Warning Older Docs! - You are viewing documentation for a previous released version of RhoMobile Suite.

Data Handling Using Rhom

What is Rhom?

Rhom is a database object mapper or ORM for RhoMobile. It provides a simple but powerful high level interface to use a local (on-device) SQLite database in terms of objects, and works hand in hand with RhoConnectClient to enable two-way synchronization between your application and a RhoConnect server.

One of its main benefits is that, instead of having to write SELECT and UPDATE statements by hand, you can carry out actions in your database by getting and setting properties on model objects.

Without Rhom, you would issue SQL statements to the database:

update product set price=119,brand='Motorola' where object='12345'

With Rhom you can achieve the same result with:

product.updateAttibutes({price: 119, brand: "Zebra"});

Object deletion in SQL:

delete from product where object='12345'

Object deletion with Rhom:

product.destroy();

What is a model?

RhoMobile applications, in general, follow the Model-View-Controller (MVC) pattern. In RhoMobile, a model can store information from two origins:

  • data created directly on the device
  • data retrieved from a RhoConnect synchronization server

Each model contains attributes that it stores information about. For example, a Product model could have as attributes name, brand, price, etc. Applications will normally have one model for each entity they handle (Customer, Product, Invoice, InvoiceLine, Order, LineItem, etc).

There are two types of models used with RhoMobile applications: Property Bag and Fixed Schema. Each of them are useful under different conditions. Be sure to consider the points below when chosing which scheme you wish to use in your application.

Property Bag Model

In a property bag model, all data is stored in a single table using the object-attribute-value pattern also referred to as the Entity-attribute-value model. This data is schemaless, which means that you don’t need to specify ahead of time what keys exist on each ORM Model. You simply set whatever key-value pairs you want, and Rhom will store and sync it.

Advantages

  • Simple to use, it doesn’t require specifying attributes
  • Data migrations are not necessary
  • Attributes can be added or removed without modifying the database schema

Disadvantages

  • For some applications, the database size may be significantly larger than fixed schema. This is because each attribute is indexed for fast lookup
  • Sync process may be slightly slower because inserts are performed at attribute level

Fixed Schema Model

In a fixed schema model, each model has a separate database table and each attribute exists as a column in the table. In this sense, fixed schema models are similar to traditional relational tables.

Advantages

  • Smaller database size, indexes can be specified only on specific attributes.
  • Sync process may perform faster because whole objects are inserted at a time.

Disadvantages

  • Schema changes must be handled with data migrations.
  • Database performance may be slow unless you specify proper indexes.

Ruby and JavaScript Access

RhoMobile applications provide definition and CRUD access to your data models in both Ruby and JavaScript, however there are some differences in capabilties between the two. Please consult the API reference and guides for further information:

Database Encryption

As of Rhodes version 3.3.3, Rhom data encryption is removed from Rhodes. This feature is only supported in Zebra RhoMobile Suite. If you wish to use this feature, you will need to upgrade to RhoMobile Suite purchase a RhoElements license is required.

If your application requires that the local database is encrypted on the filesystem, you can enable it by setting a flag in build.yml:

encrypt_database: 1

Database encryption is not supported for applications that use bulk sync at this time.

Platform Notes

  • iOS: Uses AES 128 encryption algorithm from iOS SDK.
  • Android: Uses AES 128 ecryption algorithm from Android SDK.
  • Windows Mobile: Uses RC4 algorithm from Windows Mobile SDK.
Back to Top