Скачать или смотреть Understanding Multiple Addresses: Entity vs ValueObject in Domain-Driven Design

Discover the best approach for managing multiple addresses in user registration forms through the lens of Domain-Driven Design, focusing on when to use `ValueObjects` versus `Entities`.
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Understanding Multiple Addresses: Entity vs ValueObject in Domain-Driven Design

When designing applications that involve storing user information, you may encounter a common dilemma regarding how to manage collections of related data. One such case is how to handle multiple addresses for a user in a registration form. Should these addresses be treated as an Entity or a ValueObject? This question is crucial for maintaining clarity and functionality in your domain model.

The Problem

In many applications, users can have more than one address, leading to the question: Is it better to model multiple addresses as ValueObjects or as Entities? While a single address might logically fit as a ValueObject because it doesn't require unique identification across the domain, the introduction of multiple addresses complicates this decision.

Key Considerations

Entity: An object that has a distinct identity that runs through time and different states. Entities could be changed over time.

ValueObject: An object that does not have a unique identifier and is defined only by its attributes. ValueObjects are usually immutable.

The Solution: Multiple Addresses as ValueObjects

After careful consideration, a collection of addresses can be effectively modeled as ValueObjects. Let’s explore why this approach works and how it can be executed.

Why Choose ValueObjects?

Immutability: ValueObjects are generally immutable, meaning that once an address is created, it doesn’t change. This is beneficial for maintaining data integrity.

No Unique Identity Needed: Addresses do not require global identification. Their value and amendments don't depend on a unique identifier, which aligns with the nature of a ValueObject.

Collaborative Nature: When used in collections, ValueObjects can enhance the concept of “behavior” in your system, often modeled alongside other domain-driven design principles.

Implementation Details

Even though ValueObjects do not require unique identifiers, your database design can still accommodate this structure:

Database Structure: When dealing with collections of addresses in your database:

Separate Table: You can create a separate table for addresses that stores them as individual rows linked to the User entity through a foreign key.

No Unique IDs for ValueObjects: In this structure, the addresses can still retain their uniqueness in the context of the User to which they belong without requiring unique IDs.

Example Schema

Here’s how the database structure might look:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Managing multiple addresses in your domain model by treating them as ValueObjects allows for cleaner design and a more natural user experience. Remember that how you implement these concepts in your database is an implementation detail and does not alter the core functionality of your domain model.

In summary, embrace the use of ValueObjects for collections when they naturally fit the criteria of having no unique identity and being defined by their attributes. This approach not only aligns with the principles of Domain-Driven Design but also prepares your application for a more straightforward implementation.