I know it is possible to manually add attributes to entity properties, but can the entity framework generate this for me? For example, it knows the maximum length is 6 (if you look at the properties in the entity designer).
What happens now is that I get a nasty generic error message with no indication of the field's length.
I suppose I need training in Entity Framework for MVC which I should squeeze in somewhere between deadlines. :-)
Ways to create:
In case of "Database first" this should be constraint. Checks happen in database.
CREATE TABLE suppliers
(
supplier_id numeric(4),
supplier_name varchar2(50),
CONSTRAINT check_supplier_id
CHECK (supplier_id BETWEEN 100 and 9999)
);
Example : source
In case of model first you do this with annotations or validation classes. Example Fluent valitation
public class CustomerValidator: AbstractValidator<Customer> {
public CustomerValidator() {
RuleFor(customer => customer.Surname).NotEmpty();
RuleFor(customer => customer.Forename).NotEmpty().WithMessage("Please specify a first name");
RuleFor(customer => customer.Discount).NotEqual(0).When(customer => customer.HasDiscount);
RuleFor(customer => customer.Address).Length(20, 250);
RuleFor(customer => customer.Postcode).Must(BeAValidPostcode).WithMessage("Please specify a valid postcode");
}
private bool BeAValidPostcode(string postcode) {
// custom postcode validating logic goes here
}
}
Example : source
In case of code first you can add property constraints:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Blog>().Property(p => p.BloggerName).HasMaxLength(10);
}
Example : source
ModelState.IsValid, as is the case for custom data annotations. I have to catch the exception, or use db.GetValidationErrors(), and manually call ModelState.AddModelError for each validation error. I want to know if there is a way to skip this seemingly needless step for all my generated views.You could probably achieve this by creating your own T4 templates.
However, validation is something I won't do in your data layer alone, but especially in your business layer. After all, it's not only the maximum length of a field that is important, but also whether it's mandatory or not, a number within specific ranges, validations that are dependent on other entities, and so on. Not every validation/business rule can be auto-generated, as it mostly also depends on context. Depending on your architecture you can for example don't allow the creation of an object if requirements are not fulfilled.
A nice framework for doing this kind of validation is FluentValidation. It allows you to isolate the validations in separate classes; and even reuse them.
Your data layer could be responsible for data validation like checking foreign key or other constraints.
ModelState.IsValid) without having to manually handle the exception in all my generated controllers.