Spring Data Crate

The primary goal of the Spring Data project is to make it easier to build Spring-powered applications that use new data access technologies such as non-relational databases, map-reduce frameworks, and cloud based data services.

The Spring Data project aims to provide a familiar and consistent Spring-based programming model for new datastores while retaining store-specific features and capabilities. The Spring Data Crate project provides integration with the Crate. Crate is a shared-nothing, fully searchable, document-oriented cluster data store. It is a quick and powerful massively scalable backend for data intensive apps, like the Internet of Things or real-time analytics.

Features

• Automatic table export from entities using @Table annotation
• Support for mapping rich object model/graph to and from Crate
• Support for simple and composite Primary Key using @Id annotation. Primary Key constraints
• JSR 303 bean validation support
• Support for Lifecycle call back events (before/after save etc)
• Java based configuration

NOTE: Composite primary key must contain primitive field(s) supported by Crate.

Quick Start

Checkout the project repository and issue the following command from a shell/terminal.

mvn clean install

This will generate a jar file. The jar file can be found under the 'target' folder and also in local maven repository in user's home directory in .m2folder. Add the generated jar file in your project.

Please look at spring data crate's pom.xml for required dependencies.

CrateTemplate

CrateTemplate is the central support class for Crate database operations. It provides:

• Basic POJO mapping support to and from Crate Documents
• Convenience methods to interact with the store (insert, update, delete objects) and Crate specific ones (bulk insert, bulk update and bulk delete operations)
• Exception translation into Spring's technology agnostic DAO exception hierarchy.

CrateRepository

To simplify the creation of data repositories Spring Data Crate provides a generic repository programming model. A default implementation of CrateRepository, aligning to the generic Repository Interfaces, is provided.

CrateRepository extends CrudRepository which causes CRUD methods being pulled into the interface so that you can easily save and find single entities and collections of them.

For example, given a User class with Id property of type String, a UserRepository interface can be defined as shown below:

public interface UserRepository extends CrateRepository<User, String> {
}

NOTE: Currently documents can be queried by Id. Support will be added to derive queries from method names.

Query Methods

Query Lookup Strategies

The Spring Data Crate can resolve queries using following query lookup strategies:

• CREATE constructs a query from the query method name of a repository.
• USE_DECLARED_QUERY looks up for a declared query and will throw an exception in case it is not found.
• CREATE_IF_NOT_FOUND checks first for declared query, if it is not found, it uses the CREATE strategy to create a query from a method name.

The strategy can be configured at namespace via XML by setting the query lookup strategy attribute or through the queryLookupStrategy attribute of the @EnableCrateRepositories annotation when using Java configurations.

Query creation

When using the CREATE query lookup strategy the Spring Data Crate repository infrastructure constructs a query from a method name. It strips find..By, read..By, query..By, and get.. prefixes from the method name. Then, the query is build by parsing the rest of the method name and the entity metadata.

Expressions in a method name can be combined with AND and OR.

The query creation mechanism also supports following operators: [is]greaterThan, [is]greaterThanEqual, [is]lessThan, [is]lessThanEqual, [is]Equals, Like, [is]Start[s|ing]With, End[s|ing]With, [is]Null, [is]True, and [is]False.

public interface UserRepository extends CrateRepository<User, String> {

    List<User> findByNameAndAge(String name, Integer age);
    
    List<User> findByNameOrAge(String name, Integer age);
    
    User getByEmail(String email);
    
    List<User> findByAgeGreaterThanEqual(Integer age);
}

Declared Queries

It's also possible to use the @Query annotation to define queries:

public interface UserRepository extends CrateRepository<User, String> {

    @Query("select * from users")
    List<User> getAllUsers();
}

The query annotation can also be used with parameter substitution, where the arguments passed to the method has to match the positional placeholders in the query:

public interface UserRepository extends CrateRepository<User, String> {

    @Query("select * from users where name=$1 and age=$2")
    List<User> findUsersByNameAndAge(String name, int age);
}

Application config

You can have Spring automatically create a proxy for the interface by using the following JavaConfig:

@Configuration
@EnableCrateRepositories
class ApplicationConfig extends AbstractCrateConfiguration {
}

This sets up a connection to a Crate instance and enables the detection of Spring Data repositories (through @EnableCrateRepositories).

