Define Value Objects

Learn how to define value object types that represent domain concepts without identity.

Goal

Create value object definitions for complex types like Address, Money, or Email.

Prerequisites

JD.Domain.Modeling package installed
Understanding of value object pattern

Steps

1. Create the Value Object Class

Define a POCO with value semantics:

public class Address
{
    public string Street { get; set; } = string.Empty;
    public string City { get; set; } = string.Empty;
    public string State { get; set; } = string.Empty;
    public string ZipCode { get; set; } = string.Empty;
}

2. Define as Value Object

Use .ValueObject<T>() instead of .Entity<T>():

using JD.Domain.Modeling;

var domain = Domain.Create("MyDomain")
    .ValueObject<Address>(vo => vo
        .Property(a => a.Street)
        .Property(a => a.City)
        .Property(a => a.State)
        .Property(a => a.ZipCode))
    .Build();

3. Use in Entity

Reference value objects from entities:

public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; } = string.Empty;
    public Address ShippingAddress { get; set; } = new();
    public Address BillingAddress { get; set; } = new();
}

var domain = Domain.Create("ECommerce")
    .ValueObject<Address>(vo => vo
        .Property(a => a.Street)
        .Property(a => a.City)
        .Property(a => a.State)
        .Property(a => a.ZipCode))
    .Entity<Customer>(e => e
        .Property(c => c.Id)
        .Property(c => c.Name)
        .Property(c => c.ShippingAddress)
        .Property(c => c.BillingAddress))
    .Build();

Result

Value objects are treated differently than entities:

No primary key
Compared by value, not identity
Can be embedded in entities
EF Core configurations use owned types

Next Steps

Define Enums - Add enumeration types
Create Invariants - Add validation to value objects

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