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  • how does one _model_ data from relational databases in clojure ?

    - by sandeep
    I have asked this question on twitter as well the #clojure IRC channel, yet got no responses. There have been several articles about Clojure-for-Ruby-programmers, Clojure-for-lisp-programmers.. but what is the missing part is Clojure for ActiveRecord programmers . There have been articles about interacting with MongoDB, Redis, etc. - but these are key value stores at the end of the day. However, coming from a Rails background, we are used to thinking about databases in terms of inheritance - has_many, polymorphic, belongs_to, etc. The few articles about Clojure/Compojure + MySQL (ffclassic) - delve right into sql. Of course, it might be that an ORM induces impedence mismatch, but the fact remains that after thinking like ActiveRecord, it is very difficult to think any other way. I believe that relational DBs, lend themselves very well to the object-oriented paradigm because of them being , essentially, Sets. Stuff like activerecord is very well suited for modelling this data. For e.g. a blog - simply put class Post < ActiveRecord::Base has_many :comments end class Comment < ActiveRecord::Base belongs_to :post end How does one model this in Clojure - which is so strictly anti-OO ? Perhaps the question would have been better if it referred to all functional programming languages, but I am more interested from a Clojure standpoint (and Clojure examples)

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  • How does C#'s DateTime.Now affect query plan caching in SQL Server?

    - by Bill Paetzke
    Given: Let's say we have a stored procedure. It reports data back to a user on a webpage. The user can set a date range. If the user sets today's date as the "end date," which includes today's data, the web app passes DateTime.Now to the sql proc. Let's say that one user runs a report--5/1/2010 to now--over and over several times. On the webpage, the user sees "5/1/2010" to "5/4/2010." But the web app passes DateTime.Now to the sql proc as the end date. So, the end date in the proc will always be different, although the user is querying a similar date range. Assume the number of records in the table and number of users are large. So any performance gains matter. Hence the importance of the question. Question: Does passing DateTime.Now as a parameter to a proc prevent SQL Server from caching the query plan? If so, then is the web app missing out on huge performance gains? Possible Solution: I thought DateTime.Today.AddDays(1) would be a possible solution. It would allow the user to get the latest data and always pass the same end date to the sql proc--"5/5/2010" in this case. Please speak to this as well. Sample proc and execution (if that helps to understand): CREATE PROCEDURE GetFooData @StartDate datetime @EndDate datetime AS SELECT * FROM Foo WHERE LogDate >= @StartDate AND LogDate < @EndDate Here's a sample execution using DateTime.Now: EXEC GetFooData '2010-05-01', '2010-05-04 15:41:27' -- passed in DateTime.Now Here's a sample execution using DateTime.Today.AddDays(1) EXEC GetFooData '2010-05-01', '2010-05-05' -- passed in DateTime.Today.AddDays(1) The same data is returned for both procs, since the current time is: 2010-05-04 15:41:27.

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  • google chrome extension update text after response callback

    - by Jerome
    I am writing a Google Chrome extension. I have reached the stage where I can pass messages back and forth readily but I am running into trouble with using the response callback. My background page opens a message page and then the message page requests more information from background. When the message page receives the response I want to replace some of the standard text on the message page with custom text based on the response. Here is the code: chrome.extension.sendRequest({cmd: "sendKeyWords"}, function(response) { keyWordList=response.keyWordsFound; var keyWords=""; for (var i = 0; i FIRST QUESTION: This all seems to work fine but the text on the page doesn't change. I am almost certainly because the callback completes after the page is finished loading and the rest of the code finishes before the callback completes, too. How do I update the page with the new text? Can I listen for the callback to complete or something like that? SECOND QUESTION: The procedure I am pursuing first opens the message page and then the message page requests the keyword list from background. Since I always want the keyword list, it makes more sense to just send it when I create the tab. Can I do that? Here is the code from background that opens the message page: //when request from detail page to open message page chrome.extension.onRequest.addListener(function(request, sender, sendResponse) { if(request.cmd == "openMessage") { console.log("Received Request to Open Message, Profile Score: "+request.keyWordsFound.length); keyWordList=request.keyWordsFound; chrome.tabs.create({url: request.url}, function(tab){ msgTabId=tab.id; //needed to determine if message tab has later been closed chrome.tabs.executeScript(tab.id, {file: "message.js"}); }); console.log("Opening Message"); } });

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  • Achieving Thread-Safety

    - by Smasher
    Question How can I make sure my application is thread-safe? Are their any common practices, testing methods, things to avoid, things to look for? Background I'm currently developing a server application that performs a number of background tasks in different threads and communicates with clients using Indy (using another bunch of automatically generated threads for the communication). Since the application should be highly availabe, a program crash is a very bad thing and I want to make sure that the application is thread-safe. No matter what, from time to time I discover a piece of code that throws an exception that never occured before and in most cases I realize that it is some kind of synchronization bug, where I forgot to synchronize my objects properly. Hence my question concerning best practices, testing of thread-safety and things like that. mghie: Thanks for the answer! I should perhaps be a little bit more precise. Just to be clear, I know about the principles of multithreading, I use synchronization (monitors) throughout my program and I know how to differentiate threading problems from other implementation problems. But nevertheless, I keep forgetting to add proper synchronization from time to time. Just to give an example, I used the RTL sort function in my code. Looked something like FKeyList.Sort (CompareKeysFunc); Turns out, that I had to synchronize FKeyList while sorting. It just don't came to my mind when initially writing that simple line of code. It's these thins I wanna talk about. What are the places where one easily forgets to add synchronization code? How do YOU make sure that you added sync code in all important places?

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  • Database table relationships: Always also relate to specified value (Linq to SQL in .NET Framework)

    - by sinni800
    I really can not describe my question better in the title. If anyone has suggestions: Please tell! I use the Linq to SQL framework in .NET. I ran into something which could be easily solved if the framework supported this, it would be a lot of extra coding otherwise: I have a n to n relation with a helper table in between. Those tables are: Items, places and the connection table which relates items to places and the other way. One item can be found in many places, so can one place have many items. Now of course there will be many items which will be in ALL places. Now there is a problem: Places can always be added. So I need a place-ID which encompasses ALL places, always. Like maybe a place-id "0". If the helper table has a row with the place-id of zero, this should be visible in all places. In SQL this would be a simple "Where [...] or place-id = 0", but how do I do this in Linq relations? Also, for a little side question: How could I manage "all but this place" kind of exclusions?

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  • Alternatives to the Entity Framework for Serving/Consuming an OData Interface

    - by Egahn
    I'm researching how to set up an OData interface to our database. I would like to be able to pull/query data from our DB into Excel, as a start. Eventually I would like to have Excel run queries and pull data over HTTP from a remote client, including authentication, etc. I've set up a working (rickety) prototype so far, using the ADO.NET Entity Data Model wizard in Visual Studio, and VSTO to create a test Excel worksheet with a button to pull from that ADO.NET interface. This works OK so far, and I can query the DB using Linq through the entities/objects that are created by the ADO.NET EDM wizard. However, I have started to run into some problems with this approach. I've been finding the Entity Framework difficult to work with (and in fact, also difficult to research solutions to, as there's a lot of chaff out there regarding it and older versions of it). An example of this is my being unable to figure out how to set the SQL command timeout (as opposed to the HTTP request timeout) on the DataServiceContext object that the wizard generates for my schema, but that's not the point of my question. The real question I have is, if I want to use OData as my interface standard, am I stuck with the Entity Framework? Are there any other solutions out there (preferably open source) which can set up, serve and consume an OData interface, and are easier to work with and less bloated than the Entity Framework? I have seen mention of NHibernate as an alternative, but most of the comparison threads I've seen are a few years old. Are there any other alternatives out there now? Thanks very much!

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  • Time complexity to fill hash table (homework)?

