XAF: Validation Module

Setup

// In Module (platform-agnostic):
public class MyModule : ModuleBase {
    public MyModule() {
        RequiredModuleTypes.Add(typeof(ValidationModule));
    }
}

// Or in Blazor Program.cs:
b.AddModule<ValidationModule>();

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Built-in Validation Rules

RuleRequiredField

[RuleRequiredField("Rule1", DefaultContexts.Save, "Name is required")]
public virtual string Name { get; set; }

// With custom message
[RuleRequiredField("ContactEmail_Required", DefaultContexts.Save,
    "Email address is required",
    SkipNullOrEmptyValues = false)]
public virtual string Email { get; set; }

RuleRegularExpression

[RuleRegularExpression("EmailRule", DefaultContexts.Save,
    @"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$",
    "Invalid email format")]
public virtual string Email { get; set; }

RuleRange

[RuleRange("DiscountRange", DefaultContexts.Save, 0.0, 1.0,
    "Discount must be between 0 and 1")]
public virtual double Discount { get; set; }

[RuleRange("AgePastRange", DefaultContexts.Save,
    minimumValue: "1900-01-01", maximumValue: "$today$",
    ParametersMode = ParametersMode.Expression,
    MessageTemplate = "Birth date must be in the past")]
public virtual DateTime BirthDate { get; set; }

RuleStringLength

[RuleStringLength("NameLength", DefaultContexts.Save, 100,
    MinimumLength = 2,
    MessageTemplate = "Name must be 2-100 characters")]
public virtual string Name { get; set; }

RuleUniqueValue

[RuleUniqueValue("UniqueEmail", DefaultContexts.Save,
    "This email is already in use")]
public virtual string Email { get; set; }

RuleCriteria

// Criteria-based rule (XAF criteria language)
[RuleCriteria("ActiveOrderRule", DefaultContexts.Save,
    "Status != 'Cancelled' OR CancellationReason != ''",
    "Provide a cancellation reason when cancelling an order")]
public virtual string CancellationReason { get; set; }

// Is null or empty check
[RuleCriteria("HasPhoneOrEmail", DefaultContexts.Save,
    "!IsNullOrEmpty([Phone]) OR !IsNullOrEmpty([Email])",
    "Phone or email is required")]
public virtual string Phone { get; set; }

RuleValueComparison

// Compare two dates
[RuleValueComparison("EndDateAfterStart", DefaultContexts.Save,
    ValueComparisonType.GreaterThanOrEqual,
    "@StartDate",
    ParametersMode = ParametersMode.Expression,
    MessageTemplate = "End date must be on or after start date")]
public virtual DateTime EndDate { get; set; }

// Compare to constant
[RuleValueComparison("MinAmount", DefaultContexts.Save,
    ValueComparisonType.GreaterThan, 0,
    "Amount must be greater than 0")]
public virtual decimal Amount { get; set; }

RuleIsReferenced

// Prevent deletion if referenced by other objects
[RuleIsReferenced("CannotDeleteCategory", DefaultContexts.Delete,
    typeof(Product), nameof(Product.Category),
    MessageTemplateMustNotBeReferenced = "Cannot delete category with products")]
public virtual IList<Product> Products { get; set; }

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Rule Contexts

Context	When	Description
DefaultContexts.Save	On ObjectSpace.CommitChanges	Standard "save" validation
DefaultContexts.Delete	On ObjectSpace.Delete	Validates before deletion
Custom context string	On demand	Trigger programmatically

Use custom contexts for multi-step workflows:

[RuleRequiredField("SubmitApproval", "Submit",
    "Approver is required to submit")]
public virtual Employee Approver { get; set; }

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[RuleSet] Attribute

Group rules to run together as a named context:

public class Order : BaseObject {
    [RuleRequiredField("CustomerRequired_Save", DefaultContexts.Save, "Customer required")]
    [RuleRequiredField("CustomerRequired_Submit", "Submit", "Customer required to submit")]
    public virtual Customer Customer { get; set; }

    [RuleRequiredField("ApproverRequired_Submit", "Submit", "Approver required to submit")]
    public virtual Employee Approver { get; set; }
}

---

Programmatic Validation

using DevExpress.Persistent.Validation;

// Validate using a specific context
ValidationResult result = Validator.RuleSet.ValidateObject(
    objectSpace, order, new ContextIdentifiers("Submit"));

if (!result.Valid) {
    var messages = result.Results
        .Where(r => r.State == ValidationResultType.Error)
        .Select(r => r.ErrorMessage);
    throw new UserFriendlyException(string.Join("; ", messages));
}

// Validate all objects in the context
ValidationResult allResult = Validator.RuleSet.ValidateAllTargets(
    objectSpace, new ContextIdentifiers(DefaultContexts.Save));

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Custom Validation Rule

using DevExpress.Persistent.Validation;
using DevExpress.ExpressApp.Validation;

[CodeRule]
public class FutureDateRule : RuleBase<DateTime> {
    public FutureDateRule() { }
    public FutureDateRule(IRuleBaseProperties properties) : base(properties) { }

    protected override ValidationResult IsValidInternal(DateTime value) {
        if (value > DateTime.Today)
            return CreateValidResult();
        return CreateInvalidResult($"Date must be in the future. Got: {value:d}");
    }
}

Apply the custom rule:

[FutureDateRule("DeliveryDateFuture", DefaultContexts.Save,
    MessageTemplate = "Delivery date must be in the future")]
public virtual DateTime DeliveryDate { get; set; }

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Validating on Action (Custom Context)

private void SubmitAction_Execute(object sender, SimpleActionExecuteEventArgs e) {
    var result = Validator.RuleSet.ValidateObject(
        ObjectSpace, ViewCurrentObject, new ContextIdentifiers("Submit"));

    if (!result.Valid) {
        var errors = result.Results
            .Where(r => r.State == ValidationResultType.Error)
            .Select(r => r.ErrorMessage);
        throw new UserFriendlyException("Validation failed: " + string.Join(", ", errors));
    }

    // Proceed with submit logic
    (ViewCurrentObject as Order).Submit();
    ObjectSpace.CommitChanges();
}

---

Conditional Validation (Criteria-Based)

Rules can be conditionally skipped using SkipNullOrEmptyValues or TargetCriteria:

// Only validate when Status = Active
[RuleRequiredField("ActiveContactEmail", DefaultContexts.Save,
    "Email required for active contacts",
    TargetCriteria = "Status = 'Active'")]
public virtual string Email { get; set; }

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Cross-Property Validation

// Compare EndDate to StartDate (on EndDate property)
[RuleCriteria("EndAfterStart", DefaultContexts.Save,
    "[EndDate] >= [StartDate]",
    "End date must be after start date")]
public virtual DateTime EndDate { get; set; }

// Or use RuleValueComparison with expression
[RuleValueComparison("EndDateRule", DefaultContexts.Save,
    ValueComparisonType.GreaterThanOrEqual, "@StartDate",
    ParametersMode = ParametersMode.Expression,
    MessageTemplate = "End date must be >= start date")]
public virtual DateTime EndDate { get; set; }

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Validation in Web API

Validation rules fire automatically on CommitChanges() in the Web API service. Invalid requests return HTTP 400 with validation error details in the response body.

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Source Links

• Validation Module: https://docs.devexpress.com/eXpressAppFramework/113684/validation
• Validation Rules Overview: https://docs.devexpress.com/eXpressAppFramework/113684/validation/validation-rules-overview
• Implement Validation in Code: https://docs.devexpress.com/eXpressAppFramework/113684/validation/implement-validation-rules-in-code
• RuleRequiredField: https://docs.devexpress.com/eXpressAppFramework/DevExpress.Persistent.Validation.RuleRequiredFieldAttribute
• RuleCriteria: https://docs.devexpress.com/eXpressAppFramework/DevExpress.Persistent.Validation.RuleCriteriaAttribute
• RuleUniqueValue: https://docs.devexpress.com/eXpressAppFramework/DevExpress.Persistent.Validation.RuleUniqueValueAttribute
• Validator API: https://docs.devexpress.com/eXpressAppFramework/DevExpress.Persistent.Validation.Validator