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• 2 servers, high availability and faster response

  - by user17886

  I recently bought a second webserver because I worry about hardware failure of my old server. Now that I have that second server I wish to do a little more then just have one server standby and replicate all day. As long as it's there I might as well get some advantage our of it ! I have a website powered by ubuntu 12.04, nginx, php-fpm, apc, mysql (5.5) and couchdb. Im currently testing configurations where i can achieve failover AND make good use of the extra harware for faster responses / distributed load. The setup I am testing nowinvolves heartbeat for ip failover and two identical servers. Of the two servers only one has a public ip adress. If one server crashes the other server takes over the public ip adress. On an incoming request nginx forwards the request tot php-fpm to either server a of server b (50/50 if both servers are alive). Once the request has been send to php-fpm both servers look at localhost for the mysql server. I use master-master mysql replication for this. The file system is synced with lsyncd. This works pretty well but Im reading it's discouraged by the (mysql) community. Another option I could think of is to use one server as a mysql master and one server as a web/php server. The servers would still sync their filesystem, would still run the same duplicate software (nginx,mysql) but master slave mysql replication could be used. As long as bother servers are alive I could just prefer nginx to listen to ip a and mysql to ip b. If one server is down, the other server could take over the task of the other server, simply by ip switching. But im completely new at this so I would greatly value your expert advice. Is either of the two setups any good ? If you have any thoughts on this please let me know ! PS, virtualisation, hosting on different locations or active/passive setups are not solutions im looking for. I find virtual server either too slow or too expensive. I already have a passive failover on another location. But in case of a crash I found the site was still unreachable for too long due to dns caching.

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• LINQ, "Argument types do not match" error, what does it mean, how do I address it?

  - by Biff MaGriff

  Hello, I'm new to linq and I'm trying to databind to an anonymous type. I'm using SubSonic 3.0 as my DAL. I'm doing a select from 2 tables like so var myDeal = (from u in db.Users select new { UserID = u.UserID, UserRoleID = (from ur in u.UserRoles where u.UserRoleID == ur.UserRoleID select ur).FirstOrDefault().UserRoleID }); foreach (var v in myDeal) //dies first time here { } Then when I databind or try to iterate through the collection I get the "Argument types do not match" error during run time. I'm not sure what is going on here.

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• Linq to Sql saying that item by 'Customer' already exists. Choose a different name.

  - by Anthony Potts

  I have been going round and round with a linq to sql file while using svn for quite some time. The latest is that my dbml file shows as having an error which states that An item named "Customer" already exists. Please choose a different name. And then it repeats that again. In fact, it says it for almost every object. What is my fix? I have tried renaming the one named Customer, but that didn't fix it. I don't know where to go to fix this. I went to the .dbml file and don't see any duplication, and I went to the .dbml.layout file and didn't see any duplication there either.

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• Reading XML using XDocument & Linq - check if element is NULL?

  - by adchased

  I'm using LINQ together with XDocument to read a XML File. This is the code: XDocument xml = XDocument.Load(filename); var q = from b in xml.Descendants("product") select new { name = b.Element("name").Value, price = b.Element("price").Value, extra = b.Element("extra1").Value, deeplink = b.Element("deepLink").Value }; Now the problem is, the extra1 field is not always present. There are items in the XML file without that node. If that happens it's crashing with a NullReferenceException. Is there any possibility to include a "check if null" so I can prevent it from crashing?

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• How do I get Linq-to-SQL to refresh its local copy of a database record?

  - by Gary McGill

  Suppose I have an Orders table in my database and a corresponding model class generated by the VS2008 "Linq to SQL Classes" designer. Suppose I also have a stored procedure (ProcessOrder) in my database that I use to do some processing on an order record. If I do the following: var order = dataContext.Orders.Where(o => o.id == orderId).First(); // More code here dataContext.ProcessOrder(orderId); order.Status = "PROCESSED"; dataContext.SubmitChanges(); ...then I'll get a concurrency violation if the ProcessOrder stored proc has modified the order (which is of course very likely), because L2S will detect that the order record has changed, and will fail to submit the changes to that order. That's all fairly logical, but what if I want to update the order record after calling the stored proc? How do I tell L2S to forget about its cached copy and refresh it from the DB?

