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Add App Engine Cloud Datastore metadata queries samples.
From https://cloud.google.com/appengine/docs/java/datastore/metadataqueries.
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‎appengine/datastore/src/test/java/com/example/appengine/MetadataEntityGroupTest.java

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

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

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

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