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  See the [Google Cloud Datastore docs][cloud-datastore-activation] for more details on how to activate
  Cloud Datastore for your project.

  See the [Datastore client library docs][datastore-client-lib-docs] to learn how to interact
  with the Cloud Datastore using this Client Library.

  #### Creating an authorized service object
  To make authenticated requests to Google Cloud Datastore, you must create a service object with credentials. You can then make API calls by calling methods on the Datastore service object. The simplest way to authenticate is to use [Application Default Credentials](https://developers.google.com/identity/protocols/application-default-credentials). These credentials are automatically inferred from your environment, so you only need the following code to create your service object:

  ```java
  import com.google.cloud.datastore.Datastore;
  import com.google.cloud.datastore.DatastoreOptions;

  Datastore datastore = DatastoreOptions.getDefaultInstance().getService();
  ```

  For other authentication options, see the [Authentication](https://github.com/googleapis/google-cloud-java#authentication) page.

  #### Storing data
  Objects in Datastore are known as entities. Entities are grouped by "kind" and have keys for easy access. In this code snippet, we will create a new entity representing a person and store that data by the person's email.  First, add the following imports at the top of your file:

  ```java
  import com.google.cloud.datastore.Entity;
  import com.google.cloud.datastore.Key;
  import com.google.cloud.datastore.KeyFactory;
  ```

  Then add the following code to put an entity in Datastore.

  ```java
  KeyFactory keyFactory = datastore.newKeyFactory().setKind("Person");
  Key key = keyFactory.newKey("john.doe@gmail.com");
  Entity entity = Entity.newBuilder(key)
      .set("name", "John Doe")
      .set("age", 51)
      .set("favorite_food", "pizza")
      .build();
  datastore.put(entity);
  ```

  Later, if you want to get this entity back, add the following to your code:

  ```java
  Entity johnEntity = datastore.get(key);
  ```

  #### Running a query
  In addition to retrieving entities by their keys, you can perform queries to retrieve entities by
  the values of their properties. A typical query includes an entity kind, filters to select entities
  with matching values, and sort orders to sequence the results. `google-cloud-datastore` supports two
  types of queries: `StructuredQuery` (that allows you to construct query elements) and `GqlQuery`
  (which operates using [GQL syntax](https://cloud.google.com/datastore/docs/apis/gql/gql_reference))
  in string format. In this tutorial, we will use a simple `StructuredQuery`.

  Suppose that you've added more people to Datastore, and now you want to find all people whose favorite food is pizza. Import the following:

  ```java
  import com.google.cloud.datastore.Query;
  import com.google.cloud.datastore.QueryResults;
  import com.google.cloud.datastore.StructuredQuery;
  import com.google.cloud.datastore.StructuredQuery.PropertyFilter;
  ```

  Then add the following code to your program:

  ```java
  Query<Entity> query = Query.newEntityQueryBuilder()
      .setKind("Person")
      .setFilter(PropertyFilter.eq("favorite_food", "pizza"))
      .build();
  QueryResults<Entity> results = datastore.run(query);
  while (results.hasNext()) {
    Entity currentEntity = results.next();
    System.out.println(currentEntity.getString("name") + ", you're invited to a pizza party!");
  }
  ```

  Cloud Datastore relies on indexing to run queries. Indexing is turned on by default for most types of properties. To read more about indexing, see the [Cloud Datastore Index Configuration documentation](https://cloud.google.com/datastore/docs/tools/indexconfig).

  #### Updating data
  Another thing you'll probably want to do is update your data. The following snippet shows how to update a Datastore entity if it exists.

  ``` java
  KeyFactory keyFactory = datastore.newKeyFactory().setKind("keyKind");
  Key key = keyFactory.newKey("keyName");
  Entity entity = datastore.get(key);
  if (entity != null) {
    System.out.println("Updating access_time for " + entity.getString("name"));
    entity = Entity.newBuilder(entity)
        .set("access_time", DateTime.now())
        .build();
    datastore.update(entity);
  }
  ```

  The complete source code can be found at
  [UpdateEntity.java](../../google-cloud-examples/src/main/java/com/google/cloud/examples/datastore/snippets/UpdateEntity.java).

  #### Complete source code

  In
  [AddEntitiesAndRunQuery.java](../../google-cloud-examples/src/main/java/com/google/cloud/examples/datastore/snippets/AddEntitiesAndRunQuery.java)
  we put together all the code to store data and run queries into one program. The program assumes that you are
  running on Compute Engine or from your own desktop. To run the example on App Engine, simply move
  the code from the main method to your application's servlet class and change the print statements to
  display on your webpage.

  Testing
  -------

  This library has tools to help write tests for code that uses the Datastore.

  See [TESTING.md](https://github.com/googleapis/google-cloud-java/blob/master/TESTING.md#testing-code-that-uses-datastore) to read more about testing.

  Example Applications
  --------------------
  - [`Bookshelf`](https://github.com/GoogleCloudPlatform/getting-started-java/tree/master/bookshelf) - An App Engine app that manages a virtual bookshelf.
    - This app uses `google-cloud` to interface with Cloud Datastore and Cloud Storage. It also uses Cloud SQL, another Google Cloud Platform service.
  - [`Flexible Environment/Datastore example`](https://github.com/GoogleCloudPlatform/java-docs-samples/tree/master/flexible/datastore) - A simple app that uses Cloud Datastore to list the last 10 IP addresses that visited your site.
  - [`SparkDemo`](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/master/flexible/sparkjava) - An example of using `google-cloud-datastore` from within the SparkJava and App Engine Flexible Environment frameworks.
    - Read about how it works on the example's [README page](https://github.com/GoogleCloudPlatform/java-docs-samples/tree/master/flexible/sparkjava#how-does-it-work).