Building an Adaptive Object Model

In this series of blogs, we will discuss how we build our next generation platform using Jeresy, Jackson, JSON, and Riak. But first, we will show how to build an adaptive object model, supporting multiple versions of object types simultaneously.

Object Model Requirement

For our platform, we are storing various types of configuration objects, with parent/child relationship linking objects together. Each object type has a set of fixed pre-defined properties and a set of custom properties, which can vary from customer to customers.

Support Versioned Objects

As our platform evolves, our object model will need to adapt and evolve, which means we need to support and store different versions of same object type. Properties can be added or removed between different versions.

Building an Adaptive Object Model

After some exploring, we decided to go with two set of object models, an explicit object model for Web Services and a generic persistence object model.

Here is a picture of the two object models,

The generic object graph approach consists of two layers of abstraction, a wrapper object and an inner JSON object. The wrapper layer contains the following static information that does not change from one version to another, like,

• Object name
• Object key
• Object type
• Object uri
• Object version
• A relationship map
• Parent id

and a map representation of the inner JSON object.

The inner JSON object is the JSON object created by the user or will be returned to the user. The inner JSON object can be different from version to version and from type to type. Since the platform does not need to know what is actually stored in the inner JSON object, other than a set of standard fields, like,

• Object name
• Object type
• Object version

The platform just stores the wrapper object, with inner object as an opaque map. Since the wrapper object structure does not change based on version or type and the inner object is stored as a generic Map type, the platform does not need to change every time we add a new object type or change an existing object type.

Object Validation

However, we still need to validate user supplied JSON object to make sure that it matches the correct version of the object type. We accomplish this by creating a set of validating classes and register them by type and version. When we receiving an object creation request, we will first deserialize the input JSON to a raw Map type and pull out the type and version from the map object. Then we look up the validation class based on type and version and then deserialize the input JSON object again based on the validation class.

When a new type is introduced or new version of type is introduced, we just update the validation map with the new configuration and deploy the new classes and nothing else needs to be changed.

Sequence Diagram for Web Services

Create a New Object through Web Services.

Get an Object through Web Services.