CODEWITHSUNDEEP
asp.netlinq
Milan
Milan

Reputation: 1019

How to successfully join two in-memory linq collections?

I'm trying to join one Linq collection from Data Base and one from XML file. Is this possible? I always get: Local sequence cannot be used in LINQ to SQL implementation of query operators except the Contains() operator.

Here is my code:

MyDataContext dc = new MyDataContext();
XElement CustomData;

var pages = from p in dc.Pages
            select new
            {
                Title = p.Title,
                Slug = p.Slug,
                PageId = p.PageId.ToString()
            };

var orders = from p in CustomData.Element("pages").Elements("page")
             select new
             {
                 PageId = (string)p.Attribute("id"),
                 SortOrder = (int)p.Attribute("sortOrder")
             };


var source = from p in pages
             join o in orders
             on p.PageId equals o.PageId
             select p;

source.ToList();

Upvotes: 2

Views: 1142

Answers (2)

tvanfosson
tvanfosson

Reputation: 532435

I don't think you need to do the join at all.

MyDataContext dc = new MyDataContext();
XElement CustomData;

var orders = CustomData.Element("pages").Elements("page")
                       .Select( o =>  new
                         {
                             PageId = p.Attribute("id").ToString(),
                             SortOrder = (int)p.Attribute("sortOrder")
                         });

var source = dc.Pages
               .Where( p => orders.Select( o => o.PageId)
                                  .Contains( p.PageId.ToString() ))
               .Select( p => new
                {
                  Title = p.Title,
                  Slug = p.Slug,
                  PageId = p.PageId.ToString()
                });

Upvotes: 1

Restore The Data Dumps Again
Restore The Data Dumps Again

Reputation: 39325

It doesn't look like you can do the join between the local collection (orders) and the LINQ2SQL results with deferred execution. You can execute the pages query ToList (like tvanfosson suggested originally:)) or maybe do something like this...

var source = from p in pages
             where orders.Select(o=> o.PageID).Contains(p.PageID)
             select p;

It's not quite the join you were looking for, but if you want the deferred execution of LINQ2SQL you can have it this way.

Upvotes: 0

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