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  • The Ultimate Tar Command Tutorial with 10 Practical Examples

    <b>The Geek Stuff:</b> "In this article, let us review various tar examples including how to create tar archives (with gzip and bzip compression), extract a single file or directory, view tar archive contents, validate the integrity of tar archives, finding out the difference between tar archive and file system, estimate the size of the tar archives before creating it"

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  • Simple BizTalk Orchestration & Port Tutorial

    - by bosuch
    (This is a reference for a lunch & learn I'm giving at my company) This demo will create a BizTalk process that monitors a directory for an XML file, loads it into an orchestration, and drops it into a different directory. There’s no real processing going on (other than moving the file from one location to another), but this will introduce you to Messages, Orchestrations and Ports. To begin, create a new BizTalk Project names OrchestrationPortDemo: When the solution has been created, right-click the OrchestrationPortDemo solution name and select Add -> New Item. Add a BizTalk Orchestration named DemoOrchestration: Click Add and the orchestration will be created and displayed in the BizTalk Orchestration Designer. The designer allows you to visually create your business processes: Next, you will add a message (the basic unit of communication) to the orchestration. In the Orchestration View, right-click Messages and select New Message. In the message properties window, enter DemoMessage as the Identifier (the name), and select .NET Classes -> System.Xml.XmlDocument for Message Type. This indicates that we’ll be passing a standard Xml document in and out of the orchestration. Next, you will add Send and Receive shapes to the orchestration. From the toolbox, drag a Receive shape onto the orchestration (where it says “Drop a shape from the toolbox here”). Next, drag a Send shape directly below the Receive shape. For the properties of both shapes, select DemoMessage for Message – this indicates we’ll be passing around the message we created earlier. The Operation box will have a red exclamation mark next to it because no port has been specified. We will do this in a minute. On the Receive shape properties, you must be sure to select True for Activate. This indicates that the orchestration will be started upon receipt of a message, rather than being called by another orchestration. If you leave it set to false, when you try to build the application you’ll receive the error “You must specify at least one already-initialized correlation set for a non-activation receive that is on a non self-correlating port.” Now you’ll add ports to the orchestration. Ports specify how your orchestration will send and receive messages. Drag a port from the toolbox to the left-hand Port Surface, and the Port Configuration Wizard launches. For the first port (the receive port), enter the following information: Name: ReceivePort Select the port type to be used for this port: Create a new Port Type Port Type Name: ReceivePortType Port direction of communication: I’ll always be receiving <…> Port binding: Specify later By choosing “Specify later” you are choosing to bind the port (choose where and how it will send or receive its messages) at deployment time via the BizTalk Server Administration console. This allows you to change locations later without building and re-deploying the application. Next, drag a port to the right-hand Port Surface; this will be your send port. Configure it as follows: Name: SendPort Select the port type to be used for this port: Create a new Port Type Port Type Name: SendPortType Port direction of communication: I’ll always be sending <…> Port binding: Specify later Finally, drag the green arrow on the ReceivePort to the Receive_1 shape, and the green arrow on the SendPort to the Send_1 shape. Your orchestration should look like this: Now you have a couple final steps before building and deploying the application. In the Solution Explorer, right-click on OrchestrationPortDemo and select Properties. On the Signing tab, click “Sign the assembly”, and choose <New…> from the drop-down. Enter DemoKey as the Key file name, and deselect “Protect my key file with a password”. This will create the file DemoKey.snk in your solution. Signing the assembly gives it a strong name so that it can be deployed into the global assembly cache (GAC). Next, click the Deployment tab, and enter OrchestrationPortDemo as the Application Name. Save your solution. Click “Build OrchestrationPortDemo”. Your solution should (hopefully!) build with no errors. Click “Deploy OrchestrationPortDemo”. (Note – If you’re running Server 2008, Vista or Win7, you may get an error message. If so, close Visual Studio and run it as an administrator) That’s it! Your application is ready to be configured and fired up in the BizTalk Server Administration console, so stay tuned!

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  • Hash Function Added To The PredicateEqualityComparer

    - by Paulo Morgado
    Sometime ago I wrote a predicate equality comparer to be used with LINQ’s Distinct operator. The Distinct operator uses an instance of an internal Set class to maintain the collection of distinct elements in the source collection which in turn checks the hash code of each element (by calling the GetHashCode method of the equality comparer) and only if there’s already an element with the same hash code in the collection calls the Equals method of the comparer to disambiguate. At the time I provided only the possibility to specify the comparison predicate, but, in some cases, comparing a hash code instead of calling the provided comparer predicate can be a significant performance improvement, I’ve added the possibility to had a hash function to the predicate equality comparer. You can get the updated code from the PauloMorgado.Linq project on CodePlex,

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  • BizTalk Orchestration & Port Tutorial Part 2

    - by bosuch
    In Part 1 I showed how to create and publish a simple Orchestration demo. Now we’ll finish configuring it in the admin console and test it. Open the BizTalk Server 2009 Administration Console, and expand BizTalk Server 2009 Administration, then Applications. You should have an entry for OrchestrationPortDemo – expand it as well. First, we’ll add the Receive Port – the place that we’ll drop the test file. Right-click on Receive Ports and select New One-way Receive Port. On the General tab, name it InputPort, then click over to Receive Locations.   Click New to add a new location. Your receive location can be FTP, SQL, WCF, SharePoint, or many other choices, but for this demo we’ll add a File location. Click the Configure button and set a receive folder (something like “C:\PortDemo\”) and a file mask (stick with “*.xml” for now) and click OK three times to create your Receive Port.   Next we’ll create the Send port – the location where BizTalk will drop the file. Right-click on Send Ports and choose New Static One-way Send Port. Give it an appropriate name, and configure the FILE Transport Properties as shown:   Click OK twice and your Send Port will be created. Now we’ll configure the Orchestration Bindings. Click on Orchestrations, then right-click the orchestration itself and select Properties. Select the Bindings tab. Choose BizTalkServerApplication as the host, and select the Send and Receive ports you previously created, as shown:   Now it’s time to fire everything up. Right-click on the send port you created and click Start. Once the Status column displays “Started”, click on Receive Locations and Enable the Receive Location previously created. Finally, start the Orchestration. Now, time to test! Create a simple xml file like: <root>    <Node1>Test</Node1>    <Node2>Test</Node2> </root> And drop it into the C:\PortDemo folder. After a couple of seconds the file should disappear – this indicates BizTalk has picked it up for processing. Look in the C:\PortDemo\Output folder and you should see an xml file with a GUID for a name, like {7C50104F-FC3E-4A49-B2FA-4F560A37636D}.xml. Open it to verify that it matches your input file. Practically, this demo doesn’t do a whole heck of a lot, but it shows you the basics for building, publishing and running an orchestration.

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  • How LINQ to Object statements work

