IDDD_Samples

These are the sample Bounded Contexts from the book "Implementing Domain-Driven Design" by Vaughn Vernon: http://vaughnvernon.co/?page_id=168

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Quick Overview

IDDD_Samples is a GitHub repository containing sample code for Implementing Domain-Driven Design (IDDD) patterns and practices. It provides practical examples of DDD concepts in various programming languages, including Java, C#, and Scala, to help developers understand and implement DDD in their projects.

Pros

Offers concrete implementations of DDD concepts across multiple languages
Provides real-world examples that demonstrate how to apply DDD principles
Includes comprehensive documentation and explanations for each sample
Maintained by Vaughn Vernon, a respected authority in the DDD community

Cons

Some examples may be outdated or not follow the latest best practices
Limited coverage of certain DDD patterns or advanced concepts
May require prior knowledge of DDD to fully understand the samples
Not actively maintained, with infrequent updates

Code Examples

Here are a few code examples from the Java implementation:

Defining an Entity:

public class Product extends ConcurrencySafeEntity {
    private ProductId productId;
    private String name;
    private String description;
    
    public Product(ProductId productId, String name, String description) {
        this.productId = productId;
        this.name = name;
        this.description = description;
    }
    
    // ... other methods
}

Implementing a Value Object:

public final class Money implements Serializable {
    private final BigDecimal amount;
    private final String currency;
    
    public Money(BigDecimal amount, String currency) {
        this.amount = amount;
        this.currency = currency;
    }
    
    // ... other methods
}

Using a Repository:

public interface ProductRepository {
    void add(Product product);
    Product productOfId(ProductId productId);
    void remove(Product product);
}

Getting Started

To get started with the IDDD_Samples:

Clone the repository:

git clone https://github.com/VaughnVernon/IDDD_Samples.git

Navigate to the desired language implementation (e.g., Java):
```
cd IDDD_Samples/iddd_common/src
```
Explore the code samples and accompanying documentation to understand how DDD concepts are implemented in practice.
Use the samples as a reference when implementing DDD in your own projects, adapting them to your specific domain and requirements.

Competitor Comparisons

modular-monolith-with-ddd

10,870

Full Modular Monolith application with Domain-Driven Design approach.

Pros of modular-monolith-with-ddd

Implements a modular monolith architecture, showcasing a modern approach to DDD
Provides a more comprehensive example with real-world scenarios and practices
Includes detailed documentation and architectural decision records (ADRs)

Cons of modular-monolith-with-ddd

More complex structure, which may be overwhelming for DDD beginners
Focuses on a specific architectural style, potentially limiting its applicability
Less variety in domain examples compared to IDDD_Samples

Code Comparison

IDDD_Samples:

public class BacklogItem extends ConcurrencySafeEntity {
    private BacklogItemId backlogItemId;
    private String summary;
    private String category;
    private BacklogItemStatus status;
    // ...
}

modular-monolith-with-ddd:

public class MeetingGroup : Entity, IAggregateRoot
{
    public MeetingGroupId Id { get; private set; }
    public string Name { get; private set; }
    public string Description { get; private set; }
    public MeetingGroupLocation Location { get; private set; }
    // ...
}

Both repositories demonstrate DDD concepts, but modular-monolith-with-ddd uses a more modern C# approach with cleaner separation of concerns. IDDD_Samples provides a broader range of examples in Java, which may be beneficial for learning DDD principles across different contexts.

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More focused on .NET and C# specific implementations
Includes a comprehensive test suite demonstrating best practices
Provides a ready-to-use template for new projects

Cons of CleanArchitecture

Less emphasis on Domain-Driven Design (DDD) principles
Fewer examples of complex domain logic implementations
More opinionated structure, which may not fit all project types

Code Comparison

IDDD_Samples (Java):

public class BacklogItem extends ConcurrencySafeEntity {
    private BacklogItemId backlogItemId;
    private String summary;
    private String category;
    private BacklogItemStatus status;
    // ...
}

CleanArchitecture (C#):

public class ToDoItem : BaseEntity
{
    public string Title { get; set; } = string.Empty;
    public string Description { get; set; } = string.Empty;
    public bool IsDone { get; private set; }
    public void MarkComplete() => IsDone = true;
}

Both repositories offer valuable insights into software architecture, with IDDD_Samples focusing more on DDD concepts and CleanArchitecture providing a practical .NET implementation. The choice between them depends on the specific needs of the project and the developer's preferred language and framework.

