Add App Engine Cloud Datastore metadata queries samples.

From
https://cloud.google.com/appengine/docs/java/datastore/metadataqueries.

appengine/datastore/src/test/java/com/example/appengine/MetadataEntityGroupTest.java

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+/*
+ * Copyright 2016 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.appengine;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.appengine.api.datastore.DatastoreService;
+import com.google.appengine.api.datastore.DatastoreServiceFactory;
+import com.google.appengine.api.datastore.Entities;
+import com.google.appengine.api.datastore.Entity;
+import com.google.appengine.api.datastore.EntityNotFoundException;
+import com.google.appengine.api.datastore.FetchOptions;
+import com.google.appengine.api.datastore.Key;
+import com.google.appengine.api.datastore.PreparedQuery;
+import com.google.appengine.api.datastore.Query;
+import com.google.appengine.api.datastore.Transaction;
+import com.google.appengine.api.memcache.MemcacheService;
+import com.google.appengine.api.memcache.MemcacheServiceFactory;
+import com.google.appengine.tools.development.testing.LocalDatastoreServiceTestConfig;
+import com.google.appengine.tools.development.testing.LocalMemcacheServiceTestConfig;
+import com.google.appengine.tools.development.testing.LocalServiceTestHelper;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+import java.io.PrintWriter;
+import java.io.Serializable;
+import java.io.StringWriter;
+
+/**
+ * Unit tests to demonstrate App Engine Datastore entity group metadata.
+ */
+@RunWith(JUnit4.class)
+public class MetadataEntityGroupTest {
+
+  private final LocalServiceTestHelper helper =
+      new LocalServiceTestHelper(
+          // Set no eventual consistency, that way queries return all results.
+          // https://cloud.google.com/appengine/docs/java/tools/localunittesting#Java_Writing_High_Replication_Datastore_tests
+          new LocalDatastoreServiceTestConfig().setDefaultHighRepJobPolicyUnappliedJobPercentage(0),
+          new LocalMemcacheServiceTestConfig());
+
+  private DatastoreService datastore;
+
+  @Before
+  public void setUp() {
+    helper.setUp();
+    datastore = DatastoreServiceFactory.getDatastoreService();
+  }
+
+  @After
+  public void tearDown() {
+    helper.tearDown();
+  }
+
+  // [START entity_group_1]
+  private static long getEntityGroupVersion(DatastoreService ds, Transaction tx, Key entityKey) {
+    try {
+      return Entities.getVersionProperty(ds.get(tx, Entities.createEntityGroupKey(entityKey)));
+    } catch (EntityNotFoundException e) {
+      // No entity group information, return a value strictly smaller than any
+      // possible version
+      return 0;
+    }
+  }
+
+  private static void printEntityGroupVersions(DatastoreService ds, PrintWriter writer) {
+    Entity entity1 = new Entity("Simple");
+    Key key1 = ds.put(entity1);
+    Key entityGroupKey = Entities.createEntityGroupKey(key1);
+
+    // Print entity1's entity group version
+    writer.println("version " + getEntityGroupVersion(ds, null, key1));
+
+    // Write to a different entity group
+    Entity entity2 = new Entity("Simple");
+    ds.put(entity2);
+
+    // Will print the same version, as entity1's entity group has not changed
+    writer.println("version " + getEntityGroupVersion(ds, null, key1));
+
+    // Change entity1's entity group by adding a new child entity
+    Entity entity3 = new Entity("Simple", entity1.getKey());
+    ds.put(entity3);
+
+    // Will print a higher version, as entity1's entity group has changed
+    writer.println("version " + getEntityGroupVersion(ds, null, key1));
+  }
+  // [END entity_group_1]
+
+  @Test
+  public void printEntityGroupVersions_printsVersions() throws Exception {
+    StringWriter responseWriter = new StringWriter();
+    printEntityGroupVersions(datastore, new PrintWriter(responseWriter));
+    assertThat(responseWriter.toString()).contains("version");
+  }
+
+  // [START entity_group_2]
+  // A simple class for tracking consistent entity group counts.
+  private static class EntityGroupCount implements Serializable {
+    long version; // Version of the entity group whose count we are tracking
+    int count;
+
+    EntityGroupCount(long version, int count) {
+      this.version = version;
+      this.count = count;
+    }
+
+    // Display count of entities in an entity group, with consistent caching
+    void showEntityGroupCount(
+        DatastoreService ds, MemcacheService cache, PrintWriter writer, Key entityGroupKey) {
+      EntityGroupCount egCount = (EntityGroupCount) cache.get(entityGroupKey);
+      // Reuses getEntityGroupVersion method from the previous example.
+      if (egCount != null && egCount.version == getEntityGroupVersion(ds, null, entityGroupKey)) {
+        // Cached value matched current entity group version, use that
+        writer.println(egCount.count + " entities (cached)");
+      } else {
+        // Need to actually count entities. Using a transaction to get a consistent count
+        // and entity group version.
+        Transaction tx = ds.beginTransaction();
+        PreparedQuery pq = ds.prepare(tx, new Query(entityGroupKey));
+        int count = pq.countEntities(FetchOptions.Builder.withLimit(5000));
+        cache.put(
+            entityGroupKey,
+            new EntityGroupCount(getEntityGroupVersion(ds, tx, entityGroupKey), count));
+        tx.rollback();
+        writer.println(count + " entities");
+      }
+    }
+  }
+  // [END entity_group_2]
+
+  @Test
+  public void entityGroupCount_printsCount() throws Exception {
+    StringWriter responseWriter = new StringWriter();
+    MemcacheService cache = MemcacheServiceFactory.getMemcacheService();
+    Entity entity1 = new Entity("Simple");
+    Key key1 = datastore.put(entity1);
+    Key entityGroupKey = Entities.createEntityGroupKey(key1);
+
+    EntityGroupCount groupCount = new EntityGroupCount(0, 0);
+    groupCount.showEntityGroupCount(
+        datastore, cache, new PrintWriter(responseWriter), entityGroupKey);
+
+    assertThat(responseWriter.toString()).contains(" entities");
+  }
+}

