Integrate Extjs with HAL

Question

How i could bind Spring DATA REST which outputs HAL, with ExtJS (v4.1) client, ExtJS do not have support for HAL, but how i could integrate libraries like Hyperagent.js or any JS library supporting HAL, with Extjs data model, to link Stores with the server through HAL.

Whats are the pros and cons of a such architecture ?

Answer 1

This is a very interesting question. There is not much information about how to connect ExtJs to a backend. I didn't find myself the information I was looking for when I started to develop a custom backend for an ajax proxy. I can only write from my limited experience a certainly biased answer, and I hope you will get other answers from different point of views.

I started with the idea to write a generic, standards compliant, client agnostic, RESTful API that exposes the tables in the database as they are. Finally, I ended up with a highly ExtJs specific backend, that implements many features that I perceive as they'd rather belong to the frontend.

What ExtJs imposes on the backend

ExtJs has a rigid relationship between the views and the stores. A view is bound to a store that is directly tied to a backend. That requires that the backend has to serve the data as it will be displayed in the grid. What really misses ( and this has been alleviated to some extent by ExtJs 5 ) is the ability to create a store out of the data of another store. This leads to an obligation to expose the data in a customized way related to the final view ( we already loose separation of concerns between the API and the application ).

This goes further when you want to use features like paging, remote filtering or sorting. If you have extensive data at some point you will have to because of performance issues. The way ExtJs sends the parameters for paging ( by the way this is enabled by default ), sorting and filtering looks peculiar to me, and I think this will require you to adapt your backend for ExtJs at this point. If you use filters alot, you will even need to configure them in the backend, because filter properties like starts with vs contains and case sensitivity make unfortunately not their way to the server. Again a presentation element more introduces itself into the backend.

ExtJs 4 has only a limited support for associations ( and it is not compatible with version 5 ). Advanced features of REST like the ones explained in the post linked by @Jaimie are not supported by ExtJs. ExtJs has a flat approach to REST, each table has its own endpoint. There is a way to send data from a linked table in a tree-like data structure, I wasn't able to get it work, but if you implement that you'll end up with another ExtJs specific feature in your backend.

My current approach

With all these requirements from ExtJs's side, I felt forced to write something really ExtJs specific. What I tried to avoid in the beginning is now the force of my backend : specificity.

I have a class that implements crud operations, paging, filtering and sorting for any mysql table, all secured with authentication. It does exactly what ExtJs expects it to do.

I can create a subclass for a table to allow finer grained control :

• authorization using an ACL
• serve a join or a view
• extended validation before update or delete
• custom filters
• send notifications via a websocket for special actions
• expose any data as a table ( e.g. list of files in a directory )

Conclusion

As you can see, the backend has very powerful features and is quite far from a mere data provider.

It is not an answer to your question about how to integrate a HAL REST api, but somehow it answers the pro and cons part : ExtJs has such specific requirements on its backend that without implementing them you would loose too much functionality. Modify the way ExtJs connects to the server could be an option, but I don't know to what extent you had to rewrite the code. It could require an important investment.