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• What is the max LINQ Expression Trees can do?

  - by yeeen

  What is the maximun that LINQ expression Tree can do? Can it define a class? How about a method, with all the declared name, modifiers, parametertype and return type? Must the program always define the tree himself? Is it possible to generate the tree from a given C# file? Where can I get resources to learn about writing basic to advanced Expression Tree and Expression Tree Visitor? (articles and videos will be great) Thanks for those who are able to help...

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• Another Permutation Word Conundrum... With Linq?

  - by CraigF

  I have seen many examples of getting all permutations of a given set of letters. Recursion seems to work well to get all possible combinations of a set of letters (though it doesn't seem to take into account if 2 of the letters are the same). What I would like to figure out is, could you use linq (or not) to get all possible combinations of letters down to 3 letter combinations. For example, given the letters: P I G G Y I want an array of all possible cominations of these letters so I can check against a word list (scrabble?) and eventually get a list of all possible words that you can make using those letters (from 3 letters up to the total, in this case 5 letters).

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• How to OrderBy on a generic IEnumerable (IEnumerable<T>) using LINQ in C#?

  - by Jeffrey

  In my generic repository I have below method: public virtual IEnumerable<T> GetAll<T>() where T : class { using (var ctx = new DataContext()) { ctx.ObjectTrackingEnabled = false; var table = ctx.GetTable<T>().ToList().AsReadOnly(); return table; } } T is a Linq to Sql class and I want to be able to OrderBy on a particular property. Say if T has property name "SortOrder" then do OrderBy on this property. But I am not sure how I can achieve this. So I need some helps. Thank you!

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• Can I use Linq to project a new typed datarow?

  - by itchi

  I currently have a csv file that I'm parsing with an example from here: http://alexreg.wordpress.com/2009/05/03/strongly-typed-csv-reader-in-c/ I then want to loop the records and insert them using a typed dataset xsd to an Oracle database. It's not that difficult, something like: foreach (var csvItem in csvfile) { DataSet.MYTABLEDataTable DT = new DataSet.MYTABLEDataTable(); DataSet.MYTABLERow row = DT.NewMYTABLERow(); row.FIELD1 = csvItem.FIELD1; row.FIELD2 = csvItem.FIELD2; } I was wondering how I would do something with LINQ projection: var test = from csvItem in csvfile select new MYTABLERow { FIELD1 = csvItem.FIELD1, FIELD2 = csvItem.FIELD2 } But I don't think I can create datarows like this without the use of a rowbuilder, or maybe a better constructor for the datarow?

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• why LINQ 2 SQL sometime add a field like select 1 as test, others valid fields....

  - by Fredou

  I have to concat 2 linq2sql query and I have an issue since the 2 query doesn't return the same number of columns, what is weird is after a .ToList() on the queries, they can concat without problem. The reason is, for some linq2sql reason, I have 2 more column named test and test2 which come from 2 left outer join that linq2sql automatically create, something like "select 1 as test, tablefields" Is there any good reason for that? how to remove this extra "1 as test" field? here a few of examples of what it look like: google result for linq 2 sql "select 1 as test"

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• Tag filtering Query using T-SQL and Linq-to-SQL?

  - by EdenMachine

  I'm trying to figure out how to allow a user to enter in a string of tags (keywords separated by spaces) in a textbox to filter a grid of results. Here are the tables: PACKETS *PacketID Name PACKETTAGS *PacketTagID PacketID TagID Tags *TagID Name Here is the basic query without the WHERE parameters: SELECT Packets.Name, Tags.Name AS Tag, PacketTags.PacketTagID FROM Packets INNER JOIN PacketTags ON Packets.PacketID = PacketTags.PacketID INNER JOIN Tags ON PacketTags.TagID = Tags.TagID I need to filter out all the Packets that don't have tags that match any of the words BUT ALSO ONLY include the Packets that have the tags entered in the string of text (spaces separate the tags when entered into the textbox) I'm starting with the basics by figuring this out in t-SQL first but ultimately I need to be able to do this in Linq-to-SQL

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• Using Where method in Linq 2 Entities with OR clause.

