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Creating your First Helix Resource

Creating your First Helix Resource

This document outlines the overall process of developing a resource in the Helix programming model, as well as the tools available for working with resources. It is intended as an overview of the process. For more in depth information on developing a specific type of resource, see the following resources:
  1. Tutorials - There are two tutorials of relevance - Create a New Helix Resource, and Extend a Helix Resource.
  2. Helix Pattern Catalog - This repository contains a series of self-contained Helix examples, intended to illustrate some of the core resource design patterns.

The Helix Programming Model Workflow

The Helix programming model workflow consists of three parts: defining your resource API in XML, implementing the prototypes in Java, and implementing repositories.

The extensions/cortex module includes an example resource which can serve as a starting point.

Defining and Generating the API

To define the API of your new resource, do the following: define your resources, their relationships, and more in XML, and use Maven to generate Java Interfaces for resource identifiers, prototypes and the relationships between them.

Creating the API Project

Create the API project in the cortex/resources-api directory. Refer to extensions/cortex/resources-api/example-api as a starting point. Like example-api, your project should have a pom.xml and an api.xml file. These are used to generate the interfaces under the target directory.

Parent the pom.xml file with the resources-api-parent artifact ID:

      <parent>
        <groupId>com.elasticpath.extensions.rest.definitions</groupId>
        <artifactId>resources-api-parent</artifactId>
        <version>0-SNAPSHOT</version>
      </parent>

Include the api-generator-maven-plugin artifact ID in pom.xml as well:

      <plugin>
        <groupId>com.elasticpath.rest.definitions</groupId>
        <artifactId>api-generator-maven-plugin</artifactId>
      </plugin>

The api.xml file should be located at src/main/resources/META-INF/rest-definitions/api.xml.

Defining the API

Define your API in api.xml using the API definition language. Here, you model the REST endpoints and the relationships between them by defining the family names, resources, forms, entities, and relationships.

For detailed information, see API Definition.

Generating the API

Use Maven to generate the API itself. The generated API consists of .java source and .class files as well as interfaces to implement.

To generate the API, run the following Maven command:

    mvn clean install

This generates the following:

  • Class files in target/com/elasticpath/rest/definitions/ and .java source files for reference in target/generated-sources/api-generator/com/elasticpath/rest/definitions/.
  • Resource interfaces which extend EntityResourceDefinition. Resource interfaces specify the operations to be implemented by the prototype classes.
  • Relationship interfaces which extend RelationshipDefinition. These Relationship interfaces specify the LinkTo interface, which the prototype classes will implement.
  • An entity interface which extends ResourceEntity, as well as an Identifier interface which extends ResourceIdentifier. The prototype classes inject these in as fields in order to access the Entity and Identifier properties.

Creating a Resource Prototype Bundle

Resource prototypes are Java classes which implement the resources defined by the API definition. They perform particular operations by instantiating and routing logic for CRUD and other API operations, including create, read, update, delete, submit, info and linkto. For more information see Resource Prototypes.

The Resource Prototype Project

The prototype projects must be in the cortex/helix-resources directory. Refer to extensions/cortex/helix-resources/example as a starting point. The Helix resource prototype project must include a Maven pom.xml file, and the necessary code for Marking Your Bundle as a Prototype Bundle. It also must have a Maven dependency on the Helix resource API created in the resource-api folder.

The Prototype project should have 4 packages:

  • permissions, which contains the PermissionParameterStrategy class.
  • prototype, which contains the operation prototypes for EntityResourceDefinition as defined in the API.
  • relationship, which contains the classes implementing the RelationshipDefinition interfaces from the API.
  • wiring, which contains the ServiceWiring class.

Implementing a Prototype

Prototype classes need to implement the interfaces generated from resource-api.

For more information on implementing prototypes, see Resource Prototypes.

For more information on configuring prototypes, their permissions, and more see Configuring Prototypes.

Adding a Helix Repository

Helix repositories are responsible for interacting with Commerce Engine. Repositories translate between commerce domain objects and API representations, abstracting the complexity of Commerce Engine's databases and business logic from the API layer.

Repositories typically implement either one of the interfaces in the com.elasticpath.repository package, and one or more of their methods. A resource may have multiple repositories implemented. For more information in implementing repositories, see Resource Repositories.

Running a Helix Prototype

Deploying the Resource

You will need to modify the cortex webapp pom.xml, found at cortex/ext-cortex-webapp/pom.xml. You will need to add a dependency on your resource-api artifact, as well as your resource-prototype artifact.

Under the <!-- Helix Resources --> section of the maven-dependency-plugin plugin, you will need to include the groupId of your new modules. Note that the default groupIds for extension resources have already been added: com.elasticpath.extensions.rest.repositories, and com.elasticpath.extensions.rest.resource. You only need to perform this step if you are using a different groupId.

Starting the Cortex Webapp

The Cortex webapp consists of three applications: Cortex Server, Cortex Studio and the Apache Felix Web Console. These allow you to test your resource configurations, examine the JSON responses, and troubleshoot resource loading errors.

To launch the Cortex webapp, navigate to the /cortex/ext-cortex-webapp/ directory. Then, run the following command:

  mvn clean tomcat7:run-war

This cleans out the existing target directory, starts up a tomcat7 server, and deploys the Cortex Server, Studio, and Felix webapps to the following locations:

  • Cortex Server deploys to http://localhost:9080/cortex
  • Cortex Studio deploys to http://localhost:9080/studio
  • The Felix Console deploys to http://localhost:9080/cortex/system/console/bundles

Debugging Cortex

There are numerous reasons why Cortex may fail to start up. This section can help you address and debug start up issues.

Starting the Cortex Webapp in debug mode

To debug prototype code, start up the Cortex webapp in debug mode and attach your debugger to the running process.

To start the webapp in debug mode, run mvnDebug instead of mvn from the command line while in the webapp folder:

  mvnDebug tomcat7:run-war

When you start the Cortex webapp in debug mode, the console output provides a listening port. You can use this port to attach IDEA's remote debugging to Cortex.

Attaching IDEA Remote Debugging to the Cortex Webapp

Once the Cortex webapp is running in debug mode, attach your IDE's remote debugger to the listening port:

JMX Console

In order to access Cortex with a JMX console, update your system's environment variables and add the following:

  MAVEN_JMX=-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=6969 -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management .jmxremote.authenticate=false

Module Validation

The verification phase of the Maven life cycle validates resources, APIs and prototypes. Maven validates the api.xml file in your resource's API as well as prototype identifiers and entities to ensure that the resources they point to exist. Errors can occur when maven finds an invalid identifier in your XML.

If you see errors similar to the following, you may need to check your module's validation.

Apache Felix Web Console

The Apache Felix Web Console allows developers to interact with installed bundles. There are number of subsections specific to Cortex resources that can help you understand any errors you might be receiving. For more information, see Apache Felix Web Console.