Question

I’m using Linq2SQL and I’m pretty new to it.

I’ve got a User table and a UserData table, the idea being that properties for the User object can be added / removed by adding or removing rows in the UserData table. I did not come up with this particular design but I am more or less stuck with it (as long as I can come up with a solution)

alt text http://www.86th.org/linq2sqlproblem.jpg

I’d like to populate/bind ‘FirstName’ on the User object by something along the lines of setting the value to:

 UserData.Value WHERE UserData.ItemID == User.UserID AND KeyName = 'FirstName' 

Similarly, LastName would be:

 UserData.Value WHERE UserData.ItemID == User.UserID AND KeyName = 'LastName' 

Description of the UserData Table:

• UserData.ItemID is the FK (User.UserID)
• UserData.KeyName is specifying the name of the property
• UserData.Value is the actual value.

How would I setup my User object to handle this so I could do the normal CRUD functionality on this object and have the changes carry through to both tables?

Is this even possible?

Is this bad form?

Answer 1

Quick Note

I renamed UserData to ExtendedProperty and this caused the relationship from User to ExtendedProperty to be called ExtendedProperties.

Summary of changes

1. Created a getter/setter for both FirstName and LastName in the partial User class
2. Grabbed the correct ExtendedProperty element out of the ExtendedProperties collection and either returned or updated the Value property of it.
3. Refactored into a reusable format as shown below

 partial class User {     public string FirstName     {         get { return (string)this.getExtendedProperty('FirstName').Value; }         set { this.getExtendedProperty('FirstName').Value = value; }     }      public string LastName     {         get { return (string)this.getExtendedProperty('LastName').Value; }         set { this.getExtendedProperty('LastName').Value = value; }     }      // Grab a related property out of the collection, any changes to it will be reflected in the database after a submit     private ExtendedProperty getExtendedProperty(string KeyName)     {         // grab the properties that fit the criterea         var properties = (from prop in this.ExtendedProperties where prop.KeyName == KeyName select prop);          // return value         ExtendedProperty property = properties.SingleOrDefault();          // if this is a new user then there arent going to be any properties that match         if (property == null)         {             // Define a new item to add to the collection             property = new ExtendedProperty()             {                 ItemID = this.UserID,                 KeyName = KeyName,                 Value = String.Empty             };              // Add the item we're about to return to the collection             this.ExtendedProperties.Add(property);         }          // either way we have a valid property to return at this point         return property;     } }  

I just hope this isn’t bloated / grossly inefficient.

Edit

In getExtendedProperty, it would error when setting the FirstName or LastName of a newly created User because it would not have any corresponding ExtendedProperty elements in the ExtendedProperties collection as shown below.

User expected = new User(); expected.UserID = Guid.NewGuid(); expected.UserName = 'LJ'; expected.FirstName = 'Leeroy';  // It would error here expected.LastName = 'Jenkins'; 

Because of this I added a check to ensure that new items get added to the ExtendedProperties collection if they are requested and not currently in there.

I also removed setExtendedProperty since I felt it wasn’t necessary and was just a method around a 1 liner anyway.

I would really appreciate any feedback before I accept this answer, I’ll let it sit for a few days.