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  • Deal with undefined values in code or in the template?

    - by David
    I'm writing a web application (in Python, not that it matters). One of the features is that people can leave comments on things. I have a class for comments, basically like so: class Comment: user = ... # other stuff where user is an instance of another class, class User: name = ... # other stuff And of course in my template, I have <div>${comment.user.name}</div> Problem: Let's say I allow people to post comments anonymously. In that case comment.user is None (undefined), and of course accessing comment.user.name is going to raise an error. What's the best way to deal with that? I see three possibilities: Use a conditional in the template to test for that case and display something different. This is the most versatile solution, since I can change the way anonymous comments are displayed to, say, "Posted anonymously" (instead of "Posted by ..."), but I've often been told that templates should be mindless display machines and not include logic like that. Also, other people might wind up writing alternate templates for the same application, and I feel like I should be making things as easy as possible for the template writer. Implement an accessor method for the user property of a Comment that returns a dummy user object when the real user is undefined. This dummy object would have user.name = 'Anonymous' or something like that and so the template could access it and print its name with no error. Put an actual record in my database corresponding to a user with user.name = Anonymous (or something like that), and just assign that user to any comment posted when nobody's logged in. I know I've seen some real-world systems that operate this way. (phpBB?) Is there a prevailing wisdom among people who write these sorts of systems about which of these (or some other solution) is the best? Any pitfalls I should watch out for if I go one way vs. another? Whoever gives the best explanation gets the checkmark.

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  • should i advocate migrating from access to (my)sql

    - by HotOil
    Hi: We have a windows MFC app that is written against an access database on a company server. The db is not that big: 19 MB. There are at most 2-3 users accessing it at any one time. It is used in a factory environment where access speed (or lack thereof) over the intranet becomes noticeable as it is part of the manufacturing time for our widgets. The scenario is this: as each widget is completed, it gets a record in the db.. by the end of the year, the db is larger and searching for a record takes longer and longer. The solution so far has been to manually move older records to an archival table about once a year. We are reworking other portions of this app right now, and it would be a good time to move to another db if we are going to do it. It is my understanding that if we were using sql, the search time would not go up as the table gets bigger because the entire .mdb does not have to be sent over the network each time. Is this correct? Does anyone have any insight about whether it could be worth it to go to the trouble (time and money) of migrating to a new db, or should I just add more functionality to the application we have now, and maybe automatically purge the older records from time to time, and add additional facilities to the app to get at the older records when needed? Thanks for any wisdom you can share..

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  • How to "push" updates to individual cells in a (ASP.NET) web page table/grid?

    - by dommer
    I'm building something similar to a price comparison site. This will be developed in ASP.NET/WebForms/C#/.NET 3.5. The site will be used by the public, so I have no control over the client side - and the application isn't so central to their lives that they'll go out of their way to make it work. I want to have a table/grid that displays products in rows, vendors in columns, and prices in the cells. Price updates will be arriving (at the server) continuously, and I'd like to "push" any updates to the clients' browsers - ideally only updating what has changed. So, if Vendor A changes their price on Product B, I'd want to immediately update the relevant cell in all the browsers that are viewing this information. I don't want to use any browser plug-ins (e.g. Silverlight). Javascript is fine. What's the best approach to take? Presumably my options are: 1) have the client page continuously poll the server for updates, locate the correct cell and update it; or 2) have the server be able to send updates to all the open browser pages which are listening for these updates. The first one would seem the most plausible, but I don't want to constrain the assembled wisdom of the SO community. I'm happy to purchase any third party components (e.g. a grid) that might help with this. I already have the DevExpress grid/ajax components if they provide anything useful.

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  • Qt/C++ - confused about caller/callee, object ownership

    - by Isabel
    I am creating a GUI to manipulate a robot arm. The location of the arm can be described by 6 floats (describing the positions of the various arm joints. The interface consists of a QGraphicsView with a diagram of the arm (which can be clicked to change the arm position - adjusting the 6 floats). The interface also has 6 lineEdit boxes, to also adjust those values separately. When the graphics view is clicked, and when the line edit boxes are changed, I'd like the line edit boxes / graphics view to stay in synchronisation. This brings me to confusion about how to store the 6 floats, and trigger events when they're updated. My current idea is this: The robot arm's location should be represented by a class, RobotArmLocation. Objects of this class then have methods such as obj.ShoulderRotation() and obj.SetShoulderRotation(). The MainWindow has a single instance of RobotArmLocation. Next is the bit I'm more confused about, how to join everything up. I am thinking: The MainWindow has a ArmLocationChanged slot. This is signalled whenever the location object is changed. The diagram class will have a SetRobotArmLocation(RobotArmLocation &loc). When the diagram is changed, it's free to change the location object, and fire a signal to the ArmLocationChanged slot. Likewise, changing any of the text boxes will fire a signal to that ArmLocationChanged slot. The slot then has code to synchronise all the elements. This kind of seems like a mess to me, does anyone have any other suggestions? I've also thought of the following, does it have any merrit? The RobotArmLocation class has a ValueChanged slot, the diagram and textboxes can use that directly, and bypass the MainWindow directly (seems cleaner?) thanks for any wisdom!

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  • Bash PATH: How long is too long?

    - by ajwood
    Hi, I'm currently designing a software quarantine pattern to use on Ubuntu. I'm not sure how standard "quarantine" is in this context, so here is what I hope to accomplish... Inside a particular quarantine is all of the stuff one needs to run an application (bin, share, lib, etc.). Ideally, the quarantine has no leaks, which means it's not relying on any code outside of itself on the system. A quarantine can be defined as a set of executables (and some environment settings needed to make them run). I think it will be beneficial to separate the built packages enough such that upgrading to a newer version of the quarantine won't require rebuilding the whole thing. I'll be able to update just a few packages, and then the new quarantine can use some of old parts and some of the new parts. One issue I'm wondering about is the environment variables I'll be setting up to use a particular quarantines. Is there a hard limit on how big PATH can be? (either in number of characters, or in the number of directories it contains) Might a path be so long that it affects performance? Thanks very much, Andrew p.s. Any other wisdom that might help my design would be greatly appreciated :)

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  • Is there a recommended way to communicate scientific/engineering programming to C developers?

