Create Derivations

Define computed properties and derived values.

Goal

Create derivation rules that compute values from other properties.

Prerequisites

JD.Domain.Rules package installed

Steps

1. Simple Derivation

var rules = new RuleSetBuilder<Customer>("Default")
    .Derivation("FullName", c => $"{c.FirstName} {c.LastName}")
    .Build();

2. Complex Derivation

.Derivation("TotalOrderValue", c => 
    c.Orders.Sum(o => o.TotalAmount))

.Derivation("MembershipLevel", c =>
{
    var total = c.Orders.Sum(o => o.TotalAmount);
    if (total > 10000) return "Gold";
    if (total > 5000) return "Silver";
    return "Bronze";
})

3. Use Derived Values

Generated domain types expose derived values as properties:

var customer = DomainCustomer.Create(...);
Console.WriteLine(customer.FullName);
Console.WriteLine(customer.MembershipLevel);

Result

Derivations encapsulate computed logic within the domain model, making it reusable and testable.

Next Steps

Compose Rules - Combine with other rules

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