Patterns of Enterprise Application Architecture

Compilation of sample code from the book Patterns of Enterprise Application Architecture by Martin Fowler.

I used and created this repo when I studied the book. Super worth reading it!

Read the book and learn more on each topic.

Enjoy! :)

Layering

• Presentation
• Domain Logic
• Data Source

Patterns

Domain Logic Patterns

• Transaction Script
• Domain Model
• Table Module
• Service Layer

Data Source Patterns

• Table Data Gateway
• Row Data Gateway
• Active Records
• Data Mapper

Object-Relational Behavior Patterns

• Unit of Work
• Identify Map
• Lazy Load

Object-Relational Structural Patterns

• Identity Field
• Foreign Key Mapping
• Association Table Mapping
• Dependent Mapping
• Embedded Value
• Serialized LOB
• Single Table Inheritance
• Class Table Inheritance
• Concrete Table Inheritance
• Inheritance Mappers

Object-Relational Metadata Mapping Patterns

• Metadata Mapping
• Query Object
• Repository

Web Presentation Patterns

• Model View Controller
• Page Controller
• Front Controller
• Template View
• Transform View
• Two Step View
• Application Controller

Distribution Patterns

• Remote Facade
• Data Transfer Object

Offline Concurrency Patterns

• Optimistic Offline Lock
• Pessimistic Offline Lock
• Coarse-Grained Lock
• Implicit Lock

Session State Patterns

• Client Session State
• Server Session State
• Database Session State

Base Patterns

• Gateway
• Mapper
• Layer Supertype
• Separated Interface
• Registry
• Value Object
• Money
• Special Case
• Plugin
• Service Stub
• Record Set

Details

Domain Logic Patterns

• 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.
  

Additional References

• https://martinfowler.com/eaaCatalog/
• https://www.sourcecodeexamples.net/p/p-of-eaa.html
• Lazy Load: Ghost
  • https://stackoverflow.com/questions/58243839/how-to-implement-lazy-loading-using-ghost-object-in-java