Dapper - Object reference not set to an instance of an object - sql

Question

I've recently been playing around with dapper, but I've run into a bit of a problem regarding getting data from other tables.
My database has two tables, Users and Post. I've created two classes for these tables.
My User class
public class User
{
public int UserId { get; set; }
public string Username { get; set; }
public string Email { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public DateTime JoinDate { get; set; }
}
My Post class
public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public DateTime PublishDate { get; set; }
public int UserId { get; set; }
public User User { get; set; }
}
This is my query to fetch all the post data from my database, and also get the Username who created the post.
public IEnumerable<Post> GetPosts()
{
string myQuery = "SELECT p.Title, p.PublishDate, p.PostId, p.UserId, u.Username FROM Post p INNER JOIN Users u ON p.UserId = u.UserId";
sqlConnection.Open();
var posts = sqlConnection.Query<Post>(myQuery);
return posts;
}
Here is my view code where I want to display the information:
#model IEnumerable<MvcDapperIntro.Models.Post>
#{
ViewBag.Title = "Posts";
}
#foreach (var post in Model)
{
<h3>#post.Title</h3>
<p>#post.PublishDate.ToString("dd/MM/yyyy")</p>
<p>#post.User.Username</p>
}
However, when I run my code, I get the 'Object reference not set to an instance of an object' error. Is this because I shouldn't be using:
public User User { get; set; }
to access the username property, or should I create a new class with a username field. Any input would be appreciated.

Answer 1

I get the 'Object reference not set to an instance of an object' error
I bet the issue is on this line: <p>#post.User.Username</p> and that is because you did not map the User object. You should change this code:
var posts = sqlConnection.Query<Post>(myQuery);
to this:
var posts = sqlConnection.Query<Post, User, Post>(
myQuery,
(p, u) => { p.User = u; return p; }
);