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Pros of eShopOnContainers

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Includes multiple client applications (Web, Mobile)

Cons of eShopOnContainers

More complex setup and learning curve
Less focus on core DDD principles and patterns
Potentially overwhelming for beginners in DDD

Code Comparison

IDDD_Samples (Java):

@Entity
public class Product extends AbstractEntity {
    @Basic(optional = false)
    @Column(name = "name", nullable = false)
    private String name;

    @Basic(optional = false)
    @Column(name = "price", nullable = false)
    private BigDecimal price;
}

eShopOnContainers (C#):

public class CatalogItem
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public decimal Price { get; set; }
    public string PictureFileName { get; set; }
    public int CatalogTypeId { get; set; }
    public CatalogType CatalogType { get; set; }
    public int CatalogBrandId { get; set; }
    public CatalogBrand CatalogBrand { get; set; }
    public int AvailableStock { get; set; }
}

The IDDD_Samples code focuses on core DDD concepts with a simpler entity structure, while eShopOnContainers demonstrates a more feature-rich, microservices-oriented approach with additional properties and relationships.

library

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Pros of library

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Cons of library

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Smaller community and fewer stars on GitHub

Code Comparison

IDDD_Samples (Aggregate Root):

public class Product extends ConcurrencySafeEntity {
    private ProductId productId;
    private String name;
    private String description;
    private Money price;
    // ...
}

library (Aggregate Root):

@Aggregate
public class Book {
    @AggregateId
    private BookId bookId;
    private BookType type;
    private Title title;
    private Author author;
    // ...
}

Both examples demonstrate the use of Aggregate Roots, but library uses more modern Java annotations and a more focused domain model.

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README

These are the sample Bounded Contexts from the book "Implementing Domain-Driven Design" by Vaughn Vernon:

http://vaughnvernon.co/?page_id=168

The models and surrounding architectural mechanisms may be in various states of flux as the are refined over time. Some tests may be incomplete. The code is not meant to be a reflection of a production quality work, but rather as a set of reference projects for the book.

Points of Interest

The iddd_agilepm project uses a key-value store as its underlying persistence mechanism, and in particular is LevelDB. Actually the LevelDB in use is a pure Java implementation: https://github.com/dain/leveldb

Currently iddd_agilepm doesn't employ a container of any kind (such as Spring).

The iddd_collaboration project uses Event Sourcing and CQRS. It purposely avoids the use of an object-relational mapper, showing that a simple JDBC-based query engine and DTO matter can be used instead. This technique does have its limitations, but it is meant to be small and fast and require no configuration or annotations. It is not meant to be perfect.

It may be helpful to make one additional mental note on the iddd_collaboration CQRS implementation. To keep the example simple it persists the Event Sourced write model and the CQRS read model in one thread. Since two different stores are used--LevelDB for the Event Journal and MySQL for the read model--there may be very slight opportunities for inconsistency, but not much. The idea was to keep the two models as close to consistent as possible without using the same data storage (and transaction) for both. Two different storage mechanisms were used purposely to demonstrate that they can be separate.

The iddd_identityaccess project uses object-relational mapping (Hibernate), but so as not to leave it "boring" it provides a RESTful client interface and even publishes Domain-Event notifications via REST (logs) and RabbitMQ.

Finally the iddd_common project provides a number of reusable components. This is not an attempt to be a framework, but just leverages reuse to the degree that code copying doesn't liter each project. This is not a recommendation, but it did work well and save a considerable amount of work while producing the samples.

Usage

Requires

Java 7 (8+ does not work)
MySQL Client + Server
RabbitMQ

Setup (with Docker)

To make it easy to run the tests and it requirements, the startContainers.sh script is provided. Which will start a:

MySQL Server container
RabbitMQ Server container
RabbitMQ Management container

If the mysql command is available, which is the mysql client, also the required SQL scripts will be imported into the MySQL Server.

If you use the startContainers.sh script, you don't need MySQL Server and RabbitMQ installed locally. Instead, Docker needs to be installed as the script will start MySQL and RabbitMQ in Docker containers.

Build

You can build the project by running:

./gradlew build

This automatically downloads Gradle and builds the project, including running the tests.

The Gradle build using Maven repositories was provided by Michael Andrews (Github michaelajr and Twitter @MichaelAJr). Thanks much!

I hope you benefit from the samples.

Vaughn Vernon Author: Implementing Domain-Driven Design Twitter: @VaughnVernon http://vaughnvernon.co/

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