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• MySQL count problem

  - by Skuja

  I have 3 tables users(id,name),groups(id,name) and users_groups(user_id,group_id). users and groups have many to many relationship, so the third one is for storing users and groups relations. I would like to select all the data from groups with user count in each group. So far I came up with this: SELECT groups.*, COUNT(users_groups.user_id) AS user_count FROM groups LEFT JOIN users_groups ON users_groups.group_id = groups.id The problem is that query result is not returning any of groups which has no users (users_groups doesnt have any records with group_id of those groups). How should I create my query to select all the groups and they user count, or user count as 0 if there are no users for that group?

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• In mysql, is "explain ..." always safe?

  - by tye

  If I allow a group of users to submit "explain $whatever" to mysql (via Perl's DBI using DBD::mysql), is there anything that a user could put into $whatever that would make any database changes, leak non-trivial information, or even cause significant database load? If so, how? I know that via "explain $whatever" one can figure out what tables / columns exist (you have to guess names, though) and roughly how many records are in a table or how many records have a particular value for an indexed field. I don't expect one to be able to get any information about the contents of unindexed fields. DBD::mysql should not allow multiple statements so I don't expect it to be possible to run any query (just explain one query). Even subqueries should not be executed, just explained. But I'm not a mysql expert and there are surely features of mysql that I'm not even aware of. In trying to come up with a query plan, might the optimizer actual execute an expression in order to come up with the value that an indexed field is going to be compared against? explain select * from atable where class = somefunction(...) where atable.class is indexed and not unique and class='unused' would find no records but class='common' would find a million records. Might 'explain' evaluate somefunction(...)? And then could somefunction(...) be written such that it modifies data?

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• How does Core Data determine if an NSObjects data can be dropped?

  - by Kevin

  In the app I am working on now I was storing about 500 images in Core Data. I have since pulled those images out and store them in the file system now, but in the process I found that the app would crash on the device if I had an array of 500 objects with image data in them. An array with 500 object ids with the image data in those objects worked fine. The 500 objects without the image data also worked fine. I found that I got the best performance with both an array of object ids and image data stored on the filesystem instead of in core data. The conclusion I came to was that if I had an object in an array that told Core Data I was "using" that object and Core Data would hold on to the data. Is this correct?

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• How to handle dynamic site localizations?

  - by James Simpson

  I've got a website that is currently all in english. It is an online game, so it has a bunch of different pages with static text, as well as a lot of content in a database. I am trying to expand more globally and am gearing up to release some localizations of the site. However, I'm not sure about the best way to go about setting this up so that it'll be the easiest for me to manage and the easiest for users to use as well. Should I be storing the translated texts in a database, or should this be done in a completely different way? If it matters at all, the site is written in PHP and uses MySQL.

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• Facebook user_id as MongoDB BSON ObjectId?

  - by MattDiPasquale

  I'm rebuilding Lovers on Facebook with Sinatra & Redis. I like Redis because it doesn't have the long (12-byte) BSON ObjectIds and I am storing sets of Facebook user_ids for each user. The sets are requests_sent, requests_received, & relationships, and they all contain Facebook user ids. I'm thinking of switching to MongoDB because I want to use it's geospatial indexing. If I do, I'd want to use the FB user ids as the _id field because I want the sets to be small and I want the JSON responses to be small. But, is the BSON ObjectId better (more efficient for MongoDB) to use than just an integer (fb user_id)?

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• What's the proper way of importing option lists into an Android app?

  - by Scott

  I have been storing option lists for my Android app in a cloud table. For example, categories like "historical fiction","biography","science fiction", etc. I see the following pros and cons: Pro: I can make changes to the list without sending an app update to Google Play Not normalized - I can use the text in my other data tables instead of a reference ID Con: App needs to take time to download from the web each time (or at least check for changes) English only I believe the "proper" way to do this is the use the XML resource files. But I need to make sure the selection references correctly with my data. That is, my app needs to understand that "Poetry" and "Poesía" are the same thing. Is the correct thing to do: Forget about it since I'll never get to the point where I'm translating my app anyway Use a string-array and use the index (0...x) to know what the selection is Use a 2-dimensional string-array with a reference ID in the first column and the text in the second?

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• How is timezone handled in the lifecycle of an ADO.NET + SQL Server DateTime column?

  - by stimpy77

  Using SQL Server 2008. This is a really junior question and I could really use some elaborate information, but the information on Google seems to dance around the topic quite a bit and it would be nice if there was some detailed elaboration on how this works... Let's say I have a datetime column and in ADO.NET I set it to DateTime.UtcNow. 1) Does SQL Server store DateTime.UtcNow accordingly, or does it offset it again based on the timezone of where the server is installed, and then return it offset-reversed when queried? I think I know that the answer is "of course it stores it without offsetting it again" but want to be certain. So then I query for it and cast it from, say, an IDataReader column to a DateTime. As far as I know, System.DateTime has metadata that internally tracks whether it is a UTC DateTime or it is an offsetted DateTime, which may or may not cause .ToLocalTime() and .ToUniversalTime() to have different behavior depending on this state. So, 2) Does this casted System.DateTime object already know that it is a UTC DateTime instance, or does it assume that it has been offset? Now let's say I don't use UtcNow, I use DateTime.Now, when performing an ADO.NET INSERT or UPDATE. 3) Does ADO.NET pass the offset to SQL Server and does SQL Server store DateTime.Now with the offset metadata? So then I query for it and cast it from, say, an IDataReader column to a DateTime. 4) Does this casted System.DateTime object already know that it is an offset time, or does it assume that it is UTC?

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• app.config - where should it go?

  - by Piers

  This is a follow on from here: Storing database settings outside app.config So I know it's possible to have one app.config, with different sections externalised, all with different values. But are they like the web.config files in asp.net projects where you can just copy it into the same folder as the rest of the files and it will work, or do I need to compile it in somewhere. Also, won't it be overwritten by the .exe.config file? Edit Ok, so I worded this question a bit badly. I've updated it.

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• How to efficiently implement a strategy pattern with spring ?

  - by Anth0

  I have a web application developped in J2EE 1.5 with Spring framework. Application contains "dashboards" which are simple pages where a bunch of information are regrouped and where user can modify some status. Managers want me to add a logging system in database for three of theses dashboards. Each dashboard has different information but the log should be traced by date and user's login. What I'd like to do is to implement the Strategy pattern kind of like this : interface DashboardLog { void createLog(String login, Date now); } // Implementation for one dashboard class PrintDashboardLog implements DashboardLog { Integer docId; String status; void createLog(String login, Date now){ // Some code } } class DashboardsManager { DashboardLog logger; String login; Date now; void createLog(){ logger.log(login,now); } } class UpdateDocAction{ DashboardsManager dbManager; void updateSomeField(){ // Some action // Now it's time to log dbManagers.setLogger = new PrintDashboardLog(docId, status); dbManagers.createLog(); } } Is it "correct" (good practice, performance, ...) to do it this way ? Is there a better way ? Note :I did not write basic stuff like constructors and getter/setter.

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• What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

  - by fabrizioM

  I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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• Performing centralized authorization for multiple applications

  - by Vaibhav

  Here's a question that I have been wrestling with for a while. We have a situation wherein we have a number of applications that we have created. These have grown organically over a period of time. All of these applications have permissions code built into them that controls access to various parts of the application depending on whether the currently logged in user has the necessary permissions or not. Alongside these applications is a utility application which allows an administrator to map users to permissions for all applications - the way it works is that every application has code which reads this external database of the said utility application to check if the currently logged in user has the necessary permission or not. Now, the question is this. Should the user-permissions mapping information reside in and be owned by the applications themselves, or is it okay to have this information reside within an external entity/DB (as in this case the utility application's database). Part of me thinks that application permissions are very specific to the application context itself, so shouldn't be separated from the application itself. But I am not sure. Any comments?

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• Pre Project Documentation

  - by DeanMc

  I have an issue that I feel many programmers can relate to... I have worked on many small scale projects. After my initial paper brain storm I tend to start coding. What I come up with is usually a rough working model of the actual application. I design in a disconnected fashion so I am talking about underlying code libraries, user interfaces are the last thing as the library usually dictates what is needed in the UI. As my projects get bigger I worry that so should my "spec" or design document. The above paragraph, from my investigations, is echoed all across the internet in one fashion or another. When a UI is concerned there is a bit more information but it is UI specific and does not relate to code libraries. What I am beginning to realise is that maybe code is code is code. It seems from my extensive research that there is no 1:1 mapping between a design document and the code. When I need to research a topic I dump information into OneNote and from there I prioritise features into versions and then into related chunks so that development runs in a fairly linear fashion, my tasks tend to look like so: Implement Binary File Reader Implement Binary File Writer Create Object to encapsulate Data for expression to the caller Now any programmer worth his salt is aware that between those three to do items could be a potential wall of code that could expand out to multiple files. I have tried to map the complete code process for each task but I simply don't think it can be done effectively. By the time one mangles pseudo code it is essentially code anyway so the time investment is negated. So my question is this: Am I right in assuming that the best documentation is the code itself. We are all in agreement that a high level overview is needed. How high should this be? Do you design to statement, class or concept level? What works for you?

