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• Should methods containing LINQ expressions be tested / mocked?

  - by Phil.Wheeler

  Assuming I have a class with a method that takes a System.Linq.Expressions.Expression as a parameter, how much value is there in unit testing it? public void IEnumerable<T> Find(Expression expression) { return someCollection.Where(expression).ToList(); } Unit testing or mocking these sorts of methods has been a mind-frying experience for me and I'm now at the point where I have to wonder whether it's all just not worth it. How would I unit test this method using some arbitrary expression like List<Animal> = myAnimalRepository.Find(x => x.Species == "Cat");

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• Using LINQ to search a byte array for all subarrays that start/stop with certain byte

  - by Joel B

  I'm dealing with a COM port application and we have a defined variable-length packet structure that I'm talking to a micro-controller with. The packet has delimiters for the start and stop bytes. The trouble is that sometimes the read buffer can contain extraneous characters. It seems like I'll always get the whole packet, just some extra chatter before/after the actual data. So I have a buffer that I append data to whenever new data is received from the COM port. What is the best way to search this buffer for any possible occurrences of my packet? For example: Say my packet delimiter is 0xFF and I have an array as such { 0x00, 0xFF, 0x02, 0xDA, 0xFF, 0x55, 0xFF, 0x04 } How can I create a function/LINQ-statment that returns all subarrays that start and end with the delimiter (almost like a sliding-correlator with wildcards)? The sample would return the following 3 arrays: {0xFF, 0x02, 0xDA, 0xFF}, {0xFF, 0x55, 0xFF}, and {0xFF, 0x02, 0xDA, 0xFF, 0x55, 0xFF}

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• Binding Linq To Entities query results to a datagridview

  - by Nickson

  I just started playing with Linq to entities in a windows forms application and am not understanding one behavior that looks so simple though. If i type code below, i get ReadOnly records in my dataGridView Dim x = From n in Table1 _ Select n.FirstName, n.LastName, N.Department DataGridView1.DataSource = x But if i type the following code, i get editable rows in my dataGridView Dim x = From n in Table1 _ Select n DataGridView1.DataSource = x So, basically if i specify the column names to select and databind to my DataGridView1, the rows are readonly but if i do not specify the column names and databind to the DataGridView, the rows are editable and i don't understand why.

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• attaching linq to sql datacontext to httpcontext in business layer

  - by rap-uvic

  Hello all, I need my linq to sql datacontext to be available across my business/data layer for all my repository objects to access. However since this is a web app, I want to create and destroy it per request. I'm wondering if having a singleton class that can lazily create and attach the datacontext to current HttpContext would work. My question is: would the datacontext get disposed automatically when the request ends? Below is the code for what I'm thinking. Would this accomplish my purpose: have a thread-safe datacontext instance that is lazily available and is automatically disposed when the request ends? public class SingletonDC { public static NorthwindDataContext Default { get { NorthwindDataContext defaultInstance = (NorthwindDataContext)System.Web.HttpContext.Current.Items["datacontext"]; if (defaultInstance == null) { defaultInstance = new NorthwindDataContext(); System.Web.HttpContext.Current.Items.Add("datacontext", defaultInstance); } return defaultInstance; } } }

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• LINQ: Dot Notation vs Query Expression

  - by Martín Marconcini

  I am beginning to use LINQ in general (so far toXML and toSQL). I've seen that sometimes there are two or more ways to achieve the same results. Take this simple example, as far as I understand both return exactly the same thing: SomeDataContext dc = new SomeDataContext(); var queue = from q in dc.SomeTable where q.SomeDate <= DateTime.Now && q.Locked != true orderby (q.Priority, q.TimeCreated) select q; var queue2 = dc.SomeTable .Where( q => q.SomeDate <= DateTime.Now && q.Locked != true ) .OrderBy(q => q.Priority) .ThenBy(q => q.TimeCreated); Besides any mistake I may have made in the syntax or a missing parameter or difference, the idea is that there are two ways to express the same thing; I understand that the first method has some limitations and that the "dot notation" is more complete, but besides that, are there any other advantages?

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• Return nested alias for linq expression

  - by Schotime

  I have the following Linq Expression var tooDeep = shoppers .Where(x => x.Cart.CartSuppliers.First().Name == "Supplier1") .ToList(); I need to turn the name part into the following string. x.Cart.CartSuppliers.Name As part of this I turned the Expression into a string and then split on the . and removed the First() argument. However, when I get to CartSuppliers this returns a Suppliers[] array. Is there a way to get the single type from this. eg. I need to get a Supplier back. Thanks

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• How to SET ARITHABORT ON for connections in Linq To SQL

  - by Laurence

  By default, the SQL connection option ARITHABORT is OFF for OLEDB connections, which I assume Linq To SQL is using. However I need it to be ON. The reason is that my DB contains some indexed views, and any insert/update/delete operations against tables that are part of an indexed view fail if the connection does not have ARITHABORT ON. Even selects against the indexed view itself fail if the WITH(NOEXPAND) hint is used (which you have to use in SQL Standard Edition to get the performance benefit of the indexed view). Is there somewhere in the data context I can specify I want this option ON? Or somewhere in code I can do it?? I have managed a clumsy workaround, but I don't like it .... I have to create a stored procedure for every select/insert/update/delete operation, and in this proc first run SET ARITHABORT ON, then exec another proc which contains the actual select/insert/update/delete. In other words the first proc is just a wrapper for the second. It doesn't work to just put SET ARITHABORT ON above the select/insert/update/delete code.