    - by ggkmath
    Hi, I have a lot of MATLAB code that needs to get ported to C (execution speed is critical for this work) as part of a back-end process for a web application. When I attempt to outsource this code to a C developer, I assume (correct me if I'm wrong) few C developers also understand MATLAB code (things like indexing and memory management are different, etc.). I wonder if there are any C developers out there that can recommend a procedure for me to follow to best communicate what the code does? For example, should I provide the MATLAB code and explain what it's doing line by line? Or, should I just provide the math/algorithm, explain it in plain English, and let the C developer implement it with this understanding in his/her own way (e.g. can I assume the developer understands how to work with complex math (i.e. imaginary numbers), how to generate histograms, perform an FFT, etc.)? Or, is there a better method? I expect I'm not the first to need to do this, so I wonder if any C developers out there ran into this situation and can share any conventional wisdom how they'd like this task to be transferred? Thanks in advance for any comments.

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  • Advice on Linq to SQL mapping object design

    - by fearofawhackplanet
    I hope the title and following text are clear, I'm not very familiar with the correct terms so please correct me if I get anything wrong. I'm using Linq ORM for the first time and am wondering how to address the following. Say I have two DB tables: User ---- Id Name Phone ----- Id UserId Model The Linq code generator produces a bunch of entity classes. I then write my own classes and interfaces which wrap these Linq classes: class DatabaseUser : IUser { public DatabaseUser(User user) { _user = user; } public Guid Id { get { return _user.Id; } } ... etc } so far so good. Now it's easy enough to find a users phones from Phones.Where(p => p.User = user) but surely comsumers of the API shouldn't need to be writing their own Linq queries to get at data, so I should wrap this query in a function or property somewhere. So the question is, in this example, would you add a Phones property to IUser or not? In other words, should my interface specifically be modelling my database objects (in which case Phones doesn't belong in IUser), or are they actually simply providing a set of functions and properties which are conceptually associated with a User (in which case it does)? There seems drawbacks to both views, but I'm wondering if there is a standard approach to the problem. Or just any general words of wisdom you could share. My first thought was to use extension methods but in fact that doesn't work in this case.

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  • Move to php in windows? Concern, hints, "please don't do!"?

    - by Daniel
    I am considering to move frome Microsoft languages to PHP (just for web dev) which has quite an interesting syntax, a perlish look (but a wider programmer base) and it allows me to reuse the web without reinventing it. I have some concerns too. I would be more than happy to gather some wisdom from stackoverflow community, (challenge to my opinions warmly welcome). Here are my doubts. Efficiency. Cgi are slow, what I am supposed to use? Fastcgi? Or what else? Efficiency + stability. Is PHP on windows really stable and a good choice in terms of performances? Database. I use very often MSSQL (I regret, i like it). Could I widely and efficiently interface PHP with MSSQL (using smartly stored pro, for example). XSLT + XML performance. I work quite a lot with XML and XSLT and I really find the MS xml parser a great software component. Are parser used in PHP fast, reliable and efficient (I am interested mainly in DOM, not SAX)? Objects. Is the PHP object programming model valid end efficient? 6 Regex. How efficient is PHP processing regexp? Many thanks for your advices.

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  • Looking for: nosql (redis/mongodb) based event logging for Django

    - by Parand
    I'm looking for a flexible event logging platform to store both pre-defined (username, ip address) and non-pre-defined (can be generated as needed by any piece of code) events for Django. I'm currently doing some of this with log files, but it ends up requiring various analysis scripts and ends up in a DB anyway, so I'm considering throwing it immediately into a nosql store such as MongoDB or Redis. The idea is to be easily able to query, for example, which ip address the user most commonly comes from, whether the user has ever performed some action, lookup the outcome for a specific event, etc. Is there something that already does this? If not, I'm thinking of this: The "event" is a dictionary attached to the request object. Middleware fills in various pieces (username, ip, sql timing), code fills in the rest as needed. After the request is served a post-request hook drops the event into mongodb/redis, normalizing various fields (eg. incrementing the username:ip address counter) and dropping the rest in as is. Words of wisdom / pointers to code that does some/all of this would be appreciated.

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  • Iterate Through JSON Data for Specific Element - Similar to XPath

    - by Highroller
    I am working on an embedded system and my theory of the overall process follows this methodology: 1. Send a command to the back end asking for account information in JSON format. 2. The back end writes a JSON file with all accounts and associated information (there could be 0 to 16 accounts). 3. Here's where I get stuck - use JavaScript (we are using the JQuery library) to iterate through the returned information for a specific element (similar to XPath) and build an array based on the number of elements found to populate a drop-down box to select the account you want to view and then do stuff with the account info. So my code looks like this: loadAccounts = function() { $.getJSON('/info?q=voip.accounts[]', function(result) { var sipAcnts = $("#sipacnts"); $(sipAcnts).empty(); // empty the dropdown (if necessarry) // Get the 'label' element and stick it in an array // build the array and append it to the sipAcnts dropdown // use array index to ref the accounts info and do stuff with it } So what I need is the JSON version of XPath to build the array of voip.accounts.label. The first account info looks something like this: { "result_set": { "voip.accounts[0]": { "label": "Dispatch1", "enabled": true, "user": "1234", "name": "Jane Doe", "type": "sip", "sip": { "lots and lots of stuff": }, } } } Am I over complicating the issue? Any wisdom anyone could thrown down would be greatly appreciated.

