More Apollo learning

Databases/GraphQL/Apollo/Apollo_Client.md

@@ -20,7 +20,7 @@ const client = new ApolloClient({
 });
 ```
 
-> The uri property must match the location of our Apollo server.
+> The `uri` property must match the location of our Apollo server.
 
 ## Utilising the provider
 
@@ -62,6 +62,7 @@ const TRACKS = gql`
 ```
 
 The convention is to name the query constant in `ALL_CAPS`.
+> Note that the name of the query on the client doesn't have to match the query type defined in the schema however it should reference it on the second line (`tracksFormHome)
 
 ### `useQuery` hook
 
@@ -86,3 +87,4 @@ const Tracks = () => {
 - We destructure the `loading, error, data` variables that are returned from the hook
 - We pass in our query constant as an argument.
 - In the example we just render the serialized data but we could of course pass the data as a prop and map through it in an embedded child component.
+

Databases/GraphQL/Apollo/Apollo_Server.md

@@ -111,3 +111,35 @@ const mocks = {
 
 const server = new ApolloServer({ typeDefs, mocks });
 ```
+We can now [run queries](/Databases/GraphQL/Apollo/Apollo_Client.md#running-a-query) against our server. 
+
+## Implementing resolvers
+A resolver is a [function](/Databases/GraphQL/Creating_a_GraphQL_server.md#resolvers)
+
+
+### `RESTDataSource`
+
+This is something you can apply to your server to improve the efficiency of working with REST APIs in your resolvers. 
+
+REST APIs fall victim to the "n + 1" problem: say you want to get one resource, then for each element returned of this resource you need to send another request using a property of this resource to get another resource. For each of the first requests you need to send another request once they resolve. 
+
+Here is an example of `RESTDataSource` being used. It is just a class that can be extended and which provides inbuilt methods for running fetches against a REST API:
+
+```js
+const {RESTDataSource} = require('apollo-datasource-rest');
+
+class TrackAPI extends RESTDataSource {
+  constructor() {
+    super();
+    this.baseURL = 'https://odyssey-lift-off-rest-api.herokuapp.com/';
+  }
+
+  getTracksForHome() {
+    return this.get('tracks');
+  }
+
+  getAuthor(authorId) {
+    return this.get(`author/${authorId}`);
+  }
+}
+```

Databases/GraphQL/Creating_a_GraphQL_server.md

@@ -50,6 +50,7 @@ app.use(
 
 ## Resolvers
 
+
 We will specify our resolvers in a dedicate resolver file. In GraphQL you need to define resolvers for both your queries and your mutations.
 
 To achieve this we will have a dummy object as the database containing our products and a class working as a generator function that will create a product object with certain properties, individuated by an id. We will invoke this class to create new products for the database and to retrieve existing products from the database.

Databases/GraphQL/Journey_of_GraphQL_query.md

@@ -0,0 +1,9 @@
+---
+categories:
+  - Databases
+tags: [graph-ql]
+---
+
+# The journey of a GraphQL query
+
+![](/img/graphql-journey-two.svg)