ADO.NET 中的 SQL Server 查询仅返回一个结果

Question

我正在用 ado.net 学习 asp.net mvc，我的存储库类中有这个方法

public IEnumerable<int?> GetAllUniqueYears()
{
    using (IDbConnection dbConnection = dbConnectionFactory.CreateConnection())
    {
        using (IDbCommand cmd = dbConnection.CreateCommand())
        {
            cmd.CommandText = "SELECT DISTINCT YEAR(DateAdded) As Year FROM GeoCounters";
            cmd.CommandTimeout = 1000;

            using (IDataReader reader = cmd.ExecuteReader())
            {
                if (!reader.Read())
                {
                    yield return null;
                }
                else
                {
                    yield return (int)reader["Year"];
                }
            }
        }
    }
}

当我加载我的视图时，它只有一个结果，但是当我在 SQL Server Management Studio 中运行查询时，有 4 个结果

控制器动作

public ActionResult Index()
{
        HomeIndexViewModel model = new HomeIndexViewModel()
        {
            GeoCounterDefinitions = geodefrepo.GetAll()
            .Select((x,y) => new SelectListItem
                {
                    Text = x.Id + " " + x.FriendlyDesc,
                    Value = (y + 1).ToString()
                }),
            Years = geocounterrepo.GetAllUniqueYears()
            .Select(x => new SelectListItem
            {
                Text = x.ToString(),
                Value = x.ToString()
            })
        };

        return View(model);
    }

Answer 1

你需要一个while循环。

using (IDataReader reader = cmd.ExecuteReader())
{
   while (reader.Read())
   {
      yield return (int)reader["Year"];
   }
}