Remote Facade

Provides a coarse-grained facade on fine-grained objects to improve efficiency over a network.

• Overview
• How It Works
• When to Use It

Overview

Remote calls are expensive: data may have to be marshaled, security may need to be checked, packets may need to be routed through swithces. Any inter-process call is orders of magnitude more expensive than an in-process call, even if both processes are on the same machine.

As a result, any object that’s intended to be used as a remote object needs a coarse-grained interface that minimizes the number of calls needed to get somethind one.

A Remote Facade provides a coarse-grained facade over a web of fine-grained object. None of the fine-grained objects have a remote interface, and the Remote Facade contains no domain logic, all it does is translate coarse-grained methods onto the underlying fine-grained objects.

How It Works

• Any complex logic is placed in fine-grained objects that are designed to collaborate within a single process, which is the standard object-oriented approach.

• To allow efficient access to them, a separate facade object acts as a remote interface. This facade is merely a thin skin that switches from a coarse-grained to a fine-grained interface. The facade does not contain domain logic at all.

• In a simple case, like an address object, a Remote Facade replaces all the getting and setting methods with one getter and one setter, often referred to as bulk accessors. This way all the logic of validation and computation stays on the address object where it can be factored cleanly and can be used by other fine-grained objects.

• In a more complex case, a single Remote Facade may act as a remote gateway for many fine-grained objects. For example, an order facade may be used to get and update information for an order, all its order lines, and mayne some customer data s well.

• The facade is designed to make life simpler for external users, not for the internal system.

• Remote *Facade can be stateful or stateless.

  • Stateless allows pooling, which can improve resource usage and efficiency, especially in a B2C situation.
  • Stateful requires storing session state somewhere using Client Session State or Database Session State, or an implementation of Server Session State.

When to Use It

• Whenever you need remote access to a fine-grained object model. You gain the avantages of a coarse-grained interface while still keeping the advantage of fine-grained objects.

• The most common use of this pattern is between a presentation and a Domain Model, where the two may run on different processes.

• Remote Facades imply a synchronous style of distribution. Often you can greatly improve the responsiveness of an application by going with asynchronous, message-based remote communication.