Add snippet for Collection Group Query (GoogleCloudPlatform#1399)

* Bump `com.google.cloud:google-cloud-firestore` to `1.2.0` which
  includes the new functionality
* Add `hashCode` for `City.java`

Author: BenWhitehead

firestore/pom.xml

@@ -45,7 +45,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-firestore</artifactId>
-      <version>0.81.0-beta</version>
+      <version>1.2.0</version>
     </dependency>
     <!-- [END fs-maven] -->
 

firestore/src/main/java/com/example/firestore/snippets/QueryDataSnippets.java

@@ -17,23 +17,19 @@
 package com.example.firestore.snippets;
 
 import com.example.firestore.snippets.model.City;
-
 import com.google.api.core.ApiFuture;
 import com.google.api.core.ApiFutures;
 import com.google.cloud.firestore.CollectionReference;
-import com.google.cloud.firestore.DocumentReference;
 import com.google.cloud.firestore.DocumentSnapshot;
 import com.google.cloud.firestore.Firestore;
 import com.google.cloud.firestore.Query;
 import com.google.cloud.firestore.Query.Direction;
 import com.google.cloud.firestore.QueryDocumentSnapshot;
 import com.google.cloud.firestore.QuerySnapshot;
 import com.google.cloud.firestore.WriteResult;
-
-import com.google.firestore.v1beta1.Document;
-import com.google.protobuf.Api;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.HashMap;
 import java.util.List;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
@@ -383,4 +379,66 @@ List<Query> paginateCursor() throws InterruptedException, ExecutionException, Ti
     // [END fs_paginate_cursor]
     return Arrays.asList(firstPage, secondPage);
   }
+
+  void collectionGroupQuery() throws ExecutionException, InterruptedException {
+    //CHECKSTYLE OFF: Indentation
+    //CHECKSTYLE OFF: RightCurlyAlone
+    // [START fs_collection_group_query_data_setup]
+    CollectionReference cities = db.collection("cities");
+
+    final List<ApiFuture<WriteResult>> futures = Arrays.asList(
+      cities.document("SF").collection("landmarks").document().set(new HashMap<String, String>() {{
+        put("name", "Golden Gate Bridge");
+        put("type", "bridge");
+      }}),
+      cities.document("SF").collection("landmarks").document().set(new HashMap<String, String>() {{
+        put("name", "Legion of Honor");
+        put("type", "museum");
+      }}),
+      cities.document("LA").collection("landmarks").document().set(new HashMap<String, String>() {{
+        put("name", "Griffith Park");
+        put("type", "park");
+      }}),
+      cities.document("LA").collection("landmarks").document().set(new HashMap<String, String>() {{
+        put("name", "The Getty");
+        put("type", "museum");
+      }}),
+      cities.document("DC").collection("landmarks").document().set(new HashMap<String, String>() {{
+        put("name", "Lincoln Memorial");
+        put("type", "memorial");
+      }}),
+      cities.document("DC").collection("landmarks").document().set(new HashMap<String, String>() {{
+        put("name", "National Air and Space Museum");
+        put("type", "museum");
+      }}),
+      cities.document("TOK").collection("landmarks").document().set(new HashMap<String, String>() {{
+        put("name", "Ueno Park");
+        put("type", "park");
+      }}),
+      cities.document("TOK").collection("landmarks").document().set(new HashMap<String, String>() {{
+        put("name", "National Museum of Nature and Science");
+        put("type", "museum");
+      }}),
+      cities.document("BJ").collection("landmarks").document().set(new HashMap<String, String>() {{
+        put("name", "Jingshan Park");
+        put("type", "park");
+      }}),
+      cities.document("BJ").collection("landmarks").document().set(new HashMap<String, String>() {{
+        put("name", "Beijing Ancient Observatory");
+        put("type", "museum");
+      }})
+    );
+    final List<WriteResult> landmarks = ApiFutures.allAsList(futures).get();
+    // [END fs_collection_group_query_data_setup]
+
+    // [START fs_collection_group_query]
+    final Query museums = db.collectionGroup("landmarks").whereEqualTo("type", "museum");
+    final ApiFuture<QuerySnapshot> querySnapshot = museums.get();
+    for (DocumentSnapshot document : querySnapshot.get().getDocuments()) {
+      System.out.println(document.getId());
+    }
+    // [END fs_collection_group_query]
+    //CHECKSTYLE ON: RightCurlyAlone
+    //CHECKSTYLE ON: Indentation
+  }
 }

firestore/src/main/java/com/example/firestore/snippets/model/City.java

@@ -161,4 +161,9 @@ public boolean equals(Object obj) {
         && Objects.equals(capital, city.capital)
         && Objects.equals(regions, city.regions);
   }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(name, state, country, capital, population, regions);
+  }
 }