  - by Dani

  I want to use Where method in Linq 2 entities that will be equal to this userRepository.Users.Where(u=>u.RoleID == 1 || u=>u.RoldID == 2).Select(o => new SelectListItem { Text = o.Role.RoleName, Value = o.RoleID.ToString() }).ToList(); The problem of course is in Where(u=u.RoleID == 1 || u=u.RoldID == 2) The problem is that I don't know how to use WHERE method with OR inside the WHERE clause. any ideas (the code above will not compile of-course b/c of the lambda expression. userRepository.Users returns an list of Users entities. I guess that and can be done using concatenation of .Where().Where() but I need an OR.

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• How to update a table in database using LINQ in F#?

  - by sudaly

  I have seen plenty of examples on how to query the database but nothing on how to update records. Below is the simple code that I wrote to retrieve a table, but can someone explain me how can I modify a field, say lastActiveDate, and update the table on the database Thank you, suday open System open Microsoft.FSharp.Linq let connString = "Server=localhost;Database=myDb;Trusted_Connection=True;" let db = new MyDb(connString) db.Log <- System.Console.Out let res = Query.query <@ seq { for users in db.userAccounts do yield users } @> |> List.ofSeq printfn "Totla users: %d" res.Length

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• building an ASP NET MVC site, should i go with linq to sql?

  - by aspm

  so i'm about to start a new website from scratch and i've spent about a week trying to figure out what technology to go with. i'm sold on ASP NET MVC. i'm 100% sure i'm going to love using that. but what i am not so sure about yet is using LINQ 2 SQL. so far i've gathered some data... 1) stack overflow uses it - can't be that bad 2) can be REALLY slow if you don't take advantage of compiled queries 3) will always be slower than ADO net, but can be almost just as fast if using #2 in the proper places 4) is NOT the preferred MS solution (there was a thread here on SO about dropping support) i'm itching to use it, but just want to make sure it's the best for me. i come from a heavy ADO/stored procedure and traditional asp net background (this will be my first experience with ASP MVC).

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• Upgrade to 4.0 Framework, then downgraded, now can't find Linq namespace?

  - by CubanX

  I just upgraded from VS2008 to VS2010. In the process, I allowed it to upgrade my DLL's to 4.0. I've decided that wasn't a good idea and now I've rolled back. It all works fine in VS2010, but when it hits my CI server (CruiseControl.Net), I get an error of: The type or namespace name 'Linq' does not exist in the namespace 'System' (are you missing an assembly reference? 3.5 is on the server, and other projects that use 3.5 build fine, so I don't think it's a framework issue. Anyone have any hints?

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• If I cast an IQueryable as an IEnumerable then call a Linq extension method, which implementation gets called?

  - by James Morcom

  Considering the following code: IQueryable<T> queryable; // something to instantiate queryable var enumerable = (IEnumerable<T>) queryable; var filtered = enumerable.Where(i => i > 3); In the final line, which extension method gets called? Is it IEnumerable<T>.Where(...)? Or will IQueryable<T>.Where(...) be called because the actual implementation is still obviously a queryable? Presumably the ideal would be for the IQueryable version to be called, in the same way that normal polymorphism will always use the more specific override. In Visual Studio though when I right-click on the Where method and "Go to Definition" I'm taken to the IEnumerable version, which kind of makes sense from a visual point-of-view. My main concern is that if somewhere in my app I use Linq to NHibernate to get a Queryable, but I pass it around using an interface that uses the more general IEnumerable signature, I'll lose the wonders of deferred database execution!

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• Why did the following linq to sql query generate a subquery?

  - by Xaisoft

  I did the following query: var list = from book in books where book.price > 50 select book; list = list.Take(50); I would expect the above to generate something like: SELECT top 50 id, title, price, author FROM Books WHERE price > 50 but it generates: SELECT [Limit1].[C1] as [C1] [Limit1].[id] as [Id], [Limit1].[title] as [title], [Limit1].[price] as [price], [Limit1].[author] FROM (SELECT TOP (50) [Extent1].[id] as as [Id], [Extent1].[title] as [title], [Extent1].[price] as [price], [Extent1].[author] as [author] FROM Books as [Extent1] WHERE [Extent1].[price] > 50 ) AS [Limit1] Why does the above linq query generate a subquery and where does the C1 come from?