    - by Heathcliff
    This is a homework question, but I think there's something missing from it. It asks: Provide a sequence of m keys to fill a hash table implemented with linear probing, such that the time to fill it is minimum. And then Provide another sequence of m keys, but such that the time fill it is maximum. Repeat these two questions if the hash table implements quadratic probing I can only assume that the hash table has size m, both because it's the only number given and because we have been using that letter to address a hash table size before when describing the load factor. But I can't think of any sequence to do the first without knowing the hash function that hashes the sequence into the table. If it is a bad hash function, such that, for instance, it hashes every entry to the same index, then both the minimum and maximum time to fill it will take O(n) time, regardless of what the sequence looks like. And in the average case, where I assume the hash function is OK, how am I suppossed to know how long it will take for that hash function to fill the table? Aren't these questions linked to the hash function stronger than they are to the sequence that is hashed? As for the second question, I can assume that, regardless of the hash function, a sequence of size m with the same key repeated m-times will provide the maximum time, because it will cause linear probing from the second entry on. I think that will take O(n) time. Is that correct? Thanks

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  • Problem using unicode in URLs with cgi.PATH_INFO in ColdFusion

    - by Loftx
    Hi there, My ColdFusion (MX7) site has search functionality which appends the search term to the URL e.g. http://www.example.com/search.cfm/searchterm. The problem I'm running into is this is a multilingual site, so the search term may be in another language e.g. ??????? leading to a search URL such as http://www.example.com/search.cfm/??????? The problem is when I come to retrieve the search term from the URL. I'm using cgi.PATH_INFO to retrieve the path of the search page and the search term and extracting the search term from this e.g. /search.cfm/searchterm however, when unicode characters are used in the search they are converted to question marks e.g. /search.cfm/??????. These appear actual question marks, rather than the browser not being able to format unicode characters, or them being mangled on output. I can't find any information about whether ColdFusion supports unicode in the URL, or how I can go about resolving this and getting hold of the complete URL in some way - does anyone have any ideas? Cheers, Tom

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  • OpenGLES - Rendering a background image only once and not wiping it

    - by chaosbeaker
    Hello, first time asking a question here but been watching others answers for a while. My own question is one for improving the performance of my program. Currently I'm wiping the viewFrameBuffer on each pass through my program and then rendering the background image first followed by the rest of my scene. I was wondering how I go about rendering the background image once, and only wiping the rest of the scene for updating/re-rendering. I tried using a seperate buffer but I'm not sure how to present this new buffer to the render buffer. // Set the current EAGLContext and bind to the framebuffer. This will direct all OGL commands to the // framebuffer and the associated renderbuffer attachment which is where our scene will be rendered [EAGLContext setCurrentContext:context]; glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer); // Define the viewport. Changing the settings for the viewport can allow you to scale the viewport // as well as the dimensions etc and so I'm setting it for each frame in case we want to change i glViewport(0, 0, screenBounds.size.width , screenBounds.size.height); // Clear the screen. If we are going to draw a background image then this clear is not necessary // as drawing the background image will destroy the previous image glClearColor(0.0f, 1.0f, 0.0f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); // Setup how the images are to be blended when rendered. This could be changed at different points during your // render process if you wanted to apply different effects glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); switch (currentViewInt) { case 1: { [background render:CGPointMake(240, 0) fromTopLeftBottomRightCenter:@"Bottom"]; // Other Rendering Code }} // Bind to the renderbuffer and then present this image to the current context glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer); [context presentRenderbuffer:GL_RENDERBUFFER_OES]; Hopefully by solving this I'll also be able to implement another buffer just for rendering particles as I can set them to always use a black background as their alpha source. Any help is greatly appreciated

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  • Which text margin does SWT Table use when drawing text?

