ASP.NET实体框架LINQ to Entities无法识别方法'System.DateTime ToDateTime（System.String）

Question

I am basically trying to an "Archives" of dates grouped by Month and Year. However my problem is the dates in the database are strings...not my choice.

Here is my code to get that list of date groups

var dates = dbBlog.Data
                .GroupBy(o => new
                {
                    Month = Convert.ToDateTime(o.date).Month,
                    Year = Convert.ToDateTime(o.date).Year
                })
                .Select(g => new BlogArchiveClass
                {
                    Month = g.Key.Month,
                    Year = g.Key.Year,
                    Total = g.Count()
                })
                .OrderByDescending(a => a.Year)
                .ThenByDescending(a => a.Month)
                .ToList();

But when I use it, I get this error:

LINQ to Entities does not recognize the method 'System.DateTime ToDateTime(System.String)

How would I be able to accomplish what I am doing with string dates from the database?

Answer 1

If you know the format of your string then you can probably do something that looks like this :

var dates = dbBlog.Data
            Select(d => new 
            {
                 Month = d.Month.Substring(....),
                 Year  = d.Year.Substring(....)
            })
            .GroupBy(o => new { o.Month,o.Year})
            .Select(g => new BlogArchiveClass
            {
                Month = g.Key.Month,
                Year = g.Key.Year,
                Total = g.Count()
            })
            .OrderByDescending(a => a.Year)
            .ThenByDescending(a => a.Month)
            .ToList();