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• Linq GroupBy - how to specify the grouping key at runtime?

  - by toasteroven

  is there a good way to do a Linq GroupBy where the grouping key is determined at runtime? e.g. I want the grouping key to be built from a user-selected list of fields - can you do this? I know I can do it easily if I convert everything to a table of strings, but I was wondering if there was an elegant or clever way to accomplish this otherwise. class Item { public int A, B; public DateTime D; public double X, Y, Z; } I have a List<Item> called data. I want to do things like retrieve the sum of X grouped by A, or the sums of X, Y, and Z, grouped by A and B. but what fields go into the grouping should be able to be specified at runtime in some way.

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• LINQ query for tag system: Matching any of several tags?

  - by David Veeneman

  I am just getting started with LINQ. I am creating an Entity Framework app that uses the canonical Post and Tag model. A Post contains an ID, Text, and Tags, and a Tag contains an ID, a Name, and Posts. A previous thread on StackOverflow showed me how to query for a Post that matches all Tag objects (A and B and C) in a search list. But how would I query for a Post that matches any Tag (A or B or C) in the list? Thanks for your help.

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• Please help me convert this C# 2.0 snippet to Linq.

  - by Hamish Grubijan

  This is not a homework ;) I need to both A) optimize the following code (between a TODO and a ~TODO) and B) convert it to [P]Linq. Better readability is desired. It might make sense to provide answers to A) and B) separately. Thanks! lock (Status.LockObj) { // TODO: find a better way to merge these dictionaries foreach (KeyValuePair<Guid, Message> sInstance in newSInstanceDictionary) { this.sInstanceDictionary.Add(sInstance.Key, sInstance.Value); } foreach (KeyValuePair<Guid, Message> sOperation in newSOperationDictionary) { this.sOperationDictionary.Add(sOperation.Key, sOperation.Value); } // ~TODO }

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• Is there a way to make this C# method shorter and more readable with the help of Linq?

  - by Hamish Grubijan

  The following works, but I figured - since it is all based on IEnumerable, Linq can come handy here is well. By the way, is there an equivalent to Directory.GetFiles() which would return an IEnumerable instead of the array? If it exists, then would it make the code run any faster? The last part of the question is inspired by Python language which favors lightweight generators over concrete lists. private IEnumerable<string> getFiles(string strDirectory, bool bCompressedOnly) { foreach (var strFile in Directory.GetFiles(strDirectory)) { // Don't add any existing Zip files since we don't want to delete previously compressed files. if (!bCompressedOnly || Path.GetExtension(strFile).ToLower().Equals(".zip")) { yield return strFile; } } foreach (var strDir in Directory.GetDirectories(strDirectory)) { foreach (var strFile in getFiles(strDir, bCompressedOnly)) { yield return strFile; } } }

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• How to format complex chained Linq statements for readibility?

  - by Joan Venge

  I have some code like this: var effects = xElement.Elements ( "Effects" ).Elements ( "Effect" ).Select ( e => new Effect ( ( EffectType ) Enum.Parse ( typeof ( EffectType ), ( string ) e.Elements ( "Type" ).FirstOrDefault ( ) ), e.Elements ( "Options" ).Any ( ) ? e.Elements ( "Options" ).Select ( o => ( object ) o.Elements ( "Option" ).Select ( n => n.Value ).First ( ) ) : null ) ) .ToList ( ); But currently this doesn't look as readable and I am not sure where I should add a new line and/or indent for readability. Any suggestions I could use to make consistent, readable linq blocks?

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• Linq to SQL - How to compare against a collection in the where clause?

  - by Sgraffite

  I'd like to compare against an IEnumerable collection in my where clause. Do I need to manually loop through the collection to pull out the column I want to compare against, or is there a generic way to handle this? I want something like this: public IEnumerable<Cookie> GetCookiesForUsers(IEnumerable<User> Users) { var cookies = from c in db.Cookies join uc in db.UserCookies on c.CookieID equals uc.CookieID join u in db.Users on uc.UserID equals u.UserID where u.UserID.Equals(Users.UserID) select c; return cookies.ToList(); } I'm used to using the lambda Linq to SQL syntax, but I decided to try the SQLesque syntax since I was using joins this time. What is a good way to do this?

