pipeline snippets and docs fix

Author: dlarocque

google-cloud-firestore/src/main/java/com/google/cloud/firestore/pipeline/expressions/Expression.java

@@ -1990,7 +1990,7 @@ public static Expression mapSet(
    *       a key entirely, use {@code mapRemove}.
    * </ul>
    *
-   * @param mapField The map field to set entries in.
+   * @param mapExpr The map field to set entries in.
    * @param key The key to set.
    * @param value The value to set.
    * @param moreKeyValues Additional key-value pairs to set.
@@ -2051,7 +2051,7 @@ public static Expression mapSet(
   /**
    * Creates an expression that returns the keys of a map.
    *
-   * @param mapExpr The map expression to get the keys of.
+   * @param mapExpr The expression representing the map to get the keys of.
    * @return A new {@link Expression} representing the keys of the map.
    */
   @BetaApi

samples/preview-snippets/src/main/java/com/example/firestore/PipelineSnippets.java

@@ -1167,26 +1167,65 @@ void minLogicalFunction() throws ExecutionException, InterruptedException {
   void mapGetFunction() throws ExecutionException, InterruptedException {
     // [START map_get]
     Pipeline.Snapshot result =
-        firestore
-            .pipeline()
-            .collection("books")
-            .select(mapGet(field("awards"), "pulitzer").as("hasPulitzerAward"))
-            .execute()
-            .get();
+            firestore
+                    .pipeline()
+                    .collection("books")
+                    .select(mapGet(field("awards"), "pulitzer").as("hasPulitzerAward"))
+                    .execute()
+                    .get();
     // [END map_get]
     System.out.println(result.getResults());
   }
 
   void mapSetFunction() throws ExecutionException, InterruptedException {
-    // [START map_get]
+    // [START map_set]
     Pipeline.Snapshot result =
-        firestore
-            .pipeline()
-            .collection("books")
-            .select(mapSet(field("awards"), "pulitzer").as("awards"))
-            .execute()
-            .get();
-    // [END map_get]
+            firestore
+                    .pipeline()
+                    .collection("books")
+                    .select(mapSet(field("awards"), "pulitzer", true).as("awards"))
+                    .execute()
+                    .get();
+    // [END map_set]
+    System.out.println(result.getResults());
+  }
+
+  void mapKeysFunction() throws ExecutionException, InterruptedException {
+    // [START map_keys]
+    Pipeline.Snapshot result =
+            firestore
+                    .pipeline()
+                    .collection("books")
+                    .select(mapKeys(field("awards")).as("award_categories"))
+                    .execute()
+                    .get();
+    // [END map_keys]
+    System.out.println(result.getResults());
+  }
+
+  void mapValuesFunction() throws ExecutionException, InterruptedException {
+    // [START map_values]
+    Pipeline.Snapshot result =
+            firestore
+                    .pipeline()
+                    .collection("books")
+                    .select(mapValues(field("awards")).as("award_details"))
+                    .execute()
+                    .get();
+    // [END map_values]
+    System.out.println(result.getResults());
+  }
+
+  void mapEntriesFunction() throws ExecutionException, InterruptedException {
+    // [START map_entries]
+    Pipeline.Snapshot result =
+            firestore
+                    .pipeline()
+                    .collection("books")
+                    .select(mapEntries(field("awards")).as("awards_list"))
+                    .execute()
+                    .get();
+    // [END map_entries]
     System.out.println(result.getResults());
   }