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• Data structure to build and lookup set of integer ranges

  - by actual

  I have a set of uint32 integers, there may be millions of items in the set. 50-70% of them are consecutive, but in input stream they appear in unpredictable order. I need to: Compress this set into ranges to achieve space efficient representation. Already implemented this using trivial algorithm, since ranges computed only once speed is not important here. After this transformation number of resulting ranges is typically within 5 000-10 000, many of them are single-item, of course. Test membership of some integer, information about specific range in the set is not required. This one must be very fast -- O(1). Was thinking about minimal perfect hash functions, but they do not play well with ranges. Bitsets are very space inefficient. Other structures, like binary trees, has complexity of O(log n), worst thing with them that implementation make many conditional jumps and processor can not predict them well giving poor performance. Is there any data structure or algorithm specialized in integer ranges to solve this task?

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• prolog recursion

  - by AhmadAssaf

  am making a function that will send me a list of all possible elemnts .. in each iteration its giving me the last answer .. but after the recursion am only getting the last answer back .. how can i make it give back every single answer .. thank you the problem is that am trying to find all possible distributions for a list into other lists .. the code test :- bp(3,12,[7, 3, 5, 4, 6, 4, 5, 2], Answer), format("Answer = ~w\n",[Answer]). bp(NB,C,OL,A):- addIn(C,OL,[[],[],[]],A); bp(NB,C,_,A). addIn(_,[],Result,Result). addIn(C,[Element|Rest],[F|R],Result):- member( Members , [F|R]), sumlist( Members, Sum), sumlist([Element],ElementLength), Cap is Sum + ElementLength, (Cap =< C, append([Element], Members,New), insert( Members, New, [F|R], PartialResult), addIn(C,Rest,PartialResult,Result)). by calling test .. am getting back all the list of possible answers .. now if i tried to do something that will fail like bp(3,11,[8,2,4,6,1,8,4],Answer). it will just enter a while loop .. more over if i changed the bp(NB,C,OL,A):- addIn(C,OL,[[],[],[]],A); bp(NB,C,_,A). to and instead of Or .. i get error : ERROR: is/2: Arguments are not sufficiently instantiated appreciate the help .. Thanks alot @hardmath

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• Java Executor: Small tasks or big ones?

  - by Arash Shahkar

  Consider one big task which could be broken into hundreds of small, independently-runnable tasks. To be more specific, each small task is to send a light network request and decide upon the answer received from the server. These small tasks are not expected to take longer than a second, and involve a few servers in total. I have in mind two approaches to implement this using the Executor framework, and I want to know which one's better and why. Create a few, say 5 to 10 tasks each involving doing a bunch of send and receives. Create a single task (Callable or Runnable) for each send & receive and schedule all of them (hundreds) to be run by the executor. I'm sorry if my question shows that I'm lazy to test these and see for myself what's better (at least performance-wise). My question, while looking after an answer to this specific case, has a more general aspect. In situations like these when you want to use an executor to do all the scheduling and other stuff, is it better to create lots of small tasks or to group those into a less number of bigger tasks?

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• Calling Python app/script from C#

  - by Maxim Z.

  I'm building an ASP.NET MVC (C#) site where I want to implement STV (Single Transferable Vote) voting. I've used OpenSTV for voting scenarios before, with great success, but I've never used it programmatically. The OpenSTV Google Code project offers a Python script that allows usage of OpenSTV from other applications: import sys sys.path.append("path to openstv package") from openstv.ballots import Ballots from openstv.ReportPlugins.TextReport import TextReport from openstv.plugins import getMethodPlugins (ballotFname, method, reportFname) = sys.argv[1:] methods = getMethodPlugins("byName") f = open(reportFname, "w") try: b = Ballots() b.loadUnknown(ballotFname) except Exception, msg: print >> f, ("Unable to read ballots from %s" % ballotFname) print >> f, msg sys.exit(-1) try: e = methods[method](b) e.runElection() except Exception, msg: print >> f, ("Unable to count votes using %s" % method) print >> f, msg sys.exit(-1) try: r = TextReport(e, outputFile=f) r.generateReport(); except Exception, msg: print >> f, "Unable to write report" print >> f, msg sys.exit(-1) f.close() Is there a way for me to make such a Python call from my C# ASP.NET MVC site? If so, how? Thanks in advance!

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• Objective-C / Cocoa: Uploading Images, Working Memory, And Storage.

  - by Finley Still

  Hello. I'm in the process of porting an application originally in java to cocoa, but I'm rewriting it to make it much better, since I prefer cocoa a lot anyway. One of the problems I had in the application, was that when you uploaded images to it, I had the images created, (as say an NSImage object) and then I just had them sitting in memory, the more I uploaded the more memory they took up, and I ended up running out of memory. My question is this: if I am going to have users upload images to this application in cocoa, how should I go about storing them? I don't just want to copy the file paths, because I want what is saved to contain the images, etc. Is there any way to upload an image and copy it into a different place only for my application? Then load that image with the new path name as needed? Only I would like it all to be consolidated. I'm going to implement saving by archiving one "master" object into an NSData*- so I'd like the images to be saved with that. Is there a temporary location maybe where I could write the images to disk for my application, and then when I saved, they would all be archived into a single file? Also, how do I do this? Thanks.

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• pyPDF - Retrieve page numbers from document

  - by SquidneyPoitier

  At the moment I'm looking into doing some PDF merging with pyPdf, but sometimes the inputs are not in the right order, so I'm looking into scraping each page for its page number to determine the order it should go in (e.g. if someone split up a book into 20 10-page PDFs and I want to put them back together). I have two questions - 1.) I know that sometimes the page number is stored in the document data somewhere, as I've seen PDFs that render on Adobe as something like [1243] (10 of 150), but I've read documents of this sort into pyPDF and I can't find any information indicating the page number - where is this stored? 2.) If avenue #1 isn't available, I think I could iterate through the objects on a given page to try to find a page number - likely it would be its own object that has a single number in it. However, I can't seem to find any clear way to determine the contents of objects. If I run: pdf.getPage(0).getContents() This usually either returns: {'/Filter': '/FlateDecode'} or it returns a list of IndirectObject(num, num) objects. I don't really know what to do with either of these and there's no real documentation on it as far as I can tell. Is anyone familiar with this kind of thing that could point me in the right direction?

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• Delivering activity feed items in a moderately scalable way

  - by sotangochips

  The application I'm working on has an activity feed where each user can see their friends' activity (much like Facebook). I'm looking for a moderately scalable way to show a given users' activity stream on the fly. I say 'moderately' because I'm looking to do this with just a database (Postgresql) and maybe memcached. For instance, I want this solution to scale to 200k users each with 100 friends. Currently, there is a master activity table that stores the rendered html for the given activity (Jim added a friend, George installed an application, etc.). This master activity table keeps the source user, the html, and a timestamp. Then, there's a separate ('join') table that simply keeps a pointer to the person who should see this activity in their friend feed, and a pointer to the object in the main activity table. So, if I have 100 friends, and I do 3 activities, then the join table will then grow to 300 items. Clearly this table will grow very quickly. It has the nice property, though, that fetching activity to show to a user takes a single (relatively) inexpensive query. The other option is to just keep the main activity table and query it by saying something like: select * from activity where source_user in (1, 2, 44, 2423, ... my friend list) This has the disadvantage that you're querying for users who may never be active, and as your friend list grows, this query can get slower and slower. I see the pros and the cons of both sides, but I'm wondering if some SO folks might help me weigh the options and suggest one way or they other. I'm also open to other solutions, though I'd like to keep it simple and not install something like CouchDB, etc. Many thanks!

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• Getting the first of a GROUP BY clause in SQL

  - by Michael Bleigh

  I'm trying to implement single-column regionalization for a Rails application and I'm running into some major headaches with a complex SQL need. For this system, a region can be represented by a country code (e.g. us) a continent code that is uppercase (e.g. NA) or it can be NULL indicating the "default" information. I need to group these items by some relevant information such as a foreign key (we'll call it external_id). Given a country and its continent, I need to be able to select only the most specific region available. So if records exist with the country code, I select them. If, not I want a records with the continent code. If not that, I want records with a NULL code so I can receive the default values. So far I've figured that I may be able to use a generated CASE statement to get an arbitrary sort order. Something like this: SELECT *, CASE region WHEN 'us' THEN 1 WHEN 'NA' THEN 2 ELSE 3 END AS region_sort FROM my_table WHERE region IN ('us','NA') OR region IS NULL GROUP BY external_id ORDER BY region_sort The problem is that without an aggregate function the actual data returned by the GROUP BY for a given row seems to be untameable. How can I massage this query to make it return only the first record of the region_sort ordered groups?

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• loading files through one file to hide locations

  - by Phil Jackson

  Hello all. Im currently doing a project in which my client does not want to location ( ie folder names and locations ) to be displayed. so I have done something like this: <link href="./?0000=css&0001=0001&0002=css" rel="stylesheet" type="text/css" /> <link href="./?0000=css&0001=0002&0002=css" rel="stylesheet" type="text/css" /> <script src="./?0000=js&0001=0000&0002=script" type="text/javascript"></script> </head> <body> <div id="wrapper"> <div id="header"> <div id="left_header"> <img src="./?0000=jpg&0001=0001&0002=pic" width="277" height="167" alt="" /> </div> <div id="right_header"> <div id="top-banner"></div> <ul id="navigation"> <li><a href="#" title="#" id="nav-home">Home</a></li> <li><a href="#" title="#">Signup</a></li> all works but my question being is or will this cause any complications i.e. speed of the site as all requests are being made to one single file and then loading in the appropriate data. Regards, Phil

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• What's the best way to store Logon User information for Web Application?

  - by Morgan Cheng

  I was once in a project of web application developed on ASP.NET. For each logon user, there is an object (let's call it UserSessionObject here) created and stored in RAM. For each HTTP request of given user, matching UserSessoinObject instance is used to visit user state information and connection to database. So, this UserSessionObject is pretty important. This design brings several problems found later: 1) Since this UserSessionObject is cached in ASP.NET memory space, we have to config load balancer to be sticky connection. That is, HTTP request in single session would always be sent to one web server behind. This limit scalability and maintainability. 2) This UserSessionObject is accessed in every HTTP request. To keep the consistency, there is a exclusive lock for the UserSessionObject. Only one HTTP request can be processed at any given time because it must to obtain the lock first. The performance and response time is affected. Now, I'm wondering whether there is better design to handle such logon user case. It seems Sharing-Nothing-Architecture helps. That means long user info is retrieved from database each time. I'm afraid that would hurt performance. Is there any design pattern for long user web app? Thanks.

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• Getting a certain node using DataSet

  - by MarceloRamires

  I have the following XML <xml> <ObsCont xCampo="field1"> <xTexto>example1</xTexto> </ObsCont> <ObsCont xCampo="field2"> <xTexto>example2</xTexto> </ObsCont> <ObsCont xCampo="field3"> <xTexto>example3</xTexto> </ObsCont> <field>information</field> </xml> Is there a way to get the content of "xTexto" inside the ObsCont that has "field2" value for the attribute xCampo using DataSet ? It would be desireable to have a single liner like the following: DataSet ds = new DataSet(); ds.ReadXml(StrArquivoProc); ds.Tables["xml"].Rows[0]["field"].ToString(); //field == "information" If I use the same method I'm not specifying that I want the one with the desired attribute.

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• Summarising grouped records in a dataframe in R

  - by monch1962

  Hello all, I have a data frame in R that looks like this: > TimeOffset, Source, Length > 0 1 1500 > 0.1 1 1000 > 0.2 1 50 > 0.4 2 25 > 0.6 2 3 > 1.1 1 1500 > 1.4 1 18 > 1.6 2 2500 > 1.9 2 18 > 2.1 1 37 > ... and I want to convert it to > TimeOffset, Source, Length > 0.2 1 2550 > 0.6 2 28 > 1.4 1 1518 > 1.9 2 2518 > ... Trying to put this into English, I want to group consecutive records with the same 'Source' together, then printing out a single record per group showing the highest time offset in that group, the source, and the sum of the lengths in that group. The TimeOffset values will always increase. I suspect this is possible in R, but I really don't know where to start. In a pinch I could export the data frame out and do it in e.g. Python, but I'd prefer to stay within R if possible. Thanks in advance for any assistance you can provide

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• About conversion of simplexmlobject to array.

  - by Rishi2686

  Hi guys, I tried the way you told but really messing up on some points. I am getting array fields but when it comes to children nodes, i go off the track. here giving single user's simplexml object only : SimpleXMLElement Object ( [users] = SimpleXMLElement Object ( [@attributes] = Array ( [type] = array ) [user] = Array ( [0] = SimpleXMLElement Object ( [id] = 1011 [name] = saroj [location] = SimpleXMLElement Object ( ) [description] = SimpleXMLElement Object ( ) [profile_image_url] = http://a5.example.com/profile_images/img_normal.jpg [url] = SimpleXMLElement Object ( ) [created_at] = Fri Apr 16 17:04:13 +0000 2010 [status] = SimpleXMLElement Object ( [created_at] = Wed May 26 02:56:03 +0000 2008 [id] = 1473 [text] = hi enjoying here! [in_reply_to_user_id] = SimpleXMLElement Object ( ) ) ) To get this into array I am writing code as below : $users = simplexml_load_string($xml); $arr2 = array(); foreach($users->users->user as $user) { $arr1 = array(); foreach($user as $k=>$v) { $arr1[$k] = (string) $v; } $arr2[] = $arr1; } I am getting all the fields as expected from arr2() instead of the status field which contains an array (imp: id & created_at fields repeated), it gives just key as status. While trying differently i get some of the fields of status array too. Please help me on this, i am really trying it from last two days. Help will be greatly appreciated.

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• Best way to migrate export/import from SQL Server to oracle

  - by matao

  Hi guys! I'm faced with needing access for reporting to some data that lives in Oracle and other data that lives in a SQL Server 2000 database. For various reasons these live on different sides of a firewall. Now we're looking at doing an export/import from sql server to oracle and I'd like some advice on the best way to go about it... The procedure will need to be fully automated and run nightly, so that excludes using the SQL developer tools. I also can't make a live link between databases from our (oracle) side as the firewall is in the way. The data needs to be transformed in the process from a star schema to a de-normalised table ready for reporting. What I'm thinking about is writing a monster query for SQL Server (which I mostly have already) that will denormalise and read out the data from SQL Server into a flat file using the sql server equivalent of sqlplus as a scheduled task, dump into a Well Known Location, then on the oracle side have a cron job that copies down the file and loads it with sql loader and rebuilds indexes etc. This is all doable, but very manual. Is there one or a combination of FOSS or standard oracle/SQL Server tools that could automate this for me? the Irreducible complexity is the query on one side and building indexes on the other, but I would love to not have to write the CSV dumping detail or the SQL loader script, just say dump this view out to CSV on one side, and on the other truncate and insert into this table from CSV and not worry about mapping column names and all other arcane sqlldr voodoo... best practices? thoughts? comments? edit: I have about 50+ columns all of varying types and lengths in my dataset, which is why I'd prefer to not have to write out how to generate and map each single column...

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• How to add Flex 4 spark List Item custom properties

  - by maik3l

  I'm trying to make a simple flash application providing interface for taking tests as a high school assignment. One of the requirements is to use an XML file as data source.Now, having a List component bound to the XML file with questions consisting of data such as question body, question type (ie. single choice, multiple choice, open, image etc.) and possible answers (where applicable), I was wondering if I could add some additional data (and what is the best possible way to do so) to each question upon its transfer to the List component. I am trying to achieve two main goals with this: firstly, to mark the questions to which an answer has already been given, like with such code in ItemRenderer class: <s:Label color="{data.color}" text="{data.label}"/> where data.color would be set whenever the user gives an answer to a question. Secondly, while at it, I thought of such possibility as a great way to store answers given to particular questions. In this case, the Class of the answer object would have been Object, since there has to be many type of questions (where the answer could also be a Bitmap for example). This is a question of both how to do it and if it seems a good idea at all (and if no, if there is a better way?), because I am quite new to the whole Flash Builder and Flex thing and I am not really accustomed to all the possibilities and best practices. Thanks!

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• Make Trac use a Drupal user database for authentication

  - by denisw

  I am trying to set up a Trac instance as a complement to a Drupal site and would like to give users the possibility to use their Drupal account in Trac, too, ideally in a single sign-on fashion (if the user is already logged into Drupal, he is automatically logged into Trac). The question now is how to accomplish this. I have found a plugin named DrupalIntegration which seems to implement that functionality; however, it is poorly documented - in fact, not documented at all. I managed to install it, but don't know how to configure it. Here is what I came up with from looking at the source code and the documentation of the AccountManager plugin (on which DrupalIntegration depends): [components] trac.web.auth.loginmodule = disabled acct_mgr.api = enabled acct_mgr.web_ui.LoginModule = enabled acct_mgr.web_ui.RegistrationModule = disabled TracDrupalIntegration.DrupalIntegration = enabled [account-manager] drupal_database = mysql://<usernam>:<password>@localhost/<db> password_store = DrupalIntegration (<username>, <password> and <db> are naturally substituted with the correct data). While the Trac log says: 2010-12-18 10:54:09,570 Trac[loader] DEBUG: Loading TracDrupalIntegration from /usr/lib/python2.5/site-packages/TracDrupalIntegration-0.1-py2.5.egg this doesn't seem to work: trying to log in with a Drupal username / password results in an "Invalid username or password" error. Has someone used the DrupalIntegration and can point out to me what I did wrong? Or is there any other approach you know (or even have used in the past) to integrate Drupal and Trac that way?

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• Multiple IntenseDebate Comment Counts

  - by Aristotle

  I just setup IntenseDebate on my blog this evening and am, for the most part, pleased with it. One thing I did see is that they offered me a small snippet to show the current number of comments: <script> var idcomments_acct = 'abcdefgef12345678mykey8675309acdc'; var idcomments_post_id; var idcomments_post_url; </script> <script type="text/javascript" src="http://www.intensedebate.com/js/genericLinkWrapperV2.js"></script> This is nice, but what I would like to do is have something similar on my archives page where many posts are listed - not just one. Presently the page looks like this: Some Post TitleAuthor NameShort abstract from this post... Some Post TitleAuthor NameShort abstract from this post... I would like it to look like this: Some Post TitleAuthor NameShort abstract from this post...7 Comments Some Post TitleAuthor NameShort abstract from this post...3 Comments But I'm not exactly sure how I can do this with IntenseDebate. Do they offer any sort of method to gather the total number of comments for multiple pages from a single page?

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• entity framework vNext wish list

  - by Fred Yang

  I have been intensively studying and use ef4 in my project. I do feel the improvement that it has over version 1. But I found that I have something I cannot get around easily. Here is a list I want it to be better in ef vNext. the model designer should allow multiple view of the same model, so that I don't need cram all my entity into a single view. respect user's manual edit of edmx. Currently, the some database view object simply can not be imported to the model because the designer "smartly" think that the view does not have a primary key, so that I have to manually edit the edmx to correct designer's behavior. But in the next "update from database" task, designer will revert my customization. For now, I simply fallback to manually edit the edmx file at all, or I have to use compare tool to keep the new update, and rollback and put the new update into my old edmx file manually. Designer should be improved to allow default behavior and user's manual control. I want control not to let the designer refresh the change of imported object. support user defined table function. linq is about Composability, stored proc dos not support composability. I wish I could use user defined table function which support this. What are you wishes for EF vNext?

