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Search FHIR Resources

You can search for resources in a FHIR Engine instance using the Android FHIR SDK's Search DSL or FHIR search strings. The SDK supports all defined search parameters.

See the full list of FHIR search specification support.

Search using Search DSL

The Search DSL is based on FHIR search, and most of the capabilities of FHIR search have an equivalent in Search DSL.

General search syntax

This is the simplest search syntax:

val patients = fhirEngine.search<Patient> {}

This search returns a List containing all Patient resources in the FhirEngine instance and is equivalent to the FHIR search:

GET [base]/Patient

If you're having trouble getting search to work, make sure Android Studio is using the correct version of search.

Search code completion

In most cases, use a filter to search for particular Patient resources.

fhirEngine.search<Patient> {
 filter(Patient.GIVEN, {
   value = "Kiran"
   modifier = StringFilterModifier.MATCHES_EXACTLY
 })
}

To do so, first specify a search parameter from the HAPI FHIR resource being searched. For the example above, we recommend you use Android Studio's code completion by first entering the resource followed by a dot, such as Patient., then pressing ctrl+space to see valid options. They will be of the type XClientParam!.

Search parameter code completion

Alternatively, look at the Field Summary for the HAPI FHIR Patient resource and find fields with the description "Fluent Client search parameter constant for field". These are the Patient resource fields we can search by.

HAPI FHIR Patient documentation

Not every field in a resource has search implemented, for example Patient.maritalStatus does not have a search parameter implemented in HAPI FHIR. On the other hand, HAPI FHIR provides some convenience search parameters like Patient.NAME which searches across all name-related fields but is not part of the base FHIR specification.

Next, provide a value to search for. The expected type for the value for value depends on the type of the search parameter from the HAPI FHIR resource field, or seen in the code completion pop-up. In the example above, Patient.GIVEN is a StringClientParam so value should be a String.

In addition, most parameter types have ways to control how the search is performed. In the case of String there is a modifier field. The Number, Date, and Quantity parameters have a prefix field instead, corresponding to the FHIR Search prefix.

For more details, see the examples below or look at the implementation of the specific filter type.

Using the OR operator

By default, multiple filters are considered using logical AND. You can treat them as an OR by setting the operation field. The following example returns patients with a given name or family name of exactly "Jay".

fhirEngine.search<Patient> {
 filter(Patient.GIVEN, {
   value = "Jay"
   modifier = StringFilterModifier.MATCHES_EXACTLY
 })

 filter(Patient.FAMILY, {
   value = "Jay"
   modifier = StringFilterModifier.MATCHES_EXACTLY
 })

 operation = Operation.OR
}

You can also pass multiple search criteria to the same filter. In this case, they are considered using OR by default. (Using AND on multiple search criteria is usually not useful.) The following example returns patients with a given name of exactly "Jay" or "Kat".

fhirEngine.search<Patient> {
 filter(Patient.GIVEN, {
   value = "Jay"
   modifier = StringFilterModifier.MATCHES_EXACTLY
 } , {
   value = "Kat"
   modifier = StringFilterModifier.MATCHES_EXACTLY
 })
}

Reverse chaining

The has function allows you to search for a resource based on other resources that reference it and functions similarly to FHIR Search reverse chaining. In the following example, the search will return a list of Patients that:

  1. have a RelatedPerson that references that Patient in the RelatedPerson.PATIENT field
  2. the RelatedPerson has a name matching "Ariel"

In this case, the results will include a patient resource matching patient1, plus any others that were already created in the FhirEngine.

val patient1 = Patient().apply{
  id = "1234567"
  addName(
    HumanName().apply {
      addGiven("Alex")
      family = "Lee"
    }
  )
}

val related1 = RelatedPerson().apply {
  patient.reference = "${patient1.fhirType()}/${patient1.logicalId}"
  addName(
    HumanName().apply {
      addGiven("Ariel")
      family = "Lee"
    }
  )
}

fhirEngine.create(patient1)
fhirEngine.create(related1)

val revinclude = fhirEngine.search<Patient> {
  has<RelatedPerson>(RelatedPerson.PATIENT) {
    filter (RelatedPerson.NAME, {
      value = "Ariel"
    })
  }
}

You can use has in combination with the other Search DSL features to create complex searches.

Search result modification

You can specify several fields to control search results, similar to FHIR Search results.

  • sort - specify a Date, Number, or String field to sort the results by
  • count - limit the results to a certain size
  • from - start the results from a specified index
val patients = fhirEngine.search<Patient> {
  filter (Patient.NAME, {
    modifier = StringFilterModifier.CONTAINS
    value = "Quinn"
  })
  sort(Patient.FAMILY, Order.ASCENDING)
  count = 100
  from = 0
}

Search filter parameters by type

Number

https://www.hl7.org/fhir/search.html#number

Fields

Search for all the Risk Assessments with probability greater than 0.8.

fhirEngine.search<RiskAssessment> {
  filter(RiskAssessment.PROBABILITY, {
    value = BigDecimal(0.8)
    prefix = ParamPrefixEnum.GREATERTHAN
  })
}

Date

https://www.hl7.org/fhir/search.html#date

Search for any patients born after 2013-03-14.

fhirEngine.search<Patient> {
  filter(
    Patient.BIRTHDATE,
    {
      prefix = ParamPrefixEnum.STARTS_AFTER
      value = of(DateType("2013-03-14"))
    }
  )
}

String

https://www.hl7.org/fhir/search.html#string

Search for any patients with a name with a given part containing "eve" at any position. This would include patients with the given name "Eve", "Evelyn", and also "Severine".

val patients = fhirEngine.search<Patient> {
  filter (Patient.NAME, {
    value = "eve"
    modifier = StringFilterModifier.CONTAINS
  })
}

Token

https://www.hl7.org/fhir/search.html#token

  • value - A TokenFilterValue of the value to search for. Pass the appropriate object type to the of function to create: Boolean, String, UriType, CodeType, Coding, CodeableConcept, Identifier

Search for any patient with a gender that has the code "male".

fhirEngine.search<Patient> {
  filter(Patient.GENDER, {
    value = of(CodeType("male"))
  })
}

Search for any patients that are active.

fhirEngine.search<Patient> {
  filter(Patient.ACTIVE, {
    value = of(true)
  })
}

Search for any condition with a code "123" in the code system "http://example.org/codes".

fhirEngine.search<Condition> {
  filter(Condition.CODE, {
    value = of(CodeableConcept(Coding("http://example.org/codes", "123", "")))
  })
}

Reference

https://www.hl7.org/fhir/search.html#reference

  • value - a String of a resource reference.

Search for all the observations where the subject references "Patient/123".

fhirEngine.search<Observation> {
  filter(Observation.SUBJECT, {
    value = "Patient/123"
  })
}

Quantity

https://www.hl7.org/fhir/search.html#quantity

  • prefix - A FHIR search prefix, represented by ParamPrefixEnum.
  • value - A BigDecimal of the value to search for.
  • system - A String of the URI identifying the coding system.
  • unit - A String of the coded form of the unit.

Search for all the observations where the value of is about 5.4 mg, where mg is understood as a UCUM unit.

fhirEngine.search<Observation> {
  filter(Observation.VALUE_QUANTITY, {
    prefix = ParamPrefixEnum.APPROXIMATE
    value = BigDecimal(5.4)
    system = "http://unitsofmeasure.org"
    unit = "mg"
  })
}

URI

https://www.hl7.org/fhir/search.html#uri

  • value - a String of the URI to search for.