    - by Zordid
    I got a relatively easy question - but I cannot find anything anywhere to answer it. I use a simple SWT table widget in my application that displays only text in the cells. I got an incremental search feature and want to highlight text snippets in all cells if they match. So when typing "a", all "a"s should be highlighted. To get this, I add an SWT.EraseItem listener to interfere with the background drawing. If the current cell's text contains the search string, I find the positions and calculate relative x-coordinates within the text using event.gc.stringExtent - easy. With that I just draw rectangles "behind" the occurrences. Now, there's a flaw in this. The table does not draw the text without a margin, so my x coordinate does not really match - it is slightly off by a few pixels! But how many?? Where do I retrieve the cell's text margins that table's own drawing will use? No clue. Cannot find anything. :-( Bonus question: the table's draw method also shortens text and adds "..." if it does not fit into the cell. Hmm. My occurrence finder takes the TableItem's text and thus also tries to mark occurrences that are actually not visible because they are consumed by the "...". How do I get the shortened text and not the "real" text within the EraseItem draw handler? Thanks!

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  • Node & Redis: Crucial Design Issues in Production Mode

    - by Ali
    This question is a hybrid one, being both technical and system design related. I'm developing the backend of an application that will handle approx. 4K request per second. We are using Node.js being super fast and in terms of our database struction we are using MongoDB, with Redis being a layer between Node and MongoDB handling volatile operations. I'm quite stressed because we are expecting concurrent requests that we need to handle carefully and we are quite close to launch. However I do not believe I've applied the correct approach on redis. I have a class Student, and they constantly change stages(such as 'active', 'doing homework','in lesson' etc. Thus I created a Redis DB for each state. (1 for being 'active', 2 for being 'doing homework'). Above I have the structure of the 'active' students table; xa5p - JSON stringified object #1 pQrW - JSON stringified object #2 active_student_table - {{studentId:'xa5p'}, {studentId:'pQrW'}} Since there is no 'select all keys method' in Redis, I've been suggested to use a set such that when I run command 'smembers' I receive the keys and later on do 'get' for each id in order to find a specific user (lets say that age older than 15). I've been also suggested that in fact I used never use keys in production mode. My question is, no matter how 'conceptual' it is, what specific things I should avoid doing in Node & Redis in production stage?. Are they any issues related to my design? Students must be objects and I sure can list them in a list but I haven't done yet. Is it that crucial in production stage?

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  • How To Create a Flexible Plug-In Architecture?

    - by justkt
    A repeating theme in my development work has been the use of or creation of an in-house plug-in architecture. I've seen it approached many ways - configuration files (XML, .conf, and so on), inheritance frameworks, database information, libraries, and others. In my experience: A database isn't a great place to store your configuration information, especially co-mingled with data Attempting this with an inheritance hierarchy requires knowledge about the plug-ins to be coded in, meaning the plug-in architecture isn't all that dynamic Configuration files work well for providing simple information, but can't handle more complex behaviors Libraries seem to work well, but the one-way dependencies have to be carefully created. As I seek to learn from the various architectures I've worked with, I'm also looking to the community for suggestions. How have you implemented a solid plug-in architecture? What was your worst failure (or the worst failure you've seen)? What would you do if you were going to implement a new plug-in architecture? What SDK or open source project that you've worked with has the best example of a good architecture? A few examples I've been finding on my own: Perl's Module::Plugable An SO question with a list for Java (including Sever Provider Interfaces) An SO question for C++ pointing to a Dr. Dobbs article These examples seem to play to various language strengths. Is a good plugin architecture necessarily tied to the language? Is it best to use tools to create a plugin architecture, or to do it on one's own following models?

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  • Something about Stream

    - by sforester
    I've been working on something that make use of streams and I found myself not clear about some stream concepts( you can also view another question posted by me at http://stackoverflow.com/questions/2933923/about-redirected-stdout-in-system-diagnostics-process ). 1.how do you indicate that you have finished writing a stream, writing something like a EOF? 2.follow the previous question, if I have written a EOF(or something like that) to a stream but didn't close the stream, then I want to write something else to the same stream, can I just start writing to it and no more set up required? 3.if a procedure tries to read a stream(like the stdin ) that no one has written anything to it, the reading procedure will be blocked,finally some data arrives and the procedure will just read till the writing is done,which is indicated by getting a return of 0 count of bytes read rather than being blocked, and now if the procedure issues another read to the same stream, it will still get a 0 count and return immediately while I was expecting it will be blocked since no one is writing to the stream now. So does the stream holds different states when the stream is opened but no one has written to it yet and when someone has finished a writing session? I'm using Windows the .net framework if there will by any thing platform specific. Thanks a lot!

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  • How to best launch C++ application from web page

    - by JB
    I guess there are two parts to this question, one technical and one best practice for security and doing things "right". I'm working on a little game using C++ / directx but I would like to be able to launch it from a web page by someone clicking on a link on that page. Ideally I would like the first time they clicked for it to launch an installer downloads and installs the game on their machine, and then the next time to launch an application which updates the game from a web site if it's old and then launches it. I have no problems with the expected security popups and questions the first time it runs. I want people to be certain what they are installing and understand what they are doing. But it would be nice if once it is installed they could run it with the minimum of fuss. My question then is what technologies I could use to do this? I'm thinking that it would need a browser plugin and an activex control so that first time you'd install that, and subsequently the control/plugin would be able to launch the game. I'm not sure that under newer browser secuity models that a plugin would have the permissions to be able to run an installer though or silently invoke applications on the client machine even if they are already installed. Is there a more sensible way to achive what I want to achieve? And I'm worried about the security aspects too. I want this to be convenient for users but I of course want to do it "right". I know this can be done as I've seen several mmorpg type games that launch in this way from the browser now but it's not entirely clear to me how they've done it.

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  • Attempted to render a circle in opengl es 1.1, renders as oval

    - by eipxen
    Hi all, I attempted to render a circle in opengl es 1.1 as a test before building a larger program, but it renders as an oval. Here is the code I use to generate and render my vertices: static const int numVerts = 40; static GLfloat myFirstCircle[82]; myFirstCircle[0] = 0.0f; myFirstCircle[1] = 0.0f; for (int i = 2; i < (numVerts+1)*2; i+=2) { myFirstCircle[i] = .5 * cosf(i*2*3.14159/numVerts); myFirstCircle[i+1] = .5 * sinf(i*2*3.14159/numVerts); } glVertexPointer(2, GL_FLOAT, 0, myFirstCircle); glEnableClientState(GL_VERTEX_ARRAY); glDrawArrays(GL_TRIANGLE_FAN, 0, 22); I'm still somewhat new to this system, so I may have a silly error that I do not see, but it seems to me like this should generate 40 vertices on a circle of radius .5. When it renders, the shape on screen appears to be an oval, significantly taller than it is wide. My question is thus: why is my circle rendering this way, and what could I do to fix it? This is the first question on stackoverflow, so I'm not sure how to share an image of my output.

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  • Problems migrating databinding in VB.NET from Winforms to ASP.NET 2.0

    - by David
    And this was supposed to be so easy... I have existing business and data access layers that handle the retrieval and update of the data in question. These work great with the existing Winforms application (.Net V2.0) Now, in trying to write a new web-based UI, I'm running into all sorts of problems (last time I wrote asp.net code was in 1.1). Specifically, I can't data bind a text box to a business object. Oh, sure there's the ObjectDataSource but that wants to know how to do CRUD operations on the data. What I'm looking for is something that acts like the 'classic' binding objects so that, in my code, it's as simple as retrieving the object and doing a a refresh. The data component like FormView and DetailsView are so generic-looking that it's ridiculous. The existing application would have tabbed dialogs, text boxes grouped by panels, etc. On top of that, I have a directive to use master pages and unless one control causes it, I can't seem to get the content section to expand. I can't just put a text box 'below' the bottom of "Content1" and have it resize the content section - which gives me the same results as an earlier question I posted when the footer wasn't being 'pushed down' - relative position solved that but doesn't seem to solve it with placing small text boxes in the area. What I want is fairly simple. Something like: bindingobject.datasource = businessdataobject bindingobject.refresh ...and have the text boxes refresh with the new values. Likewise to have 'businessdataobject' properties updated as the user enters new data. I was able to do this with the GridView (grdRequests.DataSource = lstRequests) by making a list of asp:BoundField tags inside the collection of the GridView. Am I tilting at windmills here?

