Bundles

Although Bundle is just another resource type in FHIR, and you can fill in the values for the fields in the way that has been described in this chapter, a Bundle is still a bit special. Bundles are used to communicate sets of resources. Usually you will first encounter them when you’re performing a search interaction. In that case, the server will send you a Bundle, and you will browse through the contents to process the data. Sometimes you will need to construct a Bundle instance and fill in the details, for example when you are going to setup a FHIR document, or want to perform a transaction, or if you’re implementing the server side response to a search request.

Looking at the content

A Bundle resource has got some fields that contain metadata about the Bundle, such as the type of Bundle, and a total if the Bundle contains a result from a search or history interaction. The resources that are put in a Bundle, are located in the entry element of the Bundle resource.

Since entry is a 0..* element and a component block, the API provides you with a list of EntryComponent in the Bundle.Entry field. You can loop through that list, or use any of the standard C# List methods to work with the list.

The fully qualified URL identifying the resource that is in the entry, is stored in the FullUrl field of the entry.
The API doesn’t know the type of resource that is in the entry, so the data type for the Resource field in the entry is the base type Resource. You will need to cast to the actual resource type if you want to have access to the fields for that type.

Tip

You can check the Resource.ResourceType field first, if you don’t know the type of resource for an entry.

Suppose we have performed a search interaction on Patient resources, and have stored the results in a variable called result. We can then loop through the resources in the Entry list like this:

foreach (var e in result.Entry)
{
        // Let's write the fully qualified url for the resource to the console:
        Console.WriteLine("Full url for this resource: " + e.FullUrl);

        var pat_entry = (Patient)e.Resource;

        // Do something with this patient, for example write the family name that's in the first
        // element of the name list to the console:
        Console.WriteLine("Patient's last name: " + pat_entry.Name[0].Family);
}

Filling a Bundle

When constructing a Bundle, you will need to look at the definition for the Bundle resource to see which elements are mandatory, just as you would do for other resource types.

Tip

If you want to create a Bundle for a batch or transaction, you can use the helper methods in the API to construct the Bundle correctly, described in the transactions paragraph.

Then, for each resource you want to include in the Bundle, you will add an EntryComponent to the Entry list. This can be done by creating an instance of type EntryComponent, which you fill with the fully qualified URL for the resource, and the resource. Or, you could use the AddResourceEntry method of the Bundle class. This second option creates cleaner code if you only need to fill in the URL and resource. However, if you need to fill in more fields for the EntryComponent class, the first option can be useful.

This example shows both ways:

var collection = new Bundle();
collection.Type = Bundle.BundleType.Collection;

var first_entry = new Bundle.EntryComponent();
first_entry.FullUrl = res1.ResourceBase.ToString() + res1.ResourceType.ToString() + res1.Id;
first_entry.Resource = res1;
collection.Entry.Add(first_entry);

// adding a second entry
collection.AddResourceEntry(res2, "urn:uuid:01d04293-ed74-4f93-aa0a-2f096a693fb1");

In this example we create a Bundle with a general collection of resources, and have set the type accordingly. The first resource we want to add, res1, is a resource that already has a technical id. For now, we have constructed the FullUrl with parts of the information that’s in the resource instance, but we could also have used the helper methods for ResourceIdentity which are in the Hl7.Fhir.Rest namespace. See About resource identity for more information.
The second resource we add to this collection, res2, is a new resource that has not been stored, and doesn’t have a technical identifier assigned to it yet. We still have to fill in the FullUrl field, as demanded by the bdl-7 constraint for Bundle in the specification. This is done by creating a temporary UUID, and representing that as a fully qualified URL with the urn:uuid: notation.