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  • Is an object still connected to a list after FirstOrDefault?

    - by Cynthia
    Here's my code: Event thisEvent = (from i in list where (i.eventID == eventID) select i).FirstOrDefault(); if (thisEvent != null) { thisEvent.eventResolved = resolved; thisEvent.eventSequence.Add(item); } "list" is a collection of IEnumerable, i.e. IEnumerable<Event> list; What I'm wondering is: after creating thisEvent using FirstOrDefault, is thisEvent still connected to list? In other words, when I change the two properties, eventResolved and eventSequence, is "list" actually changed, or is thisEvent just some totally disconnected copy of an item in "list"?

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  • Sub Query making Query slow.

    - by Muhammad Kashif Nadeem
    Please copy and paste following script. DECLARE @MainTable TABLE(MainTablePkId int) INSERT INTO @MainTable SELECT 1 INSERT INTO @MainTable SELECT 2 DECLARE @SomeTable TABLE(SomeIdPk int, MainTablePkId int, ViewedTime1 datetime) INSERT INTO @SomeTable SELECT 1, 1, DATEADD(dd, -10, getdate()) INSERT INTO @SomeTable SELECT 2, 1, DATEADD(dd, -9, getdate()) INSERT INTO @SomeTable SELECT 3, 2, DATEADD(dd, -6, getdate()) DECLARE @SomeTableDetail TABLE(DetailIdPk int, SomeIdPk int, Viewed INT, ViewedTimeDetail datetime) INSERT INTO @SomeTableDetail SELECT 1, 1, 1, DATEADD(dd, -7, getdate()) INSERT INTO @SomeTableDetail SELECT 2, 2, NULL, DATEADD(dd, -6, getdate()) INSERT INTO @SomeTableDetail SELECT 3, 2, 2, DATEADD(dd, -8, getdate()) INSERT INTO @SomeTableDetail SELECT 4, 3, 1, DATEADD(dd, -6, getdate()) SELECT m.MainTablePkId, (SELECT COUNT(Viewed) FROM @SomeTableDetail), (SELECT TOP 1 s2.ViewedTimeDetail FROM @SomeTableDetail s2 INNER JOIN @SomeTable s1 ON s2.SomeIdPk = s1.SomeIdPk WHERE s1.MainTablePkId = m.MainTablePkId) FROM @MainTable m Above given script is just sample. I have long list of columns in SELECT and around 12+ columns in Sub Query. In my From clause there are around 8 tables. To fetch 2000 records full query take 21 seconds and if I remove Subquiries it just take 4 seconds. I have tried to optimize query using 'Database Engine Tuning Advisor' and on adding new advised indexes and statistics but these changes make query time even bad. Note: As I have mentioned that this is test data to explain my question the real data has lot of tables joins columns but without Sub-Query the results us fine. Any help thanks.

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  • How to limit select items with L2E/S?

    - by orlon
    This code is a no-go var errors = (from error in db.ELMAH_Error select new { error.Application, error.Host, error.Type, error.Source, error.Message, error.User, error.StatusCode, error.TimeUtc }).ToList(); return View(errors); as it results in a 'requires a model of type IEnumerable' error. The following code of course works fine, but selects all the columns, some of which I'm simply not interested in: var errors = (from error in db.ELMAH_Error select error).ToList(); return View(errors); I'm brand spanking new to MVC2 + L2E, so maybe I'm just not thinking in the right mindset yet, but this seems counter-intuitive. Is there an easy way to select a limited number of columns, or is this just part of using an ORM?

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  • Will First() perform the OrderBy()?

    - by Martin
    Is there any difference in (asymptotic) performance between Orders.OrderBy(order => order.Date).First() and Orders.Where(order => order.Date == Orders.Max(x => x.Date)); i.e. will First() perform the OrderBy()? I'm guessing no. MSDN says enumerating the collection via foreach och GetEnumerator does but the phrasing does not exclude other extensions.

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  • Entity Framework EntityKey / Foreign Key problem.

    - by Ronny176
    Hi, I keep getting the same error: Entities in 'VlaamseOverheidMeterEntities.ObjectMeter' participate in the 'FK_ObjectMeter_Meter' relationship. 0 related 'Meter' were found. 1 'Meter' is expected. I have the following table structure: Meter 1 <- * ObjectMeter * - 1 VO_Object It is always the same scenario: The first meter is added to the database, the second meter gives the error above. I have the following code in my manager: public List<string> addTemporary(string username, string meterNaam, string readingType, string parentID) { Meter meter = new Meter(); VO_Object voObject = objectManager.getObjectByID(parentID); ObjectMeter objMeter = new ObjectMeter(); meter.readingType = (int)Enum.Parse(typeof(ReadingType), readingType); meter.isActive = true; meter.name = meterNaam; meter.startDate = DateTime.Now; meter.endDate = DateTime.Now.AddYears(6000); meter.uniqueIdentifier = "N/A"; meter.meterType = (int)Enum.Parse(typeof(MeterType), "NA"); meter.meterCategory = (int)Enum.Parse(typeof(MeterCategory), "NA"); meter.energyType = (int)Enum.Parse(typeof(EnergyType), "NA"); meter.utilityType = (int)Enum.Parse(typeof(UtilityType), "NA"); meter.unitOfMeasure = (int)Enum.Parse(typeof(UnitOfMeasure), "NA"); objMeter.valid_from = meter.startDate; objMeter.valid_until = meter.endDate; objMeter.Meter = meter; objMeter.VO_Object = voObject; createMeter(meter); List<String> str = new List<string>(); str.Add("" + meter.meterID); str.Add(meter.name); return str; } and this in my Dao Class which links to the database: internal void CreateMeter(Meter _meter) { _entities.AddToMeter(_meter); _entities.SaveChanges(); } Can someone please explain this error? Ronald