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  • Context path routing in Tomcat ( service swapping )

    - by jojovilco
    Here is what I would like to achieve: I have a web service A which I want to be able to deploy side by side with other web services of type A - different version(s). For now I assume 2 instances side by side. I need it because the service has a warm up stage, which takes some time to build up stuff from DB and only after it is ready it can start serving requests ... I was thinking to deploy to Tomcat context paths like: "/ServiceA-1.0", "/ServiceA-2.0" and then have a "virtual" context like "/ServiceA" which will point to the desired physical service e.g. "/ServiceA-1.0". So external world will know about ServiceA, but internally, my ServiceA related stack would know about versioned ServiceA url ( there are more components involved but only ServiceA is serving outer world ). When new service is ready, I would just reconfigure the "virtual" context to point to a new service. So far, I was not able to find out how to do this with Tomcat and starting to tkink it is not possible. I found suggestions to place Apache Server in front of Tomcat and do the routing there, but I do not want to enroll another piece of software unless necessary. My questions are: - is this kind of a "virtual" context and routing possible to do with Tomcat? - any other options, wisdom and lessons learned how to achieve this kind of service swapping scenario? Best, Jozef

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  • Joomla get plugin id

    - by Christian Sciberras
    I wrote a Joomla plugin which will eventually load a library. The path to library is a plugin parameter, as such when the path is incorrect, a message pops up in the backend, together with a link to edit the plugin parameters: /administrator/index.php?option=com_plugins&view=plugin&client=site&task=edit&cid[]=36 See the 36 at the end? That's my plugin's id in the database (table jos_plugins). My issue is that this id changes on installation, ie, on different installs, it would be something else. So I need to find this id programmatically. The problem is that I couldn't find this id from the plugin object itself (as to why not, that would be joomla's arguably short-sighted design decision). So unless you know about some neat trick, (I've checked and double checked JPlugin and JPluginHelper classes), I'll be using the DB. Edit; Some useful links: http://docs.joomla.org/Plugin_Developer_Overview http://api.joomla.org/Joomla-Framework/Plugin/JPlugin.html http://api.joomla.org/Joomla-Framework/Plugin/JPluginHelper.html http://forum.joomla.org/viewtopic.php?p=2227737 Guess I'll be using the wisdom from that last link...

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  • What would be a good Database strategy to manage these two product options?

    - by bemused
    I have a site that allows users to purchase "items" (imagine it as an Advertisement, or a download). There are 2 ways to purchase. Either a subscription, 70 items within 1 month (use them or lose them--at the end of the month your count is 0) or purchase each item individually as you need it. So the user could subscribe and get 70/month or pay for 10 and use them when they want until the 10 are gone. Maybe it's the late hour, but I can't isolate a solution I like and thought some users here would surely have stumbled upon something similar. One I can imagine is webhosts. They sell hosting for monthy fees and sell counts of things like you get 5 free domains with our reseller account. or something like a movie download site, you can subscribe and get 100 movies each month, or pay for a one-time package of 10 movies. so is this a web of tables and where would be a good cross between the product a user has purchased and how many they have left? products productID, productType=subscription, consumable, subscription&consumable subscriptions SubscriptionID, subscriptionStartDate, subscriptionEndDate, consumables consumableID, consumableName UserProducts userID,productID,productType ,consumptionLimit,consumedCount (if subscription check against dates), otherwise just check that consumedCount is < than limit. Usually I can layout my data in a way that I know it will work the way I expect, but this one feels a little questionable to me. Like there is a hidden detail that is going to creep up later. That's why I decided to ask for help if someone in the vast expanse can enlighten me with their wisdom and experience and clue me in to a satisfying strategy. Thank you.

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  • Router behind Router--second router (and its clients) cannot be "seen" even after both routers are D

    - by Trioke
    Couple of terminology I guess I should get out of the way for consistency's sake throughout the post: External Router/Modem - SMC 8014WG - External IP 173.32.144.134 - Internal IP 192.168.0.1 Internal Router - LinkSys WRT120N - "External" IP of 192.168.0.175 - Internal IP 192.168.1.1 - Connected via Ethernet Cable (a really long one, from the basement to the second floor) PC - IP 192.168.200 - Connected Wirelessly via WAP2 Personal. Laptop - Used to try and diagnose the problem, a 4th machine to the setup which won't be part of the final setup once everything works. The actual problem: I've tried setting the LinkySys router as a DMZ'd client on the SMC router, and then DMZ'd the actual PC on the LinkSys. So the DMZ looks like this: On the SMZ, client with IP 192.168.0.175 is DMZ'd. On the LinkSys, client with IP 192.168.1.200 is DMZ'd. No dice. I then tried port forwarding the necessary port on the SMC to the LinkSys (lets just say, port 80). Then port forwarded Port 80 on the LinkSys to the PC. Same as the DMZ scenario above, but change DMZ with port forwarding. No dice, still :(. Now here's where I went stupid--and tell me if one should never do this--I enabled both DMZ and port forwarding at the same time. I fired up Opera--my browser of choice ;)--typed in 173.32.144.134:6333 and... ... Third time is the charm they say? Well, clearly not. Otherwise I wouldn't be here ;). To diagnose the problem, I enabled "Allow remote access to the Admin panel" on the LinkSys router, and specified port 6333 as the port to use. I port forwarded port 6333 on the SMC to 192.168.0.175, and access my external IP of 173.32.144.134:6333 in hopes of seeing the Admin panel... No dice (I think I've ran out of dice by now ;)). So to see where the problem was, I connected a laptop to the SMC via LAN cable, and typed in 192.168.0.175:6333, and viola, Admin Panel access! So the problem looks like it lies with the SMC--But that's as far as I've got, I've done the port forwarding, the DMZ'ing, and I've even disabled the built-in firewall for safe measures, but nothing worked. So, here I am. Unable to connect to the PC behind the Internal router externally, and without anything to go on other than to come here and ask for the wisdom of the the superuser folks :). If any more detail is required, just ask. (Apologies in advance, if questions should never be this long winded!)

