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Doco and reorg
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‎README.md‎

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# Graphql Examples
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This splodge of code is mostly my personal explorations of `graphql-java` and how to use it in more real world examples.
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I thought I would try and make it in "example" format so that others might derive some value from it.
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I also plan to make some blog posts about this in the near future and use this code as the basis for that.
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Its built with Gradle and Java, with some Spock Groovy unit testing.
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## Example 1 - HTTP Proxy of an existing REST API
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The first example is the idea of fronting an existing REST API with graphql.
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In this case *An API of Ice And Fire*
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https://anapioficeandfire.com/Documentation
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This is not an original idea, others have done it in Node.js but hey I am a Java guy.
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The code is in `com.graphql.example.proxy.IceAndFireApiProxy`
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I wanted to explore the following:
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- Hosting a simple HTTP server of graphql - using Jetty
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- A Relay shape that turns old school page=N pagination into cursors eg https://facebook.github.io/relay/docs/getting-started.html
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- Using the `java-dataloader` to make an efficient REST proxy eg: https://github.com/graphql-java/java-dataloader
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What I learnt was :
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- `CompleteableFuture` support in graphql-java is da bomb! Wicked good.
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- Used well, `java-dataloader` is da double bomb! By priming the cache and using URLs as keys we cache the sheet out of everything
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- Relay pagination is tricky. Not impossible but tricky with forward only pagination.
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- The Relay support in graphql-java is basic (it doesn't pretend to be more I guess) and really on works if you have a complete list
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of edges in memory
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‎src/main/java/com/graphql/example/proxy/IceAndFireDataFetchers.java‎

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package com.graphql.example.proxy;
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import com.graphql.example.proxy.relay.ForwardOnlyFixedPagedDataSet;
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import com.graphql.example.proxy.relay.PagedResult;
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import com.graphql.example.util.HttpClient;
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import com.graphql.example.util.RelayUtils;
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import graphql.relay.Connection;
@@ -150,9 +152,9 @@ DataFetcher characters() {
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pageNumber -> readPagedObjects("characters", pageNumber)));
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}
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private ForwardOnlyFixedPagedDataSet.PagedResult<Map<String, Object>> readPagedObjects(String resource, int pageNumber) {
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private PagedResult<Map<String, Object>> readPagedObjects(String resource, int pageNumber) {
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log.info("Fetching {} page: {}", resource, pageNumber);
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ForwardOnlyFixedPagedDataSet.PagedResult<Map<String, Object>> pagedResult =
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PagedResult<Map<String, Object>> pagedResult =
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HttpClient.readResource(resource, qp("pageNumber", pageNumber), qp("pageSize", PAGE_SIZE));
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log.info("\tread {} {}", pagedResult.getResults().size(), resource);

‎src/main/java/com/graphql/example/proxy/relay/CursorPageAndOffset.java‎

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package com.graphql.example.proxy.relay;
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import graphql.relay.ConnectionCursor;
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import graphql.relay.DefaultConnectionCursor;
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import java.nio.charset.StandardCharsets;
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import java.util.regex.Matcher;
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import java.util.regex.Pattern;
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/**
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* This uses an encoding of page # plus full offset from the page forward
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*/
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class CursorPageAndOffset {
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private static final java.util.Base64.Encoder encoder = java.util.Base64.getEncoder();
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private static final java.util.Base64.Decoder decoder = java.util.Base64.getDecoder();
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private final static Pattern pagePattern = Pattern.compile("^page=([0-9]*)");
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private final static Pattern offsetPattern = Pattern.compile(".*;offset=([0-9]*)");
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int page;
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int offset;
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CursorPageAndOffset(int page, int offset) {
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this.page = page;
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this.offset = offset;
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}
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int getPage() {
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return page;
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}
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int getOffset() {
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return offset;
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}
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public static CursorPageAndOffset fromCursor(String cursor) {
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String s = decode(cursor);
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Matcher matcher = pagePattern.matcher(s);
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if (!matcher.find()) {
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throwInvalidCursor(s);
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}
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String page = matcher.group(1);
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matcher = offsetPattern.matcher(s);
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if (!matcher.find()) {
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throwInvalidCursor(s);
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}
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String offset = matcher.group(1);
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return new CursorPageAndOffset(Integer.parseInt(page), Integer.parseInt(offset));
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}
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ConnectionCursor toConnectionCursor() {
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return new DefaultConnectionCursor(encode("page=" + page + ";offset=" + offset));
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}
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private String encode(String s) {
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return encoder.encodeToString(s.getBytes(StandardCharsets.UTF_8));
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}
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static private String decode(String s) {
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return new String(decoder.decode(s), StandardCharsets.UTF_8);
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}
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private static void throwInvalidCursor(String cursor) {
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throw new IllegalArgumentException("Invalid paged cursor provided : " + cursor);
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}
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}