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  • query in query builder in a Table Adapter

    - by Sony
    I am working with the datasets of .net I have an Oracle Query which is working fine . but I copy the query as sql statement within Table Adapter wizard and after I clicked the Query Builder button ,there is SQL syntax error. The query is below: SELECT lead_id, NAME, ADDRESS, CITY, EMAIL, PHONE, PINCODE, STATE, QUALIFICATION, DOB, status FROM (SELECT l.lead_id, l.NAME, l.ADDRESS, l.CITY, l.EMAIL, l.PHONE, l.PINCODE, l.STATE, l.QUALIFICATION, l.DOB, CASE WHEN s.status IS NULL THEN 'Not Updated !' ELSE s.status END status, row_number() over(PARTITION BY l.lead_id ORDER BY t .CREATED_DATE DESC) rn FROM LEADS l JOIN Leads lc ON l.USER_ID = lc.USER_ID AND l.USER_ID = :iuser_id AND(l.CREATED_DATE BETWEEN (TO_DATE(:ifrom_date , 'dd-mm-yyyy') ) AND (TO_DATE (:ito_date, 'dd-mm-yyyy' ) )) LEFT JOIN LEADTRANSACTION t ON l.lead_id = t .lead_id LEFT JOIN STATUS s ON s.STATUS_ID = t .STATUS_ID) WHERE rn = 1;

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  • Is there a better way to do updates in LinqToSQL?

    - by Vaccano
    I have a list (that comes to my middleware app from the client) that I need to put in my database. Some items in the list may already be in the db (just need an update). Others are new inserts. This turns out to be much harder than I thought I would be. Here is my code to do that. I am hoping there is a better way: public void InsertClients(List<Client> clients) { var comparer = new LambdaComparer<Client>((x, y) => x.Id == y.Id); // Get a listing of all the ones we will be updating var alreadyInDB = ctx.Clients .Where(client => clients.Contains(client, comparer)); // Update the changes for those already in the db foreach (Client clientDB in alreadyInDB) { var clientDBClosure = clientDB; Client clientParam = clients.Find(x => x.Id == clientDBClosure.Id); clientDB.ArrivalTime = clientParam.ArrivalTime; clientDB.ClientId = clientParam.ClientId; clientDB.ClientName = clientParam.ClientName; clientDB.ClientEventTime = clientParam.ClientEventTime; clientDB.EmployeeCount = clientParam.EmployeeCount; clientDB.ManagerId = clientParam.ManagerId; } // Get a list of all clients that are not in my the database. var notInDB = clients.Where(x => alreadyInDB.Contains(x, comparer) == false); ctx.Clients.InsertAllOnSubmit(notInDB); ctx.SubmitChanges(); } This seems like a lot of work to do a simple update. But maybe I am just spoiled. Anyway, if there is a easier way to do this please let me know. Note: If you are curious the code to the LambdaComparer is here: http://gist.github.com/335780#file_lambda_comparer.cs

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  • Trigger on database using a web application and a winform application

    - by Michael
    Hello all, Situation: I have a web application which shows errors and where you can accept those error messages. I also have a service, which checks errors from a system and sets the error messages in the database. When I accept an error in the web application, i would like the service to know which error message has been accepted, so that it can do some other actions. My guess is that this could be done through some sort of trigger, but i can't figure out how. Can anyone help me with this?

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  • A better solution than element.Elements("Whatever").First()?

    - by codeka
    I have an XML file like this: <SiteConfig> <Sites> <Site Identifier="a" /> <Site Identifier="b" /> <Site Identifier="c" /> </Sites> </SiteConfig> The file is user-editable, so I want to provide reasonable error message in case I can't properly parse it. I could probably write a .xsd for it, but that seems kind of overkill for a simple file. So anyway, when querying for the list of <Site> nodes, there's a couple of ways I could do it: var doc = XDocument.Load(...); var siteNodes = from siteNode in doc.Element("SiteConfig").Element("SiteUrls").Elements("Sites") select siteNode; But the problem with this is that if the user has not included the <SiteUrls> node (say) it'll just throw a NullReferenceException which doesn't really say much to the user about what actually went wrong. Another possibility is just to use Elements() everywhere instead of Element(), but that doesn't always work out when coupled with calls to Attribute(), for example, in the following situation: var siteNodes = from siteNode in doc.Elements("SiteConfig") .Elements("SiteUrls") .Elements("Sites") where siteNode.Attribute("Identifier").Value == "a" select siteNode; (That is, there's no equivalent to Attributes("xxx").Value) Is there something built-in to the framework to handle this situation a little better? What I would prefer is a version of Element() (and of Attribute() while we're at it) that throws a descriptive exception (e.g. "Looking for element <xyz> under <abc> but no such element was found") instead of returning null. I could write my own version of Element() and Attribute() but it just seems to me like this is such a common scenario that I must be missing something...

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  • Need help optimizing this Django aggregate query

    - by Chris Lawlor
    I have the following model class Plugin(models.Model): name = models.CharField(max_length=50) # more fields which represents a plugin that can be downloaded from my site. To track downloads, I have class Download(models.Model): plugin = models.ForiegnKey(Plugin) timestamp = models.DateTimeField(auto_now=True) So to build a view showing plugins sorted by downloads, I have the following query: # pbd is plugins by download - commented here to prevent scrolling pbd = Plugin.objects.annotate(dl_total=Count('download')).order_by('-dl_total') Which works, but is very slow. With only 1,000 plugins, the avg. response is 3.6 - 3.9 seconds (devserver with local PostgreSQL db), where a similar view with a much simpler query (sorting by plugin release date) takes 160 ms or so. I'm looking for suggestions on how to optimize this query. I'd really prefer that the query return Plugin objects (as opposed to using values) since I'm sharing the same template for the other views (Plugins by rating, Plugins by release date, etc.), so the template is expecting Plugin objects - plus I'm not sure how I would get things like the absolute_url without a reference to the plugin object. Or, is my whole approach doomed to failure? Is there a better way to track downloads? I ultimately want to provide users some nice download statistics for the plugins they've uploaded - like downloads per day/week/month. Will I have to calculate and cache Downloads at some point? EDIT: In my test dataset, there are somewhere between 10-20 Download instances per Plugin - in production I expect this number would be much higher for many of the plugins.

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  • Collection was modified; enumeration operation may not execute

    - by Rita
    I have the below code. I am trying to remove the record and it is throwing Exception when it is removing the Record. "Collection was modified; enumeration operation may not execute." Any ideas on how to get rid of the message. Appreciate your time. //validClaimControlNo has valid ClaimControl Numbers. List<string> validClaimControlNo = new List<string>(); int count = 0; foreach (List<Field> f in records) { foreach (Field fe in f) { if (i == 0) if (!(validClaimControlNo.Contains(fe.Value))) { //if this claim is not in the Valid list, Remove that Record records.RemoveAt(count); } i++; } i = 0; count++; }

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  • SQL Server 2005: Internal Query Processor Error:

    - by Geetha
    I am trying to execute this following procedure in SQL Server 2005. I was able to execute this in my development server and when i tried to use this in the Live Server I am getting an Error "Internal Query Processor Error: The query processor could not produce a query plan. For more information, contact Customer Support Services". am using the same Database and the same format. when we searched in the web it shows some fixes to be used in sql server 2005 to avoid this error but my DBA has confirmed that all the patches are updated in our server. can anyone give me some clue on this. Query: create Procedure [dbo].[sample_Select] @ID as varchar(40) as Declare @Execstring as varchar(1000) set @Execstring = ' Declare @MID as varchar(40) Set @MID = '''+@ID+''' select * from ( select t1.field1, t1.field2 AS field2 , t1.field3 AS field3 , L.field1 AS field1 , L. field2 AS field2 from table1 AS t1 INNER JOIN MasterTable AS L ON L. field1 = t1. field2 where t1. field2 LIKE @MID ) as DataTable PIVOT ( Count(field2) FOR field3 IN (' Select @Execstring=@Execstring+ L.field2 +',' FROM MasterTable AS L inner join table1 AS t1 ON t1.field1= L.field2 Where t1.field2 LIKE @ID set @Execstring = stuff(@Execstring, len(@Execstring), 1, '') set @Execstring =@Execstring +')) as pivotTable' exec (@Execstring)

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  • View Lambdas in Visual Studio Debugger

    - by Vaccano
    I have the a simple LinqToSQL statement that is not working. Something Like this: List<MyClass> myList = _ctx.DBList .Where(x => x.AGuidID == paramID) .Where(x => x.BBoolVal == false) .ToList(); I look at _ctx.DBList in the debugger and the second item fits both parameters. Is there a way I can dig into this more to see what is going wrong?

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  • Help on MySQL table indexing when GROUP BY is used in a query

    - by Silver Light
    Thank you for your attention. There are two INNODB tables: Table authors id INT nickname VARCHAR(50) status ENUM('active', 'blocked') about TEXT Table books author_id INT title VARCHAR(150) I'm running a query against these tables, to get each author and a count of books he has: SELECT a. * , COUNT( b.id ) AS book_count FROM authors AS a, books AS b WHERE a.status != 'blocked' AND b.author_id = a.id GROUP BY a.id ORDER BY a.nickname This query is very slow (takes about 6 seconds to execute). I have an index on books.author_id and it works perfectly, but I do not know how to create an index on authors table, so that this query could use it. Here is how current EXPLAIN looks: id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE a ALL PRIMARY,id_status_nickname NULL NULL NULL 3305 Using where; Using temporary; Using filesort 1 SIMPLE b ref key_author_id key_author_id 5 a.id 2 Using where; Using index I've looked at MySQL manual on optimizing queries with group by, but could not figure out how I can apply it on my query. I'll appreciate any help and hints on this - what must be the index structure, so that MySQL could use it?

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  • Is there a way to load an existing connection string for Linq to SQL from an app.config file?

    - by Brian Surowiec
    I'm running into a really annoying problem with my Linq to SQL project. When I add everything in under the web project everything goes as expected and I can tell it to use my existing connection string stored in the web.config file and the Linq code pulls directly from the ConfigurationManager. This all turns ugly once I move the code into its own project. I’ve created an app.config file, put the connection string in there as it was in the web.config but when I try to add another table in the IDE keeps forcing me to either hardcode the connection string or creates a Settings file and puts it in there, which then adds a new entry into the app.config file with a new name. Is there a way keep my Linq code in its own project yet still refer back to my config file without the IDE continuously hardcoding the connection string or creating the Settings file? I’m converting part of my DAL over to use Linq to SQL so I’d like to use the existing connection string that our old code is using as well as keep the value in a common location, and one spot, instead of in a number of spots. Manually changing the mode to WebSettings instead of AppSettings works untill I try to add a new table, then it goes back to hardcoding the value or recreating the Settings file. I also tried to switch the project type to be a web project and then rename my app.config to web.config and then everything works as I’d like it to. I’m just not sure if there are any downfalls to keeping this as a web project since it really isn't one. The project only contains the Linq to SQL code and an implementation of my repository classes. My project layout looks like this Website -connectionString.config -web.config (refers to connectionString.config) Middle Tier -Business Logic -Repository Interfaces -etc. DAL -Linq to SQL code -Existing SPROC code -connectionString.config (linked from the web poject) -app.config (refers to connectionString.config)

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  • How to join multiple tables using LINQ-to-SQL?

    - by user603245
    Hi! I'm quite new to linq, so please bear with me. I'm working on a asp.net webpage and I want to add a "search function" (textbox where user inputs name or surname or both or just parts of it and gets back all related information). I have two tables ("Person" and "Application") and I want to display some columns from Person (name and surname) and some from Application (score, position,...). I know how I could do it using sql, but I want to learn more about linq and thus I want to do it using linq. For now I got two main ideas: 1.) var person = dataContext.GetTable<Person>(); var application = dataContext.GetTable<Application>(); var p1 = from p in Person where(p.Name.Contains(tokens[0]) || p.Surname.Contains(tokens[1])) select new {Id = p.Id, Name = p.Name, Surname = p.Surname}; //or maybe without this line //I don't know how to do the following properly var result = from a in Application where a.FK_Application.Equals(index) //just to get the "right" type of application //this is not right, but I don't know how to do it better join p1 on p1.Id == a.FK_Person 2.) The other idea is just to go through "Application" and instead of "join p1 ..." to use var result = from a in Application where a.FK_Application.Equals(index) //just to get the "right" type of application join p from Person on p.Id == a.FK_Person where p.Name.Contains(tokens[0]) || p.Surname.Contains(tokens[1]) I think that first idea is better for queries without the first "where" condition, which I also intended to use. Regardless of what is better (faster), I still don't know how to do it using linq. Also in the end I wanted to display / select just some parts (columns) of the result (joined tables + filtering conditions). I really want to know how to do such things using linq as I'll be dealing also with some similar problems with local data, where I can use only linq. Could somebody please explain me how to do it, I spent days trying to figure it out and searching on the internet for answers. Thank you for your time.

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  • Using LINQ Distinct: With an Example on ASP.NET MVC SelectListItem

    - by Joe Mayo
    One of the things that might be surprising in the LINQ Distinct standard query operator is that it doesn’t automatically work properly on custom classes. There are reasons for this, which I’ll explain shortly. The example I’ll use in this post focuses on pulling a unique list of names to load into a drop-down list. I’ll explain the sample application, show you typical first shot at Distinct, explain why it won’t work as you expect, and then demonstrate a solution to make Distinct work with any custom class. The technologies I’m using are  LINQ to Twitter, LINQ to Objects, Telerik Extensions for ASP.NET MVC, ASP.NET MVC 2, and Visual Studio 2010. The function of the example program is to show a list of people that I follow.  In Twitter API vernacular, these people are called “Friends”; though I’ve never met most of them in real life. This is part of the ubiquitous language of social networking, and Twitter in particular, so you’ll see my objects named accordingly. Where Distinct comes into play is because I want to have a drop-down list with the names of the friends appearing in the list. Some friends are quite verbose, which means I can’t just extract names from each tweet and populate the drop-down; otherwise, I would end up with many duplicate names. Therefore, Distinct is the appropriate operator to eliminate the extra entries from my friends who tend to be enthusiastic tweeters. The sample doesn’t do anything with the drop-down list and I leave that up to imagination for what it’s practical purpose could be; perhaps a filter for the list if I only want to see a certain person’s tweets or maybe a quick list that I plan to combine with a TextBox and Button to reply to a friend. When the program runs, you’ll need to authenticate with Twitter, because I’m using OAuth (DotNetOpenAuth), for authentication, and then you’ll see the drop-down list of names above the grid with the most recent tweets from friends. Here’s what the application looks like when it runs: As you can see, there is a drop-down list above the grid. The drop-down list is where most of the focus of this article will be. There is some description of the code before we talk about the Distinct operator, but we’ll get there soon. This is an ASP.NET MVC2 application, written with VS 2010. Here’s the View that produces this screen: <%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<TwitterFriendsViewModel>" %> <%@ Import Namespace="DistinctSelectList.Models" %> <asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">     Home Page </asp:Content><asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">     <fieldset>         <legend>Twitter Friends</legend>         <div>             <%= Html.DropDownListFor(                     twendVM => twendVM.FriendNames,                     Model.FriendNames,                     "<All Friends>") %>         </div>         <div>             <% Html.Telerik().Grid<TweetViewModel>(Model.Tweets)                    .Name("TwitterFriendsGrid")                    .Columns(cols =>                     {                         cols.Template(col =>                             { %>                                 <img src="<%= col.ImageUrl %>"                                      alt="<%= col.ScreenName %>" />                         <% });                         cols.Bound(col => col.ScreenName);                         cols.Bound(col => col.Tweet);                     })                    .Render(); %>         </div>     </fieldset> </asp:Content> As shown above, the Grid is from Telerik’s Extensions for ASP.NET MVC. The first column is a template that renders the user’s Avatar from a URL provided by the Twitter query. Both the Grid and DropDownListFor display properties that are collections from a TwitterFriendsViewModel class, shown below: using System.Collections.Generic; using System.Web.Mvc; namespace DistinctSelectList.Models { /// /// For finding friend info on screen /// public class TwitterFriendsViewModel { /// /// Display names of friends in drop-down list /// public List FriendNames { get; set; } /// /// Display tweets in grid /// public List Tweets { get; set; } } } I created the TwitterFreindsViewModel. The two Lists are what the View consumes to populate the DropDownListFor and Grid. Notice that FriendNames is a List of SelectListItem, which is an MVC class. Another custom class I created is the TweetViewModel (the type of the Tweets List), shown below: namespace DistinctSelectList.Models { /// /// Info on friend tweets /// public class TweetViewModel { /// /// User's avatar /// public string ImageUrl { get; set; } /// /// User's Twitter name /// public string ScreenName { get; set; } /// /// Text containing user's tweet /// public string Tweet { get; set; } } } The initial Twitter query returns much more information than we need for our purposes and this a special class for displaying info in the View.  Now you know about the View and how it’s constructed. Let’s look at the controller next. The controller for this demo performs authentication, data retrieval, data manipulation, and view selection. I’ll skip the description of the authentication because it’s a normal part of using OAuth with LINQ to Twitter. Instead, we’ll drill down and focus on the Distinct operator. However, I’ll show you the entire controller, below,  so that you can see how it all fits together: using System.Linq; using System.Web.Mvc; using DistinctSelectList.Models; using LinqToTwitter; namespace DistinctSelectList.Controllers { [HandleError] public class HomeController : Controller { private MvcOAuthAuthorization auth; private TwitterContext twitterCtx; /// /// Display a list of friends current tweets /// /// public ActionResult Index() { auth = new MvcOAuthAuthorization(InMemoryTokenManager.Instance, InMemoryTokenManager.AccessToken); string accessToken = auth.CompleteAuthorize(); if (accessToken != null) { InMemoryTokenManager.AccessToken = accessToken; } if (auth.CachedCredentialsAvailable) { auth.SignOn(); } else { return auth.BeginAuthorize(); } twitterCtx = new TwitterContext(auth); var friendTweets = (from tweet in twitterCtx.Status where tweet.Type == StatusType.Friends select new TweetViewModel { ImageUrl = tweet.User.ProfileImageUrl, ScreenName = tweet.User.Identifier.ScreenName, Tweet = tweet.Text }) .ToList(); var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct() .ToList(); var twendsVM = new TwitterFriendsViewModel { Tweets = friendTweets, FriendNames = friendNames }; return View(twendsVM); } public ActionResult About() { return View(); } } } The important part of the listing above are the LINQ to Twitter queries for friendTweets and friendNames. Both of these results are used in the subsequent population of the twendsVM instance that is passed to the view. Let’s dissect these two statements for clarification and focus on what is happening with Distinct. The query for friendTweets gets a list of the 20 most recent tweets (as specified by the Twitter API for friend queries) and performs a projection into the custom TweetViewModel class, repeated below for your convenience: var friendTweets = (from tweet in twitterCtx.Status where tweet.Type == StatusType.Friends select new TweetViewModel { ImageUrl = tweet.User.ProfileImageUrl, ScreenName = tweet.User.Identifier.ScreenName, Tweet = tweet.Text }) .ToList(); The LINQ to Twitter query above simplifies what we need to work with in the View and the reduces the amount of information we have to look at in subsequent queries. Given the friendTweets above, the next query performs another projection into an MVC SelectListItem, which is required for binding to the DropDownList.  This brings us to the focus of this blog post, writing a correct query that uses the Distinct operator. The query below uses LINQ to Objects, querying the friendTweets collection to get friendNames: var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct() .ToList(); The above implementation of Distinct seems normal, but it is deceptively incorrect. After running the query above, by executing the application, you’ll notice that the drop-down list contains many duplicates.  This will send you back to the code scratching your head, but there’s a reason why this happens. To understand the problem, we must examine how Distinct works in LINQ to Objects. Distinct has two overloads: one without parameters, as shown above, and another that takes a parameter of type IEqualityComparer<T>.  In the case above, no parameters, Distinct will call EqualityComparer<T>.Default behind the scenes to make comparisons as it iterates through the list. You don’t have problems with the built-in types, such as string, int, DateTime, etc, because they all implement IEquatable<T>. However, many .NET Framework classes, such as SelectListItem, don’t implement IEquatable<T>. So, what happens is that EqualityComparer<T>.Default results in a call to Object.Equals, which performs reference equality on reference type objects.  You don’t have this problem with value types because the default implementation of Object.Equals is bitwise equality. However, most of your projections that use Distinct are on classes, just like the SelectListItem used in this demo application. So, the reason why Distinct didn’t produce the results we wanted was because we used a type that doesn’t define its own equality and Distinct used the default reference equality. This resulted in all objects being included in the results because they are all separate instances in memory with unique references. As you might have guessed, the solution to the problem is to use the second overload of Distinct that accepts an IEqualityComparer<T> instance. If you were projecting into your own custom type, you could make that type implement IEqualityComparer<T>, but SelectListItem belongs to the .NET Framework Class Library.  Therefore, the solution is to create a custom type to implement IEqualityComparer<T>, as in the SelectListItemComparer class, shown below: using System.Collections.Generic; using System.Web.Mvc; namespace DistinctSelectList.Models { public class SelectListItemComparer : EqualityComparer { public override bool Equals(SelectListItem x, SelectListItem y) { return x.Value.Equals(y.Value); } public override int GetHashCode(SelectListItem obj) { return obj.Value.GetHashCode(); } } } The SelectListItemComparer class above doesn’t implement IEqualityComparer<SelectListItem>, but rather derives from EqualityComparer<SelectListItem>. Microsoft recommends this approach for consistency with the behavior of generic collection classes. However, if your custom type already derives from a base class, go ahead and implement IEqualityComparer<T>, which will still work. EqualityComparer is an abstract class, that implements IEqualityComparer<T> with Equals and GetHashCode abstract methods. For the purposes of this application, the SelectListItem.Value property is sufficient to determine if two items are equal.   Since SelectListItem.Value is type string, the code delegates equality to the string class. The code also delegates the GetHashCode operation to the string class.You might have other criteria in your own object and would need to define what it means for your object to be equal. Now that we have an IEqualityComparer<SelectListItem>, let’s fix the problem. The code below modifies the query where we want distinct values: var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct(new SelectListItemComparer()) .ToList(); Notice how the code above passes a new instance of SelectListItemComparer as the parameter to the Distinct operator. Now, when you run the application, the drop-down list will behave as you expect, showing only a unique set of names. In addition to Distinct, other LINQ Standard Query Operators have overloads that accept IEqualityComparer<T>’s, You can use the same techniques as shown here, with SelectListItemComparer, with those other operators as well. Now you know how to resolve problems with getting Distinct to work properly and also have a way to fix problems with other operators that require equality comparisons. @JoeMayo

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  • LINQ to SQL Profiler

    In this article we will be taking a look at the new LINQ to SQL Profiler from HibernatingRhinos. This tool gives you a view into the goings on of LINQ to SQL. Not only does it allow you to see the SQL that is generated by your LINQ queries but it also shows you information about your connections, queries, as well as alerting you to all sorts of information that you might otherwise not know about.

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  • SQL SERVER – Disk Space Monitoring – Detecting Low Disk Space on Server

    - by Pinal Dave
    A very common question I often receive is how to detect if the disk space is running low on SQL Server. There are two different ways to do the same. I personally prefer method 2 as that is very easy to use and I can use it creatively along with database name. Method 1: EXEC MASTER..xp_fixeddrives GO Above query will return us two columns, drive name and MB free. If we want to use this data in our query, we will have to create a temporary table and insert the data from this stored procedure into the temporary table and use it. Method 2: SELECT DISTINCT dovs.logical_volume_name AS LogicalName, dovs.volume_mount_point AS Drive, CONVERT(INT,dovs.available_bytes/1048576.0) AS FreeSpaceInMB FROM sys.master_files mf CROSS APPLY sys.dm_os_volume_stats(mf.database_id, mf.FILE_ID) dovs ORDER BY FreeSpaceInMB ASC GO The above query will give us three columns: drive logical name, drive letter and free space in MB. We can further modify above query to also include database name in the query as well. SELECT DISTINCT DB_NAME(dovs.database_id) DBName, dovs.logical_volume_name AS LogicalName, dovs.volume_mount_point AS Drive, CONVERT(INT,dovs.available_bytes/1048576.0) AS FreeSpaceInMB FROM sys.master_files mf CROSS APPLY sys.dm_os_volume_stats(mf.database_id, mf.FILE_ID) dovs ORDER BY FreeSpaceInMB ASC GO This will give us additional data about which database is placed on which drive. If you see a database name multiple times, it is because your database has multiple files and they are on different drives. You can modify above query one more time to even include the details of actual file location. SELECT DISTINCT DB_NAME(dovs.database_id) DBName, mf.physical_name PhysicalFileLocation, dovs.logical_volume_name AS LogicalName, dovs.volume_mount_point AS Drive, CONVERT(INT,dovs.available_bytes/1048576.0) AS FreeSpaceInMB FROM sys.master_files mf CROSS APPLY sys.dm_os_volume_stats(mf.database_id, mf.FILE_ID) dovs ORDER BY FreeSpaceInMB ASC GO The above query will now additionally include the physical file location as well. As I mentioned earlier, I prefer method 2 as I can creatively use it as per the business need. Let me know which method are you using in your production server. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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  • C#/.NET Little Wonders: Of LINQ and Lambdas - A Presentation

