Getting history

There are several ways to retrieve version history for resources with the FHIR client.

Retrieving the history of a specific resource

The version history of a specific resource can be retrieved with the History(System.Uri location, [System.DateTimeOffset? since = null], [int? pageSize = null]) function. It returns a bundle with the history for the indicated instance, for example:

var location = new Uri("http://spark.furore.com/fhir/Patient/31");
Bundle results = client.History(location);

Note that the Bundle may contain both ResourceEntries and DeletedEntries. It is possible to specify a date, to include only the changes that were made after the given date. Also you can specify the maximum number of results returned (see Paged Results below). Additionally, there is a History() overload where you can pass the location of the resource as a string in the first parameter instead.

Retrieving history for a type of resource

Sometimes you may want to retrieve the history for a type of resource instead of an instance (e.g. the versions of all Patients). In this case you can use TypeHistory<TResource>([System.DateTimeOffset? since = null], [int? pageSize = null]):

Bundle results = client.TypeHistory<Patient>();

As with the previous function, a date and pagesize can optionally be specified.

System wide history

When a system wide history is needed, retrieving all versions of all resources, the FhirClient's WholeSystemHistory([System.DateTimeOffset? since = null], [int? pageSize = null]) is used:

var lastMonth = DateTime.Today.AddMonths(-1);
Bundle results = client.WholeSystemHistory(since: lastMonth, pageSize: 20);

In this case the function retrieves all changes to all resources that have been done since the last month and limits the results to a maximum of 20. Both these parameters are optional.

Paged Results

Normally, any FHIR server will limit the number of results returned in the history. In the previous example, we explicitly limited the number of results per page to 20.

The FhirClient has a Continue function to browse a search result after the first page has been received using one of the History functions:

var result = client.TypeHistory<Patient>();

while( result != null )
{
    // Do something useful
    result = client.Continue(result);
}

Note that Continue supports a second parameter that allows you to browse forward, backward, or go immediately to the first or last page of the result.

Further reading

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