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  • Oracle 'In Touch' PartnerCast (July 1, 2014) - Be prepared for a year of growth

    - by Hartmut Wiese
    Dear Partner, We would like to invite you to join David Callaghan, Senior Vice President Oracle EMEA Alliances and Channels, and his studio guests for the next broadcast of the Oracle ‘In Touch’ PartnerCast on Tuesday 1st July 2014 from 10:30am UK / 11:30am CET. In this cast, David’s studio guests and his regional reporters will be looking at your priorities as EMEA partners and how best to grow with Oracle. We also look forward to the broadcast covering topics on the following: Highlights of FY14 Strategic themes for FY15 HCM, CRM and ERP Oracle on Oracle Exclusive for ‘In Touch’ David Callaghan questions Rich Geraffo, Senior Vice President, Global Alliances & Channels, on how the FY15 partner Global kick off relates to EMEA. Plus David provides your chance to hear from some of the newly appointed Worldwide A&C Leadership team as he discusses with Bruce Chumley VP Oracle Channel Distribution Sales & Troy Richardson VP Oracle Strategic Alliances; their core focus and strategy of growth and what they intend on bringing to the table in their new role. With lots of studio guests joining David, why not get in touch on Twitter using the hashtag #OracleInTouch or by emailing [email protected] to get your questions featured in the cast!   To find out more information and to watch previous episodes on-demand, please visit our webpage here. Best regards, Oracle EMEA Alliances & Channels

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  • SQL Strings vs. Conditional SQL Statements

    - by Yatrix
    Is there an advantage to piecemealing sql strings together vs conditional sql statements in SQL Server itself? I have only about 10 months of SQL experience, so I could be speaking out of pure ignorance here. Where I work, I see people building entire queries in strings and concatenating strings together depending on conditions. For example: Set @sql = 'Select column1, column2 from Table 1 ' If SomeCondtion @sql = @sql + 'where column3 = ' + @param1 else @sql = @sql + 'where column4 = ' + @param2 That's a real simple example, but what I'm seeing here is multiple joins and huge queries built from strings and then executed. Some of them even write out what's basically a function to execute, including Declare statements, variables, etc. Is there an advantage to doing it this way when you could do it with just conditions in the sql itself? To me, it seems a lot harder to debug, change and even write vs adding cases, if-elses or additional where parameters to branch the query.

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  • Be prepared for Patch Tuesday - Feb 2011

    - by TATWORTH
    The next patch Tuesday ( the second Tuesday of the month) is expcted to be big. Since several of the issues being fixed are already being exploited, the patches should be applied sooner rather than later. http://www.microsoft.com/technet/security/Bulletin/MS11-feb.mspx http://news.cnet.com/8301-1009_3-20030613-83.html?tag=mncol;title http://www.computerworld.com/s/article/9208038/Microsoft_to_patch_22_bugs_3_zero_days_next_week?taxonomyId=17

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  • Why can't I get a TRUE return in this prepared statement?

    - by Cortopasta
    I can't seem to get this to do anything but return false. My best guess is that the prepared statement isn't executing, but I have no idea why. private function check_credentials($plain_username, $md5_password) { global $dbcon; $ac = new ac(); $ac->dbconnect(); $userid = $dbcon->prepare('SELECT id FROM users WHERE username = :username AND password = :password LIMIT 1'); $userid->bindParam(':username', $plain_username); $userid->bindParam(':password', $md5_password); $userid->execute(); $id = $userid->fetch(); Return $id; } *EDIT:*I've even tried hard coding the username and password into the function itself to try and isolate the problem like this: private function check_credentials($plain_username, $md5_password) { global $dbcon; $plain_username = "jim"; $md5_username = "waffles"; $ac = new ac(); $ac->dbconnect(); $userid = $dbcon->prepare('SELECT id FROM users WHERE username = :username AND password = :password LIMIT 1'); $userid->bindParam(':username', $plain_username); $userid->bindParam(':password', $md5_password); $userid->execute(); print_r($dbcon->errorInfo()); $id = $userid->fetch(); Return $id; } Still nothing :-/

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  • How to convert a list object to bigdecimal in prepared statement?

    - by user1103504
    I am using prepared statement for bulk insertion of records. Iam iterating a list which contains values and their dataTypes differ. One of the data type is BigDecimal and when i try to set calling preparedstatement, it is throwing null pointer exception. My code int count = 1; for (int j = 0; j < list.size(); j++) { if(list.get(j) instanceof Timestamp) { ps.setTimestamp(count, (Timestamp) list.get(j)); } else if(list.get(j) instanceof java.lang.Character) { ps.setString(count, String.valueOf(list.get(j))); } else if(list.get(j) instanceof java.math.BigDecimal) { ps.setBigDecimal(count, (java.math.BigDecimal)list.get(j)); } else { ps.setObject(count, list.get(j)); } count++; } I tried 2 ways to convert, casting the object and tried to create a new object of type BigDecimal ps.setBigDecimal(count, new BigDecimal(list.get(j).toString)); both donot solve my problem. It is throwing null pointer exception. help is appreciated. Thanks

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  • Absolute statements in IT that are wrong

    - by Dan McGrath
    I was recently in a discussion about the absolute statement "It costs more in programming time to optimise software than it costs to throw hardware at a problem". The general thought (of which I agree with) is that as an absolute statement this is wrong. There are too many variables to ever generalise in such a way. What other statements do you hear about software/programming that simply do not work as an absolute and why?

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  • MERGE Your DML Statements in SQL Server 2008

    MERGE is a new statement introduced in the SQL:2003 standard for performing multiple DML (Data Manipulation Language) statements against a target table at once. In this article we will look into ways to take advantage of this powerful addition to SQL Server 2008.

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  • All libGDX input statements are returning TRUE at once

    - by MowDownJoe
    I'm fooling around with Box2D and libGDX and running into a peculiar problem with polling for input. Here's the code for the Screen's render() loop: @Override public void render(float delta) { Gdx.gl20.glClearColor(0, 0, .2f, 1); Gdx.gl20.glClear(GL20.GL_COLOR_BUFFER_BIT); camera.update(); game.batch.setProjectionMatrix(camera.combined); debugRenderer.render(world, camera.combined); if(Gdx.input.isButtonPressed(Keys.LEFT)){ Gdx.app.log("Input", "Left is being pressed."); pushyThingyBody.applyForceToCenter(-10f, 0); } if(Gdx.input.isButtonPressed(Keys.RIGHT)){ Gdx.app.log("Input", "Right is being pressed."); pushyThingyBody.applyForceToCenter(10f, 0); } world.step((1f/45f), 6, 2); } And the constructor is largely just setting up the World, Box2DDebugRenderer, and all the Bodies in the world: public SandBox(PhysicsSandboxGame game) { this.game = game; camera = new OrthographicCamera(800, 480); camera.setToOrtho(false); world = new World(new Vector2(0, -9.8f), true); debugRenderer = new Box2DDebugRenderer(); BodyDef bodyDef = new BodyDef(); bodyDef.type = BodyType.DynamicBody; bodyDef.position.set(100, 300); body = world.createBody(bodyDef); CircleShape circle = new CircleShape(); circle.setRadius(6f); FixtureDef fixtureDef = new FixtureDef(); fixtureDef.shape = circle; fixtureDef.density = .5f; fixtureDef.friction = .4f; fixtureDef.restitution = .6f; fixture = body.createFixture(fixtureDef); circle.dispose(); BodyDef groundBodyDef = new BodyDef(); groundBodyDef.position.set(new Vector2(0, 10)); groundBody = world.createBody(groundBodyDef); PolygonShape groundBox = new PolygonShape(); groundBox.setAsBox(camera.viewportWidth, 10f); groundBody.createFixture(groundBox, 0f); groundBox.dispose(); BodyDef pushyThingyBodyDef = new BodyDef(); pushyThingyBodyDef.type = BodyType.DynamicBody; pushyThingyBodyDef.position.set(new Vector2(400, 30)); pushyThingyBody = world.createBody(pushyThingyBodyDef); PolygonShape pushyThingyShape = new PolygonShape(); pushyThingyShape.setAsBox(40f, 10f); FixtureDef pushyThingyFixtureDef = new FixtureDef(); pushyThingyFixtureDef.shape = pushyThingyShape; pushyThingyFixtureDef.density = .4f; pushyThingyFixtureDef.friction = .1f; pushyThingyFixtureDef.restitution = .5f; pushyFixture = pushyThingyBody.createFixture(pushyThingyFixtureDef); pushyThingyShape.dispose(); } Testing this on the desktop. Basically, whenever I hit the appropriate keys, neither of the if statements in the loop return true. However, when I click in the window, both statements return true, resulting in a 0 net force on the body. Why is this?

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  • Funny statements, quotes, phrases, errors found on technical Books [closed]

    - by Felipe Fiali
    I found some funny or redundant statements on technical books I've read, I'd like to share. And I mean good, serious, technical books. Ok so starting it all: The .NET framework doesn't support teleportation From MCTS 70-536 Training kit book - .NET Framework 2.0 Application Development Foundation Teleportation in science fiction is a good example of serialization (though teleportation is not currently supported byt the .NET Framework). C# 3 is sexy From Jon Skeet's C# in Depth second Edition You may be itching to get on to the sexy stuff from C# 3 by this point, and I don’t blame you. Instantiating a class From Introduction to development II in Microsoft Dynamics AX 2009 To instantiate a class, is to create a new instance of it. Continue or break From Introduction to development II in Microsoft Dynamics AX 2009 Continue and break commands are used within all three loops to tell the execution to break or continue. These are just a few. I'll post some more later. Share some that you might have found too.

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  • Top 10 Transact-SQL Statements a SQL Server DBA Should Know

    Microsoft SQL Server is a feature rich database management system product, with an enormous number of T-SQL commands. With each feature supporting its own list of commands, it can be difficult to remember them all. MAK shares his top 10 T-SQL statements that a DBA should know. Join SQL Backup’s 35,000+ customers to compress and strengthen your backups "SQL Backup will be a REAL boost to any DBA lucky enough to use it." Jonathan Allen. Download a free trial now.

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  • How do I use pdo's prepared statement for order by and limit clauses(or can I?If not,what should I r

    - by user198729
    $sql = "SELECT * FROM table ORDER BY :sort :dir LIMIT :start, :results"; $stmt = $dbh->prepare($sql); $stmt->execute(array( 'sort' => $_GET['sort'], 'dir' => $_GET['dir'], 'start' => $_GET['start'], 'results' => $_GET['results'], ) ); I tried to use prepare to do the job,but $stmt->fetchAll(PDO::FETCH_ASSOC); returns nothing. Can someone point out what's the wrong thing I am doing?

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  • PL-SQL - Two statements with begin and end, run fine seperately but not together?

    - by Twiss
    Hi all, Just wondering if anyone can help with this, I have two PLSQL statements for altering tables (adding extra fields) and they are as follows: -- Make GC_NAB field for Next Action By Dropdown begin if 'VARCHAR2' = 'NUMBER' and length('VARCHAR2')>0 and length('')>0 then execute immediate 'alter table "SERVICEMAIL6"."ETD_GUESTCARE" add(GC_NAB VARCHAR2(10, ))'; elsif ('VARCHAR2' = 'NUMBER' and length('VARCHAR2')>0 and length('')=0) or 'VARCHAR2' = 'VARCHAR2' then execute immediate 'alter table "SERVICEMAIL6"."ETD_GUESTCARE" add(GC_NAB VARCHAR2(10))'; else execute immediate 'alter table "SERVICEMAIL6"."ETD_GUESTCARE" add(GC_NAB VARCHAR2)'; end if; commit; end; -- Make GC_NABID field for Next Action By Dropdown begin if 'NUMBER' = 'NUMBER' and length('NUMBER')>0 and length('')>0 then execute immediate 'alter table "SERVICEMAIL6"."ETD_GUESTCARE" add(GC_NABID NUMBER(, ))'; elsif ('NUMBER' = 'NUMBER' and length('NUMBER')>0 and length('')=0) or 'NUMBER' = 'VARCHAR2' then execute immediate 'alter table "SERVICEMAIL6"."ETD_GUESTCARE" add(GC_NABID NUMBER())'; else execute immediate 'alter table "SERVICEMAIL6"."ETD_GUESTCARE" add(GC_NABID NUMBER)'; end if; commit; end; When I run these two queries seperately, no problems. However, when run together as shown above, Oracle gives me an error when it starts the second statement: Error report: ORA-06550: line 15, column 1: PLS-00103: Encountered the symbol "BEGIN" 06550. 00000 - "line %s, column %s:\n%s" *Cause: Usually a PL/SQL compilation error. *Action: I'm assuming that this means the first statement is not terminated properly... is there anything I should put inbetween the statements to make it work properly? Thanks in advance everyone!

