Fluent Rules

Overview

Implement IValidationConfigurator<T> for rules that go beyond single-property attributes. The generator reads your Configure() body at compile time — it is never invoked at runtime.

[ZValidate]
public partial class OrderRequest : IValidationConfigurator<OrderRequest>
{
    public decimal Subtotal { get; set; }
    public decimal Discount { get; set; }
    public decimal Total { get; set; }
    public List<string> Items { get; set; } = new();

    public void Configure(IValidationBuilder<OrderRequest> b)
    {
        b.Rule(x => x.Items.Count > 0, "Order must have at least one item");
        b.Rule(x => x.Discount >= 0 && x.Discount <= x.Subtotal,
            "Discount cannot exceed subtotal");
        b.Rule(x => x.Total == x.Subtotal - x.Discount,
            "Total must equal Subtotal minus Discount");
    }
}

Custom Expressions — b.Rule()

Any C# expression that compiles in the class context:

b.Rule(x => x.EndDate > x.StartDate, "End must be after start");
b.Rule(x => x.ShipBy == null || x.ShipBy > DateTime.UtcNow, "Ship date must be in the future");
b.Rule(x => x.Tags.All(t => t.Length <= 20), "Each tag must be at most 20 chars");

Per-Property Chains — b.Property()

Fluent equivalent of stacking attributes:

b.Property(x => x.Username)
    .Required()
    .MinLength(3)
    .MaxLength(20)
    .Match(@"^[a-zA-Z0-9_]+$", "Only letters, numbers, underscores");

b.Property(x => x.Email)
    .Required()
    .Email();

b.Property(x => x.Role)
    .In("admin", "user", "viewer");

b.Property(x => x.CardNumber)
    .CreditCard();

Available fluent methods: .Required(), .Email(), .Url(), .NotEmpty(), .MinLength(n), .MaxLength(n), .Range(min, max), .Match(pattern), .In(values), .NotIn(values), .CreditCard(), .Phone().

Cross-Field Comparisons

b.Property(x => x.ConfirmPassword).EqualTo(x => x.Password, "Passwords must match");
b.Property(x => x.EndDate).GreaterThan(x => x.StartDate);
b.Property(x => x.Max).GreaterThanOrEqual(x => x.Min);

Method	Description
.GreaterThan(x => x.Other)	>
.GreaterThanOrEqual(x => x.Other)	>=
.LessThan(x => x.Other)	<
.LessThanOrEqual(x => x.Other)	<=
.EqualTo(x => x.Other)	==
.NotEqualTo(x => x.Other)	!=

All accept an optional message as second argument.