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  • SQLAuthority News – Meeting SQL Friends – SQLPASS 2011 Event Log

    - by pinaldave
    One of the biggest reason I go to SQLPASS is that my friends are going there too. There are so many friends with whom I often talk on Facebook and Twitter but I rarely get time to meet them as well talk with them. One thing I am usually sure that many fo them will be for sure attend SQLPASS. This is one event which every SQL Server Enthusiast should attend. Just like everybody I had pleasant time to meet many of my SQL friends. There were so many friends that I met and I did not click photo. There were so many friends who clicked photo in their camera and I do not have them. Here are 1% of the photos which I have. If you are not in the photo, it does not mean I have less respect to our friendship. Please post link to our photo together :) I was very fortunate that I was able to snap a quick photograph with Pinal Dave with Dr. David DeWitt. I stood outside of the hall waiting for Dr. to show up and when he was heading down from convention center I requested him if I can have one photo for my memory lane and very politely he agreed to have one. It indeed made my day! Pinal Dave with Dr. David DeWitt Every single time I met Steve, I make sure I have one photo for my memory. Steve is so kind every single time. If you know SQL and do not know Steve Jones, you do not know SQL (IMHO). Following is the photograph with Michael McLean. More details about this photo in future blog post! Pinal Dave, Michael McLean, and Rick Morelan Arnie always shares his wisdom with me. I still remember when I very first time visited USA, I was standing alone in corner and Arnie walked to me and introduced to every single person he know. Talking to Arnie is always pleasure and inspiring. Arnie Rowland and Pinal Dave I am now published author and have written two books so far. I am fortunate to have Rick Morelan as Co-author of both of my books. He is great guy and very easy to become friends with. I am very much impressed by him and his kindness during book co-authoring. Here is very first of our photograph together at SQLPASS. Rick Morelan and Pinal Dave Diego Nogare and I have been talking for long time on twitter and on various social media channels. I finally got chance to meet my friend from Brazil. It was excellent experience to meet a friend whom one wants to meet for long time and had never got chance earlier. Buck Woody – who does not know Buck. He is funny, kind and most important friends of every one. Buck is so kind that he does not hesitate to approach people even though he is famous and most known in community. Every time I meet him I learn something. He is always smiling and approachable. Pinal Dave and Buck Woddy Rushabh Mehta is current SQL PASS president and personal friend. He has always smiling face and tremendous love for SQL community. I often wonder where he gets all the time for all the time and efforts he puts in for community. I never miss a chance to meet and greet him. Even though he is renowned SQL Guru and extremely busy person – every single time I meet him he always asks me – “How is Nupur and Shaivi?” He even remembers my wife and daughters name. I am touched. Rushabh Mehta and Pinal Dave Nigel Sammy has extremely well sense of humor and passion from community. We have excellent synergy while we are together. The attached photo is taken while I was talking to him on Seattle Shoreline about SQL. Pinal Dave and Nigel Sammy Rick Morelan wanted my this trip to be memorable. I am vegetarian and I told him that I do not like Seafood. Well, to prove the point, he took me to fantastic Seafood restaurant in Seattle and treated me with mouth watering vegetarian dishes. I think when I go to Seattle next time, I am going to make him to take me again to the same place. Rick, Rushabh, Pinal and Paras Well, this is a short summary of few of the friends I met at Seattle. What is the life without friends, eh? Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL PASS, SQL Query, SQL Server, SQL Tips and Tricks, SQLAuthority Author Visit, SQLAuthority News, T SQL, Technology

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  • To My 24 Year Old Self, Wherever You Are&hellip;

    - by D'Arcy Lussier
    A decade is a milestone in one’s life, regardless of when it occurs. 2011 might seem like a weird year to mark a decade, but 2001 was a defining year for me. It marked my emergence into the technology industry, an unexpected loss of innocence, and triggered an ongoing struggle with faith and belief. Once you go through a valley, climbing the mountain and looking back over where you travelled, you can take in the entirety of the journey. Over the last 10 years I kept journals, and in this new year I took some time to review them. For those today that are me a decade ago, I share with you what I’ve gleamed from my experiences. Take it for what it’s worth, and safe travels on your own journeys through life. Life is a Performance-Based Sport Have confidence, believe you’re capable, but realize that life is a performance-based sport. Everything you get in life is based on whether you can show that you deserve it. Performance is also your best defense against personal attacks. Just make sure you know what standards you’re expected to hit and if people want to poke holes at you let them do the work of trying to find them. Sometimes performance won’t matter though. Good things will happen to bad people, and bad things to good people. What’s important is that you do the right things and ensure the good and bad even out in your own life. How you finish is just as important as how you start. Start strong, end strong. Respect is Your Most Prized Reward Respect is more important than status or ego. The formula is simple: Performing Well + Building Trust + Showing Dedication = Respect Focus on perfecting your craft and helping your team and respect will come. Life is a Team Sport Whatever aspect of your life, you can’t do it alone. You need to rely on the people around you and ensure you’re a positive aspect of their lives; even those that may be difficult or unpleasant. Avoid criticism and instead find ways to help colleagues and superiors better whatever environment you’re in (work, home, etc.). Don’t just highlight gaps and issues, but also come to the table with solutions. At the same time though, stand up for yourself and hold others accountable for the commitments they make to the team. A healthy team needs accountability. Give feedback early and often, and make it verbal. Issues should be dealt with immediately, and positives should be celebrated as they happen. Life is a Contact Sport Difficult moments will happen. Don’t run from them or shield yourself from experiencing them. Embrace them. They will further mold you and reveal who you will become. Find Your Tribe and Embrace Your Community We all need a tribe: a group of people that we gravitate to for support, guidance, wisdom, and friendship. Discover your tribe and immerse yourself in them. Don’t look for a non-existent tribe just to fill the need of belonging though that will leave you empty and bitter when they don’t meet your unrealistic expectations. Try to associate with people more experienced and more knowledgeable than you. You’ll always learn, and you’ll always remember you have much to learn. Put yourself out there, get involved with the community. Opportunities will present themselves. When we open ourselves up to be vulnerable, we also give others the chance to do the same. This helps us all to grow and help each other, it’s very important. And listen to your wife. (Easter *is* a romantic holiday btw, regardless of what you may think.) Don’t Believe Your Own Press Clippings (and by that I mean the ones you write) Until you have a track record of performance to refer to, any notions of grandeur are just that: notions. You lose your rookie status through trials and tribulations, not by the number of stamps in your passport. Be realistic about your own “experience and leadership” and be honest when you aren’t ready for something. And always remember: nobody really cares about you as much as you think they do. Don’t Let Assholes Get You Down The world isn’t evil, but there is evil in the world. Know the difference and don’t paint all people with the same brush. Do be wary of those that use personal beliefs to describe their business (i.e. “We’re a [religion] company”). What matters is the culture of the organization, and that will tell you the moral compass and what is truly valued. Don’t make someone or something a priority that only makes you an option. Life is unfair and enemies/opponents will succeed when you fail. Don’t waste your energy getting upset at this; the only one that will lose out is you. As mentioned earlier, nobody really cares about you as much as you think they do. Misc Ecclesiastes is bullshit. Everything is certainly *not* meaningless. Software development is about delivery, not the process. Having a great process means nothing if you don’t produce anything. Watch “The Weatherman” (“It’s not easy, but easy doesn’t enter into grownup life.”). Read Tony Dungee’s autobiography, even if you don’t like football, and even if you aren’t a Christian. Say no, don’t feel like you have to commit right away when someone asks you to.