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• Help Please, I want use LINQ to Query Count in a matrix according to a array!

  - by Bob Feng

  I have a matrix, IEnumerable<IEnumerable<int>> matrix, for example: { {10,23,16,20,2,4}, {22,13,1,33,21,11 }, {7,19,31,12,6,22}, ... } and another array: int[] arr={ 10, 23, 16, 20} I want to filter the matrix on the condition that I group all rows of the matrix which contain the same number of elements from arr. That is to say the first row in the matrix {10,23,16,20,2,4} has 4 numbers from arr, this array should be grouped with the rest of the rows with 4 numbers from arr. better to use linq, thank you very much!

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• How to build a LINQ query from text at runtime?

  - by Danvil

  I have a class A { public int X; public double Y; public string Z; // and more fields/properties ... }; and a List<A> data and can build a linq query like e.g. var q = from a in data where a.X > 20 select new {a.Y, a.Z}; Then dataGridView1.DataSource = q.ToList(); displays the selection in my DataGridView. Now the question, is it possible to build the query from a text the user has entered at runtime? Like var q = QueryFromText("from a in data where a.X > 20 select new {a.Y, a.Z}"); The point being, that the user (having programming skills) can dynamically and freely select the displayed data.

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• How is a set partitioned into valid and invalid items using LINQ?

  - by Aaron Anodide

  Is there a way to write a single LINQ expression to get the same result of the following code? var validations = new Func<conversion, bool>[] { c => c.affiliate.affiliate_id > 0, c => c.campaign_id > 0 }; var invalidConversions = from c in extractedConversions where validations.Any(valid => !valid(c)) select c; var validConversions = from c in extractedConversions where validations.All(valid => valid(c)) select c;

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• Any way for linq query to check against existing select?

  - by danrhul

  I have an an offer, that can be in any number of categories. I don't however want that offer to then appear twice or however more. I was wondering if its possible to have a where clause that ascertains whether that offer already exists in that select statement and if so obviously to ignore it. Here is the linq query: Offers = from o in offerCategories orderby o.RewardCategory.Ordering, o.Order where o.RewardOffer.IsDeleted == false select new OfferOverviewViewModel { Partner = o.RewardOffer.Partner, Description = String.Format("{0} {1}", o.RewardOffer.MainTitle, o.RewardOffer.SecondaryTitle), OfferId = o.OfferId, FeaturedOffer = o.RewardOffer.FeaturedOfferOrder.HasValue, Categories = from c in offerCategories.Where(oc => oc.OfferId == o.OfferId) orderby c.RewardCategory.Ordering select new CategoryDetailViewModel { Description = c.RewardCategory.DisplayName } },

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• LINQ to SQL, how to write a method which checks if a row exists when we have multiple tables

  - by Beles

  Hi, I'm trying to write a method in C# which can take as parameter a tabletype, column and a columnvalue and check if the got a row with a with value the method looks like: public object GetRecordFromDatabase(Type tabletype, string columnname, string columnvalue) I'm using LINQ to SQL and need to to this in a generic way so I don't need to write each table I got in the DB. I have been doing this so far for each table, but with more than 70 of these it becomes cumbersome and boring to do. Is there a way to generate the following code dynamically, And swap out the hardcoded tablenames with the values from the parameterlist? In this example I have a table in the DB named tbl_nation, which the DataContext pluralizes to tbl_nations, and I'm checking the column for the value if (DB.tbl_nations.Count(c => c.code.Equals(columnvalue)) == 1) { return DB.tbl_nations.Single(c => c.code.Equals(columnvalue)); }

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• Converting Data to XML with LINQ to XML

  Sometimes when you have all kinds of data what you really need is XML. LINQ to XML let's you employ functional construction to convert your data into XML.

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• Silverlight 4 Linq to Sql and RIA sevice for CRUD operations

  Silverloght 4 has lots of new fearures, for details visit Silverlight 4 . Let's start with a small application to perform CRUD operations using Linq to SQL and RIA Services.

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