Note This repository is developed for .netstandard2.0+
A fluent, runtime-first XML validation engine with XSD generation and documentation support.

🔎 Overview

XmlFluentValidator is a flexible XML validation library designed for scenarios where:

• Validation rules must be defined programmatically
• XML needs to be validated at runtime
• XSD schemas must be generated from code-based rules
• Some rules cannot be expressed in XSD but still need to be documented

The library combines a fluent builder API, runtime validation, and schema generation into a single, cohesive solution.

What you can do

• Define XML validation rules using a fluent, readable API
• Validate XML documents at runtime
• Generate XSD schemas directly from validation rules
• Document runtime-only rules (e.g., custom logic) using <xs:annotation>
• Mix schema validation and custom validation seamlessly

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✨ Key Features

Element Validation

• Required / optional elements
• Regex validation
• Numeric and length ranges
• Enumeration (enum-like constraints)
• MaxOccurs and cardinality rules
• Data type enforcement
• Nullable (xs:nillable) support
• Uniqueness constraints
• Fixed(constant) value

Attribute Validation

• Required attributes
• Regex, range, length, and enumeration rules
• Attribute uniqueness
• Attribute-level documentation
• Element–attribute cross-validation
• Fixed(constant) value

Advanced Capabilities

• Deeply nested paths (/customer/address/street)
• Attribute shorthand (items/item@sku)
• Cross-field validation
• Global document rules
• Custom, user-defined validation logic
• Rule severity levels
• Short-circuiting (StopOnFailure)
• Automatic XSD documentation generation

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📖 Fluent Validator API Reference

• .ForPath(xpath) → For path. Rule for specific path.
• .ForAttribute(xpath) → For attribute. Rule for specific attribute.
• .ForElement(elementPath) → For element. Rule for specific element.
• .UseSchema(schemaSet, [stopOnSchemaErrors]) → .Use schema (for validation).
• .GlobalRule(predicate, [message]) → Global rule.
• .Validate(doc) → Validates the given document.

📖 Fluent API Valdiation Rules Reference

Element Rules

• .WithElementMustExist([message]) → Must exist. The element must exist.
• .WithElementCount(predicate, [message]) → Counts.
• .WithElementValue(predicate, [message]) → Set validation rule for element value.
• .WithElementOptional([message]) → Specify the element validation as not required.
• .WithElementRequired([message]) → Set element validation rule as required.
• .WithElementValueRequired([message]) → Set element and value validation rule as required.
• .WithElementMatchesRegex(pattern, [message]) → Matches RegEx. Set element validation rule as regular expression.
• .WithElementInRange(min, max, [isInclusive], [message]) → In range. Set element validation rule as in range between minimum and maximum value.
• .WithElementUnique([message]) → Set element validation rule as unique value.
• .WithElementMaxOccurs(max, [message]) → Set element validation rule as maximum occurs.
• .WithElementValueLength(min, [max], [message]) → With element value length.
• .WithElementDataType(dataType, [message]) → With element data type.
• .WithElementEnumerator(rangeEnumerator, [message]) → With element enumerator (like enum values).
• .WithElementExactLength(length, [message]) → With element exact length.
• .WithElementDocumentation(documentation) → With element documentation. Set annotation/documentaion.
• .WithElementNullable([isNullable], [message]) → With element nullable.
• .WithElementFixedValue(fixedValue, [message]) → With element fixed(xonstant) value.

Attribute Rules

• .WithAttribute(name, predicate, [message]) → Set validation rule for element attribute.
• .WithAttributeRequired(name, [message]) → IsRequired attribute. Set attribute validation rule as required.
• .WithAttributeValueRequired(name, [message]) → IsRequired attribute. Set attribute and value validation rule as required.
• .WithAttributeMatchesRegex(name, pattern, [message]) → Attribute matches RegEx. Set attribute validation rule as regular expression.
• .WithAttributeInRange(name, min, max, [isInclusive], [message]) → Attribute in range. Set attribute validation rule as in range between minimum and maximum value.
• .WithAttributeUnique(name, [message]) → Attribute unique. Set specific attribute as unique.
• .ElementAttributeCrossRule(name, predicate, [message]) → Element attribute cross rule. Set cross validation for element and specific element attribute.
• .WithAttributeValueLength(name, min, [max], [message]) → With attribute value length.
• .WithAttributeDataType(name, dataType, [message]) → With attribute data type.
• .WithAttributeEnumerator(name, rangeEnumerator, [message]) → With attribute enumerator.
• .WithAttributeExactLength(name, length, [message]) → With attribute exact length.
• .WithAttributeDocumentation(name, documentation) → With attribute documentation.
• .WithAttributeExactLength(name, fixedValue, [message]) → With attribute fixed(xonstant) value.

Messages

• .WithMessage(template, arguments) → With message. Set custom validation message.
• .WithMessage(message) → With message. Set custom validation message.
• .WithMessageForAll(message) → With message for all.

Other rules

• .All(predicate, [message]) → All.
• .Any(predicate, [message]) → Any.
• .When(condition, [message]) → When the given condition.
• .CustomElementRule(predicate, [message]) → Custom element rule. an be used custom defined(registered) rule or defined in specific context.
• .Custom(handler, [message]) → Customs. Set the custom (user defined) validation method.
• .UseCustomRule(ruleName, [message]) → Use custom rule. Set the custom rule name for execution.
• .WithName(displayName) → With name. Set the specific name for path.
• .WithSeverity(severity) → With severity. Set the validation message severity.
• .StopOnFailure() → Stops on failure. Short-circuit within this rule chain.
• .Done() → Gets the done action. Ends the current element rule chain and returns to validator.

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Custom Rules

.Custom(ctx =>
{
    var val = ctx.Document.XPathSelectElement("/order/id")?.Value;
    if (val == "0000")
        ctx.Failures.Add(new XmlValidationFailure
        {
            Severity = Severity.Error,
            Path = "/order/id",
            Message = "ID cannot be 0000"
        });
}, "ID must not be 0000")

Global Rules

.GlobalRule(doc =>
{
    return doc.XPathSelectElements("/order/items/item").Count() <= 10;
}, "Order must not contain more than 10 items")

To get acquainted with a more detailed description, please check the content table at the first point.

No additional components or packs are required for use. So, it only needs to be added/installed in the project and can be used instantly.

In case you wish to use it in your project, u can install the package from nuget.org or specify what version you want:

Install-Package XmlFluentValidator -Version x.x.x.x

Content

1. USING
2. CHANGELOG
3. BRANCH-GUIDE