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  • Breaking 1NF to model subset constraints. Does this sound sane?

    - by Chris Travers
    My first question here. Appologize if it is in the wrong forum but this seems pretty conceptual. I am looking at doing something that goes against conventional wisdom and want to get some feedback as to whether this is totally insane or will result in problems, so critique away! I am on PostgreSQL 9.1 but may be moving to 9.2 for this part of this project. To re-iterate: Does it seem sane to break 1NF in this way? I am not looking for debugging code so much as where people see problems that this might lead. The Problem In double entry accounting, financial transactions are journal entries with an arbitrary number of lines. Each line has either a left value (debit) or a right value (credit) which can be modelled as a single value with negatives as debits and positives as credits or vice versa. The sum of all debits and credits must equal zero (so if we go with a single amount field, sum(amount) must equal zero for each financial journal entry). SQL-based databases, pretty much required for this sort of work, have no way to express this sort of constraint natively and so any approach to enforcing it in the database seems rather complex. The Write Model The journal entries are append only. There is a possibility we will add a delete model but it will be subject to a different set of restrictions and so is not applicable here. If and when we allow deletes, we will probably do them using a simple ON DELETE CASCADE designation on the foreign key, and require that deletes go through a dedicated stored procedure which can enforce the other constraints. So inserts and selects have to be accommodated but updates and deletes do not for this task. My Proposed Solution My proposed solution is to break first normal form and model constraints on arrays of tuples, with a trigger that breaks the rows out into another table. CREATE TABLE journal_line ( entry_id bigserial primary key, account_id int not null references account(id), journal_entry_id bigint not null, -- adding references later amount numeric not null ); I would then add "table methods" to extract debits and credits for reporting purposes: CREATE OR REPLACE FUNCTION debits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount < 0 THEN $1.amount * -1 ELSE NULL END; $$; CREATE OR REPLACE FUNCTION credits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount > 0 THEN $1.amount ELSE NULL END; $$; Then the journal entry table (simplified for this example): CREATE TABLE journal_entry ( entry_id bigserial primary key, -- no natural keys :-( journal_id int not null references journal(id), date_posted date not null, reference text not null, description text not null, journal_lines journal_line[] not null ); Then a table method and and check constraints: CREATE OR REPLACE FUNCTION running_total(journal_entry) returns numeric language sql immutable as $$ SELECT sum(amount) FROM unnest($1.journal_lines); $$; ALTER TABLE journal_entry ADD CONSTRAINT CHECK (((journal_entry.running_total) = 0)); ALTER TABLE journal_line ADD FOREIGN KEY journal_entry_id REFERENCES journal_entry(entry_id); And finally we'd have a breakout trigger: CREATE OR REPLACE FUNCTION je_breakout() RETURNS TRIGGER LANGUAGE PLPGSQL AS $$ BEGIN IF TG_OP = 'INSERT' THEN INSERT INTO journal_line (journal_entry_id, account_id, amount) SELECT NEW.id, account_id, amount FROM unnest(NEW.journal_lines); RETURN NEW; ELSE RAISE EXCEPTION 'Operation Not Allowed'; END IF; END; $$; And finally CREATE TRIGGER AFTER INSERT OR UPDATE OR DELETE ON journal_entry FOR EACH ROW EXECUTE_PROCEDURE je_breaout(); Of course the example above is simplified. There will be a status table that will track approval status allowing for separation of duties, etc. However the goal here is to prevent unbalanced transactions. Any feedback? Does this sound entirely insane? Standard Solutions? In getting to this point I have to say I have looked at four different current ERP solutions to this problems: Represent every line item as a debit and a credit against different accounts. Use of foreign keys against the line item table to enforce an eventual running total of 0 Use of constraint triggers in PostgreSQL Forcing all validation here solely through the app logic. My concerns are that #1 is pretty limiting and very hard to audit internally. It's not programmer transparent and so it strikes me as being difficult to work with in the future. The second strikes me as being very complex and required a series of contraints and foreign keys against self to make work, and therefore it strikes me as complex, hard to sort out at least in my mind, and thus hard to work with. The fourth could be done as we force all access through stored procedures anyway and this is the most common solution (have the app total things up and throw an error otherwise). However, I think proof that a constraint is followed is superior to test cases, and so the question becomes whether this in fact generates insert anomilies rather than solving them. If this is a solved problem it isn't the case that everyone agrees on the solution....