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• Problem with linq-to-xml

  - by phenevo

  I want by linq save my xml in csv and I have o problem. This bracket are here beacuse without it this code is not displaying (why ? ) bracket results bracket <Countries country="Albania"><Regions region="Centralna Albania"><Provinces province="Durres i okolice"><Cities city="Durres" cityCode="2B66E0ACFAEF78734E3AF1194BFA6F8DEC4C5760"><IndividualFlagsWithForObjects Status="1" /><IndividualFlagsWithForObjects Status="0" /><IndividualFlagsWithForObjects magazyn="2" /></Cities></Provinces></Regions></Countries><Countries .... XDocument loaded = XDocument.Load(@"c:\citiesxml.xml"); // create a writer and open the file TextWriter tw = new StreamWriter("c:\\XmltoCSV.txt"); // Query the data and write out a subset of contacts var contacts = (from c in loaded.Descendants("Countries") select new { Country = (string)c.Element("Country"), Region = (string)c.Element("region"), Province= (string)c.Element("province"), City = (string)c.Element("city"), Hotel = (string)c.Element("hotel") }).ToList(); Problem is that loaded.Descendants("Countries") gives me 45 countries but all fields are null.

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• Converting SQL statement into Linq

  - by DMan

  I'm trying to convert the following to a LINQ to SQL statement in C#. Can anyone give me a hand? Basically my table keeps record of all history of changes such that the created date max date for each seedlot is the most recent record and the correct one to show. SELECT reports.* FROM [dbo].[Reports] reports WHERE reports.createdDate IN ( SELECT MAX(report_max_dates.createdDate) FROM [dbo].[Reports] report_max_dates GROUP BY report_max_dates.Lot ) So far this is what I have. var result = (from report in db.Reports where report.createdDate == (from report_max in db.Reports group report_max by report_max.Lot into report_max_grouped select report_max_grouped).Max() select report); I can't figure out how to get the MAX dates for all reports and how to do an IN statement on the report.createdDate. Thansk, Dman

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• LINQ and set difference

  - by Pierre

  I have two collections a and b. I would like to compute the set of items in either a or b, but not in both (a logical exclusive or). With LINQ, I can come up with this: IEnumerable<T> Delta<T>(IEnumerable<T> a, IEnumerable<T> b) { return a.Except (b).Union (b.Except (a)); } I wonder if there are other more efficient or more compact ways of producing the difference between the two collections.

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• Use LINQ and lambdas to put string in proper case

  - by Tobias Funke

  I have this function called ProperCase that takes a string, then converts the first letter in each word to uppercase. So ProperCase("john smith") will return "John Smith". Here is the code: public string ProperCase(string input) { var retVal = string.Empty; var words = input.Split(' '); foreach (var word in words) { if (word.Length == 1) { retVal += word.ToUpper(); } else if (word.Length > 1) { retVal += word.Substring(0, 1).ToUpper() + word.Substring(1).ToLower(); } retVal += ' '; } if (retVal.Length > 0) { retVal = retVal.Substring(0, retVal.Length - 1); } return retVal; } This code workds perfectly, but I'm pretty sure I can do it more elegantly with LINQ and lambdas. Can some please show me how?

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• LINQ how to concatenate 2 db columns to display in dropdownlist

  - by Simke Nys

  I'm trying to concatenate product_name with product_prize_kg by using LINQ so I can display it as one field in a dropdownlist. When I try to do this I get the following error. value of type 'system.collections.generic.list(of anonymous type )' cannot be converted to ... My code is like this: Public Function selectAll() As List(Of tblProduct) Dim result = From product In dc.tblProducts Select New With { Key .productID = product.pk_product_id, Key .productNameKg = Convert.ToString(product.product_name) & " " & Convert.ToString(product.product_price_kg) } Return result.ToList() End Function This is the dropdownlist that I want to fill. <asp:DropDownList ID="DropDownList1" runat="server" DataSourceID="ObjectDataSource1" DataTextField="productNameKg" DataValueField="productID"> </asp:DropDownList> Thanks Grtz Simke

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• How to perform a many-to-many Linq query with Include in the EF.