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• How to define a batching routing service in WCF

  - by mattx

  I have designed a custom silverlight wcf channel that I want to leverage to selectively batch calls from the client to the server and possibly to cache on the client and short circuit calls. So far I'm just using this channel as a transport and sending the generic WCF messages that result to the WCF router service example here http://msdn.microsoft.com/en-us/magazine/cc500646.aspx?pr=blog to prototype this on the server side. So my scenario looks like this: IFooClient-MyTransportChannel-IRouterService-IFooService-Return I now need to be able to send more than one message per call through the router and carve them up and service them on the server side. Since this is just an experiment and I'm taking baby steps I will dispatch and service all the messages right away on the server side and return the batch of results. Immediately I noticed that simply making the router interface take Message[] instead of Message doesn't work due to serialization problems. I guess this makes sense. I'm not sure soap envelopes can contain other soap envelopes etc. Is there a simple way to take a collection of WCF Message objects and send them to a single method on a service where they can be split up and forwarded as appropriate? If not I'd love suggestions on how I should approach this. I want to have minimal work to do on the router service side so the goal should be to get as close to being able to "slice and forward" as possible.

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• ZeroMQ REQ/REP on ipc:// and concurrency

  - by Metiu

  I implemented a JSON-RPC server using a REQ/REP 0MQ ipc:// socket and I'm experiencing strange behavior which I suspect is due to the fact that the ipc:// underlying unix socket is not a real socket, but rather a single pipe. From the documentation, one has to enforce strict zmq_send()/zmq_recv() alternation, otherwise the out-of-order zmq_send() will return an error. However, I expected the enforcement to be per-client, not per-socket. Of course with a Unix socket there is just one pipeline from multiple clients to the server, so the server won't know who it is talking with. Two clients could zmq_send() simultaneously and the server would see this as an alternation violation. The sequence could be: ClientA: zmq_send() ClientB: zmq_send() : will it block until the other send/receive completes? will it return -1? (I suspect it will with ipc:// due to inherent low-level problems, but with TCP it could distinguish the two clients) ClientA: zmq_recv() ClientB: zmq_recv() so what about tcp:// sockets? Will it work concurrently? Should I use some other locking mechanism to work around this?

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• Active Directory Membership Provider - how to expand on this?

  - by Jaxidian

  I'm working on getting an MVC app up and running via AD Membership Provider and I'm having some issues figuring this out. I have a base configuration setup and working when I login as [email protected] + password. <connectionStrings> <add name="MyConnString" connectionString="LDAP://domaincontroller/OU=Product Users,DC=my,DC=domain,DC=com" /> </connectionStrings> <membership defaultProvider="MyProvider"> <providers> <clear /> <add name="MyProvider" connectionStringName="MyConnString" connectionUsername="my.domain.com\service_account" connectionPassword="biguglypassword" type="System.Web.Security.ActiveDirectoryMembershipProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" /> </providers> </membership> However, I'd LIKE to do some other things and I'm not sure how to go about them. Login without typing the domain (i.e. the "@my.domain.com"). I realize that this could only work if I limit myself to just one domain - that's fine. Organize users in up to N different OUs within a single OU. As you can tell from my current connection string, I'm authenticating users in my Product Users OU. I would LIKE to create OUs for various companies within this OU and put the users into those OUs. How can I authenticate across all of these different OUs? I'm trying to figure out how the Active Directory Membership Provider ties in with the Profile and Role providers. Are there AD versions of those too or am I stuck with SQL, home-grown, or finding something somebody else has coded up? Many thanks!!

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• Bind to a property of a parent element in wpf

  - by msfanboy

  Hello all, I want to bind the Height property of the RichTextBox to the Height Property of the GridViews Row. How can I do that? I do not know how to get the Rows Height as I can not access the Row in xaml what I would like to do. <my:RadGridView Height="524" ItemsSource="{Binding Lessons}" AutoGenerateColumns="False" Name="dataGrid1" VerticalAlignment="Top" SelectionMode="Single" CanUserSortColumns="False" IsFilteringAllowed="False"> <my:RadGridView.Columns> <my:GridViewDataColumn Name="ContentColumn" Width="0.3*" Header="Content"> <my:GridViewDataColumn.CellTemplate> <DataTemplate> <RichTextBox Height="{Binding ElementName=MyRowNameToBindTo,Path=Height}"> <FlowDocument> <Paragraph> <Run Text="{Binding Content}"/> </Paragraph> </FlowDocument> </RichTextBox> </DataTemplate> </my:GridViewDataColumn.CellTemplate> ...

