How to Generate UUID in C#

C# uses the term GUID (Globally Unique Identifier) instead of UUID. The System.Guid struct provides built-in support for generating RFC 4122 compliant unique identifiers.

1. Generate New GUID

Guid.NewGuid() generates a random GUID (equivalent to UUID v4), which is the most commonly used method.

using System;

class Program
{
    static void Main()
    {
        // Generate a random GUID
        Guid guid = Guid.NewGuid();
        Console.WriteLine(guid);
        // Output: 550e8400-e29b-41d4-a716-446655440000

        // Get as string
        string guidString = guid.ToString();
        Console.WriteLine(guidString);
    }
}

2. GUID Formatting Options

using System;

Guid guid = Guid.NewGuid();

// Default format with dashes (D)
Console.WriteLine(guid.ToString("D"));
// Output: 550e8400-e29b-41d4-a716-446655440000

// Without dashes (N)
Console.WriteLine(guid.ToString("N"));
// Output: 550e8400e29b41d4a716446655440000

// With braces (B)
Console.WriteLine(guid.ToString("B"));
// Output: {550e8400-e29b-41d4-a716-446655440000}

// With parentheses (P)
Console.WriteLine(guid.ToString("P"));
// Output: (550e8400-e29b-41d4-a716-446655440000)

// Hexadecimal (X)
Console.WriteLine(guid.ToString("X"));
// Output: {0x550e8400,0xe29b,0x41d4,{0xa7,0x16,0x44,0x66,0x55,0x44,0x00,0x00}}

// Uppercase
Console.WriteLine(guid.ToString("D").ToUpper());
// Output: 550E8400-E29B-41D4-A716-446655440000

3. Parse GUID from String

using System;

// Parse a GUID string
string guidString = "550e8400-e29b-41d4-a716-446655440000";
Guid guid = Guid.Parse(guidString);
Console.WriteLine(guid);

// TryParse for safe parsing
if (Guid.TryParse("550e8400-e29b-41d4-a716-446655440000", out Guid result))
{
    Console.WriteLine($"Valid GUID: {result}");
}
else
{
    Console.WriteLine("Invalid GUID format");
}

// Parse without dashes
Guid noDashes = Guid.Parse("550e8400e29b41d4a716446655440000");

4. GUID Validation

using System;

public static class GuidValidator
{
    public static bool IsValid(string value)
    {
        return Guid.TryParse(value, out _);
    }
}

// Usage
Console.WriteLine(GuidValidator.IsValid("550e8400-e29b-41d4-a716-446655440000")); // True
Console.WriteLine(GuidValidator.IsValid("not-a-guid")); // False
Console.WriteLine(GuidValidator.IsValid(null)); // False

5. GUID in Entity Framework Core

using System;
using System.ComponentModel.DataAnnotations;
using Microsoft.EntityFrameworkCore;

public class User
{
    [Key]
    public Guid Id { get; set; }
    public string Username { get; set; }
    public DateTime CreatedAt { get; set; }
}

public class AppDbContext : DbContext
{
    public DbSet Users { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity()
            .Property(u => u.Id)
            .HasDefaultValueSql("NEWID()"); // SQL Server
            // .HasDefaultValueSql("gen_random_uuid()"); // PostgreSQL
    }
}

// Usage
var user = new User
{
    Id = Guid.NewGuid(),
    Username = "johndoe",
    CreatedAt = DateTime.UtcNow
};
context.Users.Add(user);
await context.SaveChangesAsync();

6. GUID in ASP.NET Core Web API

using Microsoft.AspNetCore.Mvc;

[ApiController]
[Route("api/[controller]")]
public class UsersController : ControllerBase
{
    [HttpGet("{id:guid}")]
    public IActionResult GetUser(Guid id)
    {
        // GUID automatically parsed from route
        var user = _userService.GetById(id);
        if (user == null)
            return NotFound();

        return Ok(user);
    }

    [HttpPost]
    public IActionResult CreateUser([FromBody] CreateUserRequest request)
    {
        var user = new User
        {
            Id = Guid.NewGuid(),
            Username = request.Username
        };

        _userService.Create(user);
        return CreatedAtAction(nameof(GetUser), new { id = user.Id }, user);
    }
}

7. Empty and Nil GUID

using System;

// Empty GUID (all zeros)
Guid empty = Guid.Empty;
Console.WriteLine(empty);
// Output: 00000000-0000-0000-0000-000000000000

// Check if GUID is empty
Guid guid = Guid.NewGuid();
if (guid == Guid.Empty)
{
    Console.WriteLine("GUID is empty");
}

// Create from specific bytes
byte[] bytes = new byte[16];
Guid fromBytes = new Guid(bytes);
Console.WriteLine(fromBytes); // 00000000-0000-0000-0000-000000000000

8. Generate Multiple GUIDs

using System;
using System.Collections.Generic;
using System.Linq;

// Generate 10 GUIDs
List guids = Enumerable.Range(0, 10)
    .Select(_ => Guid.NewGuid())
    .ToList();

foreach (var guid in guids)
{
    Console.WriteLine(guid);
}

// Or using a simple loop
var guidList = new List();
for (int i = 0; i < 10; i++)
{
    guidList.Add(Guid.NewGuid());
}

9. GUID to Bytes and Back

using System;

Guid guid = Guid.NewGuid();

// Convert to byte array
byte[] bytes = guid.ToByteArray();
Console.WriteLine($"Bytes: {BitConverter.ToString(bytes)}");

// Convert back from bytes
Guid fromBytes = new Guid(bytes);
Console.WriteLine($"From bytes: {fromBytes}");

// Base64 encoding
string base64 = Convert.ToBase64String(bytes);
Console.WriteLine($"Base64: {base64}");

// Decode from Base64
byte[] decoded = Convert.FromBase64String(base64);
Guid fromBase64 = new Guid(decoded);
Console.WriteLine($"From Base64: {fromBase64}");

GUID Methods Reference

Method	Description
`Guid.NewGuid()`	Generate new random GUID
`Guid.Parse()`	Parse GUID from string
`Guid.TryParse()`	Safe parse with bool result
`Guid.Empty`	Nil GUID (all zeros)
`guid.ToByteArray()`	Convert to byte array

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