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  • php - get content from second pair of quotes in string

    - by Aaron Turecki
    I'm trying to get the contents of the second quotes and only the second quotes from a string. Right now I'm able to get the contents of all three quotes. What am I doing wrong? Is it possible to just print the second value in the output array? Text 2014-06-02 11:48:41.519 -0700 Information 94 NICOLE Client "[WebDirect] (207.230.229.204) [207.230.229.204]" opening database "FMServer_Sample" as "Admin". PHP if (preg_match_all('~(["\'])([^"\']+)\1~', $line, $matches)) $database_names = $matches[2]; print_r($database); Output [WebDirect] (207.230.229.204) [207.230.229.204], FMServer_Sample, Admin

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  • How can I access the value of a checkbox without a postback?

    - by Starwfanatic
    I have a radgrid controlling access to an application for users. There are two columns, a 'name' column and a checkbox 'access' column representing their current access permission. the checkboxes are populated from a database. I would like the to change the checkboxes to grant or deny access to the users I specify. Since there are alot of users I would like to make multiple changes and use a submit button to write the changes to the database. I do not want to postback with each checkbox change and wait for the page to "blink". My problem is that with the checkbox postback disabled, when I click submit, the value of the checkboxes are not registering the changes I make. I need a way to access the current client-side state of the checkbox or some workaround to accomplish this. Thanks in advance!

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  • Java/MySQL: Working with data in classes

    - by skiwi
    What is the best way to deal with accessing/modifying tables in a database? I have read about the Data Access Object approach, but none of the resources I have found so far indicate a clear implementation of it. So assume you have a database with a table called accounts that has columns id, name, password and email. How would you properly access it within Java? I mean most people know how to do SQL statements, but that is not really the point. I hope people here can be of help. Regards.

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  • Using Durable Services for saving wcf instances

    - by miker169
    I am currently creating a service which connects to a DAL and that can run a few stored procedures, one of the issues I am facing is that for certain times of the month, we can't update the database, (at the moment this is done manually. This is done via the user adding a note to their calendar) But I would like to automate this process, one of the possible solutions I can think of using is a durable service. When the date is lets say the 1st of the month, the Update/Insert/Delete instances can get saved to a database, and then ran after that date in a batch. Is this the intended use of durable services ? Is there a better route I could possibly take ?

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  • How to use a servlet to repsond to a request for an object

    - by Rick
    I'm sure this is easy, but I don't work with website development very often and I'm lost on this one. I have a web application that needs to support multiple clients with different settings, icons and other content. The contents of these files are in separate directories for each client. What I would like to do is respond to a request sent to a jsp/java servlet. The servlet will look up the proper folder location in a database (I have the database stuff working) and send the actual object to the requesting page whether it is xml, graphic or video. How do I do that? What methods should I be using. Help I'm lost! :(

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  • Using a password to generate two distinct hashes without reducing password security

    - by Nevins
    Hi there, I'm in the process of designing a web application that will require the storage of GPG keys in an encrypted format in a database. I'm planning on storing the user's password in a bCrypt hash in the database. What I would like to be able to do is to use that bCrypt to authenticate the user then use the combination of the stored bCrypt hash and another hash of the password to encrypt and decrypt the GPG keys. My question is whether I can do this without reducing the security of the password? I was thinking I may be able to use something like an HMAC-SHA256 of a static string using the password and a salt as the secret key. Is there a better way to do this that I haven't thought of? Thanks

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  • Storing DateTime (UTC) vs. storing DateTimeOffset

    - by Frederico
    I usually have an "interceptor" that right before reading/writing from/to the database does datetime conversion (from UTC to localtime, and from localtime to utc), so I can use DateTime.Now (derivations and comparisions) throughout the system without worrying about timezones. Regarding serialization and moving data between computers, there is no need to bother, as the datetime is always UTC. Should I continue storing my dates (SQL 2008 - datetime) in UTC format or should I instead store it using DateTimeOffset (SQL 2008 - datetimeoffset)? UTC Dates in the database (datetime type) have been working and known for so long, why change it? What are the advantages? I have already looked into articles like this one, but I'm not 100% convinced though. Any thoughts?

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  • From comma separated list to individual item result set. *mysql

    - by Raziel
    I'm doing some data migration from a horribly designed database to a less horribly designed database. There is a many to many relationship that has a primary key in one table that corresponds to a comma separated list in another. FK_ID | data ------------- 1,2 | foo 3 | bar 1,3,2 | blarg Is there a way to output the FK_ID field with each comma separated element as a single line in the result set? result set FK_ID | data ------------- 1 | foo 2 | foo 3 | bar 1 | blarg 2 | blarg 3 | blarg I'm thinking this would require some sort of recursive query which I don't think mysql has. Thanks in advance.

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  • Cannot copying tables when compiling on Device

    - by Amarpreet
    Hi guys, I am working on sqlite application with around 10 tables in database. it works fine when i run on simulator. And when i open the sqlite file from Applications folder of simulator it shows me all the tables and data. the problem arises when i run app on device. I downloaded the application from device and i checked the sqlite database files there were no tables in it. please help me solving this problem. thanks.

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  • Gujarati Font Rendering

    - by Vishal Khakhkhar
    I am having sqlite database containing gujarati words.. The sql query for the database is... BEGIN TRANSACTION; CREATE TABLE eng_guj (_id INTEGER PRIMARY KEY, eng_word , guj_word ); INSERT INTO eng_guj VALUES(1,'aardvark','??? ??????? ?????????? ?? ?????? ????? ??????.'); COMMIT; I want to display the text in textview.. but its not rendering properly.. meant Its displaying the word in gujarati like "???????" will be displayed as "??????". I already have used Typeface and different ttf fonts.

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  • Using now() in a <asp:textbox>

    - by Anthony
    Can anyone help. I am using a formview in VS 2005. I have different elements in my form databound to a database and I am performing an INSERT SQL statement. No problem. The problem is that I am trying to enter the current date into the SQL statement and I am having a problem. I can add <%now()% to the "Text" property of the asp:Textbox. But when I do, then I can't bind the textbox to a specific database column. How do I do both???? I can do this: <asp:TextBox ID="TextBox2" runat="server" Text='<%# Bind("Initiate_Date") %>' ></asp:TextBox> Or this: <asp:TextBox ID="TextBox2" runat="server" Text='<%# now() %>' ></asp:TextBox> But I don't know how to do both.

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  • InnoDB not supported by webhost. What now?

    - by Peter Perhác
    I was developing a small WAMP web application on my laptop, where I have an instance of mySQL running and I chose InnoDB for my DB engine. After several weeks' development I wanted to make it available to the public and found out the database server provided by my web host does not support InnoDB, only MyISAM. The create-and-populate script generated from the innoDB schema on my laptop, when executed against the live database, can manage to create individual TABLES but then runs into problems creating the VIEWs. Are views not supported in MyISAM? I know FOREIGN KEYs are not. That's very much why I made the choice of InnoDB... What are my chances of making my innoDB schema design work with myISAM? Is there any straightforward way of converting the whole schema from one storage engine to the other? Should I look for another web host that does provide a mysql db that supports innoDB?

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  • SQL error C# - Parameter already defined

    - by jakesankey
    Hey there. I have a c# application that parses txt files and imports the data from them into a sql db. I was using sqlite and am now working on porting it to sql server. It was working fine with sqlite but now with sql i am getting an error when it is processing the files. It added the first row of data to the db and then says "parameter @PartNumber has already been declared. Variable names must be unique within a batch or stored procedure". Here is my whole code and SQL table layout ... the error comes at the last insertCommand.ExecuteNonQuery() instance at the end of the code... SQL TABLE: CREATE TABLE Import ( RowId int PRIMARY KEY IDENTITY, PartNumber text, CMMNumber text, Date text, FeatType text, FeatName text, Value text, Actual text, Nominal text, Dev text, TolMin text, TolPlus text, OutOfTol text, FileName text ); CODE: using System; using System.Data; using System.Data.SQLite; using System.IO; using System.Text.RegularExpressions; using System.Threading; using System.Collections.Generic; using System.Linq; using System.Data.SqlClient; namespace JohnDeereCMMDataParser { internal class Program { public static List<string> GetImportedFileList() { List<string> ImportedFiles = new List<string>(); using (SqlConnection connect = new SqlConnection(@"Server=FRXSQLDEV;Database=RX_CMMData;Integrated Security=YES")) { connect.Open(); using (SqlCommand fmd = connect.CreateCommand()) { fmd.CommandText = @"IF (EXISTS (SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'RX_CMMData' AND TABLE_NAME = 'Import')) BEGIN SELECT DISTINCT FileName FROM Import; END"; fmd.CommandType = CommandType.Text; SqlDataReader r = fmd.ExecuteReader(); while (r.Read()) { ImportedFiles.Add(Convert.ToString(r["FileName"])); } } } return ImportedFiles; } private static void Main(string[] args) { Console.Title = "John Deere CMM Data Parser"; Console.WriteLine("Preparing CMM Data Parser... done"); Console.WriteLine("Scanning for new CMM data... done"); Console.ForegroundColor = ConsoleColor.Gray; using (SqlConnection con = new SqlConnection(@"Server=FRXSQLDEV;Database=RX_CMMData;Integrated Security=YES")) { con.Open(); using (SqlCommand insertCommand = con.CreateCommand()) { SqlCommand cmdd = con.CreateCommand(); string[] files = Directory.GetFiles(@"C:\Documents and Settings\js91162\Desktop\", "R303717*.txt*", SearchOption.AllDirectories); List<string> ImportedFiles = GetImportedFileList(); foreach (string file in files.Except(ImportedFiles)) { string FileNameExt1 = Path.GetFileName(file); cmdd.CommandText = @" IF (EXISTS (SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'RX_CMMData' AND TABLE_NAME = 'Import')) BEGIN SELECT COUNT(*) FROM Import WHERE FileName = @FileExt; END"; cmdd.Parameters.Add(new SqlParameter("@FileExt", FileNameExt1)); int count = Convert.ToInt32(cmdd.ExecuteScalar()); con.Close(); con.Open(); if (count == 0) { Console.WriteLine("Parsing CMM data for SQL database... Please wait."); insertCommand.CommandText = @" INSERT INTO Import (FeatType, FeatName, Value, Actual, Nominal, Dev, TolMin, TolPlus, OutOfTol, PartNumber, CMMNumber, Date, FileName) VALUES (@FeatType, @FeatName, @Value, @Actual, @Nominal, @Dev, @TolMin, @TolPlus, @OutOfTol, @PartNumber, @CMMNumber, @Date, @FileName);"; insertCommand.Parameters.Add(new SqlParameter("@FeatType", DbType.Decimal)); insertCommand.Parameters.Add(new SqlParameter("@FeatName", DbType.Decimal)); insertCommand.Parameters.Add(new SqlParameter("@Value", DbType.Decimal)); insertCommand.Parameters.Add(new SqlParameter("@Actual", DbType.Decimal)); insertCommand.Parameters.Add(new SqlParameter("@Nominal", DbType.Decimal)); insertCommand.Parameters.Add(new SqlParameter("@Dev", DbType.Decimal)); insertCommand.Parameters.Add(new SqlParameter("@TolMin", DbType.Decimal)); insertCommand.Parameters.Add(new SqlParameter("@TolPlus", DbType.Decimal)); insertCommand.Parameters.Add(new SqlParameter("@OutOfTol", DbType.Decimal)); string FileNameExt = Path.GetFullPath(file); string RNumber = Path.GetFileNameWithoutExtension(file); string RNumberE = RNumber.Split('_')[0]; string RNumberD = RNumber.Split('_')[1]; string RNumberDate = RNumber.Split('_')[2]; DateTime dateTime = DateTime.ParseExact(RNumberDate, "yyyyMMdd", Thread.CurrentThread.CurrentCulture); string cmmDate = dateTime.ToString("dd-MMM-yyyy"); string[] lines = File.ReadAllLines(file); bool parse = false; foreach (string tmpLine in lines) { string line = tmpLine.Trim(); if (!parse && line.StartsWith("Feat. Type,")) { parse = true; continue; } if (!parse || string.IsNullOrEmpty(line)) { continue; } Console.WriteLine(tmpLine); foreach (SqlParameter parameter in insertCommand.Parameters) { parameter.Value = null; } string[] values = line.Split(new[] { ',' }); for (int i = 0; i < values.Length - 1; i++) { SqlParameter param = insertCommand.Parameters[i]; if (param.DbType == DbType.Decimal) { decimal value; param.Value = decimal.TryParse(values[i], out value) ? value : 0; } else { param.Value = values[i]; } } insertCommand.Parameters.Add(new SqlParameter("@PartNumber", RNumberE)); insertCommand.Parameters.Add(new SqlParameter("@CMMNumber", RNumberD)); insertCommand.Parameters.Add(new SqlParameter("@Date", cmmDate)); insertCommand.Parameters.Add(new SqlParameter("@FileName", FileNameExt)); // insertCommand.ExecuteNonQuery(); } } } Console.WriteLine("CMM data successfully imported to SQL database..."); } con.Close(); } } } }

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  • MySQL Many to Many with Unique keys and Update/Select if Exists otherwise Insert

    - by Jayrox
    In my goal to have a Many-to-Many relationship in my MySQL database I have arrived at another bridge to build. Current Tables: Users (id, name) Tags (id, name) User_Tags (user_id, tag_id) Here is the goal: I would like to have the ability to take a tag i.e: #fb and insert it into my Tags database which has a unique constraint on name and if the tag exists I would like to return it's id I would like to insert the tag.id and the current user's user.id into User_Tags. I do not have any unique constraints on the User_Tags table because I would like to be able to track the user's most commonly used tags and present them in a list ordered by frequency of use. I am currently developing this project in PHP using prepared statements. Additionally, performance is not currently an issue as my user count is still fairly small, but it is steadily growing and may be an issue in the future.

