This code doesn't work, returns null:

User user;
string query = "select user_id from users where email = @email";
using (IDbConnection conn = _connectionFactory.GetConnection())
{
conn.Open();
User queryuser = new User {email = email};
var result = conn.Query(query, queryuser).SingleOrDefault();
user = result;
}

This code returns the user data:

User user;
string query = $"select user_id from users where email = '{email}';";
using (IDbConnection conn = _connectionFactory.GetConnection())
{
conn.Open();
var result = conn.Query(query).SingleOrDefault();
user = result;
}