Patterns of Enterprise Application Architecture

Transaction Script

Organizes business logic by procedures where each procedure handles a single request from the presentation.
Domain Model

An object model of the domain that incorporates both behavior and data.
Table Module

A single instance that handles the business logic for all rows in a database table or view.
Service Layer

Defines an application’s boundary with a layer of services that establishes a set of available operations and coordinates the application’s response in each operation.

Data Source Patterns

Table Data Gateway

An object that acts as a Gateway to a database table. One instance handles all the rows in the table.
Row Data Gateway

An object that acts as a Gateway to a single record in a data source. There is one instance per row.
Active Records

An object that wraps a row in a database table or view, encapsulates the database access, and adds domain logic on that data.
Data Mapper

A layer of Mappers (473) that moves data between objects and a database while keeping them independent of each other and the mapper itself.

Object-Relational Behavior Patterns

Unit of Work

Maintains a list of objects affected by a business transaction and coordinates the writing out of changes and the resolution of concurrency problems.
Identify Map

Ensures that each object gets loaded only once by keeping every loaded object in a map. Looks up objects using the map when referring to them.
Lazy Load

An object that doesn't contain all of the data you need but knows how to get it.
- Types:
  - Lazy Initialization
  - Virtual Proxy
  - Value Holder
  - Ghost

Object-Relational Structural Patterns

Identity Field

Saves a database ID field in an object to maintain identity between an in-memory object and a database row.
- Types:
  - Integral
  - Key Table
  - Compound Key
Foreign Key Mapping

Maps an association between objects to a foreign key reference between tables.
- Types:
  - Single-Valued Reference
  - Multi Table Find
  - Collection of References
Association Table Mapping

Saves an association as a table with foreign keys to the tables that are linked by the association.
Dependent Mapping

Has one class perform the database mapping for a child class.
Embedded Value

Maps an object into several fields of another object’s table.
Serialized LOB

Saves a graph of objects by serializing them into a single large object (LOB), which it stores in a database field.
Single Table Inheritance

Represents an inheritance hierarchy of classes as a single table that has columns for all the fields of the various classes.
Class Table Inheritance

Represents an inheritance hierarchy of classes with one table for each class.
Concrete Table Inheritance

Represents an inheritance hierarchy of classes with one table per concrete class in the hierarchy.
Inheritance Mappers

A structure to organize database mappers that handle inheritance hierarchies.

Object-Relational Metadata Mapping Patterns

Metadata Mapping

Holds details of object-relational mapping in metadata.
Query Object

An object that represents a database query.
Repository

Mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects.

Web Presentation Patterns

Model View Controller

Splits user interface interaction into three distinct roles.
Page Controller

An object that handles a request for a specific page or action on a Web site.
Front Controller

A controller that handles all requests for a Web site.
Template View

Renders information into HTML by embedding markers in an HTML page.
Transform View

A view that processes domain data element by element and transforms it into HTML.
Two Step View

Turns domain data into HTML in two steps: first by forming some kind of logical page, then rendering the logical page into HTML.
Application Controller

A centralized point for handling screen navigation and the flow of an application.

Distribution Patterns

Remote Facade

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

An object that carries data between processes in order to reduce the number of method calls.

Offline Concurrency Patterns

Optimistic Offline Lock

Prevents conflicts between concurrent business transactions by detecting a conflict and rolling back the transaction.
Pessimistic Offline Lock

Prevents conflicts between concurrent business transactions by allowing only one business transaction at a time to access data.
Coarse-Grained Lock

Locks a set of related objects with a single lock.
Implicit Lock

Allows framework or layer supertype code to acquire offline locks.

Session State Patterns

Client Session State

Stores session state on the client.
Server Session State

Keeps the session state on a server system in a serialized form.
Database Session State

Stores session data as committed data in the database.

Base Patterns

Gateway

An object that encapsulates access to an external system or resource.
Mapper

An object that sets up a communication between two independent objects.
Layer Supertype

A type that acts as the supertype for all types in its layer.
Separated Interface

Defines an interface in a separate package from its implementation.
Registry

A well-known object that other objects can use to find common objects and services.
Value Object

A small simple object, like money or a date range, whose equality isn’t based on identity.
Money

Represents a monetary value.
Special Case

A subclass that provides special behavior for particular cases.
Plugin

Links classes during configuration rather than compilation.
Service Stub

Removes dependence upon problematic services during testing.
Record Set

An in-memory representation of tabular data.