Quick Start - Generate GUID
The simplest way to generate a GUID in C# using Guid.NewGuid():
C#
// Generate random GUID (equivalent to UUID v4)
Guid guid = Guid.NewGuid();
Console.WriteLine(guid);
// Output: 550e8400-e29b-41d4-a716-446655440000
// Use in variable
var userId = Guid.NewGuid();
var orderId = Guid.NewGuid();
Console.WriteLine($"User ID: {userId}");
Console.WriteLine($"Order ID: {orderId}");GUID vs UUID: In .NET, they're the same thing. GUID is Microsoft's terminology, but System.Guid follows the UUID standard (RFC 4122).
GUID String Formats
Convert GUIDs to different string formats:
C#
Guid id = Guid.NewGuid();
// Convert to string formats
string standard = id.ToString();
// 550e8400-e29b-41d4-a716-446655440000
string formatD = id.ToString("D");
// 550e8400-e29b-41d4-a716-446655440000 (default)
string formatN = id.ToString("N");
// 550e8400e29b41d4a716446655440000 (no hyphens)
string formatB = id.ToString("B");
// {550e8400-e29b-41d4-a716-446655440000} (braces)
string formatP = id.ToString("P");
// (550e8400-e29b-41d4-a716-446655440000) (parentheses)
string formatX = id.ToString("X");
// {0x550e8400,0xe29b,0x41d4,{0xa7,0x16,0x44,0x66,0x55,0x44,0x00,0x00}}
// Uppercase
string upper = id.ToString().ToUpper();
// Generate multiple GUIDs
var guids = Enumerable.Range(0, 10)
.Select(_ => Guid.NewGuid())
.ToList();Parse GUID from String
Parse and validate GUID strings:
C#
// Parse (throws exception if invalid)
Guid guid = Guid.Parse("550e8400-e29b-41d4-a716-446655440000");
Console.WriteLine($"Parsed: {guid}");
// TryParse (returns bool, no exception)
string input = "550e8400-e29b-41d4-a716-446655440000";
if (Guid.TryParse(input, out Guid result))
{
Console.WriteLine($"Valid GUID: {result}");
}
else
{
Console.WriteLine("Invalid GUID format");
}
// ParseExact with format specifier
Guid exact = Guid.ParseExact("{550e8400-e29b-41d4-a716-446655440000}", "B");
// TryParseExact
if (Guid.TryParseExact(input, "D", out Guid exactResult))
{
Console.WriteLine($"Exact parse: {exactResult}");
}
// From byte array
byte[] bytes = new byte[16];
Guid fromBytes = new Guid(bytes);Empty GUID & Comparison
C#
// Empty GUID (all zeros) - equivalent to Nil UUID
Guid empty = Guid.Empty;
Console.WriteLine(empty);
// 00000000-0000-0000-0000-000000000000
// Check if empty
Guid myGuid = Guid.NewGuid();
if (myGuid == Guid.Empty)
{
Console.WriteLine("GUID is empty");
}
// Compare GUIDs
Guid g1 = Guid.NewGuid();
Guid g2 = Guid.NewGuid();
Console.WriteLine(g1 == g2); // false (usually)
Console.WriteLine(g1.Equals(g2)); // false
Console.WriteLine(g1.CompareTo(g2)); // -1, 0, or 1
// Default value for Guid is Empty
Guid defaultGuid = default; // Same as Guid.Empty
Guid defaultGuid2 = default(Guid);GUID v7 in .NET 9+
.NET 9 introduces support for UUID v7 (time-sortable GUIDs):
C# (.NET 9+)
// Generate UUID v7 (time-ordered)
Guid guidV7 = Guid.CreateVersion7();
// With specific timestamp
DateTimeOffset timestamp = DateTimeOffset.UtcNow;
Guid guidV7WithTime = Guid.CreateVersion7(timestamp);
// Get version
int version = guidV7.Version; // 7 for v7, 4 for v4
// Sort by creation time
var sortedGuids = new List
{
Guid.CreateVersion7(),
Guid.CreateVersion7(),
Guid.CreateVersion7()
}.OrderBy(g => g).ToList(); For .NET 8 and earlier: Use the UUIDNext NuGet package for v7 support: Install-Package UUIDNext
Entity Framework Core Integration
Use GUIDs as primary keys in Entity Framework Core:
C# - Entity Framework Core
using System;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Microsoft.EntityFrameworkCore;
public class User
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid Id { get; set; }
[Required]
[MaxLength(100)]
public string Name { get; set; }
[Required]
[MaxLength(255)]
public string Email { get; set; }
public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
}
