Conditional Validation

Conditional validation allows rules to run only when a runtime condition is true.

This is useful when validation depends on another field, request state, account type, feature flag, workflow step, or business rule.

Why Conditional Validation Exists

Many real-world forms and API payloads are not static.

Some fields are required only when:

• another field is filled
• a user selects a specific option
• an account type changes
• a feature is enabled
• a workflow enters a specific state
• an optional section becomes active

Conditional validation makes these cases explicit and reusable.

Validation Philosophy

Conditional validation separates:

• the condition that decides whether validation should run
• the validation rules that should run when the condition is true

This keeps schemas readable and avoids hiding business logic inside struct tags.

Available Pages

Basic Idea

A conditional rule checks a predicate first.

conditional.When(
	func(in *Request) bool {
		return in.AccountType == "business"
	},
	rules.Required(Form.CompanyName),
)

If the condition returns true, the nested rules are executed.

If the condition returns false, validation is skipped.

Validation Flow

condition is false
    ↓
validation skipped

condition is true
    ↓
nested rules executed

Common Use Cases

Conditional validation is commonly used for:

• business account forms
• company billing information
• password change flows
• dependent address fields
• profile completion steps
• onboarding workflows
• feature-specific settings
• role-based validation
• multi-step forms
• PATCH APIs

When to Use Conditional Validation

Use conditional validation when a field should be validated only in a specific context.

Examples:

conditional.RequiredIfStr(
	Form.CompanyName,
	func(in *Request) bool {
		return in.AccountType == "business"
	},
)

conditional.When(
	func(in *Request) bool {
		return in.ChangePassword
	},
	rules.Required(Form.NewPassword),
	rules.MinLen(Form.NewPassword, 8),
)

Conditional Rules vs When

Use convenience conditional rules when the validation pattern is common.

Use When when the condition or nested validation logic is custom.

Notes

• Conditional validation is evaluated at runtime.
• Conditions receive the full request structure.
• Nested rules run only when the condition returns true.
• Conditional validation keeps business validation explicit.
• Conditional validation works with regular rules, optional rules, and custom rules.
• Prefer When for complex logic and helper rules for simple common cases.