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Summary Fields

Summary Fields

The SummaryFields variable is a package-level map that lists, for every resource type, the fields that the FHIR specification marks with isSummary=true. This data is essential for implementing the _summary=true search parameter on a FHIR server.

What Are Summary Fields?

The FHIR specification defines a _summary search parameter that allows clients to request abbreviated versions of resources. When a client sends _summary=true, the server must return only the fields marked as summary fields in the StructureDefinition for that resource type, plus a few mandatory elements (id, meta, resourceType).

This is useful for reducing payload sizes in search results where the client only needs key identifiers and attributes rather than the full resource.

The SummaryFields Map

Each version package exports a SummaryFields variable:

var SummaryFields = map[string][]string{
    "Patient": {
        "active",
        "address",
        "birthDate",
        "communication",
        "gender",
        "generalPractitioner",
        "id",
        "identifier",
        "implicitRules",
        "link",
        "managingOrganization",
        "meta",
        "name",
        "telecom",
    },
    // ... all other resource types
}

The map is keyed by resource type name (e.g., "Patient", "Observation") and the values are sorted slices of field names that should be included in a summary response.

Usage

Basic Lookup 

import "github.com/gofhir/models/r4/v2"

fields := r4.SummaryFields["Patient"]
// Returns: ["active", "address", "birthDate", "communication", "gender",
//           "generalPractitioner", "id", "identifier", "implicitRules",
//           "link", "managingOrganization", "meta", "name", "telecom"]

Checking if a Field is a Summary Field 

import "github.com/gofhir/models/r4/v2"

func isSummaryField(resourceType, fieldName string) bool {
    fields, ok := r4.SummaryFields[resourceType]
    if !ok {
        return false
    }
    for _, f := range fields {
        if f == fieldName {
            return true
        }
    }
    return false
}

isSummaryField("Patient", "name")      // true
isSummaryField("Patient", "photo")     // false
isSummaryField("Observation", "code")  // true
isSummaryField("Observation", "note")  // false

FHIR Server Implementation

A typical FHIR server uses SummaryFields to filter resource fields before returning search results:

import (
    "encoding/json"
    "github.com/gofhir/models/r4/v2"
)

func applySummary(resourceType string, data []byte) ([]byte, error) {
    summaryFields := r4.SummaryFields[resourceType]
    if summaryFields == nil {
        return data, nil // unknown type, return as-is
    }

    // Build a set for fast lookup
    allowed := make(map[string]bool, len(summaryFields))
    for _, f := range summaryFields {
        allowed[f] = true
    }
    // Always include resourceType
    allowed["resourceType"] = true

    // Parse, filter, and re-serialize
    var full map[string]json.RawMessage
    if err := json.Unmarshal(data, &full); err != nil {
        return nil, err
    }

    filtered := make(map[string]json.RawMessage)
    for key, val := range full {
        if allowed[key] {
            filtered[key] = val
        }
    }

    return json.Marshal(filtered)
}

Coverage

The SummaryFields map includes entries for every resource type defined in the FHIR version. In R4, this covers all 148 resource types. Each entry is generated directly from the isSummary flag in the official FHIR StructureDefinitions.

The summary field lists are generated from the FHIR specification and always stay in sync with the resource struct definitions. If a field is added or removed from the summary set in a new FHIR version, the regenerated code will reflect the change automatically.

Comparison with _elements

The _summary=true parameter is a coarser mechanism than the _elements parameter. With _elements, clients specify exactly which fields they want. With _summary=true, the server returns the specification-defined summary set. SummaryFields supports the latter case; implementing _elements requires a different approach (typically JSON field filtering based on the client-provided field list).

Last updated on
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