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• parsing a xml to get some values

  - by Joan Silverstone

  Hello, i have this xml: http://www.managerleague.com/export_data.pl?data=transfers&output=xml&hide_header=0 These are player sales from a browser game. I want to save some fields from these sales. I am fetching that xml with curl and storing on my server. Then do the following: $xml_str = file_get_contents('salespage.xml'); $xml = new SimpleXMLElement($xml_str); $items = $xml->xpath('*/transfer'); print_r($items); foreach($items as $item) { echo $item['buyerTeamname'], ': ', $item['sellerTeamname'], "\n"; } The array is empty and i cant seem to get anything from it. What am i doing wrong?

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• Best datastructure for this relationship...

  - by Travis

  I have a question about database 'style'. I need a method of storing user accounts. Some users "own" other user accounts (sub-accounts). However not all user accounts are owned, just some. Is it best to represent this using a table structure like so... TABLE accounts ( ID ownerID -> ID name ) ...even though there will be some NULL values in the ownerID column for accounts that do not have an owner. Or would it be stylistically preferable to have two tables, like so. TABLE accounts ( ID name ) TABLE ownedAccounts ( accountID -> accounts(ID) ownerID -> accounts(ID) ) Thanks for the advice.

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• How can I debug a session

  - by Organ Grinding Monkey

  I have been asked to work of a very large web application and deploy it. The problem that I'm facing here is that when I deploy the application and more that 1 user logs into the system, the sessions seem to cross over i.e: Person A logs in and works on the site, all good. When person B logs in, person A will then be logged in as person B as well. I have been asked to work of a very large web application and deploy it. The problem that I'm facing here is that when I deploy the application and more that 1 user logs into the system, the sessions seem to cross over i.e: Person A logs in and works on the site, all good. When person B logs in, person A will then be logged in as person B as well. If anyone has experienced this behaviour before and can steer me in the right direction, that would be first prize, Second prize would be to show me how I can debug this situation so that I can find out where the problem is and fix it. Some information about the application. From what I've been told and what I've seen within the app is that it started as a .Net 1.1 application and got upgraded to .Net 2 and that's why the log in system was done the way it is. (The application is huge and now complete and that's why I cant rewrite the whole user authentication process, it will just take to long and I don't know what effect it might have) All the Logged in User information is stored in properties that have been added in the Global.asax.vb file. (could this be the problem?) Any help here would be greatly appreciated

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• Guidance required: FIrst time gonna work with real high end database (size = 50GB).

  - by claws

  I got a project of designing a Database. This is going to be my first big scale project. Good thing about it is information is mostly organized & currently stored in text files. The size of this information is 50GB. There are going to be few millions of records in each Table. Its going to have around 50 tables. I need to provide a web interface for searching & browsing. I'm going to use MySQL DBMS. I've never worked with a database more than 200MB before. So, speed & performance was never a concern but I followed things like normalization & Indexes. I never used any kind of testing/benchmarking/queryOptimization/whatever because I never had to care about them. But here the purpose of creating a database is to make it quickly searchable. So, I need to consider all possible aspects in design. I was browsing archives & found: http://stackoverflow.com/questions/1981526/what-should-every-developer-know-about-databases http://stackoverflow.com/questions/621884/database-development-mistakes-made-by-app-developers I'm gonna keep the points mentioned in above answers in mind. What else should I know? What else should I keep in mind?

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• Are there any less costlier alternatives to Amazon's Relational Database Services (RDS)?

  - by swapnonil

  Hi All, I have the following requirement. I have with me a database containing the contact and address details of at least 2000 members of my school alumni organization. We want to store all that information in a relation model so that This data can be created and edited on demand. This data is always backed up and should be simple to restore in case the master copy becomes unusable. All sensitive personal information residing in this database is guaranteed to be available only to authorized users. This database won't be online in the first 6 months. It will become online only after a website is built on top of it. I am not a DBA and I don't want to spend time doing things like backups. I thought Amazon's RDS with it's automatic backup facility was the perfect solution for our needs. The only problem is that being a voluntary organization we cannot spare the monthly $100 to $150 fees this service demands. So my question is, are there any less costlier alternatives to Amazon's RDS?

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• PHP 2-way encryption: I need to store passwords that can be retrieved

  - by gAMBOOKa

  I am creating an application that will store passwords, which the user can retrieve and see. The passwords are for a hardware device, so checking against hashes are out of the question. What I need to know is: How do I encrypt and decrypt a password in PHP? What is the safest algorithm to encrypt the passwords with? Where do I store the private key? Instead of storing the private key, is it a good idea to require users to enter the private key any time they need a password decrypted? (Users of this application can be trusted) In what ways can the password be stolen and decrypted? What do I need to be aware of?

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• Read a file with 2048 bytes

  - by Suresh S

  Guys i have a file which has only one line. The file has no encoding it is a simple text file with single line. For every 2048 byte in a line , there is new record of 151 byte (totally 13*151 byte = 1945 records + 85 byte empty space). similarly for the next 2048 bytes. What is the best file i/o to use? i am thinking of reading 2048 bytes from file and storing it in an array . while (offset < fileLength &&(numRead=in.read(recordChunks, offset,alength)) >= 0) { } how can i get from the read statement only 2048 bytes at a time . i am getting IndexOutofBoundException.

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• PHP: Star rating system concept?

  - by Prashant

  I am using PHP/MYSQL/JQUERY. I have a site which have news section. On news details page, I want to add star rating system which will allow user to rate the news story. I am using this jquery rating system http://www.fyneworks.com/jquery/star-rating/ Now, I am not getting what will be the database structure and then what I need to code in PHP. I need what logic will be applied for this, like if 1000 people voted for the article, some given rating as 2 or 3 or1 or 5. Then Where I should be storing (db structure) this all and what I'll calculate (in php code). If someone has any article which shows this concept please provide. Please help, to understand the logic and concept of this. Thanks!

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• how to pass session variable to model in RoR?

  - by siulamvictor

  I used a global variable in my app for passing information before. But I got a problem and thanks everyone here suggested me to store those data in session with database. I tried, but I found that I can't access the session variable in Model. I googled and knew this is the Model normal behavior, RoR won't pass the session variable to Model. So how to pass the value of the session variable into Models? or is there any other method for my use case? I need a variable storing a value, which is required in all MVCs, and should be independent between different concurrent users. Thanks everyone. :)

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• Reset application and settings on user change

  - by Don

  Currently working on a project where a login will be required to use the application. I'm trying to figure out a smarter way to reset the application if someone is somehow logged out and the next one to login is not the same user. The option I have come up with at the moment is storing all user specific data/information in a DTO but this leaves me with cleaning up some parts of the work area. Is a ResetControls my only option here? I'm afraid that when updating the application someone might forget to update that part, most likely myself now that wrote it out. Anybody with experience in this that could provide some ideas to a simple yet fairly automagic solution?

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• Log session and session changes of a asp.net web user

  - by Johan Wikström

  This is going to be a quite broad question, and any suggestions, examples, links are very welcome! I'm looking for a good way to log my users session, and actions on the site up to a certain point. The site in question is a site for doing bookings. The users start with doing a search, doing a few steps of data gathering and selections and end up with a booking. So what I need to implement is some kind of logging of the current session variables at each step the user takes. And perhaps some other valid information. Logging should preferably be done to the a database. At the end i would like to associate all these session with a booking reference. The goal is to later if something goes wrong with the booking or we need to investigate a situation have all information we need. I understand log4net is a popular choice for logging, and used it a bit myself for simple purposes, but can not find any good examples regarding my situation. This should be a common situation, i'm curious how others do it.

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• Is it possible to reference a file stored in Isolated Storage by its URI?

  - by Joel

  Using this previous question as motivation, I would like to temporarily store images and videos in Isolated Storage. My application (written in WPF/C#) will allow a user to review these temporarily stored items by viewing their contents in a MediaElement. I was hoping to set the MediaElement's Source Property to a video or image's URI stored in IsolatedStorage but I cannot figure out how to dynamically create a URI since it doesn't appear to be naively supported by IsolatedStorage. Any help would be greatly appreciated - thank you in advance! Update - 1/21/09 After battling the issue for a day, I concluded that the Isolated Storage approach is not practical for storing large video files that need to be referenced by a Uri.

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• linq Multiple Where based on conditions.

  - by Bathan

  I want to query a table with some conditions based on user input. I wrote this : IQueryable turnoQuery = dc.Turno; if (helper.FechaUltimaCitaDesde != DateTime.MinValue) { turnoQuery = turnoQuery.Where(t => t.TurnoFecha >= helper.FechaUltimaCitaDesde); } if (helper.FechaUltimaCitaHasta != DateTime.MinValue) { turnoQuery = turnoQuery.Where(t => t.TurnoFecha <= helper.FechaUltimaCitaHasta); } if (helper.SoloCitasConsumidas) { turnoQuery = turnoQuery.Where(t => t.Estado == Convert.ToInt32(EnmEstadoDelTurno.Consumido)); } else if(helper.AnuladoresDeCitas) { turnoQuery = turnoQuery.Where(t => t.Estado == Convert.ToInt32(EnmEstadoDelTurno.Cancelado) || t.Estado == Convert.ToInt32(EnmEstadoDelTurno.Ausente)); } The problem I'm having is that the "where" clause gets stepped over with the last one. Whats the correct way to do something like this on LINQ? The "helper" object is a custom class storing the user input dates for this example.

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