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  • Social Engagement: One Size Doesn't Fit Anyone

    - by Mike Stiles
    The key to achieving meaningful social engagement is to know who you’re talking to, know what they like, and consistently deliver that kind of material to them. Every magazine for women knows this. When you read the article titles promoted on their covers, there’s no mistaking for whom that magazine is intended. And yet, confusion still reigns at many brands as to exactly whom they want to talk to, what those people want to hear, and what kind of content they should be creating for them. In most instances, the root problem is brands want to be all things to all people. Their target audience…the world! Good luck with that. It’s 2012, the age of aggregation and custom content delivery. To cope with the modern day barrage of information, people have constructed technological filters so that content they regard as being “for them” is mostly what gets through. Even if your brand is for men and women, young and old, you may want to consider social properties that divide men from women, and young from old. Yes, a man might find something in a women’s magazine that interests him. But that doesn’t mean he’s going to subscribe to it, or buy even one issue. In fact he’ll probably never see the article he’d otherwise be interested in, because in his mind, “This isn’t for me.” It wasn’t packaged for him. News Flash: men and women are different. So it’s a tall order to craft your Facebook Page or Twitter handle to simultaneously exude the motivators for both. The Harris Interactive study “2012 Connecting and Communicating Online: State of Social Media” sheds light on the differing social behaviors and drivers. -65% of women (vs. 59% of men) stay glued to social because they don’t want to miss anything. -25% of women check social when they wake up, before they check email. Only 18% of men check social before e-mail. -95% of women surveyed belong to Facebook vs. 86% of men. -67% of women log in to Facebook once a day or more vs. 54% of men. -Conventional wisdom is Pinterest is mostly a woman-thing, right? That may be true for viewing, but not true for sharing. Men are actually more likely to share on Pinterest than women, 23% to 10%. -The sharing divide extends to YouTube. 68% of women use it mainly for consumption, as opposed to 52% of men. -Women are as likely to have a Twitter account as men, but they’re much less likely to check it often. 54% of women check it once a week compared to 2/3 of men. Obviously, there are some takeaways from this depending on your target. Women don’t want to miss out on anything, so serialized content might be a good idea, right? Promotional posts that lead to a big payoff could keep them hooked. Posts for women might be better served first thing in the morning. If sharing is your goal, maybe male-targeted content is more likely to get those desired shares. And maybe Twitter is a better place to aim your male-targeted content than Facebook. Some grocery stores started experimenting with male-only aisles. The results have been impressive. Why? Because while it’s true men were finding those same items in the store just fine before, now something has been created just for them. They have a place in the store where they belong. Each brand’s strategy and targets are going to differ. The point is…know who you’re talking to, know how they behave, know what they like, and deliver content using any number of social relationship management targeting tools that meets their expectations. If, however, you’re committed to a one-size-fits-all, “our content is for everybody” strategy (or even worse, a “this is what we want to put out and we expect everybody to love it” strategy), your content will miss the mark for more often than it hits. @mikestilesPhoto via stock.schng

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  • How to optimize Core Data query for full text search

    - by dk
    Can I optimize a Core Data query when searching for matching words in a text? (This question also pertains to the wisdom of custom SQL versus Core Data on an iPhone.) I'm working on a new (iPhone) app that is a handheld reference tool for a scientific database. The main interface is a standard searchable table view and I want as-you-type response as the user types new words. Words matches must be prefixes of words in the text. The text is composed of 100,000s of words. In my prototype I coded SQL directly. I created a separate "words" table containing every word in the text fields of the main entity. I indexed words and performed searches along the lines of SELECT id, * FROM textTable JOIN (SELECT DISTINCT textTableId FROM words WHERE word BETWEEN 'foo' AND 'fooz' ) ON id=textTableId LIMIT 50 This runs very fast. Using an IN would probably work just as well, i.e. SELECT * FROM textTable WHERE id IN (SELECT textTableId FROM words WHERE word BETWEEN 'foo' AND 'fooz' ) LIMIT 50 The LIMIT is crucial and allows me to display results quickly. I notify the user that there are too many to display if the limit is reached. This is kludgy. I've spent the last several days pondering the advantages of moving to Core Data, but I worry about the lack of control in the schema, indexing, and querying for an important query. Theoretically an NSPredicate of textField MATCHES '.*\bfoo.*' would just work, but I'm sure it will be slow. This sort of text search seems so common that I wonder what is the usual attack? Would you create a words entity as I did above and use a predicate of "word BEGINSWITH 'foo'"? Will that work as fast as my prototype? Will Core Data automatically create the right indexes? I can't find any explicit means of advising the persistent store about indexes. I see some nice advantages of Core Data in my iPhone app. The faulting and other memory considerations allow for efficient database retrievals for tableview queries without setting arbitrary limits. The object graph management allows me to easily traverse entities without writing lots of SQL. Migration features will be nice in the future. On the other hand, in a limited resource environment (iPhone) I worry that an automatically generated database will be bloated with metadata, unnecessary inverse relationships, inefficient attribute datatypes, etc. Should I dive in or proceed with caution?

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  • Armchair Linguists: 'code' vs. 'codes'--or why I write 'code' and my manager asks for 'codes'

