Datastore Read Consistency Policy sample. (#210)

Moved from
https://cloud.google.com/appengine/docs/java/datastore/data-consistency#datastore_query_data_consistency

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

@@ -0,0 +1,113 @@
+/*
+ * 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.DatastoreServiceConfig;
+import com.google.appengine.api.datastore.DatastoreServiceFactory;
+import com.google.appengine.api.datastore.Entity;
+import com.google.appengine.api.datastore.FetchOptions;
+import com.google.appengine.api.datastore.Query;
+import com.google.appengine.api.datastore.ReadPolicy;
+import com.google.appengine.tools.development.testing.LocalDatastoreServiceTestConfig;
+import com.google.appengine.tools.development.testing.LocalServiceTestHelper;
+import com.google.common.collect.ImmutableList;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+import java.util.List;
+
+/**
+ * Unit tests for {@link ReadPolicy}.
+ */
+@RunWith(JUnit4.class)
+public class ReadPolicyTest {
+  private final LocalServiceTestHelper helper =
+      new LocalServiceTestHelper(
+          // Set 100% eventual consistency, so we can test with other job policies.
+          // https://cloud.google.com/appengine/docs/java/tools/localunittesting#Java_Writing_High_Replication_Datastore_tests
+          new LocalDatastoreServiceTestConfig()
+              .setDefaultHighRepJobPolicyUnappliedJobPercentage(100));
+
+  @Before
+  public void setUp() {
+    helper.setUp();
+  }
+
+  @After
+  public void tearDown() {
+    helper.tearDown();
+  }
+
+  @Test
+  public void readPolicy_eventual_returnsNoResults() {
+    // [START data_consistency]
+    double deadline = 5.0;
+
+    // Construct a read policy for eventual consistency
+    ReadPolicy policy = new ReadPolicy(ReadPolicy.Consistency.EVENTUAL);
+
+    // Set the read policy
+    DatastoreServiceConfig eventuallyConsistentConfig =
+        DatastoreServiceConfig.Builder.withReadPolicy(policy);
+
+    // Set the call deadline
+    DatastoreServiceConfig deadlineConfig = DatastoreServiceConfig.Builder.withDeadline(deadline);
+
+    // Set both the read policy and the call deadline
+    DatastoreServiceConfig datastoreConfig =
+        DatastoreServiceConfig.Builder.withReadPolicy(policy).deadline(deadline);
+
+    // Get Datastore service with the given configuration
+    DatastoreService datastore = DatastoreServiceFactory.getDatastoreService(datastoreConfig);
+    // [END data_consistency]
+
+    Entity parent = new Entity("Person", "a");
+    Entity child = new Entity("Person", "b", parent.getKey());
+    datastore.put(ImmutableList.<Entity>of(parent, child));
+
+    // Even though we are using an ancestor query, the policy is set to
+    // eventual, so we should get eventually-consistent results. Since the
+    // local data store test config is set to 100% unapplied jobs, there
+    // should be no results.
+    Query q = new Query("Person").setAncestor(parent.getKey());
+    List<Entity> results = datastore.prepare(q).asList(FetchOptions.Builder.withDefaults());
+    assertThat(results).named("query results").isEmpty();
+  }
+
+  @Test
+  public void readPolicy_strong_returnsAllResults() {
+    double deadline = 5.0;
+    ReadPolicy policy = new ReadPolicy(ReadPolicy.Consistency.STRONG);
+    DatastoreServiceConfig datastoreConfig =
+        DatastoreServiceConfig.Builder.withReadPolicy(policy).deadline(deadline);
+    DatastoreService datastore = DatastoreServiceFactory.getDatastoreService(datastoreConfig);
+
+    Entity parent = new Entity("Person", "a");
+    Entity child = new Entity("Person", "b", parent.getKey());
+    datastore.put(ImmutableList.<Entity>of(parent, child));
+
+    Query q = new Query("Person").setAncestor(parent.getKey());
+    List<Entity> results = datastore.prepare(q).asList(FetchOptions.Builder.withDefaults());
+    assertThat(results).named("query results").hasSize(2);
+  }
+}