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  • Transform only one axis to log10 scale with ggplot2

    - by daroczig
    I have the following problem: I would like to visualize a discrete and a continuous variable on a boxplot in which the latter has a few extreme high values. This makes the boxplot meaningless (the points and even the "body" of the chart is too small), that is why I would like to show this on a log10 scale. I am aware that I could leave out the extreme values from the visualization, but I am not intended to. Let's see a simple example with diamonds data: m <- ggplot(diamonds, aes(y = price, x = color)) The problem is not serious here, but I hope you could imagine why I would like to see the values at a log10 scale. Let's try it: m + geom_boxplot() + coord_trans(y = "log10") As you can see the y axis is log10 scaled and looks fine but there is a problem with the x axis, which makes the plot very strange. The problem do not occur with scale_log, but this is not an option for me, as I cannot use a custom formatter this way. E.g.: m + geom_boxplot() + scale_y_log10() My question: does anyone know a solution to plot the boxplot with log10 scale on y axis which labels could be freely formatted with a formatter function like in this thread? Editing the question to help answerers based on answers and comments: What I am really after: one log10 transformed axis (y) with not scientific labels. I would like to label it like dollar (formatter=dollar) or any custom format. If I try @hadley's suggestion I get the following warnings: > m + geom_boxplot() + scale_y_log10(formatter=dollar) Warning messages: 1: In max(x) : no non-missing arguments to max; returning -Inf 2: In max(x) : no non-missing arguments to max; returning -Inf 3: In max(x) : no non-missing arguments to max; returning -Inf With an unchanged y axis labels:

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  • Given a main function and a cleanup function, how (canonically) do I return an exit status in Bash/Linux?

    - by Zac B
    Context: I have a bash script (a wrapper for other scripts, really), that does the following pseudocode: do a main function if the main function returns: $returncode = $? #most recent return code if the main function runs longer than a timeout: kill the main function $returncode = 140 #the semi-canonical "exceeded allowed wall clock time" status run a cleanup function if the cleanup function returns an error: #nonzero return code exit $? #exit the program with the status returned from the cleanup function else #cleanup was successful .... Question: What should happen after the last line? If the cleanup function was successful, but the main function was not, should my program return 0 (for the successful cleanup), or $returncode, which contains the (possibly nonzero and unsuccessful) return code of the main function? For a specific application, the answer would be easy: "it depends on what you need the script for." However, this is more of a general/canonical question (and if this is the wrong place for it, kill it with fire): in Bash (or Linux in general) programming, do you typically want to return the status that "means" something (i.e. $returncode) or do you ignore such subjectivities and simply return the code of the most recent function? This isn't Bash-specific: if I have a standalone executable of any kind, how, canonically should it behave in these cases? Obviously, this is somewhat debatable. Even if there is a system for these things, I'm sure that a lot of people ignore it. All the same, I'd like to know. Cheers!

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  • Is it possible to send OSC commands to an iPad via the Camera Connection Kit?

    - by HELVETICADE
    I'm building a small controller device that I'd like to partner with a computer. I've settled on using OSC out from my custom built hardware and am pretty satisfied with what I can get from WOscLib. Two goals I'd like to achieve are portability and a very nice ratio between battery:computing power, and this has lured me towards using iPhoneOS to accomplish my goals. I think the iPad would suit my needs perfectly, except that using wifi to broadcast OSC out from my device requires that device to be connected to a third device with a wifi chip, and this would destroy the goal of portability, whilst also introducing potential latency and stability headaches. My question is pretty simple: Can I push OSC commands FROM my controller TO an iPad via USB and the Camera Connection Kit? If I could accomplish this, the two major goals of my project would be fulfilled very nicely. This seems like it should be a simple little question, but researching this obsessively over the past few weeks has left me more almost more uncertain than if I had done no research at all. I'd really like some more confidence before I go down this route, and it seems like it should be possible. Any insight would be very, very appreciated.

