Question

If I had a User model that looks like this:

public class User
{
    public Guid Id { get; set; }
    public DateTime CreatedAtUtc { get; set; }
    public string Username { get; set; }
    public string Country { get; set; }
}

...and I'd perform a query which starts at a given row and fetches a limited amount of further rows (basically for paginating over the results) that looks like this:

var spaniards = connection.Query<User>(
                    "select * from Users where Country=@Country OFFSET 0 ROWS FETCH NEXT 10 ROWS ONLY",
                    new { Country = "Spain" }).ToList();

.. using Dapper(.Net), would it be possible to get that particular, limited result set AND the total count of rows in one single query and if so.. how?

Answer 1

解决此问题的一种方法是使用splitOn功能，以及count（1）over（）

我们假设以下sql字符串：

var sql = "select *, overall_count = COUNT(1) OVER() from Users ORDER BY Id Asc OFFSET 5 ROWS;"

以及以下dapper.net电话：

HashSet<int> hashSet = new HashSet<int>();
Func<User, int, User> map = (result, count) =>
{
   hashSet.Add(count);
   return result;
};
await connection.QueryAsync(sql, map, "overall_count").ConfigureAwait(false);

这会将dapper调用的结果分成两部分（就像加入不同的表一样）并且每次都会调用map functor，在这种情况下我们只是将计数存储在一个hashset中（然后你可以检查一下hashSet.Count是1）

希望这有帮助

PS：我不确定您的OFFSET是否在没有任何ORDER BY的情况下工作

Get Paginated SQL Server Result AND total count in one query via Dapper?

1 个答案: