Search Results

Search found 320 results on 13 pages for 'jackson tale'.

facebook twitter digg google delicious technorati stumbleupon myspace wordpress linkedin gmail igoogle windows live tumblr viadeo yahoo buzz yahoo mail yahoo bookmarks favorites email print

Page 2/13 | < Previous Page | 1 2 3 4 5 6 7 8 9 10 11 12  | Next Page >

  • A tale of two (and more) apps

    Robert Cooper gave a great lightning talk at our recent Atlanta GTUG meetup, where he discussed using a single codebase to target multiple mediums (e.g. Android, Facebook, Wave...

    Read the article

  • The tale of how the PowerShell CmdLets got installed with Azure SDK 1.4

    - by Enrique Lima
    I installed the Azure SDK 1.4 while rebuilding my laptop and ran the installation for the Windows Azure Service Management PowerShell CmdLets. Kicked off the installation script for the WASM PowerShell CmdLets by locating the path to which WASM PowerShell CmdLets was deployed to. Double clicked the startHere command. It will then open the WASM installation dialog. Click Next. Click Next. Notice the red x next to the Azure SDK 1.3, the problem is I have SDK 1.4 Here is the workaround, I go back to the location of the deployed WASM sources. Go into the setup path, then scripts>dependencies>check. Now, locate the CheckAzureSDK.ps1 file, and right-click, then edit. This is the content in the ps1 file, it check for the specific version of the Azure SDK, in this case, it is looking for version 1.3.11133.0038. We need for it to check for version 1.4.20227.1419 Now, save your ps1 file, go back to the open WASM install dialog, and click rescan. This time it should pass, then click next. A Command prompt window will appear, click any key. This completes the installation, click Close.

    Read the article

  • A Tale of Identifiers

    Identifiers aren't locators, and they aren't pointers or links either. They are a logical concept in a relational database, and, unlike the more traditional methods of accessing data, don't derive from the way that data gets stored. Identifiers uniquely identify members of the set, and it should be possible to validate and verify them. Celko somehow involves watches and taxi cabs to illustrate the point.

    Read the article

  • A Tale of Identifiers

    Identifiers aren't locators, and they aren't pointers or links either. They are a logical concept in a relational database, and, unlike the more traditional methods of accessing data, don't derive from the way that data gets stored. Identifiers uniquely identify members of the set, and it should be possible to validate and verify them. Celko somehow involves watches and taxi cabs to illustrate the point.

    Read the article

  • Simplifying the Google's PageRank Tale

    PageRank is a unique tool that defines the prominence of a particular web page. Optimizing your PR may help you a lot in enhancing your online presence and visibility. Forum posts, articles and back links are some of the important components that add lot in PR optimization.

    Read the article

  • A tale of UAC on a Windows 7 Development Machine

    - by TATWORTH
    This week I faced an interesting problem on a Windows 7 Development PC. I have run MakeLog (http://commondata.codeplex.com/releases/view/13206) sucessfully on my PC but my colleague could not run it sucessfully. Both of us are local administrators, so what I could do on my PC, he should have been able to do. The cure was to turn UAC completely off and re-boot. Once re-booted, the installation ran without incident. While I would never suggest turning off UAC normally, on development PCs, it is a liability as it stops many normal operations and occasionaly without giving a prompt.

    Read the article

  • A tale of two viewports &#8212; part one

    Back in November I started complicated research into measuring the widths and heights of variousinteresting elements in mobile browsers. This research kept me occupied for months and months; and frankly I becamea bit afraid of it because the subject is so complicated.Besides, when I re-did some tests in MarchI pretty quickly figured out I’d made some nasty mistakes in my original tests. Back to thedrawing board.However, after a review round by some browser vendors and some rewriting it’s done now.Today...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

    Read the article

  • Partitioned Tables, Indexes and Execution Plans: a Cautionary Tale

    Table partitioning is a blessing in that it makes large tables that have varying access patterns more scalable and manageable, but it is a mixed blessing. It is important to understand the down-side before using table partitioning. "SQL Backup Pro 7 improves on an already wonderful product" - Don KolendaHave you tried version 7 yet? Get faster, smaller, fully verified backups. Download a free trial of SQL Backup Pro 7.

    Read the article

  • A Tale of Search Engine Optimisation

    As such, search engine optimization becomes the part of the story where websites are literally 'optimized' so that they have the best interface, content, web pages and most traffic with a lot of links increasing their page rankings throughout the web. This is a field that is called 'internet marketing'.

    Read the article

  • how to store JSON into POJO using Jackson

    - by user2963680
    I am developing a module where i am using rest service to get data. i am not getting how to store JSON using Jackson and store it which has Queryparam also. Any help is really appreciated as I am new to this.I am trying to do server side filtering in extjs infinte grid which is sending the below request to rest service. when the page load first time, it sends http://myhost/mycontext/rest/populateGrid?_dc=9999999999999&page=1&start=0&limit=500 when you select filter on name and place, it sends http://myhost/mycontext/rest/populateGrid?_dc=9999999999999&filter=[{"type":"string","value":"Tom","field":"name"},{"type":"string","value":"London","field":"Location"}]&page=1&start=0&limit=500 I am trying to save this in POJO and then sending this to database to retrieve data. For this on rest side i have written something like this @Provider @Path("/rest") public interface restAccessPoint { @GET @Path("/populateGrid") @Produces({MediaType.APPLICATION_JSON}) public Response getallGridData(FilterJsonToJava filterparam,@QueryParam("page") String page,@QueryParam("start") String start,@QueryParam("limit") String limit); } public class FilterJsonToJava { @JsonProperty(value ="filter") private List<Filter> data; .. getter and setter below } public class Filter { @JsonProperty("type") private String type; @JsonProperty("value") private String value; @JsonProperty("field") private String field; ...getter and setters below } I am getting the below error The following warnings have been detected with resource and/or provider classes: WARNING: A HTTP GET method, public abstract javax.ws.rs.core.Response com.xx.xx.xx.xxxxx (com.xx.xx.xx.xx.json.FilterJsonToJava ,java.lang.String,java.lang.String,java.lang.String), should not consume any entity. com.xx.xx.xx.xx.json.FilterJsonToJava, and Java type class com.xx.xx.xx.FilterJsonToJava, and MIME media type application/octet-stream was not found [11/6/13 17:46:54:065] 0000001c ContainerRequ E The registered message body readers compatible with the MIME media type are: application/octet-stream com.sun.jersey.core.impl.provider.entity.ByteArrayProvider com.sun.jersey.core.impl.provider.entity.FileProvider com.sun.jersey.core.impl.provider.entity.InputStreamProvider com.sun.jersey.core.impl.provider.entity.DataSourceProvider com.sun.jersey.core.impl.provider.entity.RenderedImageProvider */* -> com.sun.jersey.core.impl.provider.entity.FormProvider ...

    Read the article

  • Make @JsonTypeInfo property optional

    - by Mark Peters
    I'm using @JsonTypeInfo to instruct Jackson to look in the @class property for concrete type information. However, sometimes I don't want to have to specify @class, particularly when the subtype can be inferred given the context. What's the best way to do that? Here's an example of the JSON: { "owner": {"name":"Dave"}, "residents":[ {"@class":"jacksonquestion.Dog","breed":"Greyhound"}, {"@class":"jacksonquestion.Human","name":"Cheryl"}, {"@class":"jacksonquestion.Human","name":"Timothy"} ] } and I'm trying to deserialize them into these classes (all in jacksonquestion.*): public class Household { private Human owner; private List<Animal> residents; public Human getOwner() { return owner; } public void setOwner(Human owner) { this.owner = owner; } public List<Animal> getResidents() { return residents; } public void setResidents(List<Animal> residents) { this.residents = residents; } } public class Animal {} public class Dog extends Animal { private String breed; public String getBreed() { return breed; } public void setBreed(String breed) { this.breed = breed; } } public class Human extends Animal { private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } } using this config: @JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.PROPERTY, property = "@class") private static class AnimalMixin { } //... ObjectMapper objectMapper = new ObjectMapper(); objectMapper.getDeserializationConfig().addMixInAnnotations(Animal.class, AnimalMixin.class); Household household = objectMapper.readValue(json, Household.class); System.out.println(household); As you can see, the owner is declared as a Human, not an Animal, so I want to be able to omit @class and have Jackson infer the type as it normally would. When I run this though, I get org.codehaus.jackson.map.JsonMappingException: Unexpected token (END_OBJECT), expected FIELD_NAME: missing property '@class' that is to contain type id (for class jacksonquestion.Human) Since "owner" doesn't specify @class. Any ideas? One initial thought I had was to use @JsonTypeInfo on the property rather than the type. However, this cannot be leveraged to annotate the element type of a list.

    Read the article

  • JsonParseException on Valid JSON

    - by user2909602
    I am having an issue calling a RESTful service from my client code. I have written the RESTful service using CXF/Jackson, deployed to localhost, and tested using RESTClient successfully. Below is a snippet of the service code: @POST @Produces("application/json") @Consumes("application/json") @Path("/set/mood") public Response setMood(MoodMeter mm) { this.getMmDAO().insert(mm); return Response.ok().entity(mm).build(); } The model class and dao work successfully and the service itself works fine using RESTClient. However, when I attempt to call this service from Java Script, I get the error below on the server side: Caused by: org.codehaus.jackson.JsonParseException: Unexpected character ('m' (code 109)): expected a valid value (number, String, array, object, 'true', 'false' or 'null') I have copied the client side code below. To make sure it has nothing to do with the JSON data itself, I used a valid JSON string (which works using RESTClient, JSON.parse() method, and JSONLint) in the vars 'json' (string) and 'jsonData' (JSON). Below is the Java Script code: var json = '{"mood_value":8,"mood_comments":"new comments","user_id":5,"point":{"latitude":37.292929,"longitude":38.0323323},"created_dtm":1381546869260}'; var jsonData = JSON.parse(json); $.ajax({ url: 'http://localhost:8080/moodmeter/app/service/set/mood', dataType: 'json', data: jsonData, type: "POST", contentType: "application/json" }); I've seen the JsonParseException a number of times on other threads, but in this case the JSON itself appears to be valid (and tested). Any thoughts are appreciated.

    Read the article

  • Turning a JSON list into a POJO

    - by Josh L
    I'm having trouble getting this bit of JSON into a POJO. I'm using Jackson configured like this: protected ThreadLocal<ObjectMapper> jparser = new ThreadLocal<ObjectMapper>(); public void receive(Object object) { try { if (object instanceof String && ((String)object).length() != 0) { ObjectDefinition t = null ; if (parserChoice==0) { if (jparser.get()==null) { jparser.set(new ObjectMapper()); } t = jparser.get().readValue((String)object, ObjectDefinition.class); } Object key = t.getKey(); if (key == null) return; transaction.put(key,t); } } catch (Exception e) { e.printStackTrace(); } } Here's the JSON that needs to be turned into a POJO: { "id":"exampleID1", "entities":{ "tags":[ { "text":"textexample1", "indices":[ 2, 14 ] }, { "text":"textexample2", "indices":[ 31, 36 ] }, { "text":"textexample3", "indices":[ 37, 43 ] } ] } And lastly, here's what I currently have for the java class: protected Entities entities; @JsonIgnoreProperties(ignoreUnknown = true) protected class Entities { public Entities() {} protected Tags tags; @JsonIgnoreProperties(ignoreUnknown = true) protected class Tags { public Tags() {} protected String text; public String getText() { return text; } public void setText(String text) { this.text = text; } }; public Tags getTags() { return tags; } public void setTags(Tags tags) { this.tags = tags; } }; //Getters & Setters ... I've been able to translate the more simple objects into a POJO, but the list has me stumped. Any help is appreciated. Thanks!

    Read the article

  • Warning: This class was probably produced by a broken compiler.

    - by Michal Dymel
    I have added Jacson libs to my android project and now I am getting such warnings in console: warning: Ignoring InnerClasses attribute for an anonymous inner class that doesn't come with an associated EnclosingMethod attribute. (This class was probably produced by a broken compiler.) I've tried to recompile libs, but it didn't help. Warnings are gone when I remove these libs from project. Everything is working fine on the device, but this annoys me ;) Do you know any solution?

    Read the article

  • How to get the ObjectId value from MongoDB?

    - by LVarayut
    I'm using Jongo with Play framework 2, java. I added some data into my MongoDB. {"_id" : ObjectId("538dafffbf6b562617252178"), ... } However, when I fetched the ObjectId from the database, it gave me like: de.undercouch.bson4jackson.types.ObjectId@484431ff instead of 538dafffbf6b562617252178. I don't quite understand how can I get the ObjectId value. My class is defined as following: public class Product { @JsonProperty("_id") protected String id; ... public Product() { } public String getId() { return id; } public void setId(String id) { this.id = id; } } EDIT In order to fetch the data, I simply use find() function provided by Jongo as following: public static Iterable<Product> findAll(){ return products().find().as(Product.class); }

    Read the article

  • Grails and googleJsonAPIService

    - by Calahad
    I am using the googleJsonAPIService to manipulate users (CRUD). This is how I get the Directory instance: def getBuilder() { def builder def httpTransport = googleJsonAPIService.makeTransport() def jsonFactory = googleJsonAPIService.makeJsonFactory() def requestInitialiser = googleJsonAPIService.getRequestInitialiser() builder = new Directory.Builder(httpTransport, jsonFactory, requestInitialiser); return builder } Directory getGoogleService() { Directory googleService = getBuilder().build() return googleService; } Once I have this service, I use it to get a user's details (in my own service) for example: def query = getGoogleService().users().get(id) return handleException { query.execute() } I manually populate a DTO with the result of that query, and this is where my question comes: Is there an elegant way to have this mapping (object returned to DTO) done automatically so all I have to do is pass the class of the object to be returned? This is the structure of the object returned by google : ["agreedToTerms":true,"changePasswordAtNextLogin":false, "creationTime":"2013-11-04T04:33:35.000Z", "emails":[{"address":"[email protected]","primary":true}],...]

    Read the article

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

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

    Read the article

  • Failed to load resource: the server responded with a status of 406 (Not Acceptable)

    - by skip
    I am trying to send json data and get back json data as well. I've <annotation-driven /> configured in my servlet-context.xml and I am using Spring framework version 3.1.0.RELEASE. When I send the request the browser tells me that it is not happy with the data returned from the server and gives me 406 error. And when I see the response from the server I see the whole 406 page returned by tomcat 6 server. I have got following in my pom for Jackson/Jackson processor: <!-- Jackson --> <dependency> <groupId>org.codehaus.jackson</groupId> <artifactId>jackson-core-asl</artifactId> <version>1.9.4</version> </dependency> <dependency> <groupId>org.codehaus.jackson</groupId> <artifactId>jackson-mapper-asl</artifactId> <version>1.9.4</version> </dependency> <dependency> <groupId>org.codehaus.jackson</groupId> <artifactId>jackson-xc</artifactId> <version>1.9.4</version> </dependency> <!-- Jackson JSON Processor --> <dependency> <groupId>org.codehaus.jackson</groupId> <artifactId>jackson-mapper-asl</artifactId> <version>1.8.1</version> </dependency> Following is the jquery code I am using to send the json request: $(function(){$(".sutmit-button").click(function(){ var dataString=$("#app-form").serialize(); $.ajax({ type:"POST", url:"apply.json", data:dataString, success:function(data, textStatus, jqXHR){ console.log(jqXHR.status); console.log(data); $('.postcontent').html("<div id='message'></div>"); $('#message').html("<h3>Request Submitted</h3>").append("<p>Thank you for submiting your request.</p>").hide().fadeIn(1500,function(){$('#message');}); }, error:function(jqXHR, textStatus, errorThrown) { console.log(jqXHR.status); $('.postcontent').html("<div id='message'></div>"); $('#message').html("<h3>Request failed.</h3>").hide().fadeIn(1500,function(){$('#message');}); }, dataType: "json" }); return false;});}); Following is the Controller that is handling the request: @RequestMapping(method = RequestMethod.POST, value="apply", headers="Accept=application/json") public @ResponseBody Application processFranchiseeApplicationForm(HttpServletRequest request) { //... Application application = new Application(...); //... logger.debug(application); return application; } I am not able to figure out the reason why I might be getting this error. Could someone help me understand why am I getting the given error? Thanks.

    Read the article

  • JSON: Jackson stream parser - is it really worth it?

    - by synic
    I'm making pretty heavy use of JSON parsing in an app I'm writing. Most of what I have done is already implemented using Android's built in JSONObject library (is it json-lib?). JSONObject appears to create instances of absolutely everything in the JSON string... even if I don't end up using all of them. My app currently runs pretty well, even on a G1. My question is this: are the speed and memory benefits from using a stream parser like Jackson worth all the trouble? By trouble, I mean this: As far as I can tell, there are three downsides to using Jackson instead of the built in library: Dependency on an external library. This makes your .apk bigger in the end. Not a huge deal. Your app is more fragile. Since the parsing is not done automatically, it is more vulnerable to changes in the JSON text that it's parsing. I'm extremely worried that malformed JSON will result in infinite loops (as pull parsing requires a lot of while loops). Writing code to parse JSON via a stream parser is ugly and tedious.

    Read the article

  • A tale of two user ids: Why does NFS not recognize a new user id?

    - by user76177
    I have two servers running RHEL6. The main server, which I will refer to as server, is a database server. The application server, which I will refer to as client, mounts a directory from server via NFS. There is a user, appuser, on both client and server. However, appuser's id on client is 502. appuser's id on server is 506. Both users need read and write capability on the NFS share. To facilitate this, I made the share owned by appuser on server. Of course, client does not recognize that ownership, since appuser has a different id on client. So I did the following: Changed id of user in /etc/passwd on client to be 506 **Changed ownership of appuser's $HOME on client to be appuser again so that I could log in. Now, when I go to look at the NFS share from the client side, I see that it is owned by 502. 502 is the OLD id for appuser on client. I can't change ownership of the NFS share from client, since that is a volume that physically resides on server. I need to make sure that the NFS share shows ownership of appuser from both server and client. What step have I missed since changing the appuser id on client? NOTE: I have not rebooted client or done anything else yet.

    Read the article

  • Python Multiword Index

    - by Manab Chetia
    index = {'Michael': [['mj.com',1], ['Nine.com',9],['i.com', 34]], / 'Jackson': [['One.com',4],['mj.com', 2],['Nine.com', 10], ['i.com', 45]], / 'Thriller' : [['Seven.com', 7], ['Ten.com',10], ['One.com', 5], ['mj.com',3]} # In this dictionary (index), for eg: 'KEYWORD': # [['THE LINK in which KEYWORD is present,'POSITION # of KEYWORD in the page specified by link']] eg: Michael is present in MJ.com, NINE.com, and i.com at positions 1, 9, 34 of respective pages. Please help me with a python procedure which takes index and KEYWORDS as input. When i enter 'MICHAEL'. The result should be: >>['mj.com', 'nine.com', 'i.com'] When I enter 'MICHAEL JACKSON'. The result should be : >>['mj.com', 'Nine.com'] as 'Michael' and 'Jackson' are present at 'mj.com' and 'nine.com' consecutively i.e. in positions (1,2) & (9,10) respectively. The result should not show 'i.com' even though it contains both KEYWORDS but they are not placed consecutively. When I enter 'MICHAEL JACKSON THRILLER', the result should be ['mj.com'] as the 3 words 'MICHAEL', 'JACKSON', 'THRILLER' are placed consecutively in 'mj.com' ie positions (1, 2, 3) respectively. If I enter 'THRILLER JACKSON' or 'THRILLER FEDERER', the result should be NONE.

    Read the article

  • 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.

    Read the article

facebook twitter digg google delicious technorati stumbleupon myspace wordpress linkedin gmail igoogle windows live tumblr viadeo yahoo buzz yahoo mail yahoo bookmarks favorites email print

< Previous Page | 1 2 3 4 5 6 7 8 9 10 11 12  | Next Page >