    - by Ukko
    I wanted to tap into the collective wisdom here to see if I can get some insight into one of my pet peeves, people who thread "code" as a countable noun. Let me also preface this by saying that I am not talking about anyone who speaks english as a second language, this is a native phenomenon. For those of us who slept through grammar class there are two classes of nouns which basically refer to things that are countable and non-countable (sometimes referred to as count and noncount). For instance 'sand' is a non-count noun and 'apple' is count. You can talk about "two apples" but "two sands" does not parse. The bright students then would point out a word like "beer" where is looks like this is violated. Beer as a substance is certainly a non-count noun, but I can ask for "two beers" without offending the grammar police. The reason is that there are actually two words tied up in that one utterance, Definition #1 is a yummy golden substance and Definition #2 is a colloquial term for a container of said substance. #1 is non-count and #2 is countable. This gets to my problem with "codes" as a countable noun. In my mind the code that we programmers write is non-count, "I wrote some code today." When used in the plural like "Have you got the codes" I can only assume that you are asking if I have the cryptographically significant numbers for launching a missile or the like. Every time my peer in marketing asks about when we will have the new codes ready I have a vision of rooms of code breakers going over the latest Enigma coded message. I corrected the usage in all the documents I am asked to review, but then I noticed that our customer was also using the work "codes" when they meant "code". At this point I have realized that there is a significant sub-population that uses "codes" and they seem to be impervious to what I see as the dominant "correct" usage. This is the part I want some help on, has anyone else noticed this phenomenon? Do you know what group it is associated with, old Fortran programmer perhaps? Is it a regionalism? I have become quick to change my terms when I notice a customer's usage, but it would be nice to know if I am sending a proposal somewhere what style they expect. I would hate to get canned with a review of "Ha, these guy's must be morons they don't even know 'code' is plural!"

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  • Workflow for statistical analysis and report writing

    - by ws
    Does anyone have any wisdom on workflows for data analysis related to custom report writing? The use-case is basically this: Client commissions a report that uses data analysis, e.g. a population estimate and related maps for a water district. The analyst downloads some data, munges the data and saves the result (e.g. adding a column for population per unit, or subsetting the data based on district boundaries). The analyst analyzes the data created in (2), gets close to her goal, but sees that needs more data and so goes back to (1). Rinse repeat until the tables and graphics meet QA/QC and satisfy the client. Write report incorporating tables and graphics. Next year, the happy client comes back and wants an update. This should be as simple as updating the upstream data by a new download (e.g. get the building permits from the last year), and pressing a "RECALCULATE" button, unless specifications change. At the moment, I just start a directory and ad-hoc it the best I can. I would like a more systematic approach, so I am hoping someone has figured this out... I use a mix of spreadsheets, SQL, ARCGIS, R, and Unix tools. Thanks! PS: Below is a basic Makefile that checks for dependencies on various intermediate datasets (w/ ".RData" suffix) and scripts (".R" suffix). Make uses timestamps to check dependencies, so if you 'touch ss07por.csv', it will see that this file is newer than all the files / targets that depend on it, and execute the given scripts in order to update them accordingly. This is still a work in progress, including a step for putting into SQL database, and a step for a templating language like sweave. Note that Make relies on tabs in its syntax, so read the manual before cutting and pasting. Enjoy and give feedback! http://www.gnu.org/software/make/manual/html%5Fnode/index.html#Top R=/home/wsprague/R-2.9.2/bin/R persondata.RData : ImportData.R ../../DATA/ss07por.csv Functions.R $R --slave -f ImportData.R persondata.Munged.RData : MungeData.R persondata.RData Functions.R $R --slave -f MungeData.R report.txt: TabulateAndGraph.R persondata.Munged.RData Functions.R $R --slave -f TabulateAndGraph.R report.txt

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  • Sanity check on this idea for an Image Viewer in a web app

    - by Charlie Flowers
    I have an approach in mind for an image viewer in a web app, and want to get a sanity check and any thoughts you stackoverflowers might have. Here's the whirlwind nutshell summary: I'm working on an ASP.NET MVC application that will run in my company's retail stores. Even though it is a web application, we own the store machines and have control over them. We have a "windows agent" running on the store machine which we can talk to via http post (it is a WCF service, and our web app has permission to talk to it from the browser). One of the web pages needs to be an "image viewer" page with some common things like Rotate & Zoom. Now, there are some WebForms controls that offer Rotate and Zoom. However, they take up server resources and generate a good bit of traffic between the server and the browser. For example, the Rotate function would cause an ajax call to the server, which would then generate a new image written to a .NET Canvas object, which would then be written to a file on the server, which would then be returned from the ajax call and refreshed inside the browser. Normally, that's a pretty good way of doing things. But in our case, we have code running on the store machine that we can communicate with. This leads me to consider the following approach: When the user asks to view an image, we tell our "windows agent" to download it from our image server to the store machine. We then redirect our browser to our image viewer page, which will pull the image from the local file we just wrote to the store machine. When the user clicks "Rotate", we cause JavaScript code in the browser to call our "windows agent" software, asking it to perform the "Rotate" function. The "windows agent" does the rotation using the same kind of imaging control that would formerly have been used on the server, but it does so now on the store machine. Javascript in the browser then refreshes the image on the page to show the newly rotated image. Zoom and similar features would be implemented the same way. This seems to be much more efficient, scalable, and responsive for the end-users. However, I've never heard of anything like it being done, mostly because it's rare to have this combination of a web app plus a "windows agent" on the client machine. What do you think? Feasible? Reasonable? Any pitfalls I overlooked or improvements / suggestions you can see? Has anyone done anything like this who would like to offer the wisdom of experience? Thanks!

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  • Many-To-Many Query with Linq-To-NHibernate

