FluentValidation unique name validation using database

Question

I have Category model that has Name field, and every category name must be unique. I have made validation and it works when I try to create new Category but I have problem when trying to edit it. For now it's just checking if the name exists and of course it does when I try to edit same category.

Model

[Validator(typeof(CategoryValidator))]
public class Category
{
    public int ID { get; set; }
    public string Name { get; set; }
    virtual public ICollection<Image> Images { get; set; }
}

public class CategoryValidator : AbstractValidator<Category>
{
    public CategoryValidator()
    {
        RuleFor(x => x.Name).NotEmpty().WithMessage("Category name is required.").Must(UniqueName).WithMessage("This category name already exists.");
    }

    private bool UniqueName(string name)
    {
        ProjecteDataContext _db = new ProjecteDataContext();
        var category = _db.Categories.Where(x => x.Name.ToLower() == name.ToLower()).SingleOrDefault();

        if (category == null) return true;
        return false;
    }
}

As you can see I have UniqueName(string name) function, but how can I pass ID, or whole model in it so I can check if it's same id as model I'm trying to edit then it pass. How could I pass something like UniqueName(string name, int? id)? I discovered FluentValidation only today and I can't figure out.

Answer 1

Predicate Validator (aka Must) has an overload, which accepts predicate with two parameters (validated object and property value). In your case predicate will have type Func<Category, string, bool>. So just add Category parameter to your unique name validation method:

private bool UniqueName(Category category, string name)
{
        ProjecteDataContext _db = new ProjecteDataContext();
        var dbCategory = _db.Categories
                            .Where(x => x.Name.ToLower() == name.ToLower())
                            .SingleOrDefault();

        if (dbCategory == null) 
            return true;

        return dbCategory.ID == category.ID;
}