  - by despart

  Hi, I don't know how to perform this query using Linq and the EF. Imagine I have three tables A, B and C. A and B have a many-to-many relationship. B and C have a 1-to-many relationship. I want to obtain records from B including C but filtering from A's Id. I can get easily the records from B: var b = Context.A.Where(x => x.Id.Equals(aId)).SelectMany(x => x.B); but when I try to include C I don't know how to do it: //This doesn't work var b = Context.A.Where(x => x.Id.Equals(aId)).SelectMany(x => x.B.Include("C")); Also I've tried this with no luck (it is equivalent to the above): //Not working var b = (from a in Context.A.Where(x => x.Id.Equals(aId)) from b in a.B.Include("C") select b); Thanks for your help.

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• LINQ OrderBy with more than one field

  - by brainimus

  I have a list that I need sorted by two fields. I've tried using OrderBy in LINQ but that only allows me to specify one field. I'm looking for the list to be sorted by the first field and then if there are any duplicates in the first field to sort by the second field. For example I want the results to look like this (sorted by last name then first name). Adams, John Smith, James Smith, Peter Thompson, Fred I've seen that you can use the SQL like syntax to accomplish this but I am looking for a way to do it with the OrderBy method. IList<Person> listOfPeople = /*The list is filled somehow.*/ IEnumerable<Person> sortedListOfPeople = listOfPeople.OrderBy(aPerson => aPerson.LastName, aPerson.FirstName); //This doesn't work.

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• Equality Comparison with Multiple Instances/IEqualityComparer problems in LINQ

  - by Stacey

  This is similar to my last question; but from a different angle. http://stackoverflow.com/questions/2792393/see-if-item-exists-once-in-enumerable-linq Given the following set of items, and lists containing them... Item 1 Item 2 Item 3 Item 4 Item 5 class Item { string Name { get; set; } } List<Item> available = new List<Item>() { Item 1 Item 1 Item 2 Item 3 Item 5 } List<Item> selected = new List<Item>() { Item 1 Item 2 Item 3 } I need to make a third List that has everything from "available", except what is in "selected". However 'Item 1' is in 'available' twice, but only in 'selected' once. Since they are instances of the same item, I am having trouble figuring out the appropriate logic to accomodate this. The final array should look like... List<Item> selectable = new List<Item>() { Item 1 Item5 }

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• Insert xelements using LINQ Select?

  - by Simon Woods

  I have a source piece of xml into which I want to insert multiple elements which are created dependant upon certain values found in the original xml At present I have a sub which does this for me: <Extension()> Public Sub AddElements(ByVal xml As XElement, ByVal elementList As IEnumerable(Of XElement)) For Each e In elementList xml.Add(e) Next End Sub And this is getting invoked in a routine as follows: Dim myElement = New XElement("NewElements") myElement.AddElements( xml.Descendants("TheElements"). Where(Function(e) e.Attribute("FilterElement") IsNot Nothing). Select(Function(e) New XElement("NewElement", New XAttribute("Text", e.Attribute("FilterElement").Value)))) Is it possible to re-write this using Linq syntax so I don't need to call out to the Sub AddElements but could do it all in-line Many Thx Simon

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• Empty namespace using Linq Xml

  - by porum

  I'm trying to create a sitemap using Linq to Xml, but am getting an empty namespace attribute, which I would like to get rid of. e.g. XNamespace ns = "http://www.sitemaps.org/schemas/sitemap/0.9"; XDocument xdoc = new XDocument(new XDeclaration("1.0", "utf-8", "true"), new XElement(ns + "urlset", new XElement("url", new XElement("loc", "http://www.example.com/page"), new XElement("lastmod", "2008-09-14")))); The result is ... <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"> <url xmlns=""> <loc>http://www.example.com/page</loc> <lastmod>2008-09-14</lastmod> </url> </urlset> I would rather not have the xmlns="" on the url element. I can strip it out using Replace on the final xdoc.ToString(), but is there a more correct way?

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• Weird mapping error in linq-to-sql dbml file in VS2010

  - by rwwilden

  Since I switched to VS2010, several times a day I get a compilation error in my dbml file: DBML1005: Mapping between DbType 'bigint' and Type 'MyNamespace.SecurityToken' in Column 'SecurityToken' of Type 'Employee' is not supported When I restart VS2010 the error disappears. I have no problems running my application using this dbml file (specifically, there are no problems getting correct values inside the SecurityToken property of Employee objects). The SecurityToken property is of an enum type defined as follows: [Flags] public enum SecurityToken : long { None = 1, Admin = 2, ...... } The SecurityToken column in the database is of type bigint. Am I missing something? It's especially weird that the error only happens sometimes, when I'm writing code that isn't related at all to the LINQ model.

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• Build dynamic LINQ?

