c# - LINQ 查询中的增量

Question

您好，我有以下代码，它返回 Listitem 类型的列表。我想为每个选定的 ListItem 增加一个值。

public static List<System.Web.UI.WebControls.ListItem> GetMyCompassTUTListContent(List<int> ContentID, Int32 CountryID)
{
    int Counter = 0;
    List<System.Web.UI.WebControls.ListItem> litems = new List<System.Web.UI.WebControls.ListItem>();
    using (DbDataContext objContext = new DbDataContext())
    {
        if (CountryID == (int)MyCompassBLL.Constants.Country.Australia)
        {
            litems = objContext.Contents.Where(x => ContentID.Contains(x.ID)).Select(x => new System.Web.UI.WebControls.ListItem { Text = x.Text, y = (y + 1) }).ToList();
        }
        else
        {
            litems = objContext.ContentCountries.Where(x => ContentID.Contains(x.ContentID) && x.CountryID == CountryID).Select(x => new System.Web.UI.WebControls.ListItem { Text = x.Text, Value = (Counter + 1).ToString() }).ToList();
        }
    }
    return litems;
}

请帮帮我。我无法做到这一点，因为我无法找到如何在递增后将值重新分配给变量计数器的方法。

提前致谢

Answer 1

Select 的重载也提供了当前项的索引。你可以用那个。但是，大多数数据库查询提供程序不支持它，因此您需要进行数据库查询，然后确保调用 Select 的 Enumerable 重载以添加索引:

public static List<ListItem> GetMyCompassTUTListContent(
    List<int> ContentID, Int32 CountryID)
{
    //Note this is IEnumerable, not IQueryable, this is important.
    IEnumerable<string> query;
    using (DbDataContext objContext = new DbDataContext())
    {

        if (CountryID == (int)MyCompassBLL.Constants.Country.Australia)
        {
            query = objContext.Contents.Where(x => ContentID.Contains(x.ID))
                .Select(x => x.Text);
        }
        else
        {
            query = objContext.ContentCountries
                .Where(x => ContentID.Contains(x.ContentID)
                    && x.CountryID == CountryID)
                .Select(x => x.Text);
        }
        return query.Select((text, index) => new ListItem
        {
            Text = text,
            Value = (index + 1).ToString(),
        })
        .ToList();
    }
}