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• Efficient way to store order in mySQL for list of items

  - by ninumedia

  I want to code cleaner and more efficiently and I wanted to know any other suggestions for the following problem: I have a mySQL database that holds data about a set of photograph names. Oh, say 100 photograph names Table 1: (photos) has the following fields: photo_id, photo_name Ex data: 1 | sunshine.jpg 2 | cloudy.jpg 3 | rainy.jpg 4 | hazy.jpg ... Table 2: (categories) has the following fields: category_id, category_name, category_order Ex data: 1 | Summer Shots | 1,2,4 2 | Winter Shots | 2,3 3 | All Seasons | 1,2,3,4 ... Is it efficient to store the order of the photos in this manner per entry via comma delimited values? It's one approach I have seen used before but I wanted to know if something else is faster in run time. Using this way I don't think it is possible to do a direct INNER JOIN on the category table and photo table to get a single matched list of all the photographs per category. Ex: Summer shots - sunshine.jpg, cloudy.jpg, hazy.jpg because it was matched against 1,2,4 The iteration through all the categories and then the photos will have a O(n^2) and there has to be a better/faster way. Please educate me :)

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• (Oracle) How get total number of results when using a pagination query?

  - by BestPractices

  I am using Oracle 10g and the following paradigm to get a page of 15 results as a time (so that when the user is looking at page 2 of a search result, they see records 16-30). select * from ( select rownum rnum, a.* from (my_query) a where rownum <= 30 ) where rnum > 15; Right now I'm having to run a separate SQL statement to do a "select count" on "my_query" in order to get the total number of results for my_query (so that I can show it to the user and use it to figure out total number of pages, etc). Is there any way to get the total number of results without doing this via a second query, i.e. by getting it from above query? I've tried adding "max(rownum)", but it doesn't seem to work (I get an error [ORA-01747] that seems to indicate it doesnt like me having the keyword rownum in the group by). My rationale for wanting to get this from the original query rather than doing it in a separate SQL statement is that "my_query" is an expensive query so I'd rather not run it twice (once to get the count, and once to get the page of data) if I dont have to; but whatever solution I can come up with to get the number of results from within a single query (and at the same time get the page of data I need) should not add much if any additional overhead, if possible. Please advise. Here is exactly what I'm trying to do for which I receive an ORA-01747 error because I believe it doesnt like me having ROWNUM in the group by. Note, If there is another solution that doesnt use max(ROWNUM), but something else, that is perfectly fine too. This solution was my first thought as to what might work. SELECT * FROM (SELECT r.*, ROWNUM RNUM, max(ROWNUM) FROM (SELECT t0.ABC_SEQ_ID AS c0, t0.FIRST_NAME, t0.LAST_NAME, t1.SCORE FROM ABC t0, XYZ t1 WHERE (t0.XYZ_ID = 751) AND t0.XYZ_ID = t1.XYZ_ID ORDER BY t0.RANK ASC) r WHERE ROWNUM <= 30 GROUP BY r.*, ROWNUM) WHERE RNUM > 15

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• SQL Server log backups "stalling"

  - by MattK

  I have interited a box running SQL Server 2008 and Windows 2003, and have had a few events where largeish (35GB) log backups "stall", both before and after the installation of SQL 2008 SP1. The server log ships to a standby, so regular log backups are taken at 15 minute intervals. However, after an index reorg causes the log to grow to about 35GB (on a DB with about 17GB of data), the next log backup runs to ~95% completion, then seems to stop. The process shows as suspended, with a wait state of BACKUPIO. CPU, read, and write activity on the SPID also does not change, and the process stays in this state for hours, when normally a backup of this size should complete in about 20 minutes. This server has a single RAID-1 volume, thus the source database files and destination backup files are on the same volume. However, I cannot determine if another process is blocking the backup. The backup SPID cannot be killed, and the only way to terminate the log backup and clear the lock on the backup file is to cycle the SQL Server service. There was one event where the backup terminated completely, with an error that another process had locked the backup file, but no details about what that process was. Can anyone suggest a cause or diagnostic process to this situation?

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