Custom converters can be added by overridding methods provided in AbstractCrateConfiguration class.

By default, a crate client will be created to connect to Crate running on localhost on port 4300. A custom host and port can be specified as shown below:

@Configuration
@EnableCrateRepositories
class ApplicationConfig extends AbstractCrateConfiguration {

  @Override
  public CrateClient crateClient() {
		return new CrateClient("<host>:<port>");
  }
}

The same configuration would look like this in XML:

<bean name="crateTemplate" class="org.springframework.data.crate.core.CrateTemplate">
	<constructor-arg ref="client"/>
</bean>

<crate:client id="client" servers="127.0.0.1:4300"/>

<crate:repositories base-package="com.acme.repository"/>

The servers attribute takes a comma separated string of host:port

NOTE: Currently adding custom converters via XML is not supported.

This will find the repository interface and register a proxy object in the container. You can use it as shown below:

@Table(name="users", numberOfReplicas="2", refreshInterval=1500, columnPolicy=ColumnPolicy.DYNAMIC)
public class User {

	@Id
	private String id;

	// JSR-303 annotations
	@Email
	@NotBlank
	private String email;

	/** Optional. If other constructors are defined, then annotate one of them
	@PersistenceConstructor
	public User(String id, String email) {
		this.id = id;
		this.email = email;
	}**/

	// getters and setters
}

Changes to the numberOfReplicas table parameter will be reflected to the database on application restarts. Details about table parameters can be found here Table Parameters

NOTE: Crate currently does not return refresh_interval and column_policy from information_schema.tables. To change the values of these two table parameters, you will have to execute the queries manually from Crate's crash command line tool.

alter table my_table set (refresh_interval = <NEW_VALUE>);
alter table my_table set (column_policy = <NEW_VALUE>);

@Service
public class UserService {

  private UserRepository repository;

  @Autowired
  public UserService(UserRepository repository) {
    this.repository = repository;
  }

  public void doStuff() {

     repository.deleteAll();

     User user = new User();
     user.setId("abc123");
     user.setEmail("[email protected]");

     repository.save(user);

	 repository.refreshTable();

     User dbUser = repository.findById(user.getId());
     List<User> users = repository.findAll();
 }

}

NOTE: Information about table refresh can be found here Refresh

Schema Export

Spring Data Crate can export tables from entities annotated with @Table annotation. By default, the table name will be derived from the entity package and class name. Otherwise, the name will be used from the name attribute of the annotation @Table(name="myTable").

To enable automatic creation of tables, register the following bean as shown below:

@Configuration
@EnableCrateRepositories
class ApplicationConfig extends AbstractCrateConfiguration {

	@Bean
	public CratePersistentEntitySchemaManager cratePersistentEntitySchemaManager() throws Exception {
		return new CratePersistentEntitySchemaManager(crateTemplate(), CREATE_DROP);
	}
}

The CratePersistentEntitySchemaManager can be configured to ignore failures and enabled (useful if using the spring's environment abstraction to enable/disable schema export) as follows:

@Configuration
@EnableCrateRepositories
class ApplicationConfig extends AbstractCrateConfiguration {

	@Bean
	public CratePersistentEntitySchemaManager cratePersistentEntitySchemaManager() throws Exception {
		CratePersistentEntitySchemaManager manager = new CratePersistentEntitySchemaManager(crateTemplate(), CREATE_DROP)
		manager.setIgnoreFailures(true); // defaults to false
		manager.setEnabled(false); // defaults to true
		return manager;
	}
}

If the CratePersistentEntitySchemaManager is not enabled, tables will not be exported to Crate.

Full configuration would look like this in XML:

<bean name="crateTemplate" class="org.springframework.data.crate.core.CrateTemplate">
	<constructor-arg ref="client"/>
</bean>

<crate:client id="client" servers="127.0.0.1:4300"/>

<crate:repositories base-package="com.acme.repository"/>

<crate:schema-export ignoreFailures="false" export-option="CREATE_DROP" enabled="true"/>

There are 3 schema export options

- CREATE
- CREATE_DROP
- UPDATE

CREATE will create the tables if they do not exist.

CRATE_DROP will do the same as CREATE but will drop all the tables on application shutdown.

UPDATE will create the tables if they do not exist. Otherwise, the tables will be updated if new fields are added to the entities resulting in new columns being added to the tables.