    - by rajbk
    This post goes into detail as to now LINQ statements work when querying a collection of objects. This topic assumes you have an understanding of how generics, delegates, implicitly typed variables, lambda expressions, object/collection initializers, extension methods and the yield statement work. I would also recommend you read my previous two posts: Using Delegates in C# Part 1 Using Delegates in C# Part 2 We will start by writing some methods to filter a collection of data. Assume we have an Employee class like so: 1: public class Employee { 2: public int ID { get; set;} 3: public string FirstName { get; set;} 4: public string LastName {get; set;} 5: public string Country { get; set; } 6: } and a collection of employees like so: 1: var employees = new List<Employee> { 2: new Employee { ID = 1, FirstName = "John", LastName = "Wright", Country = "USA" }, 3: new Employee { ID = 2, FirstName = "Jim", LastName = "Ashlock", Country = "UK" }, 4: new Employee { ID = 3, FirstName = "Jane", LastName = "Jackson", Country = "CHE" }, 5: new Employee { ID = 4, FirstName = "Jill", LastName = "Anderson", Country = "AUS" }, 6: }; Filtering We wish to  find all employees that have an even ID. We could start off by writing a method that takes in a list of employees and returns a filtered list of employees with an even ID. 1: static List<Employee> GetEmployeesWithEvenID(List<Employee> employees) { 2: var filteredEmployees = new List<Employee>(); 3: foreach (Employee emp in employees) { 4: if (emp.ID % 2 == 0) { 5: filteredEmployees.Add(emp); 6: } 7: } 8: return filteredEmployees; 9: } The method can be rewritten to return an IEnumerable<Employee> using the yield return keyword. 1: static IEnumerable<Employee> GetEmployeesWithEvenID(IEnumerable<Employee> employees) { 2: foreach (Employee emp in employees) { 3: if (emp.ID % 2 == 0) { 4: yield return emp; 5: } 6: } 7: } We put these together in a console application. 1: using System; 2: using System.Collections.Generic; 3: //No System.Linq 4:  5: public class Program 6: { 7: [STAThread] 8: static void Main(string[] args) 9: { 10: var employees = new List<Employee> { 11: new Employee { ID = 1, FirstName = "John", LastName = "Wright", Country = "USA" }, 12: new Employee { ID = 2, FirstName = "Jim", LastName = "Ashlock", Country = "UK" }, 13: new Employee { ID = 3, FirstName = "Jane", LastName = "Jackson", Country = "CHE" }, 14: new Employee { ID = 4, FirstName = "Jill", LastName = "Anderson", Country = "AUS" }, 15: }; 16: var filteredEmployees = GetEmployeesWithEvenID(employees); 17:  18: foreach (Employee emp in filteredEmployees) { 19: Console.WriteLine("ID {0} First_Name {1} Last_Name {2} Country {3}", 20: emp.ID, emp.FirstName, emp.LastName, emp.Country); 21: } 22:  23: Console.ReadLine(); 24: } 25: 26: static IEnumerable<Employee> GetEmployeesWithEvenID(IEnumerable<Employee> employees) { 27: foreach (Employee emp in employees) { 28: if (emp.ID % 2 == 0) { 29: yield return emp; 30: } 31: } 32: } 33: } 34:  35: public class Employee { 36: public int ID { get; set;} 37: public string FirstName { get; set;} 38: public string LastName {get; set;} 39: public string Country { get; set; } 40: } Output: ID 2 First_Name Jim Last_Name Ashlock Country UK ID 4 First_Name Jill Last_Name Anderson Country AUS Our filtering method is too specific. Let us change it so that it is capable of doing different types of filtering and lets give our method the name Where ;-) We will add another parameter to our Where method. This additional parameter will be a delegate with the following declaration. public delegate bool Filter(Employee emp); The idea is that the delegate parameter in our Where method will point to a method that contains the logic to do our filtering thereby freeing our Where method from any dependency. The method is shown below: 1: static IEnumerable<Employee> Where(IEnumerable<Employee> employees, Filter filter) { 2: foreach (Employee emp in employees) { 3: if (filter(emp)) { 4: yield return emp; 5: } 6: } 7: } Making the change to our app, we create a new instance of the Filter delegate on line 14 with a target set to the method EmployeeHasEvenId. Running the code will produce the same output. 1: public delegate bool Filter(Employee emp); 2:  3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: var employees = new List<Employee> { 9: new Employee { ID = 1, FirstName = "John", LastName = "Wright", Country = "USA" }, 10: new Employee { ID = 2, FirstName = "Jim", LastName = "Ashlock", Country = "UK" }, 11: new Employee { ID = 3, FirstName = "Jane", LastName = "Jackson", Country = "CHE" }, 12: new Employee { ID = 4, FirstName = "Jill", LastName = "Anderson", Country = "AUS" } 13: }; 14: var filterDelegate = new Filter(EmployeeHasEvenId); 15: var filteredEmployees = Where(employees, filterDelegate); 16:  17: foreach (Employee emp in filteredEmployees) { 18: Console.WriteLine("ID {0} First_Name {1} Last_Name {2} Country {3}", 19: emp.ID, emp.FirstName, emp.LastName, emp.Country); 20: } 21: Console.ReadLine(); 22: } 23: 24: static bool EmployeeHasEvenId(Employee emp) { 25: return emp.ID % 2 == 0; 26: } 27: 28: static IEnumerable<Employee> Where(IEnumerable<Employee> employees, Filter filter) { 29: foreach (Employee emp in employees) { 30: if (filter(emp)) { 31: yield return emp; 32: } 33: } 34: } 35: } 36:  37: public class Employee { 38: public int ID { get; set;} 39: public string FirstName { get; set;} 40: public string LastName {get; set;} 41: public string Country { get; set; } 42: } Lets use lambda expressions to inline the contents of the EmployeeHasEvenId method in place of the method. The next code snippet shows this change (see line 15).  For brevity, the Employee class declaration has been skipped. 1: public delegate bool Filter(Employee emp); 2:  3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: var employees = new List<Employee> { 9: new Employee { ID = 1, FirstName = "John", LastName = "Wright", Country = "USA" }, 10: new Employee { ID = 2, FirstName = "Jim", LastName = "Ashlock", Country = "UK" }, 11: new Employee { ID = 3, FirstName = "Jane", LastName = "Jackson", Country = "CHE" }, 12: new Employee { ID = 4, FirstName = "Jill", LastName = "Anderson", Country = "AUS" } 13: }; 14: var filterDelegate = new Filter(EmployeeHasEvenId); 15: var filteredEmployees = Where(employees, emp => emp.ID % 2 == 0); 16:  17: foreach (Employee emp in filteredEmployees) { 18: Console.WriteLine("ID {0} First_Name {1} Last_Name {2} Country {3}", 19: emp.ID, emp.FirstName, emp.LastName, emp.Country); 20: } 21: Console.ReadLine(); 22: } 23: 24: static bool EmployeeHasEvenId(Employee emp) { 25: return emp.ID % 2 == 0; 26: } 27: 28: static IEnumerable<Employee> Where(IEnumerable<Employee> employees, Filter filter) { 29: foreach (Employee emp in employees) { 30: if (filter(emp)) { 31: yield return emp; 32: } 33: } 34: } 35: } 36:  The output displays the same two employees.  Our Where method is too restricted since it works with a collection of Employees only. Lets change it so that it works with any IEnumerable<T>. In addition, you may recall from my previous post,  that .NET 3.5 comes with a lot of predefined delegates including public delegate TResult Func<T, TResult>(T arg); We will get rid of our Filter delegate and use the one above instead. We apply these two changes to our code. 1: public class Program 2: { 3: [STAThread] 4: static void Main(string[] args) 5: { 6: var employees = new List<Employee> { 7: new Employee { ID = 1, FirstName = "John", LastName = "Wright", Country = "USA" }, 8: new Employee { ID = 2, FirstName = "Jim", LastName = "Ashlock", Country = "UK" }, 9: new Employee { ID = 3, FirstName = "Jane", LastName = "Jackson", Country = "CHE" }, 10: new Employee { ID = 4, FirstName = "Jill", LastName = "Anderson", Country = "AUS" } 11: }; 12:  13: var filteredEmployees = Where(employees, emp => emp.ID % 2 == 0); 14:  15: foreach (Employee emp in filteredEmployees) { 16: Console.WriteLine("ID {0} First_Name {1} Last_Name {2} Country {3}", 17: emp.ID, emp.FirstName, emp.LastName, emp.Country); 18: } 19: Console.ReadLine(); 20: } 21: 22: static IEnumerable<T> Where<T>(IEnumerable<T> source, Func<T, bool> filter) { 23: foreach (var x in source) { 24: if (filter(x)) { 25: yield return x; 26: } 27: } 28: } 29: } We have successfully implemented a way to filter any IEnumerable<T> based on a  filter criteria. Projection Now lets enumerate on the items in the IEnumerable<Employee> we got from the Where method and copy them into a new IEnumerable<EmployeeFormatted>. The EmployeeFormatted class will only have a FullName and ID property. 1: public class EmployeeFormatted { 2: public int ID { get; set; } 3: public string FullName {get; set;} 4: } We could “project” our existing IEnumerable<Employee> into a new collection of IEnumerable<EmployeeFormatted> with the help of a new method. We will call this method Select ;-) 1: static IEnumerable<EmployeeFormatted> Select(IEnumerable<Employee> employees) { 2: foreach (var emp in employees) { 3: yield return new EmployeeFormatted { 4: ID = emp.ID, 5: FullName = emp.LastName + ", " + emp.FirstName 6: }; 7: } 8: } The changes are applied to our app. 1: public class Program 2: { 3: [STAThread] 4: static void Main(string[] args) 5: { 6: var employees = new List<Employee> { 7: new Employee { ID = 1, FirstName = "John", LastName = "Wright", Country = "USA" }, 8: new Employee { ID = 2, FirstName = "Jim", LastName = "Ashlock", Country = "UK" }, 9: new Employee { ID = 3, FirstName = "Jane", LastName = "Jackson", Country = "CHE" }, 10: new Employee { ID = 4, FirstName = "Jill", LastName = "Anderson", Country = "AUS" } 11: }; 12:  13: var filteredEmployees = Where(employees, emp => emp.ID % 2 == 0); 14: var formattedEmployees = Select(filteredEmployees); 15:  16: foreach (EmployeeFormatted emp in formattedEmployees) { 17: Console.WriteLine("ID {0} Full_Name {1}", 18: emp.ID, emp.FullName); 19: } 20: Console.ReadLine(); 21: } 22:  23: static IEnumerable<T> Where<T>(IEnumerable<T> source, Func<T, bool> filter) { 24: foreach (var x in source) { 25: if (filter(x)) { 26: yield return x; 27: } 28: } 29: } 30: 31: static IEnumerable<EmployeeFormatted> Select(IEnumerable<Employee> employees) { 32: foreach (var emp in employees) { 33: yield return new EmployeeFormatted { 34: ID = emp.ID, 35: FullName = emp.LastName + ", " + emp.FirstName 36: }; 37: } 38: } 39: } 40:  41: public class Employee { 42: public int ID { get; set;} 43: public string FirstName { get; set;} 44: public string LastName {get; set;} 45: public string Country { get; set; } 46: } 47:  48: public class EmployeeFormatted { 49: public int ID { get; set; } 50: public string FullName {get; set;} 51: } Output: ID 2 Full_Name Ashlock, Jim ID 4 Full_Name Anderson, Jill We have successfully selected employees who have an even ID and then shaped our data with the help of the Select method so that the final result is an IEnumerable<EmployeeFormatted>.  Lets make our Select method more generic so that the user is given the freedom to shape what the output would look like. We can do this, like before, with lambda expressions. Our Select method is changed to accept a delegate as shown below. TSource will be the type of data that comes in and TResult will be the type the user chooses (shape of data) as returned from the selector delegate. 1:  2: static IEnumerable<TResult> Select<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, TResult> selector) { 3: foreach (var x in source) { 4: yield return selector(x); 5: } 6: } We see the new changes to our app. On line 15, we use lambda expression to specify the shape of the data. In this case the shape will be of type EmployeeFormatted. 1:  2: public class Program 3: { 4: [STAThread] 5: static void Main(string[] args) 6: { 7: var employees = new List<Employee> { 8: new Employee { ID = 1, FirstName = "John", LastName = "Wright", Country = "USA" }, 9: new Employee { ID = 2, FirstName = "Jim", LastName = "Ashlock", Country = "UK" }, 10: new Employee { ID = 3, FirstName = "Jane", LastName = "Jackson", Country = "CHE" }, 11: new Employee { ID = 4, FirstName = "Jill", LastName = "Anderson", Country = "AUS" } 12: }; 13:  14: var filteredEmployees = Where(employees, emp => emp.ID % 2 == 0); 15: var formattedEmployees = Select(filteredEmployees, (emp) => 16: new EmployeeFormatted { 17: ID = emp.ID, 18: FullName = emp.LastName + ", " + emp.FirstName 19: }); 20:  21: foreach (EmployeeFormatted emp in formattedEmployees) { 22: Console.WriteLine("ID {0} Full_Name {1}", 23: emp.ID, emp.FullName); 24: } 25: Console.ReadLine(); 26: } 27: 28: static IEnumerable<T> Where<T>(IEnumerable<T> source, Func<T, bool> filter) { 29: foreach (var x in source) { 30: if (filter(x)) { 31: yield return x; 32: } 33: } 34: } 35: 36: static IEnumerable<TResult> Select<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, TResult> selector) { 37: foreach (var x in source) { 38: yield return selector(x); 39: } 40: } 41: } The code outputs the same result as before. On line 14 we filter our data and on line 15 we project our data. What if we wanted to be more expressive and concise? We could combine both line 14 and 15 into one line as shown below. Assuming you had to perform several operations like this on our collection, you would end up with some very unreadable code! 1: var formattedEmployees = Select(Where(employees, emp => emp.ID % 2 == 0), (emp) => 2: new EmployeeFormatted { 3: ID = emp.ID, 4: FullName = emp.LastName + ", " + emp.FirstName 5: }); A cleaner way to write this would be to give the appearance that the Select and Where methods were part of the IEnumerable<T>. This is exactly what extension methods give us. Extension methods have to be defined in a static class. Let us make the Select and Where extension methods on IEnumerable<T> 1: public static class MyExtensionMethods { 2: static IEnumerable<T> Where<T>(this IEnumerable<T> source, Func<T, bool> filter) { 3: foreach (var x in source) { 4: if (filter(x)) { 5: yield return x; 6: } 7: } 8: } 9: 10: static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector) { 11: foreach (var x in source) { 12: yield return selector(x); 13: } 14: } 15: } The creation of the extension method makes the syntax much cleaner as shown below. We can write as many extension methods as we want and keep on chaining them using this technique. 1: var formattedEmployees = employees 2: .Where(emp => emp.ID % 2 == 0) 3: .Select (emp => new EmployeeFormatted { ID = emp.ID, FullName = emp.LastName + ", " + emp.FirstName }); Making these changes and running our code produces the same result. 1: using System; 2: using System.Collections.Generic; 3:  4: public class Program 5: { 6: [STAThread] 7: static void Main(string[] args) 8: { 9: var employees = new List<Employee> { 10: new Employee { ID = 1, FirstName = "John", LastName = "Wright", Country = "USA" }, 11: new Employee { ID = 2, FirstName = "Jim", LastName = "Ashlock", Country = "UK" }, 12: new Employee { ID = 3, FirstName = "Jane", LastName = "Jackson", Country = "CHE" }, 13: new Employee { ID = 4, FirstName = "Jill", LastName = "Anderson", Country = "AUS" } 14: }; 15:  16: var formattedEmployees = employees 17: .Where(emp => emp.ID % 2 == 0) 18: .Select (emp => 19: new EmployeeFormatted { 20: ID = emp.ID, 21: FullName = emp.LastName + ", " + emp.FirstName 22: } 23: ); 24:  25: foreach (EmployeeFormatted emp in formattedEmployees) { 