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Create custom Aidbox Search resource

Objectives

  • Understand how to create an Aidbox Search resource and use it

Before you begin

The problem

Let's say we want to search by email (in Patient.telecom field), domain case-insensitively. FHIR Search API can't handle it because the domain is part of the email value (ContactPoint.value), and FHIR does not offer a way to extract it.

The solution

The solution is to use SQL to extract it. We use the Search resource, an Aidbox-specific resource, to create a search parameter using SQL.

Let's create our patients to search for:

PUT /fhir/Patient/pt1

telecom:
- system: email
  value: john@SOMECOMPANY.COM
- system: email
  value: john@dundermifflin.com

PUT /fhir/Patient/pt2

telecom:
- system: email
  value: mike@SOMECOMPANY.COM
- system: email
  value: mike@dundermifflin.com

Next, we can play with SQL (use ChatGPT) to get the desired behavior. Let's use split_part and lower SQL functions to search by domain:

SELECT
id,
resource,
EXISTS (
  SELECT 1 FROM jsonb_array_elements(p.resource -> 'telecom') AS email
  WHERE email ->> 'system' = 'email'
    AND split_part(lower(email ->> 'value'), '@', 2) = lower('somecompany.com')
)
FROM patient p

In DB Console, we get results:

Then we can rewrite it like this:

SELECT *
FROM patient p
WHERE
EXISTS (
  SELECT 1 FROM jsonb_array_elements(p.resource -> 'telecom') AS email
  WHERE email ->> 'system' = 'email'
    AND split_part(lower(email ->> 'value'), '@', 2) = lower('somecompany.com'))

And create Search resource using Search.where expression (note how we use {{table}} and {{param}} placeholders):

PUT /Search/Patient.email-domain
content-type: text/yaml
accept: text/yaml

resourceType: Search
id: Patient.email-domain
name: email-domain
resource:
  id: Patient
  resourceType: Entity
where: EXISTS ( SELECT 1 FROM jsonb_array_elements({{table}}.resource -> 'telecom') AS email WHERE email ->> 'system' = 'email' AND split_part(lower(email ->> 'value'), '@', 2) = lower({{param}}::text))

Then check search:

GET /fhir/Patient?email-domain=somecompany.com

This returned both patients. See the SQL:

GET /fhir/Patient?email-domain=somecompany.com&_explain=1

query:
  - >-
    SELECT "patient".* FROM "patient" WHERE (EXISTS ( SELECT 1 FROM
    jsonb_array_elements("patient".resource -> 'telecom') AS email WHERE email
    ->> 'system' = 'email' AND split_part(lower(email ->> 'value'), '@', 2) =
    lower(?::text))) LIMIT ? OFFSET ? 
  - somecompany.com
  - 100
  - 0

That's it

We've created a Search resource that solves the problem that FHIR Search cannot solve.

The good thing about Search resource is that it can be used just like SearchParameter (except, we cannot use modifiers) and can be combined with actual SearchParameters, e.g. GET /fhir/Patient?email-domain=somecompany.com&name=john. The downside is that, using Search resource, we only change WHERE and ORDER BY expressions, not the whole SQL. Sometimes it is inconvenient, and you should use AidboxQuery instead.

See more:

{% content-ref url="../../../api/rest-api/aidbox-search.md" %} aidbox-search.md {% endcontent-ref %}

Other examples

Encounter.subject performance optimization

PUT /Search/Encounter.subject
content-type: text/yaml
accept: text/yaml

resourceType: Search
id: Encounter.subject
name: subject 
resource: 
  id: Encounter
  resourceType: Entity
where: "resource #>> '{ subject, id }' = ANY ({{param}}::text[])"
multi: array

Patient.deceased

PUT /Search/Patient.deceased
content-type: text/yaml
accept: text/yaml

resourceType: Search
id: Patient.deceased
name: deceased
resource:
  id: Patient
  resourceType: Entity
where: "coalesce((resource#>>'{deceased,boolean}')::boolean, resource ?? 'deceased', false) = {{param}}"

User.identifier

PUT /Search/User.identifier
content-type: text/yaml
accept: text/yaml

resourceType: Search
id: User.identifier
name: identifier
param-parser: token
token-sql:
  only-code: 'knife_extract_text({{table}}.resource, ''[["identifier","value"]]'') && ARRAY[{{param.code}}]'
  only-system: 'knife_extract_text({{table}}.resource, ''[["identifier",  "system"]]'') && ARRAY[{{param.system}}]'
  no-system: 'knife_extract_text({{table}}.resource, ''[["identifier","value"]]'') && ARRAY[{{param.code}}]'
  both: '(knife_extract_text({{table}}.resource, ''[["identifier","value"]]'') && ARRAY[{{param.code}}]) AND ({{table}}.resource->''identifier'' @> jsonb_build_array(jsonb_build_object(''system'', {{param.system}}::text, ''value'', {{param.code}}::text)))'
  text: 'array_to_string(knife_extract({{table}}.resource, ''[["identifier"]]''), '''') ilike {{param.text}}'
  text-format: '%?%'
where: '(knife_extract_text({{table}}.resource, ''[["identifier","value"]]'') && ARRAY[{{param.code}}]) AND ({{table}}.resource->''identifier'' @> jsonb_build_array(jsonb_build_object(''system'', {{param.system}}::text, ''value'', {{param.code}}::text)))'
resource: {id: User, resourceType: Entity}

ServiceRequest.subject performance optimization

PUT /Search/ServiceRequest.subject
content-type: text/yaml
accept: text/yaml

resourceType: Search
name: subject
resource: {id: ServiceRequest, resourceType: Entity}
where: "{{table}}.resource#>> '{ subject, id }' = {{param.id}}"
param-parser: reference

Search and sort by field in the related resource

PUT /Search/Patient.organization-name
content-type: text/yaml
accept: text/yaml

resourceType: Search
name: organization-name
resource: {id: Patient, resourceType: Entity}
where: "(select org.resource ->> 'name' from organization org where {{table}}.resource #>> '{ managingOrganization, id }' = org.id) = {{param}}::text"
order-by: "(select org.resource ->> 'name' from organization org where {{table}}.resource #>> '{ managingOrganization, id }' = org.id)"