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  • Alternate method to dependent, nested if statements to check multiple states

    - by octopusgrabbus
    Is there an easier way to process multiple true/false states than using nested if statements? I think there is, and it would be to create a sequence of states, and then use a function like when to determine if all states were true, and drop out if not. I am asking the question to make sure there is not a preferred Clojure way to do this. Here is the background of my problem: I have an application that depends on quite a few input files. The application depends on .csv data reports; column headers for each report (.csv files also), so each sequence in the sequence of sequences can be zipped together with its columns for the purposes of creating a smaller sequence; and column files for output data. I use the following functions to find out if a file is present: (defn kind [filename] (let [f (File. filename)] (cond (.isFile f) "file" (.isDirectory f) "directory" (.exists f) "other" :else "(cannot be found)" ))) (defn look-for [filename expected-type] (let [find-status (kind-stat filename expected-type)] find-status)) And here are the first few lines of a multiple if which looks ugly and is hard to maintain: (defn extract-re-values "Plain old-fashioned sub-routine to process real-estate values / 3rd Q re bills extract." [opts] (if (= (utl/look-for (:ifm1 opts) "f") 0) ; got re columns? (if (= (utl/look-for (:ifn1 opts) "f") 0) ; got re data? (if (= (utl/look-for (:ifm3 opts) "f") 0) ; got re values output columns? (if (= (utl/look-for (:ifm4 opts) "f") 0) ; got re_mixed_use_ratio columns? (let [re-in-col-nams (first (utl/fetch-csv-data (:ifm1 opts))) re-in-data (utl/fetch-csv-data (:ifn1 opts)) re-val-cols-out (first (utl/fetch-csv-data (:ifm3 opts))) mu-val-cols-out (first (utl/fetch-csv-data (:ifm4 opts))) chk-results (utl/chk-seq-len re-in-col-nams (first re-in-data) re-rec-count)] I am not looking for a discussion of the best way, but what is in Clojure that facilitates solving a problem like this.

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  • Generate MERGE statements from a table