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. Today I’m giving a brief beginner’s guide to LINQ and Lambdas at the St. Louis .NET User’s Group so I thought I’d post the presentation here as well.  I updated the presentation a bit as well as added some notes on the query syntax.  Enjoy! The C#/.NET Fundaments: Of Lambdas and LINQ Presentation Of Lambdas and LINQ View more presentations from BlackRabbitCoder   Technorati Tags: C#, CSharp, .NET, Little Wonders, LINQ, Lambdas

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  • SQL SERVER – Weekly Series – Memory Lane – #049

    - by Pinal Dave
    Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2007 Two Connections Related Global Variables Explained – @@CONNECTIONS and @@MAX_CONNECTIONS @@CONNECTIONS Returns the number of attempted connections, either successful or unsuccessful since SQL Server was last started. @@MAX_CONNECTIONS Returns the maximum number of simultaneous user connections allowed on an instance of SQL Server. The number returned is not necessarily the number currently configured. Query Editor – Microsoft SQL Server Management Studio This post may be very simple for most of the users of SQL Server 2005. Earlier this year, I have received one question many times – Where is Query Analyzer in SQL Server 2005? I wrote small post about it and pointed many users to that post – SQL SERVER – 2005 Query Analyzer – Microsoft SQL SERVER Management Studio. Recently I have been receiving similar question. OUTPUT Clause Example and Explanation with INSERT, UPDATE, DELETE SQL Server 2005 has a new OUTPUT clause, which is quite useful. OUTPUT clause has access to insert and deleted tables (virtual tables) just like triggers. OUTPUT clause can be used to return values to client clause. OUTPUT clause can be used with INSERT, UPDATE, or DELETE to identify the actual rows affected by these statements. OUTPUT clause can generate a table variable, a permanent table, or temporary table. Even though, @@Identity will still work with SQL Server 2005, however I find the OUTPUT clause very easy and powerful to use. Let us understand the OUTPUT clause using an example. Find Name of The SQL Server Instance Based on database server stored procedures has to run different logic. We came up with two different solutions. 1) When database schema is very much changed, we wrote completely new stored procedure and deprecated older version once it was not needed. 2) When logic depended on Server Name we used global variable @@SERVERNAME. It was very convenient while writing migrating script which depended on the server name for the same database. Explanation of TRY…CATCH and ERROR Handling With RAISEERROR Function One of the developers at my company thought that we can not use the RAISEERROR function in new feature of SQL Server 2005 TRY… CATCH. When asked for an explanation he suggested SQL SERVER – 2005 Explanation of TRY… CATCH and ERROR Handling article as excuse suggesting that I did not give example of RAISEERROR with TRY…CATCH. We all thought it was funny. Just to keep records straight, TRY… CATCH can sure use RAISEERROR function. Different Types of Cache Objects Serveral kinds of objects can be stored in the procedure cache: Compiled Plans: When the query optimizer finishes compiling a query plan, the principal output is compiled plan. Execution contexts: While executing a compiled plan, SQL Server has to keep track of information about the state of execution. Cursors: Cursors track the execution state of server-side cursors, including the cursor’s current location within a resultset. Algebrizer trees: The Algebrizer’s job is to produce an algebrizer tree, which represents the logic structure of a query. Open SSMS From Command Prompt – sqlwb.exe Example This article is written by request and suggestion of Sr. Web Developer at my organization. Due to the nature of this article most of the content is referred from Book On-Line. sqlwbcommand prompt utility which opens SQL Server Management Studio. Squib command does not run queries from the command prompt. sqlcmd utility runs queries from command prompt, read for more information. 2008 Puzzle – Solution – Computed Columns Datatype Explanation Just a day before I wrote article SQL SERVER – Puzzle – Computed Columns Datatype Explanation which was inspired by SQL Server MVP Jacob Sebastian. I suggest that before continuing this article read the original puzzle question SQL SERVER – Puzzle – Computed Columns Datatype Explanation.The question was if the computed column was of datatype TINYINT how to create a Computed Column of datatype INT? 2008 – Find If Index is Being Used in Database It is very often I get a query that how to find if any index is being used in the database or not. If any database has many indexes and not all indexes are used it can adversely affect performance. If the number of indices are higher it reduces the INSERT / UPDATE / DELETE operation but increase the SELECT operation. It is recommended to drop any unused indexes from table to improve the performance. 2009 Interesting Observation – Execution Plan and Results of Aggregate Concatenation Queries If you want to see what’s going on here, I think you need to shift your point of view from an implementation-centric view to an ANSI point of view. ANSI does not guarantee processing the order. Figure 2 is interesting, but it will be potentially misleading if you don’t understand the ANSI rule-set SQL Server operates under in most cases. Implementation thinking can certainly be useful at times when you really need that multi-million row query to finish before the backup fire off, but in this case, it’s counterproductive to understanding what is going on. SQL Server Management Studio and Client Statistics Client Statistics are very important. Many a times, people relate queries execution plan to query cost. This is not a good comparison. Both parameters are different, and they are not always related. It is possible that the query cost of any statement is less, but the amount of the data returned is considerably larger, which is causing any query to run slow. How do we know if any query is retrieving a large amount data or very little data? 2010 I