26: Console.WriteLine("ID {0} Full_Name {1}", 27: emp.ID, emp.FullName); 28: } 29: Console.ReadLine(); 30: } 31: } 32:  33: public static class MyExtensionMethods { 34: static IEnumerable<T> Where<T>(this IEnumerable<T> source, Func<T, bool> filter) { 35: foreach (var x in source) { 36: if (filter(x)) { 37: yield return x; 38: } 39: } 40: } 41: 42: static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector) { 43: foreach (var x in source) { 44: yield return selector(x); 45: } 46: } 47: } 48:  49: public class Employee { 50: public int ID { get; set;} 51: public string FirstName { get; set;} 52: public string LastName {get; set;} 53: public string Country { get; set; } 54: } 55:  56: public class EmployeeFormatted { 57: public int ID { get; set; } 58: public string FullName {get; set;} 59: } Let’s change our code to return a collection of anonymous types and get rid of the EmployeeFormatted type. We see that the code produces the same output. 1: using System; 2: using System.Collections.Generic; 3:  4: public class Program 5: { 6: [STAThread] 7: static void Main(string[] args) 8: { 9: var employees = new List<Employee> { 10: new Employee { ID = 1, FirstName = "John", LastName = "Wright", Country = "USA" }, 11: new Employee { ID = 2, FirstName = "Jim", LastName = "Ashlock", Country = "UK" }, 12: new Employee { ID = 3, FirstName = "Jane", LastName = "Jackson", Country = "CHE" }, 13: new Employee { ID = 4, FirstName = "Jill", LastName = "Anderson", Country = "AUS" } 14: }; 15:  16: var formattedEmployees = employees 17: .Where(emp => emp.ID % 2 == 0) 18: .Select (emp => 19: new { 20: ID = emp.ID, 21: FullName = emp.LastName + ", " + emp.FirstName 22: } 23: ); 24:  25: foreach (var emp in formattedEmployees) { 26: Console.WriteLine("ID {0} Full_Name {1}", 27: emp.ID, emp.FullName); 28: } 29: Console.ReadLine(); 30: } 31: } 32:  33: public static class MyExtensionMethods { 34: public static IEnumerable<T> Where<T>(this IEnumerable<T> source, Func<T, bool> filter) { 35: foreach (var x in source) { 36: if (filter(x)) { 37: yield return x; 38: } 39: } 40: } 41: 42: public static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector) { 43: foreach (var x in source) { 44: yield return selector(x); 45: } 46: } 47: } 48:  49: public class Employee { 50: public int ID { get; set;} 51: public string FirstName { get; set;} 52: public string LastName {get; set;} 53: public string Country { get; set; } 54: } To be more expressive, C# allows us to write our extension method calls as a query expression. Line 16 can be rewritten a query expression like so: 1: var formattedEmployees = from emp in employees 2: where emp.ID % 2 == 0 3: select new { 4: ID = emp.ID, 5: FullName = emp.LastName + ", " + emp.FirstName 6: }; When the compiler encounters an expression like the above, it simply rewrites it as calls to our extension methods.  So far we have been using our extension methods. The System.Linq namespace contains several extension methods for objects that implement the IEnumerable<T>. You can see a listing of these methods in the Enumerable class in the System.Linq namespace. Let’s get rid of our extension methods (which I purposefully wrote to be of the same signature as the ones in the Enumerable class) and use the ones provided in the Enumerable class. Our final code is shown below: 1: using System; 2: using System.Collections.Generic; 3: using System.Linq; //Added 4:  5: public class Program 6: { 7: [STAThread] 8: static void Main(string[] args) 9: { 10: var employees = new List<Employee> { 11: new Employee { ID = 1, FirstName = "John", LastName = "Wright", Country = "USA" }, 12: new Employee { ID = 2, FirstName = "Jim", LastName = "Ashlock", Country = "UK" }, 13: new Employee { ID = 3, FirstName = "Jane", LastName = "Jackson", Country = "CHE" }, 14: new Employee { ID = 4, FirstName = "Jill", LastName = "Anderson", Country = "AUS" } 15: }; 16:  17: var formattedEmployees = from emp in employees 18: where emp.ID % 2 == 0 19: select new { 20: ID = emp.ID, 21: FullName = emp.LastName + ", " + emp.FirstName 22: }; 23:  24: foreach (var emp in formattedEmployees) { 25: Console.WriteLine("ID {0} Full_Name {1}", 26: emp.ID, emp.FullName); 27: } 28: Console.ReadLine(); 29: } 30: } 31:  32: public class Employee { 33: public int ID { get; set;} 34: public string FirstName { get; set;} 35: public string LastName {get; set;} 36: public string Country { get; set; } 37: } 38:  39: public class EmployeeFormatted { 40: public int ID { get; set; } 41: public string FullName {get; set;} 42: } This post has shown you a basic overview of LINQ to Objects work by showning you how an expression is converted to a sequence of calls to extension methods when working directly with objects. It gets more interesting when working with LINQ to SQL where an expression tree is constructed – an in memory data representation of the expression. The C# compiler compiles these expressions into code that builds an expression tree at runtime. The provider can then traverse the expression tree and generate the appropriate SQL query. You can read more about expression trees in this MSDN article.