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• Finding if a target number is the sum of two numbers in an array via LINQ and get the and Indices

  - by Dr.H

  Hello I am new to Linq , I found this thread which explain 90% of what I need http://stackoverflow.com/questions/2331882?tab=newest#tab-top , thanks "pdr" but what I need is to get the Indices too , here is my modification I get the index of the first number but I don't know how to get the index of the second number int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; var result = from item in numbers.Select((n1, idx) => new { n1,idx, shortList = numbers.Take(idx) }) from n2 in item.shortList where item.n1 + n2 == 7 select new { nx1 = item.n1,index1=item.idx, nx2=n2 };

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• Query data using LINQ to SQL and Entity Framework with foreign key? (Help me please)

  - by The Wind

  Hello! There is a problem I need help with your query on the data using LINQ to SQL and Entity Framework (I'm using Visual Studio 2010). My picure here: http://img.tamtay.vn/files/photo2/2010/5/28/10/962/4bff3a3b_1093f58f_untitled-1.gif I have three tables: tbl NewsDetails tblNewsCategories tblNewsInCategories (See screen 1 in my picture) Now, I want to retrieve records in the tblNewsDetails table, with condition: CategoryId=1, as the following results: (See screen 2 in my picture) But NewsID and CategoryId in tblNewsInCategories table is two foreign key, I do not see them and I do not know how to use them in your code. My code has errors: (See screen 3 in my picture) Please help me. Thanks! (I am a new member, should not have the right to insert images)

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• How can I subsample data from a time series with LINQ to SQL?

  - by Chris Farmer

  I have a database table full of time points and experimental values at those time points. I need to retrieve the values for an experiment and create a thumbnail image showing an XY plot of its data. Because the actual data set for each experiment is potentially 100,000 data points and my image is only 100 pixels wide, I want to sample the data before creating the image. My current query (which retrieves all the data without sampling) is something simple like this: var points = from p in db.DataPoints where p.ExperimentId == myExperimentId orderby p.Time select new { X = p.Time, Y = p.Value } So, how can I best take every nth point from my result set in a LINQ to SQL query?

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• What's elegant way to rewrite following LINQ statement using extension methods?

  - by Jakub Šturc

  I have following LINQ statement and I want to rewrite it using extension methods. from x in e from y in e from z in e select new { x, z } One possible solution is: e.Join(e, x => 42, y => 42, (x, y) => new { x, y }) Join(e, _ => 42, z => 42, (_, z) => new { _.x, z }); However this is everything but elegant. Do you any idea how to improve beauty of second expression?

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• How do I improve the efficiency of the queries executed by this generic Linq-to-SQL data access clas

  - by Lee D

  Hi all, I have a class which provides generic access to LINQ to SQL entities, for example: class LinqProvider<T> //where T is a L2S entity class { DataContext context; public virtual IEnumerable<T> GetAll() { return context.GetTable<T>(); } public virtual T Single(Func<T, bool> condition) { return context.GetTable<T>().SingleOrDefault(condition); } } From the front end, both of these methods appear to work as you would expect. However, when I run a trace in SQL profiler, the Single method is executing what amounts to a SELECT * FROM [Table], and then returning the single entity that meets the given condition. Obviously this is inefficient, and is being caused by GetTable() returning all rows. My question is, how do I get the query executed by the Single() method to take the form SELECT * FROM [Table] WHERE [condition], rather than selecting all rows then filtering out all but one? Is it possible in this context? Any help appreciated, Lee

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• C#: How to remove items from the collection of a IDictionary<E, ICollection<T>> with LINQ?

  - by Rosarch

  Here is what I am trying to do: private readonly IDictionary<float, ICollection<IGameObjectController>> layers; foreach (ICollection<IGameObjectController> layerSet in layers.Values) { foreach (IGameObjectController controller in layerSet) { if (controller.Model.DefinedInVariant) { layerSet.Remove(controller); } } } Of course, this doesn't work, because it will cause a concurrent modification exception. (Is there an equivalent of Java's safe removal operation on some iterators?) How can I do this correctly, or with LINQ?