appengine/datastore/src/test/java/com/example/appengine/MetadataKindsTest.java

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+/*
+ * Copyright 2016 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.appengine;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.appengine.api.datastore.DatastoreService;
+import com.google.appengine.api.datastore.DatastoreServiceFactory;
+import com.google.appengine.api.datastore.Entities;
+import com.google.appengine.api.datastore.Entity;
+import com.google.appengine.api.datastore.Query;
+import com.google.appengine.api.datastore.Query.CompositeFilterOperator;
+import com.google.appengine.api.datastore.Query.Filter;
+import com.google.appengine.api.datastore.Query.FilterOperator;
+import com.google.appengine.api.datastore.Query.FilterPredicate;
+import com.google.appengine.tools.development.testing.LocalDatastoreServiceTestConfig;
+import com.google.appengine.tools.development.testing.LocalServiceTestHelper;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+import java.io.PrintWriter;
+import java.io.StringWriter;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Unit tests to demonstrate App Engine Datastore kinds metadata.
+ */
+@RunWith(JUnit4.class)
+public class MetadataKindsTest {
+
+  private final LocalServiceTestHelper helper =
+      new LocalServiceTestHelper(
+          // Set no eventual consistency, that way queries return all results.
+          // https://cloud.google.com/appengine/docs/java/tools/localunittesting#Java_Writing_High_Replication_Datastore_tests
+          new LocalDatastoreServiceTestConfig()
+              .setDefaultHighRepJobPolicyUnappliedJobPercentage(0));
+
+  private StringWriter responseWriter;
+  private DatastoreService datastore;
+
+  @Before
+  public void setUp() {
+    helper.setUp();
+    datastore = DatastoreServiceFactory.getDatastoreService();
+    responseWriter = new StringWriter();
+  }
+
+  @After
+  public void tearDown() {
+    helper.tearDown();
+  }
+
+  // [START kind_query_example]
+  void printLowercaseKinds(DatastoreService ds, PrintWriter writer) {
+
+    // Start with unrestricted kind query
+    Query q = new Query(Entities.KIND_METADATA_KIND);
+
+    List<Filter> subFils = new ArrayList();
+
+    // Limit to lowercase initial letters
+    subFils.add(
+        new FilterPredicate(
+            Entity.KEY_RESERVED_PROPERTY,
+            FilterOperator.GREATER_THAN_OR_EQUAL,
+            Entities.createKindKey("a")));
+
+    String endChar = Character.toString((char) ('z' + 1)); // Character after 'z'
+
+    subFils.add(
+        new FilterPredicate(
+            Entity.KEY_RESERVED_PROPERTY,
+            FilterOperator.LESS_THAN,
+            Entities.createKindKey(endChar)));
+
+    q.setFilter(CompositeFilterOperator.and(subFils));
+
+    // Print heading
+    writer.println("Lowercase kinds:");
+
+    // Print query results
+    for (Entity e : ds.prepare(q).asIterable()) {
+      writer.println("  " + e.getKey().getName());
+    }
+  }
+  // [END kind_query_example]
+
+  @Test
+  public void printLowercaseKinds_printsKinds() throws Exception {
+    datastore.put(new Entity("alpha"));
+    datastore.put(new Entity("beta"));
+    datastore.put(new Entity("NotIncluded"));
+    datastore.put(new Entity("zed"));
+
+    printLowercaseKinds(datastore, new PrintWriter(responseWriter));
+
+    String response = responseWriter.toString();
+    assertThat(response).contains("alpha");
+    assertThat(response).contains("beta");
+    assertThat(response).contains("zed");
+    assertThat(response).doesNotContain("NotIncluded");
+  }
+}