Mapping a code table in BLToolkit

Question

In my database, there is one large "code" table with system code look-ups for values used all over the system. Like so:

[TableName("code_entries")]                         public class Code {
    [MapField("code_nbr")][PrimaryKey, Identity]    public int Id;
    [MapField("code")]                              public string Value;
}

I am new to BLToolkit, and am hoping that there is a concept similar to the static Mappings I have seen, but that will allow me to easily map occurrences of these codes in other tables to their respective values. For instance:

    [TableName("person")]                               public class Person {
        [MapField("person_nbr")][PrimaryKey, Identity]  public int Id;
        [MapField("dob")][Nullable]                     public int BirthDate;
        [MapField("eye_color")][Nullable]               public int EyeColorCode;
        [MapField("hair_color")][Nullable]              public int HairColorCode;    
}

If EyeColorCode and HairColorCode above map to values in the Codes table, can I create an easy way to map that data within the OR classes and obtain the whole object in a single query?

I'd like to end up with something like:

// person.Id = 1
// person.DOB = some date
// person.EyeColor = "Blue"
// person.HairColor = "Brown"

Answer 1

It's not really what you wanted but you could use Associations

so you could add this to your Person class

[Association(ThisKey="eye_color", OtherKey="code_nbr", CanBeNull=true)]
public Code EyeColor;

[Association(ThisKey="hair_color", OtherKey="code_nbr", CanBeNull=true)]
public Code HairColor;

And then do something like

from p in db.Person
select new
{
    Id        = p.Id,
    DOB       = p.BirthDate,
    EyeColor  = p.EyeColor.Value,
    HairColor = p.HairColor.Value
};

Anyway these seem like the type of codes that almost never change I usually put these on the client at startup and then fill in the description when I display the data, makes everything a lot easier, and if I can't find an Id then I just refresh the collection

Answer 2

Thanks David. I went with your approach, but modified it slightly to make it a little less painful form me. I added associations to my classes as in your example:

[Association(ThisKey = "EyeColorCode", OtherKey = "Id")]    public Code EyeColor { get; set; }
[Association(ThisKey = "HairColorCode", OtherKey = "Id")]   public Code HairColor { get; set; }

Then I wrote an extension method. It takes a new object, and merges all the writable properties into the source object. Using this, I don't need to specify every single property in my query, i.e.:

from p in db.Person
select p.PropertyUnion(new Person() {
{
    EyeColor  = p.EyeColor,
    HairColor = p.HairColor
};

This saves me quite a bit of code for some of my more complex objects, and I think it is more readable. Here is the code for the extension method:

/// <summary>
/// Union by retrieving all non-null properties from source parameter and setting those properties on the instance object
/// </summary>
public static T PropertyUnion<T>(this T destination, T source) {
    // Don't copy from a null object
    if (Object.ReferenceEquals(source, null) || Object.ReferenceEquals(destination, null)) {
        return destination;
    }
    // copy properties
    foreach (var property in source.GetType().GetProperties()) {
        if (!property.CanWrite || !property.CanRead)
            continue;
        var match = destination.GetType().GetProperty(property.Name);
        if (!match.CanWrite || !match.CanRead)
            throw new MethodAccessException("Matching property '" + match.Name + "' must allow both read and write operations.");
        var value = property.GetValue(source, null);
        if (value != null && !value.Equals(Activator.CreateInstance(property.PropertyType)))
            match.SetValue(destination, value, null);
    }
    return destination;
}

Thanks again for your help!