Representing paths in SQL Server database (ASP.NET MVC)

Question

I am writing a small bookmarking tool in ASP.NET MVC, and each bookmark is stored in a folder. I am currently representing this by simply storing a path as a string in the database, but when it comes to beginning to display items by folder and list folders this seems like an efficient way to do it.

Is there any built-in way to represent and then manipulate paths in a database? Or an accepted best practice?

Answer 1

If you are talking paths like in filesystem paths, then you might want to start thinking about about a trees and a hierachical system.

In essence, you will have an additional table in a form named like Category or something, which is self referencing with a ParentId . With this you can iterate along your caegories until, there is no parent or child item, depending on the direction of your query and build a path with the result of your query. This of course can get ugly, if your bookmarkings have more then 1 category. You will want to get some additional validation into this.

The following code is acutally from an article on the web, which I used myself, but I can't find the article again, to quote it as the source.

public class Category
{
    public int CategoryId { get; set; }
    public string Name { get; set; }
    public int? ParentId { get; set; }
    public virtual Category Parent { get; set; }
    public virtual ICollection<Category> Children { get; set; }
}

public class CategoryMapping : EntityTypeConfiguration<Category> 
{
    public CategoryMapping() 
    {
        HasKey(x => x.CategoryId);

        Property(x => x.CategoryId).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

        Property(x => x.Name)
            .IsRequired()
            .HasMaxLength(255);

        //Parent is optional, because root node has no parent
        HasOptional(x => x.Parent)
            .WithMany(x => x.Children)
            .HasForeignKey(x => x.ParentId)
            .WillCascadeOnDelete(false);
    }
}

References:

• http://sqllessons.com/categories.html
• http://www.sitepoint.com/hierarchical-data-database/
• Entity Framework Code First Self Referencing Parent Child with Payload