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• Translate LINQ to sql statement

  - by zielu1

  Hi, I want to translate LINQ expression tree to SQL statement and I don't want to write my own code for this. Example: var query = from c in Customers where c.Country == "UK" && c.City == "London" select c); To SELECT ... FROM Customers AS c WHERE c.Country = "UK" AND c.City = "London" I know DataContext.Log, but I want to use: query.ToSqlStatementString() Thanks

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• Order by descending based on condition

  - by Vinni

  Hello All, I want to write a LINQ to Entity query which does order by ascending or descending based on input parameter, Is there any way for that. Following is the my code. Please suggest. public List<Hosters_HostingProviderDetail> GetPendingApproval(SortOrder sortOrder) { List<Hosters_HostingProviderDetail> returnList = new List<Hosters_HostingProviderDetail>(); int pendingStateId = Convert.ToInt32(State.Pending); //If the sort order is ascending if (sortOrder == SortOrder.ASC) { var hosters = from e in context.Hosters_HostingProviderDetail where e.ActiveStatusID == pendingStateId orderby e.HostingProviderName ascending select e; returnList = hosters.ToList<Hosters_HostingProviderDetail>(); return returnList; } else { var hosters = from e in context.Hosters_HostingProviderDetail where e.StateID == pendingStateId orderby e.HostingProviderName descending select e; returnList = hosters.ToList<Hosters_HostingProviderDetail>(); return returnList; } }

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• Repository vs Data Access

  - by vdh_ant

  Hi guys In the context of the n-tier application, is there a difference between what you would consider your data access classes to be and your repositories? I tend to think yes but I just wanted to see what other thought. My thinking is that the job of the repository is just to contain and execute the raw query itself, where as the data access class would create the context, execute the repository (passing in the context), handle mapping the data model to the domain model and return the result back up... What do you guys think? Also do you see any of this changing in a Linq to XML scenario (assuming that you change the context for the relevant XDocument)? Cheers Anthony

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• Instantiate object from Linq to XML Query

  - by objectsbinding

  Hi All I have the following class public class CountrySpecificPIIEntity { public string Country { get; set; } public string CreditCardType { get; set; } public String Api { get; set; } public List<String> FilterList { get; set; } } I am trying to use a linq to XMl query to create a list of instances of type CountrySpecificPIIEntity. The XML is as below <piisettings> <country countrycode="DE"> <creditcardype credicardtype="mastercard"> <api api="INSERT_FILTERS"> <filters> <filter>FIRSTNAME</filter> <filter>HOUSENUMBER</filter> <filter>ADDITIONALADDRESSINFO</filter> <filter>EMAIL</filter> </filters> </api> </creditcardype> <creditcardype credicardtype="visa"> <api api="INSERT_FILTERS"> <filters> <filter>STATE</filter> <filter>EMAIL</filter> </filters> </api> </creditcardype> <creditcardype credicardtype="visa"> <api api="UPDATE_FILTERS"> <filters> <filter>STATE</filter> <filter>EMAIL</filter> </filters> </api> </creditcardype> </country> <country countrycode="GB"> <creditcardype credicardtype="americanexpress"> <api api="INSERT_FILTERS"> <filters> <filter>STREET</filter> <filter>ZIP</filter> <filter>CITY</filter> <filter>STATE</filter> <filter>EMAIL</filter> </filters> </api> </creditcardype> <creditcardype credicardtype="debank"> <api api="INSERT_FILTERS"> <filters> <filter>IPADDRESSCUSTOMER</filter> <filter>FIRSTNAME</filter> <filter>SURNAME</filter> <filter>HOUSENUMBER</filter> <filter>STREET</filter> <filter>ZIP</filter> <filter>CITY</filter> <filter>STATE</filter> <filter>EMAIL</filter> </filters> </api> </creditcardype> </country> </piisettings> what should the Linq to XML query be?

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• Why is the use of abstractions (such as LINQ) so taboo?