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• How do I transfer this logic into a LINQ statement?

  - by Geoffrey

  I can't get this bit of logic converted into a Linq statement and it is driving me nuts. I have a list of items that have a category and a createdondate field. I want to group by the category and only return items that have the max date for their category. So for example, the list contains items with categories 1 and 2. The first day (1/1) I post two items to both categories 1 and 2. The second day (1/2) I post three items to category 1. The list should return the second day postings to category 1 and the first day postings to category 2. Right now I have it grouping by the category then running through a foreach loop to compare each item in the group with the max date of the group, if the date is less than the max date it removes the item. There's got to be a way to take the loop out, but I haven't figured it out!

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• Clone LINQ To SQL object Extension Method throws object dispose exception....

  - by gtas

  Hello all, I have this extension method for cloning my LINQ To SQL objects: public static T CloneObjectGraph<T>(this T obj) where T : class { var serializer = new DataContractSerializer(typeof(T), null, int.MaxValue, false, true, null); using (var ms = new System.IO.MemoryStream()) { serializer.WriteObject(ms, obj); ms.Position = 0; return (T)serializer.ReadObject(ms); } } But while i carry objects with not all references loaded, while qyuerying with DataLoadOptions, sometimes it throws the object disposed exception, but thing is I don't ask for references that is not loaded (null). e.g. I have Customer with many references and i just need to carry on memory the Address reference EntityRef< and i don't Load anything else. But while i clone the object this exception forces me to load all the EntitySet< references with the Customer object, which might be too much and slow down the application speed. Any suggestions?

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• LINQ and paging with a DataTable - can't get Skip working?

  - by Kit Menke

  Ok so this might be a dumb question, but I can't seem to figure it out. I thought I'd try out LINQ against a DataTable. I got my query working and now I'm trying to implement some simple paging. DataTable dataTable = null; dataTable = GetAllDataTables(); var query = from r in dataTable.AsEnumerable() orderby r.Field<string>(Constants.fileName) select r; query.Skip(WPP_PAGE_SIZE * pageIndex).Take(WPP_PAGE_SIZE); My problem is that I get an error at query.Skip(...). Error 1 'System.Data.OrderedEnumerableRowCollection' does not contain a definition for 'Skip' and no extension method 'Skip' accepting a first argument of type 'System.Data.OrderedEnumerableRowCollection' could be found (are you missing a using directive or an assembly reference?) References I have: Microsoft.SharePoint System System.Core System.Data System.Data.DataSetExtensions System.Web System.Xml What am I missing?

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• Possible to use Tables of same type in Linq to SQL?

  - by Schneider

  Lets say I've got an object model, where I have many collections of the same type. For example something like class StockMarketData { List<SummaryData> WeeklySummary; List<SummaryData> MonthlySummary; } class SummaryData { DateTime DateTime {get; set;} double Value {get; set;} } Those lists will map onto database tables. If you actually use L2S to generate a model from the database you will get something like: class StockMarketData { List<WeeklySummaryData> WeeklySummary; List<MonthlySummaryData> MonthlySummary; } Even though WeeklySummaryData and MonthlySummaryData have the same shape. Is it possible for Linq to SQL to create tables from a database of summary data, but get each table to contain the same type (such as shown in the top example).

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• Free hosting solution for a very low-traffic website [duplicate]

