Question

我正在尝试跳过并从查询中获取，但得到了转换错误：

Error   1   Cannot implicitly convert type 'System.Linq.IQueryable<tblComment>' to 'System.Linq.IOrderedQueryable<tblComment>'. An explicit conversion exists (are you missing a cast?)
Error   2   Cannot implicitly convert type 'System.Linq.IQueryable<tblComment>' to 'System.Linq.IOrderedQueryable<tblComment>'. An explicit conversion exists (are you missing a cast?)

在线：

if(ToSkip > 0)
    q = q.Skip(ToSkip);
if(ToTake > 0)
    q = q.Take(ToTake);

这是完整的方法，任何帮助表示赞赏！我想要做的就是过滤掉指定的记录，直到它们为止。

此外，这是一种很好的方法，还是数据库每次都会返回所有记录？即，它会获取所有记录，然后跳过并采取？我希望提高效率。

/// <summary>
/// Fetches all comments from a category
/// </summary>
/// <param name="Category">Category ID of comments to fetch</param>
/// <param name="Identifier">Identifier ID for category</param>
/// <param name="ToTake">How many to take in query. 0 = all</param>
/// <param name="ToSkip">How many to skip.</param>
/// <returns></returns>
public static Comment[] FetchCommentsByNewest(int Category, int Identifier, int ToSkip, int ToTake)
{
    Comment[] Comments = new Comment[1];

    using (DataClassesDataContext db = new DataClassesDataContext())
    {
        // Loop each comment and insert newest first to array
        var q = (from c in db.tblComments where c.CategoryID == Category && c.IdentifierID == Identifier orderby c.PostDate descending select c);
        if(ToSkip > 0)
            q = q.Skip(ToSkip);
        if(ToTake > 0)
            q = q.Take(ToTake);
        Comments = new Comment[q.Count()];
        int i = 0;
        foreach (var Rec in q)
        {

            i++;
        }
    }

    return Comments;
}

Answer 1

您可以通过将代码更改为此来绕过它：

var q = (
   from c in db.tblComments 
   where c.CategoryID == Category && c.IdentifierID == Identifier 
   orderby c.PostDate descending select c
)
.Skip(ToSkip > 0 ? ToSkip : 0)
.Take(ToTake > 0 ? ToTake : int.MaxValue);

Answer 2

使用与ChrisF相同的逻辑并使用返回q.ToArray（）完成语句，或者如果需要模型类，例如评论然后使用AutoMapper http://automapper.codeplex.com/

之类的东西

或

return q.select( x=>  new Comment{Name = x.Name, Description = x.Description}).ToArray();

注意： ToArray或ToList（）将导致执行查询。

Linq和C＃，跳过记录，投射错误

2 个答案: