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  • Using transactions with LINQ-to-SQL

    - by Jalpesh P. Vadgama
    Today one of my colleague asked that how we can use transactions with the LINQ-to-SQL Classes when we use more then one entities updated at same time. It was a good question. Here is my answer for that.For ASP.NET 2.0  or higher version have a new class called TransactionScope which can be used to manage transaction with the LINQ. Let’s take a simple scenario we are having a shopping cart application in which we are storing details or particular order placed into the database using LINQ-to-SQL. There are two tables Order and OrderDetails which will have all the information related to order. Order will store particular information about orders while OrderDetails table will have product and quantity of product for particular order.We need to insert data in both tables as same time and if any errors comes then it should rollback the transaction. To use TransactionScope in above scenario first we have add a reference to System.Transactions like below. After adding the transaction we need to drag and drop the Order and Order Details tables into Linq-To-SQL Classes it will create entities for that. Below is the code for transaction scope to use mange transaction with Linq Context. MyContextDataContext objContext = new MyContextDataContext(); using (System.Transactions.TransactionScope tScope = new System.Transactions.TransactionScope(TransactionScopeOption.Required)) { objContext.Order.InsertOnSubmit(Order); objContext.OrderDetails.InsertOnSumbit(OrderDetails); objContext.SubmitChanges(); tScope.Complete(); } Here it will commit transaction only if using blocks will run successfully. Hope this will help you. Technorati Tags: Linq,Transaction,System.Transactions,ASP.NET

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  • use Data Annotation to my Linq to SQL

    - by Khalid Omar
    i have a mvc web project and i'm using linq to sql i'm using dataannotaion like this public class ClientValidation { [Required] public string name1st { get; set; } } then in the linq class i add that above client class [global::System.Data.Linq.Mapping.TableAttribute(Name = "dbo.Client")] [MetadataType(typeof(ClientValidation))] public partial class Client : INotifyPropertyChanging, INotifyPropertyChanged { } every thing is going ok the question is when i re generate the linq when i add table or change any thing in database i need to rewrite [MetadataType(typeof(ClientValidation))] is there any other method to enable me regenerate the model and keep the data annotation as it

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  • how to use a generated dbml classes to deserialize xml via linq?

    - by Eelco Meuter
    Hi, I have a complex data structure, which I boiled down in a dbml file with one class and 6 one-to-many relations. This data must also be read via xml. The xml structure is something like: <table id=1> <column 1></column 1> <column n></column n> <m-n table x> <column 1></column 1> </m-n table x> </table> where the tag <m-n table x> is one of the six related tables. The idea is to generate an xsd based upon the dbml, which I can use to create and validate a xml. This xml can hopefully deserialized into the dbml classes. The question is: Can this be done? If so, how do I generate the xsd. I use a sql server express 2008 r2 as backend. Thanks in advance for your time!

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  • Transactions in LINQ to SQL applications

    - by nikolaosk
    In this post I would like to talk about LINQ to SQL and transactions.When I have a LINQ to SQL class I always get asked this question, "How does LINQ treat Transactions?". When we use the DeleteOnSubmit() method or the InsertOnSubmit() method, all of those commands at some point are translated into T-SQL commands and then are executed against the database. All of those commands live in transactions and they follow the basic rules of transaction processing. They do succeed together or fail together...(read more)

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  • Parallel LINQ - PLINQ

    - by nmarun
    Turns out now with .net 4.0 we can run a query like a multi-threaded application. Say you want to query a collection of objects and return only those that meet certain conditions. Until now, we basically had one ‘control’ that iterated over all the objects in the collection, checked the condition on each object and returned if it passed. We obviously agree that if we can ‘break’ this task into smaller ones, assign each task to a different ‘control’ and ask all the controls to do their job - in-parallel, the time taken the finish the entire task will be much lower. Welcome to PLINQ. Let’s take some examples. I have the following method that uses our good ol’ LINQ. 1: private static void Linq(int lowerLimit, int upperLimit) 2: { 3: // populate an array with int values from lowerLimit to the upperLimit 4: var source = Enumerable.Range(lowerLimit, upperLimit); 5:  6: // Start a timer 7: Stopwatch stopwatch = new Stopwatch(); 8: stopwatch.Start(); 9:  10: // set the expectation => build the expression tree 11: var evenNumbers =   from num in source 12: where IsDivisibleBy(num, 2) 13: select num; 14: 15: // iterate over and print the returned items 16: foreach (var number in evenNumbers) 17: { 18: Console.WriteLine(string.Format("** {0}", number)); 19: } 20:  21: stopwatch.Stop(); 22:  23: // check the metrics 24: Console.WriteLine(String.Format("Elapsed {0}ms", stopwatch.ElapsedMilliseconds)); 25: } I’ve added comments for the major steps, but the only thing I want to talk about here is the IsDivisibleBy() method. I know I could have just included the logic directly in the where clause. I called a method to add ‘delay’ to the execution of the query - to simulate a loooooooooong operation (will be easier to compare the results). 1: private static bool IsDivisibleBy(int number, int divisor) 2: { 3: // iterate over some database query 4: // to add time to the execution of this method; 5: // the TableB has around 10 records 6: for (int i = 0; i < 10; i++) 7: { 8: DataClasses1DataContext dataContext = new DataClasses1DataContext(); 9: var query = from b in dataContext.TableBs select b; 10: 11: foreach (var row in query) 12: { 13: // Do NOTHING (wish my job was like this) 14: } 15: } 16:  17: return number % divisor == 0; 18: } Now, let’s look at how to modify this to PLINQ. 1: private static void Plinq(int lowerLimit, int upperLimit) 2: { 3: // populate an array with int values from lowerLimit to the upperLimit 4: var source = Enumerable.Range(lowerLimit, upperLimit); 5:  6: // Start a timer 7: Stopwatch stopwatch = new Stopwatch(); 8: stopwatch.Start(); 9:  10: // set the expectation => build the expression tree 11: var evenNumbers = from num in source.AsParallel() 12: where IsDivisibleBy(num, 2) 13: select num; 14:  15: // iterate over and print the returned items 16: foreach (var number in evenNumbers) 17: { 18: Console.WriteLine(string.Format("** {0}", number)); 19: } 20:  21: stopwatch.Stop(); 22:  23: // check the metrics 24: Console.WriteLine(String.Format("Elapsed {0}ms", stopwatch.ElapsedMilliseconds)); 25: } That’s it, this is now in PLINQ format. Oh and if you haven’t found the difference, look line 11 a little more closely. You’ll see an extension method ‘AsParallel()’ added to the ‘source’ variable. Couldn’t be more simpler right? So this is going to improve the performance for us. Let’s test it. So in my Main method of the Console application that I’m working on, I make a call to both. 1: static void Main(string[] args) 2: { 3: // set lower and upper limits 4: int lowerLimit = 1; 5: int upperLimit = 20; 6: // call the methods 7: Console.WriteLine("Calling Linq() method"); 8: Linq(lowerLimit, upperLimit); 9: 10: Console.WriteLine(); 11: Console.WriteLine("Calling Plinq() method"); 12: Plinq(lowerLimit, upperLimit); 13:  14: Console.ReadLine(); // just so I get enough time to read the output 15: } YMMV, but here are the results that I got:    It’s quite obvious from the above results that the Plinq() method is taking considerably less time than the Linq() version. I’m sure you’ve already noticed that the output of the Plinq() method is not in order. That’s because, each of the ‘control’s we sent to fetch the results, reported with values as and when they obtained them. This is something about parallel LINQ that one needs to remember – the collection cannot be guaranteed to be undisturbed. This could be counted as a negative about PLINQ (emphasize ‘could’). Nevertheless, if we want the collection to be sorted, we can use a SortedSet (.net 4.0) or build our own custom ‘sorter’. Either way we go, there’s a good chance we’ll end up with a better performance using PLINQ. And there’s another negative of PLINQ (depending on how you see it). This is regarding the CPU cycles. See the usage for Linq() method (used ResourceMonitor): I have dual CPU’s and see the height of the peak in the bottom two blocks and now compare to what happens when I run the Plinq() method. The difference is obvious. Higher usage, but for a shorter duration (width of the peak). Both these points make sense in both cases. Linq() runs for a longer time, but uses less resources whereas Plinq() runs for a shorter time and consumes more resources. Even after knowing all these, I’m still inclined towards PLINQ. PLINQ rocks! (no hard feelings LINQ)

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  • Retrieving data using stored procedures with LINQ to SQL in an ASP.Net application

    - by nikolaosk
    In this post I would like to present a step by step example on how to use stored procedures with LINQ to SQL. Many people will wonder why I am bothering talking about LINQ to SQL so much. First of all I give a lot of seminars where people want to learn LINQ to SQL.A lot of people like and use LINQ to SQL in their projects. There are a lot of people right now who use it extensively. In this post I will use two stored procedures that return data from the database. If you want to check out how to use...(read more)

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  • Select,Insert,Update and Delete data with LINQ to SQL in an ASP.Net application

    - by nikolaosk
    As you might have guessed I am continuing my LINQ to SQL posts. I am teaching a course right now on ADO.Net 3.5 (LINQ & EF) and I know a lot of people who have learned through my blog and my style of writing. I am going to use a step by step example to demonstrate how to select,update,insert,delete data through LINQ to SQL into the database. If you want to have a look on how to return data from a database with LINQ to SQL and stored procedures click here . If you want to have a look on how to...(read more)

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  • Compiled Linq & String.Contains

    - by sharru
    i'm using linq-to-sql and i'm use complied linq for better performance. I have a users table with a INT field called "LookingFor" that can have the following values.1,2,3,12,123,13,23. I wrote a query to return the users based on the "lookingFor" column i want to return all users that contains the "lookingFor" value (not only those equal to it). In example if user.LookingFor = 12 , and query paramter is 1 this user should be selected. private static Func<NeDataContext, int, IQueryable<int>> MainSearchQuery = CompiledQuery.Compile((NeDataContext db, int lookingFor) => (from u in db.Users where (lookingFor == -1 ? true : u.LookingFor.ToString().Contains(lookingFor) select u.username); This WORKS on non complied linq but throws error when using complied. How do i fix it to work using complied linq? I get this error: Only arguments that can be evaluated on the client are supported for the String.Contains method.

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  • MVC using LINQ? - Can't return anonymous types

    - by BlueRaja
    I'd like to implement MVC while using LINQ (specifically, LINQ-to-entities). The way I would do this is have the Controller generate (or call something which generates) the result-set using LINQ, then return that to the View to display the data. The problem is, if I do: return (from o in myTable select o); All the columns are read from the database, even the ones (potentially dozens) I don't want. And - more importantly - I can't do something like this: return (from o in myTable select new { o.column }); because there is no way to make anonymous types type-safe! I know for sure there is no nice, clean way of doing this in 3.5 (this is not clean...), but what about 4.0? Is there anything planned, or even proposed? Without something like duck-typing-for-LINQ, or type-safe anonymous return values (it seems to me the compiler should certainly be capable of that), it appears to be nearly impossible to cleanly separate the Controller from the View.

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  • Is it possible to compile a query in linq-to-objects

    - by Luke101
    I have a linq to objects query in a recursive loop and afraid when the objects approach more then 1000 and a have more then 100 users on the site -- my website will break. so is it possible to compile a linq to objects query. The linq query does nothing more then find the direct children of a node.

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  • Is it possible to compile a query for linq-to-objects

    - by Luke101
    I have a linq to objects query in a recursive loop and afraid when the objects approach more then 1000 and a have more then 100 users on the site -- my website will break. so is it possible to compile a linq to objects query. The linq query does nothing more then find the direct children of a node.

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  • Add LINQ Auto-Generated Value Marker [Column(IsDbGenerated=true)] in Buddy Class

    - by Alex
    Hello, is it possible to decorate a field of a LINQ generated class with [Column(IsDbGenerated=true)] using a buddy class (which is linked to the LINQ class via [MetadataType(typeof(BuddyMetadata))]) ? My goal is to be able to clear and repopulate the LINQ ORM designer without having to set the "Auto Generate Value" property manually every time to re-establish the fact that certain columns are autogenerated. Thanks!

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  • LINQ-to-SQL vs stored procedures?

    - by scottmarlowe
    I took a look at the "Beginner's Guide to LINQ" post here on StackOverflow (http://stackoverflow.com/questions/8050/beginners-guide-to-linq), but had a follow-up question: We're about to ramp up a new project where nearly all of our database op's will be fairly simple data retrievals (there's another segment of the project which already writes the data). Most of our other projects up to this point make use of stored procedures for such things. However, I'd like to leverage LINQ-to-SQL if it makes more sense. So, the question is this: For simple data retrievals, which approach is better, LINQ-to-SQL or stored procs? Any specific pro's or con's? Thanks.

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  • LINQ-to-SQL vs stored procedures?

    - by scottmarlowe
    I took a look at the "Beginner's Guide to LINQ" post here on StackOverflow (http://stackoverflow.com/questions/8050/beginners-guide-to-linq), but had a follow-up question: We're about to ramp up a new project where nearly all of our database op's will be fairly simple data retrievals (there's another segment of the project which already writes the data). Most of our other projects up to this point make use of stored procedures for such things. However, I'd like to leverage LINQ-to-SQL if it makes more sense. So, the question is this: For simple data retrievals, which approach is better, LINQ-to-SQL or stored procs? Any specific pro's or con's? Thanks.

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  • Performing LINQ Self Join

    - by senfo
    I'm not getting the results I want for a query I'm writing in LINQ using the following: var config = (from ic in repository.Fetch() join oc in repository.Fetch() on ic.Slot equals oc.Slot where ic.Description == "Input" && oc.Description == "Output" select new Config { InputOid = ic.Oid, OutputOid = oc.Oid }).Distinct(); The following SQL returns 53 rows (which is correct), but the above LINQ returns 96 rows: SELECT DISTINCT ic.Oid AS InputOid, oc.Oid AS OutputOid FROM dbo.Config AS ic INNER JOIN dbo.Config AS oc ON ic.Slot = oc.Slot WHERE ic.Description = 'Input' AND oc.Description = 'Output' How would I replicate the above SQL in a LINQ query? Update: I don't think it matters, but I'm working with LINQ to Entities 4.0.

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  • Can a loosely typed language be considered true object oriented?

    - by user61852
    Can a loosely typed programming language like PHP be really considered object oriented? I mean, the methods don't have returning types and method parameters has no declared type either. Doesn't class design require methods to have a return type? Don't methods signatures have specifically-typed parameters? How can OOP techniques help you code in PHP if you always have to check the types of parameters received because the language doesn't enforce types? Please, if I'm wrong, explain it to me. When you design things using UML, then code classes in PHP with no return-typed methods and no-type parameters... Is the code really compliant with the UML design? You spend time designing the architecture of your software, then the compiler doesn't force the programmer to follow your design while coding, letting he/she assign any object variable to any other variable with no "type-mismatch" warning.

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  • Filtering data in LINQ with the help of where clause

    - by vik20000in
     LINQ has bought with itself a super power of querying Objects, Database, XML, SharePoint and nearly any other data structure. The power of LINQ lies in the fact that it is managed code that lets you write SQL type code to fetch data.  Whenever working with data we always need a way to filter out the data based on different condition. In this post we will look at some of the different ways in which we can filter data in LINQ with the help of where clause. Simple Filter for an array. Let’s say we have an array of number and we want to filter out data based on some condition. Below is an example int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var lowNums =                 from num in numbers                 where num < 5                 select num;   Filter based on one of the property in the class. With the help of LINQ we can also filer out data from a list based on value of some property. var soldOutProducts =                 from prod in products                 where prod.UnitsInStock == 0                 select prod; Filter based on Multiple of the property in the class. var expensiveInStockProducts =         from prod in products         where prod.UnitsInStock > 0 && prod.UnitPrice > 3.00M         select prod; Filter based on the index of the Item in the list.In the below example we can see that we are able to filter data based on the index of the item in the list. string[] digits = { "zero", "one", "two", "three", "four", "five", "six"}; var shortDigits = digits.Where((digit, index) => digit.Length < index); There are many other way in which we can filter out data in LINQ. In the above post I have tried and shown few ways using the LINQ. Vikram

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  • LINQ aggregate left join on SQL CE

    - by P Daddy
    What I need is such a simple, easy query, it blows me away how much work I've done just trying to do it in LINQ. In T-SQL, it would be: SELECT I.InvoiceID, I.CustomerID, I.Amount AS AmountInvoiced, I.Date AS InvoiceDate, ISNULL(SUM(P.Amount), 0) AS AmountPaid, I.Amount - ISNULL(SUM(P.Amount), 0) AS AmountDue FROM Invoices I LEFT JOIN Payments P ON I.InvoiceID = P.InvoiceID WHERE I.Date between @start and @end GROUP BY I.InvoiceID, I.CustomerID, I.Amount, I.Date ORDER BY AmountDue DESC The best equivalent LINQ expression I've come up with, took me much longer to do: var invoices = ( from I in Invoices where I.Date >= start && I.Date <= end join P in Payments on I.InvoiceID equals P.InvoiceID into payments select new{ I.InvoiceID, I.CustomerID, AmountInvoiced = I.Amount, InvoiceDate = I.Date, AmountPaid = ((decimal?)payments.Select(P=>P.Amount).Sum()).GetValueOrDefault(), AmountDue = I.Amount - ((decimal?)payments.Select(P=>P.Amount).Sum()).GetValueOrDefault() } ).OrderByDescending(row=>row.AmountDue); This gets an equivalent result set when run against SQL Server. Using a SQL CE database, however, changes things. The T-SQL stays almost the same. I only have to change ISNULL to COALESCE. Using the same LINQ expression, however, results in an error: There was an error parsing the query. [ Token line number = 4, Token line offset = 9,Token in error = SELECT ] So we look at the generated SQL code: SELECT [t3].[InvoiceID], [t3].[CustomerID], [t3].[Amount] AS [AmountInvoiced], [t3].[Date] AS [InvoiceDate], [t3].[value] AS [AmountPaid], [t3].[value2] AS [AmountDue] FROM ( SELECT [t0].[InvoiceID], [t0].[CustomerID], [t0].[Amount], [t0].[Date], COALESCE(( SELECT SUM([t1].[Amount]) FROM [Payments] AS [t1] WHERE [t0].[InvoiceID] = [t1].[InvoiceID] ),0) AS [value], [t0].[Amount] - (COALESCE(( SELECT SUM([t2].[Amount]) FROM [Payments] AS [t2] WHERE [t0].[InvoiceID] = [t2].[InvoiceID] ),0)) AS [value2] FROM [Invoices] AS [t0] ) AS [t3] WHERE ([t3].[Date] >= @p0) AND ([t3].[Date] <= @p1) ORDER BY [t3].[value2] DESC Ugh! Okay, so it's ugly and inefficient when run against SQL Server, but we're not supposed to care, since it's supposed to be quicker to write, and the performance difference shouldn't be that large. But it just doesn't work against SQL CE, which apparently doesn't support subqueries within the SELECT list. In fact, I've tried several different left join queries in LINQ, and they all seem to have the same problem. Even: from I in Invoices join P in Payments on I.InvoiceID equals P.InvoiceID into payments select new{I, payments} generates: SELECT [t0].[InvoiceID], [t0].[CustomerID], [t0].[Amount], [t0].[Date], [t1].[InvoiceID] AS [InvoiceID2], [t1].[Amount] AS [Amount2], [t1].[Date] AS [Date2], ( SELECT COUNT(*) FROM [Payments] AS [t2] WHERE [t0].[InvoiceID] = [t2].[InvoiceID] ) AS [value] FROM [Invoices] AS [t0] LEFT OUTER JOIN [Payments] AS [t1] ON [t0].[InvoiceID] = [t1].[InvoiceID] ORDER BY [t0].[InvoiceID] which also results in the error: There was an error parsing the query. [ Token line number = 2, Token line offset = 5,Token in error = SELECT ] So how can I do a simple left join on a SQL CE database using LINQ? Am I wasting my time?

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  • whats wrong in this LINQ synatx?

    - by Saurabh Kumar
    Hi, I am trying to convert a SQL query to LINQ. Somehow my count(distinct(x)) logic does not seem to be working correctly. The original SQL is quite efficient(or so i think), but the generated SQL is not even returning the correct result. I am trying to fix this LINQ to do what the original SQL is doing, AND in an efficient way as the original query is doing. Help here would be really apreciated as I am stuck here :( SQL which is working and I need to make a comparable LINQ of: SELECT [t1].[PersonID] AS [personid] FROM [dbo].[Code] AS [t0] INNER JOIN [dbo].[phonenumbers] AS [t1] ON [t1].[PhoneCode] = [t0].[Code] INNER JOIN [dbo].[person] ON [t1].[PersonID]= [dbo].[Person].PersonID WHERE ([t0].[codetype] = 'phone') AND ( ([t0].[CodeDescription] = 'Home') AND ([t1].[PhoneNum] = '111') OR ([t0].[CodeDescription] = 'Work') AND ([t1].[PhoneNum] = '222') ) GROUP BY [t1].[PersonID] HAVING COUNT(DISTINCT([t1].[PhoneNum]))=2 The LINQ which I made is approximately as below: var ids = context.Code.Where(predicate); var rs = from r in ids group r by new { r.phonenumbers.person.PersonID} into g let matchcount=g.Select(p => p.phonenumbers.PhoneNum).Distinct().Count() where matchcount ==2 select new { personid = g.Key }; Unfortunately, the above LINQ is NOT generating the correct result, and is actually internally getting generated to the SQL shown below. By the way, this generated query is also reading ALL the rows(about 19592040) around 2 times due to the COUNTS :( Wich is a big performance issue too. Please help/point me to the right direction. Declare @p0 VarChar(10)='phone' Declare @p1 VarChar(10)='Home' Declare @p2 VarChar(10)='111' Declare @p3 VarChar(10)='Work' Declare @p4 VarChar(10)='222' Declare @p5 VarChar(10)='2' SELECT [t9].[PersonID], ( SELECT COUNT(*) FROM ( SELECT DISTINCT [t13].[PhoneNum] FROM [dbo].[Code] AS [t10] INNER JOIN [dbo].[phonenumbers] AS [t11] ON [t11].[PhoneType] = [t10].[Code] INNER JOIN [dbo].[Person] AS [t12] ON [t12].[PersonID] = [t11].[PersonID] INNER JOIN [dbo].[phonenumbers] AS [t13] ON [t13].[PhoneType] = [t10].[Code] WHERE ([t9].[PersonID] = [t12].[PersonID]) AND ([t10].[codetype] = @p0) AND ((([t10].[codetype] = @p1) AND ([t11].[PhoneNum] = @p2)) OR (([t10].[codetype] = @p3) AND ([t11].[PhoneNum] = @p4))) ) AS [t14] ) AS [cnt] FROM ( SELECT [t3].[PersonID], ( SELECT COUNT(*) FROM ( SELECT DISTINCT [t7].[PhoneNum] FROM [dbo].[Code] AS [t4] INNER JOIN [dbo].[phonenumbers] AS [t5] ON [t5].[PhoneType] = [t4].[Code] INNER JOIN [dbo].[Person] AS [t6] ON [t6].[PersonID] = [t5].[PersonID] INNER JOIN [dbo].[phonenumbers] AS [t7] ON [t7].[PhoneType] = [t4].[Code] WHERE ([t3].[PersonID] = [t6].[PersonID]) AND ([t4].[codetype] = @p0) AND ((([t4].[codetype] = @p1) AND ([t5].[PhoneNum] = @p2)) OR (([t4].[codetype] = @p3) AND ([t5].[PhoneNum] = @p4))) ) AS [t8] ) AS [value] FROM ( SELECT [t2].[PersonID] FROM [dbo].[Code] AS [t0] INNER JOIN [dbo].[phonenumbers] AS [t1] ON [t1].[PhoneType] = [t0].[Code] INNER JOIN [dbo].[Person] AS [t2] ON [t2].[PersonID] = [t1].[PersonID] WHERE ([t0].[codetype] = @p0) AND ((([t0].[codetype] = @p1) AND ([t1].[PhoneNum] = @p2)) OR (([t0].[codetype] = @p3) AND ([t1].[PhoneNum] = @p4))) GROUP BY [t2].[PersonID] ) AS [t3] ) AS [t9] WHERE [t9].[value] = @p5 Thanks!

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  • LINQ to SQL - Tracking New / Dirty Objects

    - by Joseph Sturtevant
    Is there a way to determine if a LINQ object has not yet been inserted in the database (new) or has been changed since the last update (dirty)? I plan on binding my UI to LINQ objects (using WPF) and need it to behave differently depending whether or not the object is already in the database. MyDataContext context = new MyDataContext(); MyObject obj; if (new Random().NextDouble() > .5) obj = new MyObject(); else obj = context.MyObjects.First(); // How can I distinguish these two cases? The only simple solution I can think of is to set the primary key of new records to a negative value (my PKs are an identity field and will therefore be set to a positive integer on INSERT). This will only work for detecting new records. It also requires identity PKs, and requires control of the code creating the new object. Is there a better way to do this? It seems like LINQ must be internally tracking the status of these objects so that it can know what to do on context.SubmitChanges(). Is there some way to access that "object status"? Clarification Apparently my initial question was confusing. I'm not looking for a way to insert or update records. I'm looking for a way, given any LINQ object, to determine if that object has not been inserted (new) or has been changed since its last update (dirty).

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  • Castle ActiveRecord / NHibernate Linq Querys with ValueTypes

    - by Thomas Schreiner
    Given the following code for our Active Record Entites and ValueTypes Linq is not working for us. [ActiveRecord("Person")] public class PersonEntity : ActiveRecordLinqBase<PersonEntity> { string _name; [Property("Name", Length = 20, ColumnType = "string", Access = PropertyAccess.FieldCamelcaseUnderscore)] public Name Name { get { return NameValue.Create(_name);} set { _name = value.DataBaseValue; } } ... } public abstract class Name : IValueType { string DataBaseValue {get;set;} ... } public class Namevalue : Name { string _name; private NameValue(string name) { _name = name; } public static NameValue Create(string name) { return new NameValue(name); } ... } We tried to use linq in the following way so far with no success: var result = from PersonEntity p in PersonEntity.Queryable where p.Name == "Thomas" select p; return result.First(); // throws exception Cannot convert string into Name We tried and implemented a TypeConverter for Name, but the converter never got called. Is there a way to have linq working with this ValueTypes? Update: Using NHibernate.UserTypes.IUserType it sortof works. I Implemented the Interface as described here: http://stackoverflow.com/questions/1565056/how-to-implement-correctly-iusertype I still had to add a ConversionOperator from string to Name and had to call it Explicitly in the linq Statement, even though it was defined as implicit. var result = from PersonEntity p in PersonEntity.Queryable where p.Name == (Name)"Thomas" select p; return result.First(); //Now works

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  • I do I iterate the records in a database using LINQ when I have already built the LINQ DB code?

    - by Seth Spearman
    I asked on SO a few days ago what was the simplest quickest way to build a wrapper around a recently completed database. I took the advice and used sqlmetal to build linq classes around my database design. Now I am having two problems. One, I don't know LINQ. And, two, I have been shocked to realize how hard it is to learn. I have a book on LINQ (Linq In Action by Manning) and it has helped some but at the end of the day it is going to take me a couple of weeks to get traction and I need to make some progress on my project today. So, I am looking for some help getting started. Click HERE To see my simple database schema. Click HERE to see the vb class that was generated for the schema. My needs are simple. I have a console app. The main table is the SupplyModel table. Most of the other tables are child tables of the SupplyModel table. I want to iterate through each of Supply Model records. I want to grab the data for a supply model and then DoStuff with the data. And I also need to iterate through the child records, for each supply model, for example the NumberedInventories and DoStuff with that as well. I want to only iterate the SupplyModels that are have IDs that are in an array of strings containing the IDs. I need help doing this in VB rather than C# if possible. Thanks for your help. Seth

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  • Converting a Linq expression tree that relies on SqlMethods.Like() for use with the Entity Framework

    - by JohnnyO
    I recently switched from using Linq to Sql to the Entity Framework. One of the things that I've been really struggling with is getting a general purpose IQueryable extension method that was built for Linq to Sql to work with the Entity Framework. This extension method has a dependency on the Like() method of SqlMethods, which is Linq to Sql specific. What I really like about this extension method is that it allows me to dynamically construct a Sql Like statement on any object at runtime, by simply passing in a property name (as string) and a query clause (also as string). Such an extension method is very convenient for using grids like flexigrid or jqgrid. Here is the Linq to Sql version (taken from this tutorial: http://www.codeproject.com/KB/aspnet/MVCFlexigrid.aspx): public static IQueryable<T> Like<T>(this IQueryable<T> source, string propertyName, string keyword) { var type = typeof(T); var property = type.GetProperty(propertyName); var parameter = Expression.Parameter(type, "p"); var propertyAccess = Expression.MakeMemberAccess(parameter, property); var constant = Expression.Constant("%" + keyword + "%"); var like = typeof(SqlMethods).GetMethod("Like", new Type[] { typeof(string), typeof(string) }); MethodCallExpression methodExp = Expression.Call(null, like, propertyAccess, constant); Expression<Func<T, bool>> lambda = Expression.Lambda<Func<T, bool>>(methodExp, parameter); return source.Where(lambda); } With this extension method, I can simply do the following: someList.Like("FirstName", "mike"); or anotherList.Like("ProductName", "widget"); Is there an equivalent way to do this with Entity Framework? Thanks in advance.

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  • Simpler Linq to XML queries with the DLR

    - by Xavier
    Hi folks, I have a question regarding Linq to XML queries and how we could possibly make them more readable using the new dynamic keyword. At the moment I am writing things like: var result = from p in xdoc.Elements("product") where p.Attribute("type").Value == "Services" select new { ... } What I would like to write is something like: var result = from p in xdoc.Products where p.Type == "Services" select new { ... } I know I can do this with Linq to XSD which is pretty good already, but obviously this requires an XSD schema and I don't always have one. I am sure there should be a way to achieve this using the new dynamic features of .NET 4.0 but I'm not sure how or if anyone already had a go at this. Obviously I would loose some of the advantages of Linq to XSD (typed members and compile time checks) but it wouldn't be worse than the original solution and would certainly be more readable. Anyone has an idea? Thanks

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  • Need to debug LINQ simple queries in Visual Studio 2010

    - by maxima120
    I often get in a position when I need to know why my LINQ doesnt work as intended... I use object collections and extensions. I dont want spend more than couple of minutes on it. LINQ supposed to make developer's life easier not harder. I hoped VS 2010 will have it fixed but I now use RC and it still doesnt let me type LINQ and check what is going on... Says as before "Expression cannot contain lambda expressions"... Is there some add-on for Visual Studio so I can quickly and effectively run ad-hoc queries and find out what is going on and where I am wrong?

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