Question

i get this error

{'Method 'System.DateTime ConvertTimeFromUtc(System.DateTime, System.TimeZoneInfo)' has no supported translation to SQL.'}   

when i try to execute this linq to sql

var query = from p in db.Posts             let categories = GetCategoriesByPostId(p.PostId)             let comments = GetCommentsByPostId(p.PostId)             select new Subnus.MVC.Data.Model.Post             {                 Categories = new LazyList<Category>(categories),                 Comments = new LazyList<Comment>(comments),                 PostId = p.PostId,                 Slug = p.Slug,                 Title = p.Title,                 CreatedBy = p.CreatedBy,                 CreatedOn = TimeZoneInfo.ConvertTimeFromUtc(p.CreatedOn, TimeZoneInfo.FindSystemTimeZoneById('Romance Standard Time')),                 Body = p.Body             }; return query; 

is there another place i can convert the date to right format currently i have a macro i my _global.spark fil but that seems wrong

<macro name='DateAndTime' Date='DateTime'> # Date = TimeZoneInfo.ConvertTimeFromUtc(Date, TimeZoneInfo.FindSystemTimeZoneById('Romance Standard Time')); ${Date.ToString('MMMM d, yyyy')} at ${Date.ToString('hh:mm')} </macro> <macro name='Date' Date='DateTime'> # Date = TimeZoneInfo.ConvertTimeFromUtc(Date, TimeZoneInfo.FindSystemTimeZoneById('Romance Standard Time')); ${Date.ToString('MMMM d, yyyy')} </macro>  

Update: i now understand where the code does not work but when i remove it i get then same error for this code

 public IQueryable<Subnus.MVC.Data.Model.Comment> GetCommentsByPostId(int postId)     {         var query = from c in db.Comments                     where c.PostId == postId                     select new Subnus.MVC.Data.Model.Comment                     {                         Body = c.Body,                         EMail = c.EMail,                         Date = c.CreatedOn,                         WebSite = c.Website,                         Name = c.Name                     };          return query;     } 

Answer 1

LINQ-to-SQL only translates a subset of operations – and it trying (and failing) to write ConvertTimeFromUtc as TSQL. Some operations have TSQL counterparts (dateadd/datediff/etc) – but not all. You might choose to do your projection (select) using the raw value, and only do the ConvertTimeFromUtc once you have the object in memory (via LINQ-to-Objects).

For example – you could create the objects just using p.CreatedOn, then do the rest afterwards. Not ideal, but life. LINQ-to-Entities claims better translation options, but is significantly more complex. Depending on your scenario, LINQ-to-SQL also offers udf support, which sometimes lets you offload these things to the db – if there is a way of writing it as a udf – for example, you could write a method on the data-context and mark is as a composable function ([Function]), then something like:

 ...     CreatedOn = ctx.MapDate(p.CreatedOn)  .... 

Which would then use the TSQL from [Function] – i.e. something like:

....     dbo.MapDate(t2.CreatedOn) ....