FHIR search has a lot of capabilities, but in some cases, there aren't enough. For example, we want to get a patient resource with an additional field 'encounters' that contains all encounters of that patient, but it's not possible to implement it with FHIR search API. Aidbox has a solution for such complex tasks, and this tutorial is about how to solve this kind of problem.
Prepare Data
We need some sample data to see results of our queries. Let's create it using Batch/Transaction.
Copy the following snippet to the Aidbox.Cloud REST Console.
Our next step is obtaining aggregated data by patients.
patient-encounters.sql
SELECT
p.id AS patient_id,
json_agg(e.resource::jsonb) AS encounters
FROM
patient AS p
JOIN encounter AS e
ON p.id = e.resource->'subject'->>'id'
GROUP BY p.id;
Looks good but there's no information about the encounter id.
patients-encounters-with-ids.sql
SELECT
p.id AS patient_id,
json_agg(e.resource::jsonb) AS encounters
FROM (SELECT id,
resource_type,
jsonb_set(
jsonb_set(resource, '{id}', to_jsonb(id)),
'{resourceType}',
to_jsonb(resource_type))
AS resource
FROM patient) AS p
JOIN (SELECT id,
resource_type,
jsonb_set(
jsonb_set(resource, '{id}', to_jsonb(id)),
'{resourceType}',
to_jsonb(resource_type))
AS resource
FROM encounter) AS e
ON p.id = e.resource->'subject'->>'id'
GROUP BY p.id;
Additionally, we added resourceType and id to the patient resource but didn't use it yet. Let's put encounters to the patient resource and take only one patient by the specified id.
patients-with-encounters-and-ids.sql
SELECT
p.id AS id,
jsonb_set(p.resource, '{encounters}', json_agg(e.resource::jsonb)::jsonb) AS resource
FROM (SELECT id,
resource_type,
jsonb_set(
jsonb_set(resource, '{id}', to_jsonb(id)),
'{resourceType}',
to_jsonb(resource_type))
AS resource
FROM patient) AS p
JOIN (SELECT id,
resource_type,
jsonb_set(
jsonb_set(resource, '{id}', to_jsonb(id)),
'{resourceType}',
to_jsonb(resource_type))
AS resource
FROM encounter) AS e
ON p.id = e.resource->'subject'->>'id'
GROUP BY p.id, p.resource
HAVING p.id = 'patient1';
The result should look like the following table (but without pretty printing):
Now let's make the results of this query accessible via REST API. To do that, we need to create the AidboxQuery resource:
POST /AidboxQuery
Accept: text/yaml
Content-Type: text/yaml
id: patient-with-encounters
params:
patient-id: {isRequired: true}
query: |
SELECT
jsonb_set(p.resource, '{encounters}', json_agg(e.resource::jsonb)::jsonb) AS resource
FROM (SELECT id,
resource_type,
jsonb_set(
jsonb_set(resource, '{id}', to_jsonb(id)),
'{resourceType}',
to_jsonb(resource_type))
AS resource
FROM patient) AS p
JOIN (SELECT id,
resource_type,
jsonb_set(
jsonb_set(resource, '{id}', to_jsonb(id)),
'{resourceType}',
to_jsonb(resource_type))
AS resource
FROM encounter) AS e
ON p.id = e.resource->'subject'->>'id'
GROUP BY p.id, p.resource
HAVING p.id = {{params.patient-id}};
# Status: 201
query: >-
SELECT
jsonb_set(p.resource, '{encounters}', json_agg(e.resource::jsonb)::jsonb) AS
resource
FROM (SELECT id,
resource_type,
jsonb_set(
jsonb_set(resource, '{id}', to_jsonb(id)),
'{resourceType}',
to_jsonb(resource_type))
AS resource
FROM patient) AS p
JOIN (SELECT id,
resource_type,
jsonb_set(
jsonb_set(resource, '{id}', to_jsonb(id)),
'{resourceType}',
to_jsonb(resource_type))
AS resource
FROM encounter) AS e
ON p.id = e.resource->'subject'->>'id'
GROUP BY p.id, p.resource
HAVING p.id = {{params.patient-id}};
params:
patient-id:
isRequired: true
id: >-
patient-with-encounters
resourceType: AidboxQuery
meta:
lastUpdated: '2022-07-08T12:15:55.520339Z'
createdAt: '2022-07-08T12:15:55.520339Z'
versionId: '21'
Pay attention to the end of the query: we used {{params.patient-id}} which takes the value from the request and passes it to the query securely (using PostgreSQL PREPARE statement). This means that the user of our custom search can change some parameters of the query and get different results.
Let's try it in action!
GET /$query/patient-with-encounters?patient-id=patient1