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  • JSF: Avoid nested update calls

    - by dhroove
    I don't know if I am on right track or not still asking this question. I my JSF project I have this tree structure: <p:tree id="resourcesTree" value="#{someBean.root}" var="node" selectionMode="single" styleClass="no-border" selection="#{someBean.selectedNode}" dynamic="true"> <p:ajax listener="#{someBean.onNodeSelect}" update=":centerPanel :tableForm :tabForm" event="select" onstart="statusDialog.show();" oncomplete="statusDialog.hide();" /> <p:treeNode id="resourcesTreeNode" > <h:outputText value="#{node}" id="lblNode" /> </p:treeNode> </p:tree> I have to update this tree after I added something or delete something.. But whenever I update this still its nested update also call I mean to say it also call to update these components ":centerPanel :tableForm :tabForm"... This give me error that :tableForm not found in view because this forms load in my central panel and this tree is in my right panel.. So when I am doing some operation on tree is it not always that :tableForm is in my central panel.. (I mean design is something like this only) So now my question is that can I put some condition or there is any way so that I can specify when to update nested components also and when not.... In nut shell is there any way to update only :resoucesTree is such a way that nested updates are not called so that I can avoid error... Thanks in advance.

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  • Auto increment with a Unit Of Work

    - by Derick
    Context I'm building a persistence layer to abstract different types of databases that I'll be needing. On the relational part I have mySQL, Oracle and PostgreSQL. Let's take the following simplified MySQL tables: CREATE TABLE Contact ( ID varchar(15), NAME varchar(30) ); CREATE TABLE Address ( ID varchar(15), CONTACT_ID varchar(15), NAME varchar(50) ); I use code to generate system specific alpha numeric unique ID's fitting 15 chars in this case. Thus, if I insert a Contact record with it's Addresses I have my generated Contact.ID and Address.CONTACT_IDs before committing. I've created a Unit of Work (amongst others) as per Martin Fowler's patterns to add transaction support. I'm using a key based Identity Map in the UoW to track the changed records in memory. It works like a charm for the scenario above, all pretty standard stuff so far. The question scenario comes in when I have a database that is not under my control and the ID fields are auto-increment (or in Oracle sequences). In this case I do not have the db generated Contact.ID beforehand, so when I create my Address I do not have a value for Address.CONTACT_ID. The transaction has not been started on the DB session since all is kept in the Identity Map in memory. Question: What is a good approach to address this? (Avoiding unnecessary db round trips) Some ideas: Retrieve the last ID: I can do a call to the database to retrieve the last Id like: SELECT Auto_increment FROM information_schema.tables WHERE table_name='Contact'; But this is MySQL specific and probably something similar can be done for the other databases. If do this then would need to do the 1st insert, get the ID and then update the children (Address.CONTACT_IDs) – all in the current transaction context.

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  • After Delete Trigger Fires Only After Delete?

    - by Brandi
    I thought "after delete" meant that the trigger is not fired until after the delete has already taken place, but here is my situation... I made 3, nearly identical SQL CLR after delete triggers in C#, which worked beautifully for about a month. Suddenly, one of the three stopped working while an automated delete tool was run on it. By stopped working, I mean, records could not be deleted from the table via client software. Disabling the trigger caused deletes to be allowed, but re-enabling it interfered with the ability to delete. So my question is 'how can this be the case?' Is it possible the tool used on it futzed up the memory? It seems like even if the trigger threw an exception, if it is AFTER delete, shouldn't the records be gone? All the trigger looks like is this: ALTER TRIGGER [sysdba].[AccountTrigger] ON [sysdba].[ACCOUNT] AFTER DELETE AS EXTERNAL NAME [SQL_IO].[SQL_IO.WriteFunctions].[AccountTrigger] GO The CLR trigger does one select and one insert into another database. I don't yet know if there are any errors from SQL Server Mgmt Studio, but will update the question after I find out.

