Create Invariants

Define always-true rules that validate entity state.

Goal

Create invariant rules that must always be true for an entity to be in a valid state.

Prerequisites

JD.Domain.Rules package installed
Entity definitions created

Steps

1. Create Rule Set Builder

using JD.Domain.Rules;

var rules = new RuleSetBuilder<Customer>("Default")

2. Add Invariant Rules

var rules = new RuleSetBuilder<Customer>("Default")
    .Invariant("Name.Required", c => !string.IsNullOrWhiteSpace(c.Name))
    .WithMessage("Customer name is required")
    
    .Invariant("Email.Format", c => c.Email.Contains("@"))
    .WithMessage("Email must be valid")
    
    .Build();

3. Evaluate Rules

using JD.Domain.Runtime;

var engine = DomainRuntime.CreateEngine(manifest);
var result = engine.Evaluate(customer, rules);

if (!result.IsValid)
{
    foreach (var error in result.Errors)
    {
        Console.WriteLine(error.Message);
    }
}

Result

Invariant rules enforce entity validity at runtime and during construction of generated domain types.

Next Steps

Create Validators - Context-dependent rules
Compose Rules - Combine rule sets

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