  - by d daly

  Hi Im using #LINQ# to query data, but can anyone tell me how to build the query dynamically, if the user only wants to report on say 1 of the 3 fields? (see below) Thanks DD var query = from cl in db.tblClaims join cs in db.tblCases on cl.ref_no equals cs.ref_no where cl.claim_status == "Appeal" && cl.appeal_date >= Convert.ToDateTime(txtReferedFromDate.Text) && cl.appeal_date <= Convert.ToDateTime(txtReferedToDate.Text) && cs.referred_from_lho == dlLHO.Text && cs.adviser == dlAdviser.Text select new { Ref = cs.ref_no, ClaimType = cl.claim_type, ClaimStatus = cl.claim_status, AppealDate = cl.appeal_date }; gvReport.DataSource = query;

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• C# and Linq: Generating SQL Backup/Restore From Code

  - by mdvaldosta

  I'm working with a C# and Linq to SQL Winforms app and needed to integrate backup and restores through the program. I used SMO and got it working pretty smoothly. The issue, however, is that the app is deployed using ClickOnce, which I like very much - but since I had to include the dll's the download size jumped from 3mb = 15mb. I know they've only got to download it once, but it also sucks for me as Visual Studio 2010 seems to upload the dll's every time and that takes a while on AT&T broadband (eh). So, anyone have any suggestion on how I can work out an effective backup/restore solution without using SMO objects?

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• help with linq query

  - by Luis

  Hi, i am trying to get some data, but i dont know how can i do a if in linq, this is how i am trying to do from so in db.Operations where ((opType!= "0" ? so.Operation == int.Parse(opType) : false) && (idState!=0 ? so.State == idState : false) && (start != null ? so.StartDate == start : false) && (end !=null ? so.EndDate == end : false)) select so the optype is a Int, the idState is a Int, end is a datetime, start is a datime what i am trying to do is, if those aren't null they add to the query function, so i can get all data together

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• Make a Linq-to-SQL Generated User Class Inherit from MembershipUser

  - by Adam Albrecht

  I am currently building a custom Membership Provider for my Asp.net MVC website. I have an existing database with a Users table and I'm using Linq-to-Sql to automatically generates this class for me. What I would like to do is have this generated User class inherit from the MembershipUser class so I can more easily use it in my custom Membership Provider in methods such as GetUser. I already have all the necessary columns in the table. Is there any way to do this? Or am I going about this the completely wrong way? Thanks!

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• Populate DataTable with LINQ in C#

  - by RaYell

  I have a method in my app that populates DataTable with the data using the following code: DataTable dt = this.attachmentsDataSet.Tables["Attachments"]; foreach (Outlook.Attachment attachment in this.mailItem.Attachments) { DataRow dr = dt.NewRow(); dr["Index"] = attachment.Index; dr["DisplayName"] = String.Format( CultureInfo.InvariantCulture, "{0} ({1})", attachment.FileName, FormatSize(attachment.Size)); dr["Name"] = attachment.FileName; dr["Size"] = attachment.Size; dt.Rows.Add(dr); } I was wondering if I could achieve the same functionality using LINQ in order to shorten this code a bit. Any ideas?

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• LINQ DefaultIfEmpty(), generating inferred argument error

  - by Refracted Paladin

  I am trying to get the below linq query to return -1 if there isn't any current value. I was looking at this article on MSDN, here, and it seemed that DefaultIfEmpty() was what I wanted. Unfortunately, I am getting a The type arguments cannot be inferred from the usage. Try specifying the type arguments explicitly. error. I guess I am not sure what that means or what it is telling me to do. Can someone explain, please. public static int CheckForDRIID(int personID) { using (var context = ConnectDataContext.Create()) { var masterIndex = (from applicationAssociation in context.tblApplicationAssociations where applicationAssociation.ApplicationID == 1 && applicationAssociation.PersonID == personID select applicationAssociation.PersonApplicationID).DefaultIfEmpty(-1).Single(); return Convert.ToInt32(masterIndex); } }

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• Group by/count in LINQ against SQL Compact 3.5 SP2

  - by bash74

  Hello, I am using LINQ-To-Entities in C# and run queries against a SQL Compact Server 3.5 SP2. What I try to achieve is a simple group by with an additional where clause which includes a Count(). var baseIdent="expression"; var found=from o in ObservedElements where o.ObservedRoots.BaseIdent==baseIdent group o by o.ID into grouped where grouped.Count()==1 select new {key=grouped.Key, val=grouped}; foreach(var res in found){ //do something here } This query throws the famous exception "A parameter is not allowed in this location. Ensure that the '@' sign and all other parameters are in a valid location in the SQL statement." When I either omit the where clause OR directly enter the expression "expression" in the query (where o.ObservedRoots.BaseIdent=="expression") everything just works fine. Does anybody know how to solve this? Workaround would also be fine? Thanks in advance, Sebastian

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