    - by rjygraham
    Ok guys (and gals), this one has been driving me nuts all night and I'm turning to your collective wisdom for help. I'm using Fluent Nhibernate and Linq-To-NHibernate as my data access story and I have the following simplified DB structure: CREATE TABLE [dbo].[Classes]( [Id] [bigint] IDENTITY(1,1) NOT NULL, [Name] [nvarchar](100) NOT NULL, [StartDate] [datetime2](7) NOT NULL, [EndDate] [datetime2](7) NOT NULL, CONSTRAINT [PK_Classes] PRIMARY KEY CLUSTERED ( [Id] ASC ) CREATE TABLE [dbo].[Sections]( [Id] [bigint] IDENTITY(1,1) NOT NULL, [ClassId] [bigint] NOT NULL, [InternalCode] [varchar](10) NOT NULL, CONSTRAINT [PK_Sections] PRIMARY KEY CLUSTERED ( [Id] ASC ) CREATE TABLE [dbo].[SectionStudents]( [SectionId] [bigint] NOT NULL, [UserId] [uniqueidentifier] NOT NULL, CONSTRAINT [PK_SectionStudents] PRIMARY KEY CLUSTERED ( [SectionId] ASC, [UserId] ASC ) CREATE TABLE [dbo].[aspnet_Users]( [ApplicationId] [uniqueidentifier] NOT NULL, [UserId] [uniqueidentifier] NOT NULL, [UserName] [nvarchar](256) NOT NULL, [LoweredUserName] [nvarchar](256) NOT NULL, [MobileAlias] [nvarchar](16) NULL, [IsAnonymous] [bit] NOT NULL, [LastActivityDate] [datetime] NOT NULL, PRIMARY KEY NONCLUSTERED ( [UserId] ASC ) I omitted the foreign keys for brevity, but essentially this boils down to: A Class can have many Sections. A Section can belong to only 1 Class but can have many Students. A Student (aspnet_Users) can belong to many Sections. I've setup the corresponding Model classes and Fluent NHibernate Mapping classes, all that is working fine. Here's where I'm getting stuck. I need to write a query which will return the sections a student is enrolled in based on the student's UserId and the dates of the class. Here's what I've tried so far: 1. var sections = (from s in this.Session.Linq<Sections>() where s.Class.StartDate <= DateTime.UtcNow && s.Class.EndDate > DateTime.UtcNow && s.Students.First(f => f.UserId == userId) != null select s); 2. var sections = (from s in this.Session.Linq<Sections>() where s.Class.StartDate <= DateTime.UtcNow && s.Class.EndDate > DateTime.UtcNow && s.Students.Where(w => w.UserId == userId).FirstOrDefault().Id == userId select s); Obviously, 2 above will fail miserably if there are no students matching userId for classes the current date between it's start and end dates...but I just wanted to try. The filters for the Class StartDate and EndDate work fine, but the many-to-many relation with Students is proving to be difficult. Everytime I try running the query I get an ArgumentNullException with the message: Value cannot be null. Parameter name: session I've considered going down the path of making the SectionStudents relation a Model class with a reference to Section and a reference to Student instead of a many-to-many. I'd like to avoid that if I can, and I'm not even sure it would work that way. Thanks in advance to anyone who can help. Ryan

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  • Which programming language to choose? (for a specific problem/domain, details inside)

    - by Bijan
    I am building a trading portfolio management system that is responsible for production, optimization, and simulation of non-high frequency trading portfolios (dealing with 1min or 3min bars of data, not tick data). I plan on employing Amazon web services to take on the entire load of the application. I have four choices that I am considering as language. a) Java b) C++ c) C# d) Python Here is the scope of the extremes of the project scope. This isn't how it will be, maybe ever, but it's within the scope of the requirements: Weekly simulation of 10,000,000 trading systems. (Each trading system is expected to have its own data mining methods, including feature selection algorithms which are extremely computationally-expensive. Imagine 500-5000 features using wrappers. These are not run often by any means, but it's still a consideration) Real-time production of portfolio w/ 100,000 trading strategies Taking in 1 min or 3 min data from every stock/futures market around the globe (approx 100,000) Portfolio optimization of portfolios with up to 100,000 strategies. (rather intensive algorithm) Speed is a concern, but I believe that Java can handle the load. I just want to make sure that Java CAN handle the above requirements comfortably. I don't want to do the project in C++, but I will if it's required. The reason C# is on there is because I thought it was a good alternative to Java, even though I don't like Windows at all and would prefer Java if all things are the same. Python - I've read somethings on PyPy and pyscho that claim python can be optimized with JIT compiling to run at near C-like speeds.... That's pretty much the only reason it is on this list, besides that fact that Python is a great language and would probably be the most enjoyable language to code in, which is not a factor at all for this project, but a perk. To sum up: - real time production - weekly simulations of a large number of systems - weekly/monthly optimizations of portfolios - large numbers of connections to collect data from There is no dealing with millisecond or even second based trades. The only consideration is if Java can possibly deal with this kind of load when spread out of a necessary amount of EC2 servers. Thank you guys so much for your wisdom.

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  • Question about Architecture for Viewing Images in ASP.NET MVC App

    - by Charlie Flowers
    I have an approach in mind for an image viewer in a web app, and want to get a sanity check and any thoughts you stackoverflowers might have. Here's the whirlwind nutshell summary: I'm working on an ASP.NET MVC application that will run in my company's retail stores. Even though it is a web application, we own the store machines and have control over them. We have a "windows agent" running on the store machine which we can talk to from the browser via javascript (it is a WCF service, and our web app has permission to talk to it from the browser). One of the web pages needs to be an "image viewer" page with some common things like Rotate & Zoom. Now, there are some WebForms controls that offer Rotate and Zoom. However, they take up server resources and generate a good bit of traffic between the server and the browser. For example, the Rotate function would cause an ajax call to the server, which would then generate a new image written to a .NET Canvas object, which would then be written to a file on the server, which would then be returned from the ajax call and refreshed inside the browser. Normally, that's a pretty good way of doing things. But in our case, we have code running on the store machine that we can communicate with. This leads me to consider the following approach: When the user asks to view an image, we tell our "windows agent" to download it from our image server to the store machine. We then redirect our browser to our image viewer page, which will pull the image from the local file we just wrote to the store machine. When the user clicks "Rotate", we cause JavaScript code in the browser to call our "windows agent" software, asking it to perform the "Rotate" function. The "windows agent" does the rotation using the same kind of imaging control that would formerly have been used on the server, but it does so now on the store machine. Javascript in the browser then refreshes the image on the page to show the newly rotated image. Zoom and similar features would be implemented the same way. This seems to be much more efficient, scalable, and responsive for the end-users. However, I've never heard of anything like it being done, mostly because it's rare to have this combination of a web app plus a "windows agent" on the client machine. What do you think? Feasible? Reasonable? Any pitfalls I overlooked or improvements / suggestions you can see? Has anyone done anything like this who would like to offer the wisdom of experience? Thanks!

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