  - by user966939

  This question already has an answer here: How to find web hosting that meets my requirements? 4 answers I run a very low-traffic website (about 40 users, basically all of which are daily active on the site). I don't see it changing anytime soon either, as there is no way to sign up on the site right now. Until now I have just been using a sub-directory on a friend's host (shared), to host the web site. But in only a few weeks from now, his subscription will end, and he has no plans on renewing it. So of course this means I'll have to move on to something else. But I don't think I'll find someone who'd be willing to share a... shared host with me again. And besides, the software used on that server is ancient (PHP 4.4.9 + MySQL 4.1.22). There's one obvious solution that comes to mind, I guess: choose a better host and pay for it myself. The problem here is that I have no real fixed income, as I'm only a student. So even if the pricing is dirt cheap, I just can't be certain I will be able to afford it, every single month, for... at least 2 years maybe? So I've looked at free hosting solutions instead. The least requirement I had was that it was completely free of ads. But no matter where I look, I always find something in a corner or two ("what can you expect from a free host?" - yeah I know, but I guess it was worth a shot). For example, on Byethost (one of the free hosts I tried), if you trigger a PHP error while error reporting is set to E_ALL, you will spawn some hidden ad... Besides Byethost, I've tried 000Webhost, x10Hosting, 2Freehosting/1Freehosting, Wink.ws, and they are only worse. Okay, I'm running low on ideas. But! What if I just hosted the site myself, on my own computer? That could work. I actually do have my computer on practically 24/7. But not really. Sometimes I need to reboot it, and sometimes we even have power outages. And what if the hardware needs an upgrade? It's not such a big deal for me if the site went down, because I know what's going on; but what about the users? If I do decide to host it myself, is there some way to show users an alternate page instead of them just seeing a generic "server not found" page in the browser when the site is not accessible? Or is there something I have been missing out on? Is there a different kind of "web hosting" solution out there that I haven't heard of? Here is what I'm really looking for: Free (as in, no costs) NO ads Bandwidth enough for a low-traffic forum with roughly 40 users (Semi-)Up-to-date PHP and MySQL (at least not older than a year) No standard (non-extension) PHP functions turned off - such as sleep() The mbstring extension is enabled Disk space: at least 5 MB At least one MySQL database Some bonus points would be: Max execution time of PHP scripts can be set Remote access to MySQL database What would be the best solution for me? Is there one?

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• Can anyone tell me if this is possible to do in Linq?

  - by user275561

  So I have been working and trying for a couple of hours. I am creating a BubbleBreaker type of game. I Can do it using for loop or while but I am trying to also get practice in using Linq. Here is what I am trying to do in pesudo code. Each Bubble has a Column and Row Property. If The bubble subtracts one from its Column property and finds the same Color bubble, it should Select it then Subtract -1 and see if two bubbles away there is also a same color bubble. If there is then subtract -2 and so on. So What I am trying to do is var test= _theBubbles.TakeWhile((i, s) => i.BubbleColor== bubble.BubbleColor)//Then somehow tell it to do bubble.Column-s and then Subtract s from bubble.Column So the Idea is to keep looking down the column till the bubble isnt the same

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• How to pull a RANDOM and UNIQUE record from SQL via LINQ.

  - by Jeremy H

  Okay, I found lots of posts on SO about how to pull a RANDOM item from the database when using LINQ. There seems to be a couple of differnet ways to handle this. What I need to do though is pull a RANDOM item from the database that the user has not seen before. The data I am pulling from the database is very small. Is there any way I can just hit the database once for 1000 records and then randomly scroll through those? Should I put a cookie on the users system recording the IDs of which items they have seen, pull a random record, check to see if it is seen and if so, pull from the database again? That seems like performance issues just waiting to happen. I don't expect anyone to code it for me, I am just looking for concepts and pointing in the right direction of how I should go about this. Need more details? Just let me know!

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• How do I add multiple joins (Fetches) to a joined table using nhibernate and LINQ ?

  - by ooo

  i have these tables /entities VacationRequestDate table which has a VacationRequestId field that links with VacationRequest table VacationRequest has PersonId and RequestStatusId fields that links with Person and RequestStatus respectively. i have this query so far: IEnumerable<VacationRequestDate> dates = Session.Query<VacationRequestDate>().Fetch(r => r.VacationRequest).ThenFetch(p=>p.RequestStatus).ToList(); this works fine and joins with VacationRequest and then VacationRequest joins with RequestStatus but i can't figure out how to add an additional EAGER join to the VacationRequest table. If i add a Fetch at the end, it refers to the VacationRequestDate table If i add a ThenFetch at the end, it refers to the RequestStatus table I can't find any api that will refer to the VacationRequest table as the reference point. how would you add multiple joins to a joined table using nhibernate LINQ ?