    - by Bill Graziano
    We have a requirement to build a test environment where certain tables get reset from production every night.  These are mainly lookup tables.  I played around with all kinds of fancy solutions and finally settled on a series of MERGE statements.  And being lazy I didn’t want to write them myself.  The stored procedure below will generate a MERGE statement for the table you pass it.  If you have identity values it populates those properly.  You need to have primary keys on the table for the joins to be generated properly.  The only thing hard coded is the source database.  You’ll need to update that for your environment.  We actually used a linked server in our situation. CREATE PROC dba_GenerateMergeStatement (@table NVARCHAR(128) )ASset nocount on; declare @return int;PRINT '-- ' + @table + ' -------------------------------------------------------------'--PRINT 'SET NOCOUNT ON;--'-- Set the identity insert on for tables with identitiesselect @return = objectproperty(object_id(@table), 'TableHasIdentity')if @return = 1 PRINT 'SET IDENTITY_INSERT [dbo].[' + @table + '] ON; 'declare @sql varchar(max) = ''declare @list varchar(max) = '';SELECT @list = @list + [name] +', 'from sys.columnswhere object_id = object_id(@table)SELECT @list = @list + [name] +', 'from sys.columnswhere object_id = object_id(@table)SELECT @list = @list + 's.' + [name] +', 'from sys.columnswhere object_id = object_id(@table)-- --------------------------------------------------------------------------------PRINT 'MERGE [dbo].[' + @table + '] AS t'PRINT 'USING (SELECT * FROM [source_database].[dbo].[' + @table + ']) as s'-- Get the join columns ----------------------------------------------------------SET @list = ''select @list = @list + 't.[' + c.COLUMN_NAME + '] = s.[' + c.COLUMN_NAME + '] AND 'from INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk , INFORMATION_SCHEMA.KEY_COLUMN_USAGE cwhere pk.TABLE_NAME = @tableand CONSTRAINT_TYPE = 'PRIMARY KEY'and c.TABLE_NAME = pk.TABLE_NAMEand c.CONSTRAINT_NAME = pk.CONSTRAINT_NAMESELECT @list = LEFT(@list, LEN(@list) -3)PRINT 'ON ( ' + @list + ')'-- WHEN MATCHED ------------------------------------------------------------------PRINT 'WHEN MATCHED THEN UPDATE SET'SELECT @list = '';SELECT @list = @list + ' [' + [name] + '] = s.[' + [name] +'],'from sys.columnswhere object_id = object_id(@table)-- don't update primary keysand [name] NOT IN (SELECT [column_name] from INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk , INFORMATION_SCHEMA.KEY_COLUMN_USAGE c where pk.TABLE_NAME = @table and CONSTRAINT_TYPE = 'PRIMARY KEY' and c.TABLE_NAME = pk.TABLE_NAME and c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME)-- and don't update identity columnsand columnproperty(object_id(@table), [name], 'IsIdentity ') = 0 --print @list PRINT left(@list, len(@list) -3 )-- WHEN NOT MATCHED BY TARGET ------------------------------------------------PRINT ' WHEN NOT MATCHED BY TARGET THEN';-- Get the insert listSET @list = ''SELECT @list = @list + '[' + [name] +'], 'from sys.columnswhere object_id = object_id(@table)SELECT @list = LEFT(@list, LEN(@list) - 1)PRINT ' INSERT(' + @list + ')'-- get the values listSET @list = ''SELECT @list = @list + 's.[' +[name] +'], 'from sys.columnswhere object_id = object_id(@table)SELECT @list = LEFT(@list, LEN(@list) - 1)PRINT ' VALUES(' + @list + ')'-- WHEN NOT MATCHED BY SOURCEprint 'WHEN NOT MATCHED BY SOURCE THEN DELETE; 'PRINT ''PRINT 'PRINT ''' + @table + ': '' + CAST(@@ROWCOUNT AS VARCHAR(100));';PRINT ''-- Set the identity insert OFF for tables with identitiesselect @return = objectproperty(object_id(@table), 'TableHasIdentity')if @return = 1 PRINT 'SET IDENTITY_INSERT [dbo].[' + @table + '] OFF; 'PRINT ''PRINT 'GO'PRINT '';

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  • SQL statements in seperate file

    - by tony
    Hello, I'm working on .net project and writing an application that interacts with database. I currently have some SQL statements in the code and I want to put these statements in separate file with solution. So, later when the application gets deployed, and if I want to update SQL statements, I could just update the statements in the file and just replace the file instead of redeploying the whole solution. Thank you for your help.

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  • MySQLi - Should every statement be prepared?

    - by Kerry
    I know its supposed to improve performance and clean strings, but lets say there are no variables? Might just be a SELECT COUNT( `column` ) AS count FROM `table` Should that be prepared? Is there any case that a SELECT statement should not be prepared?

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  • How can I use Databound variables in conditional statements within Custom Databound controls?

    - by William Calleja
    I'm developing my custom DataBound Controls that make use of an '<ItemTemplate>' tag and '<%# %>' server tags to generate some data however I need to make a conditional statement within one of my Databound controls as shown below. <custom:DataboundControl runat="server"> <ItemTemplate> <% if(((Dictionary<string, string>)Container.DataItem)["MyVariable"]=="" { %> <!-- Conditional Code Happens Here --> <% } %> </ItemTemplate> </custom:DataboundControl> Right now my code isn't working because the compiler cannot recognize my Container.DataItem variable within a <% %> tag and a <%# %> tag doesn't support conditional statements. What can I use?

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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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