validation

Validation

Overview

The Validation component provides utilities for validating data in a structured and reusable way. It offers a collection of validation functions for common validation tasks, such as checking required fields, validating string lengths, matching patterns, validating dates, and more. It also provides a ValidationResult type for collecting and managing validation errors.

Features

• String Validation: Validate required fields, minimum/maximum length, and pattern matching
• Date Validation: Validate past dates and date ranges
• Collection Validation: Validate all items in a collection or check if all items satisfy a condition
• Structured Results: Collect validation errors with field-specific error messages
• Error Integration: Seamless integration with the errors package for consistent error handling
• Composable Design: Build complex validation logic by combining simple validation rules
• Generic Support: Type-safe validation with Go generics

Installation

go get github.com/abitofhelp/servicelib/validation

Quick Start

package main

import (
    "fmt"
    
    "github.com/abitofhelp/servicelib/validation"
)

type User struct {
    Name     string
    Email    string
    Password string
}

func main() {
    user := User{
        Name:     "John Doe",
        Email:    "invalid-email",
        Password: "123",
    }
    
    // Create a validation result
    result := validation.NewValidationResult()
    
    // Validate the user
    validation.Required(user.Name, "name", result)
    validation.Pattern(user.Email, `^[^@]+@[^@]+\.[^@]+$`, "email", result)
    validation.MinLength(user.Password, 8, "password", result)
    
    // Check if validation passed
    if !result.IsValid() {
        fmt.Printf("Validation failed: %v\n", result.Error())
        return
    }
    
    fmt.Println("Validation passed!")
}

API Documentation

Core Types

The validation package provides a ValidationResult type for collecting and managing validation errors.

ValidationResult

ValidationResult holds the result of a validation operation and provides methods for adding errors and checking validity.

type ValidationResult struct {
    // Contains unexported fields
}

// NewValidationResult creates a new ValidationResult
func NewValidationResult() *ValidationResult

// AddError adds an error to the validation result
func (v *ValidationResult) AddError(msg, field string)

// IsValid returns true if there are no validation errors
func (v *ValidationResult) IsValid() bool

// Error returns the validation errors as an error
func (v *ValidationResult) Error() error

Validation Functions

The validation package provides several validation functions for common validation tasks.

String Validation

// Required validates that a string is not empty
func Required(value, field string, result *ValidationResult)

// MinLength validates that a string has a minimum length
func MinLength(value string, min int, field string, result *ValidationResult)

// MaxLength validates that a string has a maximum length
func MaxLength(value string, max int, field string, result *ValidationResult)

// Pattern validates that a string matches a regular expression
func Pattern(value, pattern, field string, result *ValidationResult)

// ValidateID validates that an ID is not empty
func ValidateID(id, field string, result *ValidationResult)

Date Validation

// PastDate validates that a date is in the past
func PastDate(value time.Time, field string, result *ValidationResult)

// ValidDateRange validates that a start date is before an end date
func ValidDateRange(start, end time.Time, startField, endField string, result *ValidationResult)

Collection Validation

// AllTrue validates that all items in a slice satisfy a predicate
func AllTrue[T any](items []T, predicate func(T) bool) bool

// ValidateAll validates all items in a slice
func ValidateAll[T any](items []T, validator func(T, int, *ValidationResult), result *ValidationResult)

Examples

For complete, runnable examples, see the following files in the EXAMPLES directory:

• Basic Usage - Shows basic usage of the validation package
• Custom Validation - Shows how to create custom validation rules
• Collection Validation - Shows how to validate collections
• Integration with Forms - Shows how to validate form data

Best Practices

1. Create a Single ValidationResult: Create a single ValidationResult for each validation operation to collect all errors
2. Use Descriptive Field Names: Use descriptive field names that match your API or UI field names
3. Compose Validation Rules: Build complex validation logic by combining simple validation rules
4. Validate Early: Validate input data as early as possible in your application flow
5. Return All Errors: Return all validation errors at once rather than one at a time for better user experience

Troubleshooting

Common Issues

Validation Errors Not Being Collected

If validation errors are not being collected properly:

• Ensure you're passing the same ValidationResult instance to all validation functions
• Check that you're calling AddError with the correct field name
• Verify that you're checking IsValid() before proceeding with your logic

Regular Expression Patterns Not Matching

If your pattern validation is not working as expected:

• Test your regular expression pattern separately to ensure it's correct
• Remember that Go uses RE2 syntax, which doesn't support some advanced features
• Consider using a more specific validation function for common patterns (email, URL, etc.)

Related Components

• Errors - The validation package integrates with the errors package for error handling
• Model - The validation package can be used to validate model objects

Contributing

Contributions to this component are welcome! Please see the Contributing Guide for more information.

License

This project is licensed under the MIT License - see the LICENSE file for details.