Create Validators

Define context-dependent validation rules.

Goal

Create validator rules that depend on external context or perform async operations.

Prerequisites

JD.Domain.Rules package installed
Understanding of invariants

Steps

1. Create Synchronous Validator

var rules = new RuleSetBuilder<Customer>("Default")
    .Validator("Email.Unique", c => CheckEmailUnique(c.Email))
    .WithMessage("Email already exists")
    .Build();

bool CheckEmailUnique(string email)
{
    // Check database, external service, etc.
    return !existingEmails.Contains(email);
}

2. Create Async Validator

var rules = new RuleSetBuilder<Customer>("Default")
    .Validator("Email.Unique", async (c, ctx) => 
        await _repository.IsEmailUniqueAsync(c.Email))
    .WithMessage("Email already exists")
    .Build();

3. Use Context Parameter

.Validator("CanModify", (c, ctx) => 
    c.OwnerId == ctx.User.Id)
.WithMessage("You can only modify your own customer record")

Result

Validators enable complex validation that depends on external state or requires I/O operations.

Next Steps

Create Policies - Authorization rules
Compose Rules - Combine validators

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