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  • Flex DataGrid reads a field from lastResult.node as number

    - by Nemi
    Why Flex 3 DataGrid reads a string from XML lastResult.node as number? A field is saved as var_char in mysql, php reads it as string and pass it OK. If there are more then 16 charaters it gets rounded.... For example: this in database cell: 12345678901234567 gets read in DataGrid as nubmer as 12345678901234568 this is in database cell: 5555544444222223333377777 php reads it same and puts it in XML flex reads XML into arrayCollection and DataGrid reads it as: 5.55554444422222e+24 So it reads it as number, why? And how to make it read as String? I tried with labelFunction, no help.

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  • Should I stick only to AWS RDS Automated Backup or DB Snapshots?

    - by James Wise
    I am using AWS RDS for MySQL. With it comes on backup, I understand that amazon provides two types of backup - automated backup and database (DB) snapshot. The difference is explain in here - http://aws.amazon.com/rds/faqs/#23. However, I am still confuse if should I stick to automated backup only or both automated and manual (db snapshots). What do you think guys? What's the setup of your own? I heard to others that automated backup is not reliable due to some unrecoverable database when the DB instance is crashed so the DB snapshots are the way to rescue you. If I will do daily DB snapshots as similar settings to automated backup, I have gonna pay much bunch of bucks. Hope anyone could enlighten me or advise me the right set up. Thanks. James

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  • Pylons and Pisa (xhtml2pdf): blank page in IE

    - by Utaal
    I'm using pylons to serve a dynamically generated pdf document for reporting: my approach works in firefox & chrome (it displays the pdf inline if the plugin is available or otherwise downloads it) but IE (7 & 8) only show a blank page and doesn't prompt for download. IE correctly shows PDFs generated by other websites, though. Don't know if it matters but the page is accessed through HTTPS. My controller does the following: renders the source page through mako converts the html to pdf using pisa adds these headers to the response: Content-type: application/pdf and Content-disposition: inline; filename=file.pdf Do you have any suggestion? I seem to be stuck and cannot think of anything else to try.

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  • Is it possible to dynamically set a static string during *class* Initialisation?

    - by LonnieBest
    I'm trying to dynamically create a connection string during compile time: public static string ConnectionString { get { string connectionString = @"Data Source=" + myLibrary.common.GetExeDir() + @"\Database\db.sdf;"; return connectionString; } } I keep running into type initialisation errors. I was trying to avoid having to set the connection string for all applications that user my code library. The location of the database is different for each project that uses the library. I have code that can determine the correction string, but was wanting run it during compile time. Is this even possible?

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  • Can you hide tables from a MySQL user in phpMyAdmin?

    - by AK
    I have a MySQL user added to a database that I would like to prevent from viewing certain tables. I can limit their privileges through MySQL by preventing them from running statements like DROP or ALTER. But is it possible to prevent them from viewing certain tables in phpMyAdmin? If there isn't a MySQL privilege that controls this (I wouldn't imagine there would be), is there a configuration in phpMyAdmin that allows this? I understand one workaround here is to move the tables to a new database that they're not added to. This isn't an option for my application.

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  • uninitialized constant Encoding rake db:migrate

    - by Denis
    Hi, My RoR App use rails 2.1.2 When I run rake db:migrate --trace I get the following error, Any idea? ** Invoke db:migrate (first_time) ** Invoke environment (first_time) ** Execute environment ** Execute db:migrate rake aborted! uninitialized constant Encoding /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activesupport/lib/active_support/dependencies.rb:278:in `load_missing_constant' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activesupport/lib/active_support/dependencies.rb:467:in `const_missing' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activesupport/lib/active_support/dependencies.rb:479:in `const_missing' /Library/Ruby/Gems/1.8/gems/sqlite3-0.0.8/lib/sqlite3/encoding.rb:9:in `find' /Library/Ruby/Gems/1.8/gems/sqlite3-0.0.8/lib/sqlite3/database.rb:66:in `initialize' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb:13:in `new' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb:13:in `sqlite3_connection' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb:292:in `send' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb:292:in `connection=' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb:260:in `retrieve_connection' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb:78:in `connection' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activerecord/lib/active_record/migration.rb:408:in `initialize' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activerecord/lib/active_record/migration.rb:373:in `new' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activerecord/lib/active_record/migration.rb:373:in `up' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/activerecord/lib/active_record/migration.rb:356:in `migrate' /Users/denisjacquemin/Documents/code/projects/BmfOnRails/vendor/rails/railties/lib/tasks/databases.rake:99 /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `call' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `execute' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `each' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `execute' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:597:in `invoke_with_call_chain' /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/monitor.rb:242:in `synchronize' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:583:in `invoke' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `each' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:2001:in `run' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/lib/rake.rb:1998:in `run' /Users/denisjacquemin/.gem/ruby/1.8/gems/rake-0.8.7/bin/rake:31 /usr/bin/rake:19:in `load' /usr/bin/rake:19 My database.yml development: adapter: sqlite3 database: db/development.sqlite3 pool: 5 timeout: 5000 thanks

