数据库中不需要的属性的必需属性

Question

I have a form, where some fields are mandatory. A few of the mandatory fields have not always been mandatory, hence there are null values in the database.

If I add [Required] for the property, I will get a SqlNullValueException, because there are null values in the database.

What is the best practice to get a field to behave as if it had a [Required] attribute?

[Required]
public string? foo { get; set; }

Answer 1

You're a bit light on context here, but I assume you are using Entity Framework and you have a class setup for the entity and this is what has your [required] field. I am then assuming you are using this same class with your form.

If this is the case then, I would advise you to create a second class which will act as your view model. This way you have a data model (entity class) and a view model (front end specific class). Then you can easily separate the logic of the two behaviours.

You can use something like AutoMapper to make transferring of property values between the two a little easier too.