Enumerations

FHIR makes extensive use of terminologies, with many elements represented as “codes”. The allowed values for a code are defined by valuesets. When an element is bound to an enumerable and fixed valueset, and it cannot contain any other codes beyond those specified in that valueset (referred to in FHIR terminology as a “required” valueset), the SDK generates a .NET enum to represent that valueset. This approach ensures that only valid codes can be used and makes the allowed codes easily accessible through IntelliSense.

For instance, the Patient resource has a fixed ValueSet for the gender element.

This is translated into an enumeration in the SDK:

Since this code is always a primitive, you can simply assign the appropriate enum value to its “helper property”:

pat.Gender = AdministrativeGender.Male;

Code<T>

The coded element in the POCO uses a specialized datatype, which is a subclass of Code called Code<T>. Here, T represents the generated enum type. Like all primitive types, both Code and Code<T> have a Value property. However, for Code, the Value property is of type string, whereas for Code<T>, the Value property is of the enum type:

class Code
{
    ...
    public string Value { ... }
    ...
}

class Code<T> : Code // other details omitted
{
    ...
    new public T? Value { ... }

    /// <summary>
    /// The literal of the code value, taken from the enum in <see cref="Value"/>.
    /// </summary>
    public override string? Literal { ... }

    /// <summary>
    /// The system of the code value, taken from the enum in <see cref="Value"/>.
    /// </summary>
    public override string? System { ... }
}

This design allows you to retrieve the coded value either as a string or as the parsed enum value. However, exercise caution: if you set the Code.Value to a string that is not part of the enum, attempting to access Code<T>.Value will result in an exception.

Code<T> also provides direct access to the valueset’s canonical url (System) and literal value (Literal). The Literal property contains the same value as the string representation of Code.