encourage all of you to go through complete series and write your own on the subject. If you write an article and send it to me, I will publish it on this blog with due credit to you. If you write on your own blog, I will update this blog post pointing to your blog post. SQL SERVER – ORDER BY Does Not Work – Limitation of the View 1 SQL SERVER – Adding Column is Expensive by Joining Table Outside View – Limitation of the View 2 SQL SERVER – Index Created on View not Used Often – Limitation of the View 3 SQL SERVER – SELECT * and Adding Column Issue in View – Limitation of the View 4 SQL SERVER – COUNT(*) Not Allowed but COUNT_BIG(*) Allowed – Limitation of the View 5 SQL SERVER – UNION Not Allowed but OR Allowed in Index View – Limitation of the View 6 SQL SERVER – Cross Database Queries Not Allowed in Indexed View – Limitation of the View 7 SQL SERVER – Outer Join Not Allowed in Indexed Views – Limitation of the View 8 SQL SERVER – SELF JOIN Not Allowed in Indexed View – Limitation of the View 9 SQL SERVER – Keywords View Definition Must Not Contain for Indexed View – Limitation of the View 10 SQL SERVER – View Over the View Not Possible with Index View – Limitations of the View 11 SQL SERVER – Get Query Running in Session I was recently looking for syntax where I needed a query running in any particular session. I always remembered the syntax and ha d actually written it down before, but somehow it was not coming to mind quickly this time. I searched online and I ended up on my own article written last year SQL SERVER – Get Last Running Query Based on SPID. I felt that I am getting old because I forgot this really simple syntax. Find Total Number of Transaction on Interval In one of my recent Performance Tuning assignments I was asked how do someone know how many transactions are happening on a server during certain interval. I had a handy script for the same. Following script displays transactions happened on the server at the interval of one minute. You can change the WAITFOR DELAY to any other interval and it should work. 2011 Here are two DMV’s which are newly introduced in SQL Server 2012 and provides vital information about SQL Server. DMV – sys.dm_os_volume_stats – Information about operating system volume DMV – sys.dm_os_windows_info – Information about Operating System SQL Backup and FTP – A Quick and Handy Tool I have used this tool extensively since 2009 at numerous occasion and found it to be very impressive. What separates it from the crowd the most – it is it’s apparent simplicity and speed. When I install SQLBackupAndFTP and configure backups – all in 1 or 2 minutes, my clients are always impressed. Quick Note about JOIN – Common Questions and Simple Answers In this blog post we are going to talk about join and lots of things related to the JOIN. I recently started office hours to answer questions and issues of the community. I receive so many questions that are related to JOIN. I will share a few of the same over here. Most of them are basic, but note that the basics are of great importance. 2012 Importance of User Without Login Question: “In recent version of SQL Server we can create user without login. What is the use of it?” Great question indeed. Let me first attempt to answer this question but after reading my answer I need your help. I want you to help him as well with adding more value to it. Preserve Leading Zero While Coping to Excel from SSMS Earlier I wrote two articles about how to efficiently copy data from SSMS to Excel. Since I wrote that post there are plenty of interest generated on this subject. There are a few questions I keep on getting over this subject. One of the question is how to get the leading zero preserved while copying the data from SSMS to Excel. Well it is almost the same way as my earlier post SQL SERVER – Excel Losing Decimal Values When Value Pasted from SSMS ResultSet. The key here is in EXCEL and not in SQL Server. Solution – 2 T-SQL Puzzles – Display Star and Shortest Code to Display 1 Earlier on this blog we had asked two puzzles. The response from all of you is nothing but Amazing. I have received 350+ responses. Many are valid and many were indeed something I had not thought about it. I strongly suggest you read all the puzzles and their answers here - trust me if you start reading the comments you will not stop till you read every single comment. Seriously trust me on it. Personally I have learned a lot from it. Identify Most Resource Intensive Queries – SQL in Sixty Seconds #028 – Video http://www.youtube.com/watch?v=TvlYy-TGaaA Importance of User Without Login – T-SQL Demo Script Earlier I wrote a blog post about SQL SERVER – Importance of User Without Login and my friend and SQL Expert Vinod Kumar has written excellent follow up blog post about Contained Databases inside SQL Server 2012. Now lots of people asked me if I can also explain the same concept again so here is the small demonstration for it. Let me show you how login without user can help. Before we continue on this subject I strongly recommend that you read my earlier blog post here. In following demo I am going to demonstrate following situation. Login using the System Admin account Create a user without login Checking Access Impersonate the user without login Checking Access Revert Impersonation Give Permission to user without login Impersonate the user without login Checking Access Revert Impersonation Clean up Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • LINQ to Twitter v2.0.8 Released

    - by Joe Mayo
    Today, I released LINQ to Twitter v2.0.8. Besides normal maintenance, this release includes the Twitter Geo API and the Suggested Users API. LINQ to Twitter is hosted on CodePlex.com: http://linqtotwitter.codeplex.com/ In addition to new functionality, I've made much progress toward LINQ to Twitter documentation; primarily in the Making API Calls area: http://linqtotwitter.codeplex.com/wikipage?title=Making%20API%20Calls&referringTitle=Documentation There's also a discussion forum where you can ask and view questions: http://linqtotwitter.codeplex.com/Thread/List.aspx As always, constructive feedback is welcome. Joe

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