  - by Matthew Patrick Cashatt

  I am an independent contractor and, as such, I interview 3-4 times a year for new gigs. I am in the midst of that cycle now and got turned down for an opportunity even though I felt like the interview went well. The same thing has happened to me a couple of times this year. Now, I am not a perfect guy and I don't expect to be a good fit for every organization. That said, my batting average is lower than usual so I politely asked my last interviewer for some constructive feedback, and he delivered! The main thing, according to the interviewer, was that I seemed to lean too much towards the use of abstractions (such as LINQ) rather than towards lower-level, organically grown algorithms. On the surface, this makes sense--in fact, it made the other rejections make sense too because I blabbed about LINQ in those interviews as well and it didn't seem that the interviewers knew much about LINQ (even though they were .NET guys). So now I am left with this question: If we are supposed to be "standing on the shoulders of giants" and using abstractions that are available to us (like LINQ), then why do some folks consider it so taboo? Doesn't it make sense to pull code "off the shelf" if it accomplishes the same goals without extra cost? It would seem to me that LINQ, even if it is an abstraction, is simply an abstraction of all the same algorithms one would write to accomplish exactly the same end. Only a performance test could tell you if your custom approach was better, but if something like LINQ met the requirements, why bother writing your own classes in the first place? I don't mean to focus on LINQ here. I am sure that the JAVA world has something comparable, I just would like to know why some folks get so uncomfortable with the idea of using an abstraction that they themselves did not write. UPDATE As Euphoric pointed out, there isn't anything comparable to LINQ in the Java world. So, if you are developing on the .NET stack, why not always try and make use of it? Is it possible that people just don't fully understand what it does?

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• Are there any good resources for refactoring existing C# code to use LINQ while keeping your tests passing?

  - by Paddyslacker

  I've been teaching myself a little LINQ and an exercise I thought would be useful was to take my existing Project Euler C# code, which I built using Test Driven Development and gradually convert it to LINQ. I realise that LINQ is not always the best solution for all of the Project Euler problems, but I don't want to get into that here. I'm wondering whether or not it's feasible to refactor "traditional" OO C# code to use LINQ and functional programming syntax whilst keeping all of your tests passing. I can't find a way to make the tiny steps I'm used to making using TDD when converting to LINQ and this is a roadblock for me. I seem to have to make large changes to come up with a single function that I then replace whole chunks of my code with. I realise I could write this from scratch in LINQ, but in the real world, I'd like to be able to replace parts of my existing C# code to take advantage of LINQ where appropriate. Has anyone been successful with this approach? What resources did you find useful for refactoring existing C# code to use LINQ whilst taking a Test Driven Development approach?

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• Linq2sql code generator misbehaving

  - by Martin

  Sometime the linq2sql just makes its mind up about things. I've been pulling my hair for the past hours trying to work out what I'm doing differently from all the other times when I don't get ForeignKeyReferenceAlreadyHasValueException. Turns out that if (this._Activity.HasLoadedOrAssignedValue) { throw new System.Data.Linq.ForeignKeyReferenceAlreadyHasValueException(); } is present on my primary key in this particular table, and in no other. No matter what I do with the association, I've even tried deleting and dragging the thing back to the designer, it's still there and I'm sure it's not supposed to be. I know why, of course, but I don't know why, so to speak. A while back the association went the other way. Whereas I've left that era behind me, the code generator seems to exhibit phantom pains. The same phenomenon, is responsible for me having to change the namespace in the designer.cs everytime I make changes in the designer. I made the mistake of renaming my namespace and the code generator just doesn't get it. Somebody please help this poor boy out.

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• How to store a list in a column of a database table.

  - by John Berryman

  Howdy! So, per Mehrdad's answer to a related question, I get it that a "proper" database table column doesn't store a list. Rather, you should create another table that effectively holds the elements of said list and then link to it directly or through a junction table. However, the type of list I want to create will be composed of unique items (unlike the linked question's fruit example). Furthermore, the items in my list are explicitly sorted - which means that if I stored the elements in another table, I'd have to sort them every time I accessed them. Finally, the list is basically atomic in that any time I wish to access the list, I will want to access the entire list rather than just a piece of it - so it seems silly to have to issue a database query to gather together pieces of the list. AKX's solution (linked above) is to serialize the list and store it in a binary column. But this also seems inconvenient because it means that I have to worry about serialization and deserialization. Is there any better solution? If there is no better solution, then why? It seems that this problem should come up from time to time. ... just a little more info to let you know where I'm coming from. As soon as I had just begun understanding SQL and databases in general, I was turned on to LINQ to SQL, and so now I'm a little spoiled because I expect to deal with my programming object model without having to think about how the objects are queried or stored in the database. Thanks All! John

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• Is saving to database just to get an ID a bad hack?

