Code Monkey’s Cubicle

Awhile back I had a discussion about user permissions with a client. Specifically how to store the permissions in the database. As a software developer I wanted my object model to have explicit control over the security model. If you wanted to alter a person’s security you’d need to do so via a utility program or perhaps an administrative panel within the software.

The client wanted to be able to alter a field within a table in the database to change permissions. He thought it was much more efficient to have a DBA hop into the database and change a field. He further thought have a bunch of fields Boolean fields like “Read”, “Write”, “Publish”, “Edit”, and “Delete” were too cumbersome. He wanted to have a bit string where each bit represented a yes/no relationship with a type of permission.

This is something that can be represented beautiful with a special type of enum. Adding the [Flags] attribute to an enum turns it into a bit string just like above. It is implemented as follows.

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[Flags]
public enum Permissions {
     None = 0
     Read = 0x0001,
     Write = 0x0002,
     ReadWrite = Permissions.Read | Permissions.Write,
     Execute = 0x0004,
     Delete = 0x0005
}

As you can see it looks as though it is a simple enum but isn’t quite that. You are allowed to combine enum values to create other values.

What is especially great is that

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Permissions permissions = Permissions.Read | Permissions.Execute;
User user = new User("robber.baron", permissions);
 
Console.Writeline(user.permissions.ToString());

The output of the final line is very user friendly. The output is:

Read, Execute

This is a native part of the common language runtime and is part of the .Net base library. This is a fantastic and simple language feature that provides a simple and intuitive way of dealing with the concept of bit strings without custom code.

I’ll never worry about having to implement a bit string again. In fact I might start using them more often.