Added documentation for how to query unions

Updated resource list schemas

FAQ.md

@@ -159,8 +159,8 @@ module.exports.patientResolver = function patientResolver (root, args, ctx, info
       // Errors need to be formatted in a specific way, you can see more
       // of en explanation on this in the Error handling section below
       if (err) {
+        logger.error(err);
         let error = errorUtils.internal(version, err.message);
-        logger.error(error);
         reject(errorUtils.formatErrorForGraphQL(error));
       } else {
         resolve(patient);
@@ -267,6 +267,7 @@ You can't perform metadata queries and get back capability statements like you w
 **NOTE**: All these examples are providing the query string to use, not the full request. Your request should include this as a query argument, e.g. `query=<query string here>`.
 
 List all queries:
+
 ```graphql
 {
   __type(name:"Query"){
@@ -280,6 +281,7 @@ List all queries:
 ```
 
 List all mutations:
+
 ```graphql
 {
   __type(name:"Mutation"){
@@ -293,6 +295,7 @@ List all mutations:
 ```
 
 For a more complete list which include's all their arguments and return fields, try this (for our example server, this returns almost 50,000 lines of JSON):
+
 ```graphql
 query TypeIntrospectionQuery{
   # Can also use __type(name:"Mutation"){ 
@@ -399,3 +402,25 @@ fetch('http://localhost:3000/3_0_1/$graphiql', {
 })
 .catch(err => console.error('Unable to generate schema'))
 ```
+
+## Querying a Union
+When you query any of the list resources, the return format is a bundle-like resource, which can contain one of many types of resources. In GraphQL, these are called unions and GraphQL has a unique way to query against unions using fragments (currently only a ResourceList type will be a union in this repo). When you ask for a `Bundle.entry[n].resource`, you have to tell GraphQL which type of resource the fields you want belong to. Here is an example GraphQL query on a PatientList:
+
+```graphql
+{
+  PatientList(gender:"male",name:"Joe"){
+    entry {
+      resource {
+        ... on Patient {
+          resourceType
+          id
+          gender
+          name { given }
+        }
+      }
+    }
+  }
+}
+```
+
+Since PatientList returns a bundle, we ask for the `entry` property in the bundle which is an array of objects that contains a `resource` property. This resource property is a `ResourceList` type so when querying it you need to use fragments, otherwise, you cannot get properties from the resource. See [https://graphql.org/learn/schema/#union-types](https://graphql.org/learn/schema/#union-types) for more information on Union types.

README.md

@@ -32,6 +32,7 @@ See our [Frequently Asked Questions](#frequently-asked-questions) for explanatio
 - [How are errors supposed to be handled?](./FAQ.md#error-handling)
 - [How do I configure which resources I support and with what capabilities?](./FAQ.md#resource-configuration)
 - [Can I do metadata queries?](./FAQ.md#metadata-query)
+- [How do I ask for specific fields in a response when the response is a bundle (or some other union of types)?](./FAQ.md#querying-a-union)
 
 ## Architecture
 We designed this project in the way that we did so we can support multiple versions simultaneously and add new versions very quickly.  Everything in `src/resources` is generated by an internal tool that reads [Structure Definitions](https://www.hl7.org/fhir/structuredefinition.html) downloaded from the official FHIR website. The tool output's schemas, inputs, parameter files, custom scalars, and profile endpoints, which includes files used to register queries and mutations with the server as well as resolvers.