Search for all the value sets with the exact URL "http://example.org/fhir/ValueSet/123".

fhirEngine.search<ValueSet> {
  filter(ValueSet.URL, {
    value = "http://example.org/fhir/ValueSet/123"
  })
}

Search query examples

Complex search queries

Search for Patients in India who have completed their Influenza vaccination.

fhirEngine.search<Patient> {
   has<Immunization>(Immunization.PATIENT) {
     filter(
       Immunization.VACCINE_CODE, {
         value = of(Coding("http://hl7.org/fhir/sid/cvx", "140", "Influenza, seasonal, injectable, preservative free"))
       }
     )

     // Follow Immunization.ImmunizationStatus
     filter(Immunization.STATUS, {
         value = of(Coding("http://hl7.org/fhir/event-status", "completed", ""))
       }
     )
   }

   filter(
     Patient.ADDRESS_COUNTRY, {
       modifier = StringFilterModifier.MATCHES_EXACTLY
       value = "IN"
     }
   )
 }

Search Patient compartment for Encounters and Observations

Search for all Encounters and Observations where the subject is patient ID "123".

val observations =
 fhirEngine.search<Observation> {
   filter(Observation.SUBJECT, { value = "Patient/123" })
 }

val conditions =
 fhirEngine.search<Condition> {
   filter(Condition.SUBJECT, { value = "Patient/123" })
}

Search Patients with Observation by Code

Search for all Patients where they are the subject of an Observation with the code "http://snomed.info/sct|386661006" or "http://loinc.org|45701-0" (different codes for fever).

val patients = fhirEngine.search<Patient> {
 has<Observation>(Observation.SUBJECT) {
   filter(
     Observation.CODE,
     {
       of(Coding("http://snomed.info/sct", "386661006", "Fever" ))
     }, {
       of(Coding("http://loinc.org", "45701-0", "Fever"))
     }
   )
 }
}

Search using FHIR search queries

You can also search resources in a FHIR Engine instance using FHIR search queries.

Complex queries including FHIRPath expressions, global common search parameters, modifiers, prefixes, chained parameters are not supported.

val result = fhirEngine.search("Patient?active=true&gender=male&_sort=-name,gender&_count=11")

Adding custom search parameters

You can define custom search parameters, in addition to the ones defined in the FHIR spec, add them to FHIR Engine and use them to search for resources. Adding custom search parameters is particularly useful when you want to search for extensions defined in custom profiles.

Setting up custom search parameters

class FhirApplicationTest : Application(){

  override fun onCreate() {
    super.onCreate()

    FhirEngineProvider.init(
      FhirEngineConfiguration(
        enableEncryptionIfSupported = true,
        RECREATE_AT_OPEN,
        ServerConfiguration("https://hapi.fhir.org/baseR4/"),
        customSearchParameters = listOf(
          SearchParameter().apply {
            url = "http://example.com/SearchParameter/patient-mothersMaidenName"
            addBase("Patient")
            name = "mothers-maiden-name"
            code = "mothers-maiden-name"
            type = Enumerations.SearchParamType.STRING
            expression =
              "Patient.extension('http://hl7.org/fhir/StructureDefinition/patient-mothersMaidenName').value.as(String)"
            description = "search on mother's maiden name"
          },
// Additional String Type Search param for Patient.identifier for value matching along with the standard Token Type provided by FHIR.
          SearchParameter().apply {
            url = "http://example.com/SearchParameter/patient-identifierPartial"
            addBase("Patient")
            name = "identifierPartial"
            code = "identifierPartial"
            type = Enumerations.SearchParamType.STRING
            expression = "Patient.identifier.value"
            description = "Search the identifier"
          }
        )
      )
    )
  }
}

Searching with the added custom search parameters

// Identifier partial search returns all Patients whose Patient.identifier.value starts with 5005- .
fhirEngine.search<Patient> {
  filter(
    StringClientParam("identifierPartial"),
    {
      value = "5005-"
      modifier = StringFilterModifier.STARTS_WITH
    }
  )
}

// searching with the extension returns all Patients who have Marca as their Maiden name.
// (custom extension http://example.com/SearchParameter/patient-mothersMaidenName).
fhirEngine.search<Patient> {
  filter(
    StringClientParam("mothers-maiden-name"),
    {
      value = "Marca"
      modifier = StringFilterModifier.MATCHES_EXACTLY
    }
  )
}

NOTE: The engine doesn't automatically reindex existing resources after a new SearchParameter is added. Resources created after the new SearchParameter is created will be indexed accordingly. Updates to the existing resources will result in the reindexing of the resource.