validation

Validation Example

This example demonstrates how to use go-playground/validator/v10 for input and output validation in gorkflow workflows.

Overview

The example shows a user registration workflow with three steps:

1. Validate User - Validates registration input and creates a user
2. Send Email - Sends a welcome email
3. Format Result - Formats the final workflow output

Each step uses struct validation tags to enforce data constraints.

Validation Tags Used

UserRegistrationInput

type UserRegistrationInput struct {
    Email    string `validate:"required,email"`
    Username string `validate:"required,min=3,max=20,alphanum"`
    Age      int    `validate:"required,gte=18,lte=120"`
    Password string `validate:"required,min=8"`
}

• Email: Required, must be valid email format
• Username: Required, 3-20 characters, alphanumeric only
• Age: Required, between 18 and 120
• Password: Required, minimum 8 characters

ValidatedUserOutput

type ValidatedUserOutput struct {
    UserID   string `validate:"required,uuid4"`
    Email    string `validate:"required,email"`
    Username string `validate:"required"`
    IsActive bool   `json:"isActive"`
}

• UserID: Required, must be valid UUID v4
• Email: Required, must be valid email
• Username: Required

EmailSentOutput

type EmailSentOutput struct {
    MessageID string `validate:"required"`
    Status    string `validate:"required,oneof=sent failed pending"`
    SentTo    string `validate:"required,email"`
}

• MessageID: Required
• Status: Required, must be one of: sent, failed, pending
• SentTo: Required, must be valid email

How to Enable Validation

Option 1: Use Default Validation Config (Recommended)

step := workflow.NewStep(
    "my_step",
    "My Step",
    handler,
    workflow.WithValidation(workflow.DefaultValidationConfig),
)

This enables both input and output validation with fail-on-error behavior.

Option 2: Custom Validation Config

step := workflow.NewStep(
    "my_step",
    "My Step",
    handler,
    workflow.WithValidation(workflow.ValidationConfig{
        ValidateInput:         true,
        ValidateOutput:        true,
        FailOnValidationError: true,
        CustomValidator:       nil, // Use default validator
    }),
)

Option 3: Input or Output Only

// Validate input only
step := workflow.NewStep(
    "my_step",
    "My Step",
    handler,
    workflow.WithInputValidation(),
)

// Validate output only
step := workflow.NewStep(
    "my_step",
    "My Step",
    handler,
    workflow.WithOutputValidation(),
)

Option 4: Custom Validator Instance

import "github.com/go-playground/validator/v10"

// Create custom validator with custom rules
customValidator := validator.New()
customValidator.RegisterValidation("custom_rule", myCustomValidationFunc)

step := workflow.NewStep(
    "my_step",
    "My Step",
    handler,
    workflow.WithCustomValidator(customValidator),
    workflow.WithValidation(workflow.DefaultValidationConfig),
)

Running the Example

cd example/validation
go run main.go

Expected Output

The example runs 4 test cases:

✅ Example 1: Valid Input

All validation passes, workflow completes successfully.

❌ Example 2: Invalid Email

Input validation fails with error:

validation failed:
  - field 'Email' failed on 'email' tag: got value 'not-an-email'

❌ Example 3: Username Too Short

Input validation fails with error:

validation failed:
  - field 'Username' failed on 'min' tag (param: 3): got value 'ab'

❌ Example 4: Age Below Minimum

Input validation fails with error:

validation failed:
  - field 'Age' failed on 'gte' tag (param: 18): got value '16'

Validation Error Handling

When validation fails:

1. Input Validation: Fails before the step handler executes
2. Output Validation: Fails after the step handler executes
3. Error Format: Provides detailed information about which field failed and why
4. Workflow Behavior:
   • If FailOnValidationError: true → Step fails, workflow stops
   • If FailOnValidationError: false → Error logged, execution continues

Common Validation Tags

Here are some commonly used validation tags from go-playground/validator:

String Validators

• required - Field must not be empty
• email - Must be valid email format
• url - Must be valid URL
• min=N - Minimum length
• max=N - Maximum length
• len=N - Exact length
• alphanum - Alphanumeric characters only
• alpha - Alphabetic characters only
• numeric - Numeric characters only
• oneof=val1 val2 - Must be one of the specified values

Numeric Validators

• eq=N - Equal to N
• ne=N - Not equal to N
• gt=N - Greater than N
• gte=N - Greater than or equal to N
• lt=N - Less than N
• lte=N - Less than or equal to N

Format Validators

• uuid - Valid UUID (any version)
• uuid4 - Valid UUID v4
• ip - Valid IP address
• ipv4 - Valid IPv4 address
• ipv6 - Valid IPv6 address
• datetime=layout - Valid datetime with specified layout

Cross-Field Validators

• eqfield=Field - Equal to another field
• nefield=Field - Not equal to another field
• gtfield=Field - Greater than another field
• ltfield=Field - Less than another field

Benefits of Using Validation

1. Early Error Detection: Catch invalid data before processing
2. Type Safety: Enforce data contracts between steps
3. Self-Documenting: Validation tags serve as documentation
4. Consistent Error Messages: Standardized error format
5. Reduced Boilerplate: No need to write manual validation code
6. Production Ready: Battle-tested validation library

See Also

• go-playground/validator Documentation
• Validation Tag Reference
• Custom Validation Functions