public class AppDbContext : DbContext
{
public DbSet Users { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
// SQL Server: use NEWSEQUENTIALID() for better performance
modelBuilder.Entity()
.Property(u => u.Id)
.HasDefaultValueSql("NEWSEQUENTIALID()");
// PostgreSQL: use gen_random_uuid()
// .HasDefaultValueSql("gen_random_uuid()");
}
}
// Alternative: Generate GUID in code
public class Product
{
public Guid Id { get; set; } = Guid.NewGuid();
public string Name { get; set; }
}
// Usage
using (var context = new AppDbContext())
{
var user = new User
{
Name = "Bob Wilson",
Email = "bob@example.com"
};
context.Users.Add(user);
await context.SaveChangesAsync();
Console.WriteLine($"Created user with ID: {user.Id}");
} ASP.NET Core Web API
Use GUIDs in Web API controllers and routing:
C# - ASP.NET Core
using Microsoft.AspNetCore.Mvc;
[ApiController]
[Route("api/[controller]")]
public class UsersController : ControllerBase
{
private readonly AppDbContext _context;
public UsersController(AppDbContext context)
{
_context = context;
}
[HttpGet("{id:guid}")]
public async Task GetUser(Guid id)
{
// id is automatically parsed from route
var user = await _context.Users.FindAsync(id);
if (user == null)
return NotFound();
return Ok(user);
}
[HttpPost]
public async Task CreateUser([FromBody] CreateUserDto dto)
{
var user = new User
{
Id = Guid.NewGuid(),
Name = dto.Name,
Email = dto.Email
};
_context.Users.Add(user);
await _context.SaveChangesAsync();
return CreatedAtAction(
nameof(GetUser),
new { id = user.Id },
user
);
}
[HttpPut("{id:guid}")]
public async Task UpdateUser(
Guid id,
[FromBody] UpdateUserDto dto)
{
var user = await _context.Users.FindAsync(id);
if (user == null)
return NotFound();
user.Name = dto.Name;
user.Email = dto.Email;
await _context.SaveChangesAsync();
return NoContent();
}
[HttpDelete("{id:guid}")]
public async Task DeleteUser(Guid id)
{
var user = await _context.Users.FindAsync(id);
if (user == null)
return NotFound();
_context.Users.Remove(user);
await _context.SaveChangesAsync();
return NoContent();
}
} Convert To/From Bytes
C#
Guid guid = Guid.NewGuid();
// To byte array (16 bytes)
byte[] bytes = guid.ToByteArray();
Console.WriteLine($"Byte array length: {bytes.Length}"); // 16
// From byte array
Guid fromBytes = new Guid(bytes);
// To Base64 (shorter string representation)
string base64 = Convert.ToBase64String(guid.ToByteArray());
Console.WriteLine($"Base64: {base64}");
// Example: "AISEDuKbQdSnFkRmVUQAAA=="
// From Base64
byte[] base64Bytes = Convert.FromBase64String(base64);
Guid fromBase64 = new Guid(base64Bytes);
// Span support (.NET Core 2.1+)
Span span = stackalloc byte[16];
guid.TryWriteBytes(span);
Guid fromSpan = new Guid(span); ADO.NET Database Operations
C# - ADO.NET
using System.Data.SqlClient;
public class UserRepository
{
private string _connectionString;
public async Task CreateUser(string name, string email)
{
using var conn = new SqlConnection(_connectionString);
await conn.OpenAsync();
var cmd = new SqlCommand(
"INSERT INTO users (id, name, email) OUTPUT INSERTED.id VALUES (@id, @name, @email)",
conn
);
var userId = Guid.NewGuid();
cmd.Parameters.AddWithValue("@id", userId);
cmd.Parameters.AddWithValue("@name", name);
cmd.Parameters.AddWithValue("@email", email);
var returnedId = (Guid)await cmd.ExecuteScalarAsync();
return returnedId;
}
public async Task GetUserById(Guid id)
{
using var conn = new SqlConnection(_connectionString);
await conn.OpenAsync();
var cmd = new SqlCommand(
"SELECT id, name, email FROM users WHERE id = @id",
conn
);
cmd.Parameters.Add("@id", System.Data.SqlDbType.UniqueIdentifier).Value = id;
using var reader = await cmd.ExecuteReaderAsync();
if (await reader.ReadAsync())
{
return new User
{
Id = reader.GetGuid(0),
Name = reader.GetString(1),
Email = reader.GetString(2)
};
}
return null;
}
}