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  • linq where clause and count result in null exception.

    - by nestling
    The code below works unless p.School.SchoolName turns out to be null, in which case it results in a NullReferenceException. if (ExistingUsers.Where(p => p.StudentID == item.StaffID && p.School.SchoolName == item.SchoolID).Count() > 0) { // Do stuff. } ExistingUsers is a list of users: public List<User> ExistingUsers; Here is the relevant portion of the stacktrace: System.NullReferenceException: Object reference not set to an instance of an object. at System.Linq.Enumerable.WhereListIterator1.MoveNext() at System.Linq.Enumerable.Count[TSource](IEnumerable1 source) How should I handle this where clause? Thanks very much in advance.

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  • Linq to SQL and SQL Server Compact Error: "There was an error parsing the query."

    - by Jeremy
    I created a SQL server compact database (MyDatabase.sdf), and populated it with some data. I then ran SQLMetal.exe and generated a linq to sql class (MyDatabase.mdf) Now I'm trying to select all records from a table with a relatively straightforward select, and I get the error: "There was an error parsing the query. [ Token line number = 3,Token line offset = 67,Token in error = MAX]" Here is my select code: public IEnumerable ListItems() { MyDatabase db_m = new MyDatabase("c:\mydatabase.sdf"); return this.db_m.TestTable.Select(test = new Item() { .... } } I've read that Linq to SQL works with Sql Compact, is there some other configuration I need to do?

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  • How do you use the LINQ to SQL designer to generate accessor methods for subclasses?

    - by Pricey
    Above is the LINQ to SQL designer view for my data context. Below is the relevant code: public System.Data.Linq.Table<ActivityBase> ActivityBases { get { return this.GetTable<ActivityBase>(); } } ... [Table(Name="dbo.Activities")] [InheritanceMapping(Code="1", Type=typeof(ActivityBase), IsDefault=true)] [InheritanceMapping(Code="2", Type=typeof(Project))] [InheritanceMapping(Code="3", Type=typeof(ProjectActivity))] [InheritanceMapping(Code="5", Type=typeof(Task))] [InheritanceMapping(Code="4", Type=typeof(Activity))] public abstract partial class ActivityBase : INotifyPropertyChanging, INotifyPropertyChanged { ... Is there a way to generate accessor methods for the subclasses as shown in the inheritance mapping above (Project, Task, etc...) without doing it manually? I added them manually but then a change in the designer overwrites any manual changes. Am i doing this wrong? should I not be making accessors for the sub classes? filtering from ActivityBase seems worse to me. Thanks for any help on this.

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  • Using LINQ to query database through a proxy server of some kind?

    - by Mustafakidd
    Hey All Sorry for using (perhaps) the wrong lingo, but my question may be clearer if you view this diagram as you read it. http://dl.dropbox.com/u/13256/DIAGRAM.PNG Our client is requiring us to adhere to the server configuration (poorly) diagrammed in the above image. The web server is accessible over port 80 and is where our web application is hosted - a second firewall permits this web server to access a second server which in turn is the only server permitted to access the database server. My question is: How do I deploy a web application that uses LINQ-to-SQL in this environment? Is there a way to proxy my LINQ queries through the app server so that the database connection goes through that server? This is uncharted territory for me, as we always have had access to the DB server directly from our web server in the past. Any help is appreciated. Thanks Mustafa

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  • How to make linq master detail query for 0..n relationship?

    - by JK
    Given a classic DB structure of Orders has zero or more OrderLines and OrderLine has exactly one Product, how do I write a linq query to express this? The output would be OrderNumber - OrderLine - Product Name Order-1 null null // (this order has no lines) Order-2 1 Red widget I tried this query but is not getting the orders with no lines var model = (from po in Orders from line in po.OrderLines select new { OrderNumber = po.Id, OrderLine = line.LineNumber, ProductName = line.Product.ProductDescription, } ) I think that the 2nd from is limiting the query to only those that have OrderLines, but I dont know another way to express it. LINQ is very non-obvious if you ask me!

