type that will be used by the validation, unless it is overriden by Validation.HandlerType property.

[stsrki]

Thanks for reporting it.

You're right. It seems that it always fallbacks to DataAnnotationValidationHandler internally in our _DataGridCell component.

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We will fix it for the next maintenance release.