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  • File descriptor limits and default stack sizes

    - by Charles
    Where I work we build and distribute a library and a couple complex programs built on that library. All code is written in C and is available on most 'standard' systems like Windows, Linux, Aix, Solaris, Darwin. I started in the QA department and while running tests recently I have been reminded several times that I need to remember to set the file descriptor limits and default stack sizes higher or bad things will happen. This is particularly the case with Solaris and now Darwin. Now this is very strange to me because I am a believer in 0 required environment fiddling to make a product work. So I am wondering if there are times where this sort of requirement is a necessary evil, or if we are doing something wrong. Edit: Great comments that describe the problem and a little background. However I do not believe I worded the question well enough. Currently, we require customers, and hence, us the testers, to set these limits before running our code. We do not do this programatically. And this is not a situation where they MIGHT run out, under normal load our programs WILL run out and seg fault. So rewording the question, is requiring the customer to change these ulimit values to run our software to be expected on some platforms, ie, Solaris, Aix, or are we as a company making it to difficult for these users to get going? Bounty: I added a bounty to hopefully get a little more information on what other companies are doing to manage these limits. Can you set these pragmatically? Should we? Should our programs even be hitting these limits or could this be a sign that things might be a bit messy under the covers? That is really what I want to know, as a perfectionist a seemingly dirty program really bugs me.

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  • How to handle image/gif type response on client side using GWT

    - by user200340
    Hi all, I have a question about how to handle image/gif type response on client side, any suggestion will be great. There is a service which responds for retrieving image (only one each time at the moment) from database. The code is something like, JDBC Connection Construct MYSQL query. Execute query If has ResultSet, retrieve first one { //save image into Blob image, “img” is the only entity in the image table. image = rs.getBlob("img"); } response.setContentType("image/gif"); //set response type InputStream in = image.getBinaryStream(); //output Blob image to InputStream int bufferSize = 1024; //buffer size byte[] buffer = new byte[bufferSize]; //initial buffer int length =0; //read length data from inputstream and store into buffer while ((length = in.read(buffer)) != -1) { out.write(buffer, 0, length); //write into ServletOutputStream } in.close(); out.flush(); //write out The code on client side .... imgform.setAction(GWT.getModuleBaseURL() + "serviceexample/ImgRetrieve"); .... ClickListener { OnClick, then imgform.submit(); } formHandler { onSubmit, form validation onSubmitComplete ??????? //handle response, and display image **Here is my question, i had tried Image img = new Image(GWT.getHostPageBaseURL() +"serviceexample/ImgRetrieve"); mg.setSize("300", "300"); imgpanel.add(img); but i only got a non-displayed image with 300X300 size.** } So, how should i handle the responde in this case? Thanks,

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  • c++ callback syntax in a class

    - by Mr Bell
    I am trying to figure out the syntax to register a callback with this 3rd party software. I think it is probably a basic question, I just am not too familiar with c++. They have a method for registering a callback function so their code can call a function in my code when an event happens. They provided a working example that registers the callback from the main file, but I want to know how to do it when working inside a class Their method signature: smHTRegisterHeadPoseCallback(smEngineHandle engine_handle, void *user_data, smHTHeadPoseCallback callback_fun); Working example from the main file: void STDCALL receiveHeadPose(void *,smEngineHeadPoseData head_pose, smCameraVideoFrame video_frame) { ... } void main() { ... smHTRegisterHeadPoseCallback(engine_handle,0,receiveHeadPose) ... } But I want to use this from my class MyClass.h class FaceEngine { public: void STDCALL receiveFaceData(void *, smEngineFaceData face_data, smCameraVideoFrame video_frame); ... MyClass.cpp void FaceEngine::Start(void) { rc = smHTRegisterFaceDataCallback(hFaceAPIEngine,0,&FaceEngine::receiveFaceData); ... Results in this compiler error: Error 1 error C2664: 'smHTRegisterFaceDataCallback' : cannot convert parameter 3 from 'void (__stdcall FaceEngine::* )(void *,smEngineFaceData,smCameraVideoFrame)' to 'smHTFaceDataCallback' d:\stuff\programming\visual studio 2008\projects\tut02_vertices\faceengine.cpp 43 Beard If my question isn't clear please let me know how I can clarify.

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