src/main/java/com/graphql/example/proxy/ForwardOnlyFixedPagedDataSet.java renamed to src/main/java/com/graphql/example/proxy/relay/ForwardOnlyFixedPagedDataSet.java

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package com.graphql.example.proxy;
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package com.graphql.example.proxy.relay;
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import graphql.relay.Connection;
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import graphql.relay.ConnectionCursor;
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import graphql.relay.DefaultConnection;
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import graphql.relay.DefaultConnectionCursor;
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import graphql.relay.DefaultEdge;
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import graphql.relay.DefaultPageInfo;
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import graphql.relay.Edge;
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import graphql.relay.PageInfo;
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import graphql.schema.DataFetchingEnvironment;
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import java.nio.charset.StandardCharsets;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.List;
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import java.util.function.Function;
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import java.util.regex.Matcher;
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import java.util.regex.Pattern;
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//
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// the ice and fire API uses page=n&pageSize=n pagination and we cant know the
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public class ForwardOnlyFixedPagedDataSet {
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/**
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* This uses an encoding of page # plus full offset from the page forward
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*/
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static class PageAndOffset {
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private static final java.util.Base64.Encoder encoder = java.util.Base64.getEncoder();
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private static final java.util.Base64.Decoder decoder = java.util.Base64.getDecoder();
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private final static Pattern pagePattern = Pattern.compile("^page=([0-9]*)");
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private final static Pattern offsetPattern = Pattern.compile(".*;offset=([0-9]*)");
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int page;
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int offset;
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PageAndOffset(int page, int offset) {
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this.page = page;
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this.offset = offset;
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}
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int getPage() {
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return page;
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}
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int getOffset() {
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return offset;
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}
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public static PageAndOffset fromCursor(String cursor) {
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String s = decode(cursor);
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Matcher matcher = pagePattern.matcher(s);
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if (!matcher.find()) {
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throwInvalidCursor(s);
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}
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String page = matcher.group(1);
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matcher = offsetPattern.matcher(s);
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if (!matcher.find()) {
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throwInvalidCursor(s);
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}
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String offset = matcher.group(1);
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return new PageAndOffset(Integer.parseInt(page), Integer.parseInt(offset));
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}
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ConnectionCursor toConnectionCursor() {
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return new DefaultConnectionCursor(encode("page=" + page + ";offset=" + offset));
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}
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private String encode(String s) {
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return encoder.encodeToString(s.getBytes(StandardCharsets.UTF_8));
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}
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static private String decode(String s) {
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return new String(decoder.decode(s), StandardCharsets.UTF_8);
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}
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private static void throwInvalidCursor(String cursor) {
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throw new IllegalArgumentException("Invalid paged cursor provided : " + cursor);
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}
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}
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/**
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* The results that come back from the page retrieval function need to tell us
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* the list of results and the whether their is a next page or not
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*/
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public static class PagedResult<T> {
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private final List<T> results;
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private final boolean hasNextPage;
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public PagedResult(List<T> results, boolean hasNextPage) {
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this.results = results;
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this.hasNextPage = hasNextPage;
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}
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public List<T> getResults() {
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return results;
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}
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public boolean hasNextPage() {
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return hasNextPage;
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}
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}
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/**
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* Called to get a realy {@link graphql.relay.Connection} of edges where the underlying dataset
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* is a set of fixed size pages of data that can ONLY be read in a forward only manner
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throw new IllegalArgumentException("You must provide a positive value for 'first'");
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}
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boolean afterPresent = env.getArgument("after") != null;
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String zeroZeroDefault = new PageAndOffset(0, 0).toConnectionCursor().toString();
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String zeroZeroDefault = new CursorPageAndOffset(0, 0).toConnectionCursor().toString();
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String afterCursor = getArg(env, "after", zeroZeroDefault);
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PageAndOffset desiredPageAndOffset = PageAndOffset.fromCursor(afterCursor);
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CursorPageAndOffset desiredPageAndOffset = CursorPageAndOffset.fromCursor(afterCursor);
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int startPage = desiredPageAndOffset.getPage();
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List<Edge<T>> edges = new ArrayList<>();
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PagedResult<T> pagedResult = pageOfDataRetriever.apply(startPage);
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for (T obj : pagedResult.getResults()) {
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ConnectionCursor edgeCursor = new PageAndOffset(startPage, fullOffset).toConnectionCursor();
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ConnectionCursor edgeCursor = new CursorPageAndOffset(startPage, fullOffset).toConnectionCursor();
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if (fullOffset == desiredPageAndOffset.getOffset()) {
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addToEdges = true;
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}