  - by Narsil

  I hope the title is not too confusing. I am trying to make folders with linq-to-sql objects' IDs. Actually I have to create folders before I should save them. I will use them to keep user uploaded files. As you can see I have to create the folder with the FileID before I can save it there. So I just save a record which will be edited or maybe deleted File newFile = new File(); ...//add some values to fields so they don't throw rule violations db.AddFile(newFile); db.Save(); System.IO.Directory.CreateDirectory("..Uploads/"+newFile.FileId.ToString()); After that I will have to edit some fields and save again. Of course user might stop upload and I would have to delete it. I know I can write a stored procedure to get the next available FileID but some other upload happening at the same time would get the same number. So they would write in same directory which is a thing I don't want. Should I go on with this, would there be some problems? Can you think of a better way?

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• Passing in a lambda to a Where statement

  - by sonicblis

  I noticed today that if I do this: var items = context.items.Where(i => i.Property < 2); items = items.Where(i => i.Property > 4); Once I access the items var, it executes only the first line as the data call and then does the second call in memory. However, if I do this: var items = context.items.Where(i => i.Property < 2).Where(i => i.Property > 4); I get only one expression executed against the context that includes both where statements. I have a host of variables that I want to use to build the expression for the linq lambda, but their presence or absence changes the expression such that I'd have to have a rediculous number of conditionals to satisfy all cases. I thought I could just add the Where() statements as in my first example above, but that doesn't end up in a single expression that contains all of the criteria. Therefore, I'm trying to create just the lambda itself as such: //bogus syntax if (var1 == "something") var expression = Expression<Func<item, bool>>(i => i.Property == "Something); if (var2 == "somethingElse") expression = expression.Where(i => i.Property2 == "SomethingElse"); And then pass that in to the where of my context.Items to evaluate. A) is this right, and B) if so, how do you do it?

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• Nullable One To One Relationships with Integer Keys in LINQ-to-SQL

  - by Craig Walker

  I have two objects (Foo and Bar) that have a one-to-zero-or-one relationship between them. So, Foo has a nullable foreign key reference to Bar.ID and a (nullbusted) unique index to enforce the "1" side. Bar.ID is an int, and so Foo.BarID is a nullable int. The problem occurs in the LINQ-to-SQL DBML mapping of .NET types to SQL datatypes. Since int is not a nullable type in .NET, it gets wrapped in a Nullable<int>. However, this is not the same type as int, and so Visual Studio gives me this error message when I try to create the OneToOne Association between them: Cannot create an association "Bar_Foo". Properties do not have matching types: "ID", "BarID". Is there a way around this?

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• LINQ to read XML (C#)

  - by aximili

  I got this XML file <root> <level1 name="A"> <level2 name="A1" /> <level2 name="A2" /> </level1> <level1 name="B"> <level2 name="B1" /> <level2 name="B2" /> </level1> <level1 name="C" /> </root> Could someone give me a C# code using LINQ, the simplest way to print this result: (Note the extra space if it is a level2 node) A A1 A2 B B1 B2 C Currently I got this code XDocument xdoc = XDocument.Load("data.xml")); var lv1s = from lv1 in xdoc.Descendants("level1") select lv1.Attribute("name").Value; foreach (var lv1 in lv1s) { result.AppendLine(lv1); var lv2s = from lv2 in xdoc...??? } Thank you!

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• LinQ to objects GroupBy() by object and Sum() by amount

  - by Daniil Harik

  Hello, I have pretty simple case which I started solving using foreach(), but then I thought I could do It using Linq Basically I have IList that contains PaymentTransaction objects and there are 2 properties Dealer and Amount I want to GroupBy() by Dealer and Sum() bv amount. I tried to accomplish this using following code, but unfortunately it does not work var test = paymentTransactionDao.GetAll().GroupBy(x => x.Dealer).Sum(x => x.Amount); Want exactly I'm doing wrong here? I'm sorry if this question is too simple. Thank You

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• .DBML file and LINQ to SQL

  - by Rishabh Ohri

  In my DBML file I have mapped some tables and stored procedures, and the stored procedures return type is ISingleResult . T is some mapped table. But I want to take the data into my own created entities rather than LINQ to SQL created entites. The entites created by me are also the same as the mapped table entities and their use lies when we send data across the a web service. So , how can I proceed by creating a wrapper around the DBML file so that I always get data in my own created entites.

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• parse Linq To Xml with attribute nodes

  - by Manoj

  I am having xml with following structure <ruleDefinition appId="3" customerId = "acf"> <node alias="element1" id="1" name="department"> <node alias="element2" id="101" name="mike" /> <node alias="element2" id="102" name="ricky" /> <node alias="element2" id="103" name="jim" /> </node> </ruleDefinition> Here nodes are differentiated using alias and not with node tag. As you can see top level node element1 has same node name "node" as element2. I want to parse this XML based on attribute alias. What should be the Linq-To-Xml code (using C#)to acheive this?

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• Linq - How to query specific columns and return a lists

  - by Billy Logan

  Hello Everyone, I am trying to write a linq query that will only return certain columns from my entity object into a list object. Below is my code which produces an error(can't implicitly convert a generic list of anonymous types to a generic list of type TBLPROMOTION): List<TBLPROMOTION> promotionInfo = null; promotionInfo = (from p in matches orderby p.PROMOTION_NM descending select new { p.EFFECTIVE_DT, p.EXPIRE_DT, p.IS_ACTIVE, p.PROMOTION_DESC, p.PROMOTION_ID, p.PROMOTION_NM }).ToList(); What would be the best way to accomplish this. I do not want to do a "select p" in this case and return all the columns associated with the query. thanks in advance, Billy

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• In LINQ-SQL, wrap the DataContext is an using statement - pros cons

  - by hIpPy

  Can someone pitch in their opinion about pros/cons between wrapping the DataContext in an using statement or not in LINQ-SQL in terms of factors as performance, memory usage, ease of coding, right thing to do etc. Update: In one particular application, I experienced that, without wrapping the DataContext in using block, the amount of memory usage kept on increasing as the live objects were not released for GC. As in, in below example, if I hold the reference to List of q object and access entities of q, I create an object graph that is not released for GC. DataContext with using using (DBDataContext db = new DBDataContext()) { var q = from x in db.Tables where x.Id == someId select x; return q.toList(); } DataContext without using and kept alive DBDataContext db = new DBDataContext() var q = from x in db.Tables where x.Id == someId select x; return q.toList(); Thanks.

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• LINQ OrderBy: best search results at top of results list

  - by p.campbell

  Consider the need to search a list of Customer by both first and last names. The desire is to have the results list sorted by the Customer with the most matches in the search terms. FirstName LastName ---------- --------- Foo Laurie Bar Jackson Jackson Bro Laurie Foo Jackson Laurie string[] searchTerms = new string[] {"Jackson", "Laurie"}; //want to find those customers with first, last or BOTH names in the searchTerms var matchingCusts = Customers .Where(m => searchTerms.Contains(m.FirstName) || searchTerms.Contains(m.LastName)) .ToList(); /* Want to sort for those results with BOTH FirstName and LastName matching in the search terms. Those that match on both First and Last should be at the top of the results, the rest who match on one property should be below. */ return matchingCusts.OrderBy(m=>m); Desired Sort: Jackson Laurie (matches on both properties) Foo Laurie Bar Jackson Jackson Bro Laurie Foo How can I achieve this desired functionality with LINQ and OrderBy / OrderByDescending?

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• linq sort many 2 many question

  - by user169867

  My main entity is called [Contract]. Contract has a many 2 many relationship w/ [Service]. When I query for a list of Contracts I grab the 1st Service available like this: q.Select(c => new ContractSearchResult() { ContractID = c.ContractID, FirstService = c.Contract2Service.FirstOrDefault().Service.Name, ServiceCount = c.Contract2Service.Count, } ).ToList(); q is an IQueryable that has some filtering & paging already applied. (When I display this list I show the FirstService if there's only 1. If 1 I show "My1stService (3)" to show I'm seeing the 1st of 3 services) This works fine. My question is this: Is there any way to sort by FirstService? Or is this impossible? I haven't found a way of expressing this in linq. Any help would be appreciated.

