DDevelopment & Design

Simple HBase ORM

When dealing with data stored in HBase, you are quick to come to a conclusion, that it is extremaly inconvenient to reach to it via HBase native API. It is very verbose and you always need to convert between bytes and simple types – a pain. While I wa…When dealing with data stored in HBase, you are quick to come to a conclusion, that it is extremaly inconvenient to reach to it via HBase native API. It is very verbose and you always need to convert between bytes and simple types – a pain. While I wa…

When dealing with data stored in HBase, you are quick to come to a
conclusion, that it is extremaly inconvenient to reach to it
via HBase native API. It is very verbose and you always need to convert
between bytes and simple types – a pain.

While I was working on a project of mine, I thought, why not to easy
those pains and fetch real objects from HBase.

And that’s how this simplistic, hackish ORM came to life. It is no match
for projects like Kundera
(a JPA compliant solution), or n-orm. Nevertheless, it just suits my needs :)

Project sources are hosted on GitHub: https://github.com/zygm0nt/hbase-annotations

To make use of this, you need to have an entity class with annotations:

  • @Column – with argument specifying column family and column name, ie.
    @Column(“cf:column-name”)
  • @Id – will store row key in this property,
  • and optionaly @Value – for Spring Expression Language, in case you
    need to perform some extraction on the value.

Annotations should be on setter methods.

Now you have your model annotated and ready to be fetched from HBase.

The actual work is done with a service class, that should extend class
BaseHadoopInteraction just as class
SimpleHBaseClient does.

Then it is possible to just call:

Note that there are more methods you can use on BaseHadoopInteraction.
You can also do:

  • scan
  • scan with key ranges
  • delete

What you won’t get from this simple ORM is:

  • automatic object updating,
  • nested objects,
  • saving to HBase – ’cause I didn’t have a need for that,

Hope you’ll find this piece of code useful. If you see room for
improvements while staying in project’s scope – please drop me a
message.

And if you are searching for a full-fledged ORM solution for interacting with HBase, just head
straight to Kundera project website :)

— Previous article

Saint Nicholas in CSS

Next article —

Distributed scans with HBase

You May Also Like
DDevelopment & Design

Simple trick to DRY your Grails controller

Grails controllers are not very DRY. It's easy to find duplicated code fragments in default generated controller. Take a look at code sample below. It is duplicated four times in show, edit, update and delete actions:

class BookController {
def show() {
def bookInstance = Book.get(params.id)
if (!bookInstance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
return
        }
        [bookInstance: bookInstance]
    }
}

Why is it duplicated?

There is a reason for that duplication, though. If you move this snippet to a method, it can redirect to "list" action, but it can't prevent controller from further execution. After you call redirect, response status changes to 302, but after method exits, controller still runs subsequent code.

Solution

At TouK we've implemented a simple trick to resolve that situation:

  1. wrap everything with a simple withStoppingOnRender method,
  2. whenever you want to render or redirect AND stop controller execution - throw EndRenderingException.

We call it Big Return - return from a method and return from a controller at once. Here is how it works:

class BookController {
def show(Long id) {
withStoppingOnRender {
Book bookInstance = Book.get(id)
validateInstanceExists(bookInstance)
            [bookInstance: bookInstance]
        }
    }

protected Object withStoppingOnRender(Closure closure) {
try {
return closure.call()
        } catch (EndRenderingException e) {}
    }

private void validateInstanceExists(Book instance) {
if (!instance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
throw new EndRenderingException()
        }
    }
}

class EndRenderingException extends RuntimeException {}

Example usage

For simple CRUD controllers, you can use this solution and create some BaseController class for your controllers. We use withStoppingOnRender in every controller so code doesn't look like a spaghetti, we follow DRY principle and code is self-documented. Win-win-win! Here is a more complex example:

class DealerController {
@Transactional
def update() {
withStoppingOnRender {
Dealer dealerInstance = Dealer.get(params.id)
validateInstanceExists(dealerInstance)
validateAccountInExternalService(dealerInstance)
checkIfInstanceWasConcurrentlyModified(dealerInstance, params.version)
            dealerInstance.properties = params
saveUpdatedInstance(dealerInstance)
redirectToAfterUpdate(dealerInstance)
        }
    }
}