‎src/main/java/com/graphql/example/proxy/relay/PagedResult.java‎

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package com.graphql.example.proxy.relay;
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import java.util.List;
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/**
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* The results that come back from the page retrieval function need to tell us
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* the list of results and the whether their is a next page or not
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*/
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public class PagedResult<T> {
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private final List<T> results;
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private final boolean hasNextPage;
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public PagedResult(List<T> results, boolean hasNextPage) {
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this.results = results;
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this.hasNextPage = hasNextPage;
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}
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public List<T> getResults() {
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return results;
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}
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public boolean hasNextPage() {
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return hasNextPage;
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}
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}

‎src/main/java/com/graphql/example/util/HttpClient.java‎

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package com.graphql.example.util;
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import com.graphql.example.proxy.ForwardOnlyFixedPagedDataSet;
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import com.graphql.example.proxy.relay.PagedResult;
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import okhttp3.HttpUrl;
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import okhttp3.OkHttpClient;
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import okhttp3.Request;
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}
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}
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public static <T> ForwardOnlyFixedPagedDataSet.PagedResult<T> readResource(String resource, HttpQueryParameter... params) {
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public static <T> PagedResult<T> readResource(String resource, HttpQueryParameter... params) {
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HttpUrl.Builder urlBuilder = new HttpUrl.Builder();
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urlBuilder.scheme("https").host("www.anapioficeandfire.com").addPathSegment("api").addPathSegment(resource);
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if (params != null) {
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DataAndResponse dataAndResponse = readResourceUrl(url);
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List<T> data = (List<T>) dataAndResponse.getData();
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return new ForwardOnlyFixedPagedDataSet.PagedResult<>(data, hasNext(dataAndResponse.getResponse()));
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return new PagedResult<>(data, hasNext(dataAndResponse.getResponse()));
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}
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//

‎src/test/groovy/com/graphql/example/proxy/ForwardOnlyFixedPagedDataSetTest.groovy‎

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package com.graphql.example.proxy
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import com.graphql.example.proxy.relay.ForwardOnlyFixedPagedDataSet
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import com.graphql.example.proxy.relay.PagedResult
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import graphql.schema.DataFetchingEnvironment
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import graphql.schema.DataFetchingEnvironmentBuilder
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import spock.lang.Specification
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for (int i = 0; i < count; i++) {
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l.add("item" + i)
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}
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return new ForwardOnlyFixedPagedDataSet.PagedResult(l, hasNextPage)
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return new PagedResult(l, hasNextPage)
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}
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}

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