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• How to do Linq aggregates when there might be an empty set?

  - by Shaul

  I have a Linq collection of Things, where Thing has an Amount (decimal) property. I'm trying to do an aggregate on this for a certain subset of Things: var total = myThings.Sum(t => t.Amount); and that works nicely. But then I added a condition that left me with no Things in the result: var total = myThings.Where(t => t.OtherProperty == 123).Sum(t => t.Amount); And instead of getting total = 0 or null, I get an error: System.InvalidOperationException: The null value cannot be assigned to a member with type System.Decimal which is a non-nullable value type. That is really nasty, because I didn't expect that behavior. I would have expected total to be zero, maybe null - but certainly not to throw an exception! What am I doing wrong? What's the workaround/fix?

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• How can I transform a DataTable in a group-by date DataTable with LINQ?

  - by alex

  I have a untyped DataTable that looks like this (srcTbl): date col_1 col_2 ... col_n 1.3.2010 00:00 12.5 0 ... 100 1.3.2010 01:00 0 0 ... 100 1.3.2010 22:00 0 0 ... 100 1.3.2010 23:00 12.5 0 ... 100 ... 31.3.2010 00:00 2 0 ... 100 31.3.2010 01:00 2 0 ... 200 I need to sum up the rows grouped by dates to get a DataTable like that (dstTbl): date, col_1 col_2 ... col_n 1.3.2010 15 0 ... 400 ... 31.3.2010 4 0 ... 300 Is this possible by using LINQ and if then how?

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• C# / Entity Framework / Linq question regarding calling a method when a class is accessed...

  - by Daniel

  So this is probably really basic, but I'm fairly new to all this. I am using Entity Framework with POCO entities. I want to call a method when a class property is set. I am trying to build an advertisement platform. I have a Customer class, a Venue class and an Advertisement class. I have my indexes set up in such a way that I can call customer.venue. However, I want to be able to call Customer.Venue.CurrentAdvertisement and have it execute a method (if CurrentAdvertisement is null) and return the current advertisement. I know I can explicitly set it every time, but I want to be able to override my classes so that whenever the CurrentAdvertisement property is accessed via LINQ it runs that method to return an ad. In order to do this I need to pass the Venue class a variable (venue name).

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• What are the best blogs for staying up to date on C#, ASP.NET, LINQ, SQL, C++, Ruby, Java, Python?

  - by Arj

  Apologies if this repeats another - but I couldn't fine one like it. My day to day programming spans a fair number of technologies: C#, ASP.NET, LINQ / SQL, C++, Ruby, Java, Python in approximately that order. It's a struggle to keep up to date on any of best practices, new ideas, innovation and improvements, let alone all. Therefore, what would your top 1 blog be in each of these technologies and which technology do you find easiest to stay up to date with? I'd have a bias towards blogs with broad and high level rather than narrow and detailed content / solutions / examples.

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• ASP.NET MVC / Linq-to-SQL classes: Can I get it to infer readable display names?

  - by Gary McGill

  If I have a table Orders with fields CustomerID, OrderID and OrderDate, then the "Linq-to-SQL classes" generated class will be called Orders, with members called CustomerID, OrderID and OrderDate. So far so good. However, if I then do Html.LabelFor(m => m.OrderDate) then the generated text will be "OrderDate" instead of "Order Date". I tried using Order_Date as the field name, but that didn't work. Is there any way to get it to infer a better display name? [I know that I can use data annotations to specify the display name explicitly, but I really don't want to do that for all my classes/members - I just want it to work by convention.]

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• Another Permutation Word Conundrum... With Linq?

  - by CraigF

  I have seen many examples of getting all permutations of a given set of letters. Recursion seems to work well to get all possible combinations of a set of letters (though it doesn't seem to take into account if 2 of the letters are the same). What I would like to figure out is, could you use linq (or not) to get all possible combinations of letters down to 3 letter combinations. For example, given the letters: P I G G Y I want an array of all possible cominations of these letters so I can check against a word list (scrabble?) and eventually get a list of all possible words that you can make using those letters (from 3 letters up to the total, in this case 5 letters).

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