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  • How do you implement caching in Linq to SQL?

    - by Glenn Slaven
    We've just started using LINQ to SQL at work for our DAL & we haven't really come up with a standard for out caching model. Previously we had being using a base 'DAL' class that implemented a cache manager property that all our DAL classes inherited from, but now we don't have that. I'm wondering if anyone has come up with a 'standard' approach to caching LINQ to SQL results? We're working in a web environment (IIS) if that makes a difference. I know this may well end up being a subjective question, but I still think the info would be valuable. EDIT: To clarify, I'm not talking about caching an individual result, I'm after more of an architecture solution, as in how do you set up caching so that all your link methods use the same caching architecture.

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  • Is it possible to create ICriteria/ICriterion from LINQ or HQL?

    - by adrin
    I am creating a method that can create filter understood by NHibernate (by filter i mean a set of ICriteria object for example) from my abstract filter object. public static IEnumerable<ICriterion> ToNhCriteria(this MyCriteria criteria) { // T4 generated function // lots of result.Add(Expression.Or(Expression.Eq(),Expression.Eq)) expression trees - hard to generate // Is there a way to generate HQL/Linq query here istead? } then i want to do something like session.CreateCriteria<Entity>().Add(myCriteria.ToNhCriteria()) to filter entities. The problem is that using Expression. methods (Expression.Or etc) is quite tedious (the method is generated and i have multiple or statements that have to be joined into an expression somehow). Is there a way to avoid using Expression.Or() and create ICrietrion / ICriteria using LINQ or HQL?

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  • Quaere - Anyone using it yet? (LINQ to Objects for Java)

    - by Marty Pitt
    Hi there I'm a .NET guy originally, working in Java recently, and finding I'm really missing LINQ to Objects, specifically for performing filtering against collections. A few people here on Stack Overflow have answered the "LINQ for Java?" question with a single word : Quaere However, on the site it clearly states "Pre-Beta", and there's been no commits to their code for over a year, so I'm guessing the project is pretty much dead. Is anyone actually using this, and / or have any experience with it? The second most common answer appears to be "use Google Collections". Is this the most appropriate Java way? Cheers Marty

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  • .Remove(object) on a List<T> returned from LINQ to SQL compiled query won't delete the Object right

    - by soldieraman
    I am returning two lists from the database using LINQ to SQL compiled query. While looping the first list I remove duplicates from the second list as I dont want to process already existing objects again. eg. //oldCustomers is a List returned by my Compiled Linq to SQL Statmenet that I have added a .ToList() at the end to //Same goes for newCustomers for (Customer oC in oldCustomers) { //Do some processing newCustomers.Remove(newCusomters.Find(nC=> nC.CustomerID == oC.CusomterID)); } for (Cusomter nC in newCustomers) { //Do some processing } DataContext.SubmitChanges() I expect this to only save the changes that have been made to the customers in my processing and not Remove or Delete any of my customers from the database. Correct? I have tried it and it works fine - but I am trying to know if there is any rare case it might actually get removed

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  • Update specific rows in LINQ to SQL result set.

    - by davemackey
    I have a page with a form on it and needs a range of dates. Thus I've placed a number of textboxes on the page into which users can type dates. When the user clicks the save button I want to trigger a LINQ update to the SQL Server...all the rows already exist, so I'm just updating existing data. How can I do this? For example, lets say my table looks like this: Column Names: Description dateValue Column Values: Birthdate 1/1/1990 Anniversary 1/10/1992 Death 1/1/1993 I want to do something like this: hupdate.Description("Birthdate").dateValue = TextBox1.Text hupdate.Description("Anniversary").dateValue = TextBox2.Text hupdate.Description("Death").dateValue = TextBox3.Text hconfig.SubmitChanges() Is there a way to do this with LINQ?

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  • How to convert this foreach loop into Linq code?

    - by a-galkin
    I am new one with Linq and I would like to modify my old c# code to use Linq. The idea of this code to select all tables where it's not set and reference’s field PrimaryTable equal "myTable" foreach (Table table in dbServer.Tables) { if (!table.IsSet) { foreach (Reference refer in table.References) { if (refer.PrimaryTable == "myTable") { tables.Add(table); } } } } After digging in internet I have got this code var q = from table in dbServer.Tables let refers = from refer in table.References where refer.PrimaryTable == "myTable" select refer.ForeignTable where refers.Contains(table.Name) select table; But it does not work at all and I need your help to make it works. Thanks in advance.

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