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• Linq query - multiple where, with extension method

  - by Cj Anderson

  My code works for ORs as I've listed it below but I want to use AND instead of OR and it fails. I'm not quite sure what I'm doing wrong. Basically I have a Linq query that searches on multiple fields in an XML file. The search fields might not all have information. Each element runs the extension method, and tests the equality. Any advice would be appreciated. refinedresult = From x In theresult _ Where x.<thelastname>.Value.TestPhoneElement(LastName) Or _ x.<thefirstname>.Value.TestPhoneElement(FirstName) Or _ x.<id>.Value.TestPhoneElement(Id) Or _ x.<number>.Value.TestPhoneElement(Telephone) Or _ x.<location>.Value.TestPhoneElement(Location) Or _ x.<building>.Value.TestPhoneElement(building) Or _ x.<department>.Value.TestPhoneElement(Department) _ Select x Public Function TestPhoneElement(ByVal parent As String, ByVal value2compare As String) As Boolean 'find out if a value is null, if not then compare the passed value to see if it starts with Dim ret As Boolean = False If String.IsNullOrEmpty(parent) Then Return False End If If String.IsNullOrEmpty(value2compare) Then Return ret Else ret = parent.ToLower.StartsWith(value2compare.ToLower.Trim) End If Return ret End Function

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• LINQ to SQL vs Entity Framework for an app with a future SQL Azure version

  - by Craig L

  I've got a vertical market Dot Net Framework 1.1 C#/WinForms/SQL Server 2000 application. Currently it uses ADO.Net and Microsoft's SQLHelper for CRUD operations. I've successfully converted it to Dot Net Framework 4 C#/WinForms/ SQL Server 2008. What I'd like to do is also offer my customers the ability to use SQL Azure as a backend storage for their data instead of local/LAN SQL Server. If I know SQL Azure is in my application's future, should I: A. Switch to LINQ to SQL B. Swith to Entity Framework C. Stick with ADO.Net and SQLHelper Thanks !

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• Compile error when calling ToList() when accessing many to many with Linq To Entities

  - by KallDrexx

  I can't figure out what I am doing wrong. I have the following method: public IList<WObject> GetRelationshipMembers(int relId) { var members = from r in _container.ObjectRelationships where r.Id == relId select r.WObjects; return members.ToList<WObject>(); } This returns the following error: Instance argument: cannot convert from 'System.Linq.IQueryable<System.Data.Objects.DataClasses.EntityCollection<Project.DomainModel.Entities.WObject>>' to 'System.Collections.Generic.IEnumerable<Project.DomainModel.Entities.WObject>' How can I convert the EntityCollection to a list without lazy loading?

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• How to do a STAR search in LINQ

  - by aNui

  I'm not sure about clarity of the STAR word. I'm implementing a search method using linq-to-object in c#. And I want to do a search with * (star) operator like most of search apps or web can do. e.g. If I typed "p*", results should be everything starting with "p". And it should work for prefix star, suffix star or star in the middle. And it would be great if the search can do with "-" (minus/NOT) operator or "+" (plus/OR) operator or "AND" operator Thanks in advance.

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• Dynamic Linq Library Help

  - by Alon

  Hi, I have the following class: public class Item { public Dictionary<string, string> Data { get; set; } } and a list of it: List<Item> items; I need to filter and order this list dynamicly using SQL-Like strings. The catch is, that I need to order it by the Data dictionary. For example: Order By Data["lastname"] or Where Data["Name"].StartsWith("a"). I thought to use the dynamic linq library, but is there any way that my clients can write without the Data[]? For example: Name.StartsWith("abc") instead of Data["Name"].StartsWith("abc") ? Thank you.

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• Using LINQ to find a common prefix?

  - by Roger Lipscombe

  I've got two sequences: IEnumerable<string> x = new[] { "a", "b", "c" }; IEnumerable<string> y = new[] { "a", "b", "d", "e" }; I'd like to find the common prefix of these two sequences (i.e. "a", "b"). Is there a succinct way to do this in LINQ? Bear in mind that these aren't really IEnumerable<string>; they're IEnumerable<PathComponent>, where I have an implementation of IEqualityComparer<PathComponent>.

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