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  • building objects from xml file at runtime and intializing, in one pass?

    - by KaluSingh Gabbar
    I have to parse the XML file and build objects representation based on that, now once I get all these data I create entries in various database for these data objects. I have to do second pass over that for value as in the first pass all I could do is build the assets in various databases. and in second pass I get the values for all the data and put it in the database. I have a feeling that this can be done in a single pass but I just want to see what are your opinions. As I am just a student who started with professional work, experienced ppl please help. Can someone who have ideas or done similar work, please provide some light on the topic so that I can think over the possibility of the work and get the prototype going based on your suggestion. Thanks a lot for your precious time, I honestly appreciate it.

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  • Search relevance from XML docs (XQuery?) vs MySQL

    - by Marius
    Hello there, I have a website where documents are saved in xml documents, all with the same structure. I need a search engine where I am able to choose documents with the highest relevance according to the key words given by a searching user. I thought it could (?) be a good idea to have one using XQuery rather than having the information stored twice (in XML docs + mysql database) and querying the mysql database for relevance searches. Is XQuery any good for this, and how, and what speed can I expect on +1000 documents of about 7kb each. Thank you for your time. Kind regards

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  • Is a many-to-many relationship with extra fields the right tool for my job?

    - by whichhand
    Previously had a go at asking a more specific version of this question, but had trouble articulating what my question was. On reflection that made me doubt if my chosen solution was correct for the problem, so this time I will explain the problem and ask if a) I am on the right track and b) if there is a way around my current brick wall. I am currently building a web interface to enable an existing database to be interrogated by (a small number of) users. Sticking with the analogy from the docs, I have models that look something like this: class Musician(models.Model): first_name = models.CharField(max_length=50) last_name = models.CharField(max_length=50) dob = models.DateField() class Album(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) class Instrument(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) Where I have one central table (Musician) and several tables of associated data that are related by either ForeignKey or OneToOneFields. Users interact with the database by creating filtering criteria to select a subset of Musicians based on data the data on the main or related tables. Likewise, the users can then select what piece of data is used to rank results that are presented to them. The results are then viewed initially as a 2 dimensional table with a single row per Musician with selected data fields (or aggregates) in each column. To give you some idea of scale, the database has ~5,000 Musicians with around 20 fields of related data. Up to here is fine and I have a working implementation. However, it is important that I have the ability for a given user to upload there own annotation data sets (more than one) and then filter and order on these in the same way they can with the existing data. The way I had tried to do this was to add the models: class UserDataSets(models.Model): user = models.ForeignKey(User) name = models.CharField(max_length=100) description = models.CharField(max_length=64) results = models.ManyToManyField(Musician, through='UserData') class UserData(models.Model): artist = models.ForeignKey(Musician) dataset = models.ForeignKey(UserDataSets) score = models.IntegerField() class Meta: unique_together = (("artist", "dataset"),) I have a simple upload mechanism enabling users to upload a data set file that consists of 1 to 1 relationship between a Musician and their "score". Within a given user dataset each artist will be unique, but different datasets are independent from each other and will often contain entries for the same musician. This worked fine for displaying the data, starting from a given artist I can do something like this: artist = Musician.objects.get(pk=1) dataset = UserDataSets.objects.get(pk=5) print artist.userdata_set.get(dataset=dataset.pk) However, this approach fell over when I came to implement the filtering and ordering of query set of musicians based on the data contained in a single user data set. For example, I could easily order the query set based on all of the data in the UserData table like this: artists = Musician.objects.all().order_by(userdata__score) But that does not help me order by the results of a given single user dataset. Likewise I need to be able to filter the query set based on the "scores" from different user data sets (eg find all musicians with a score 5 in dataset1 and < 2 in dataset2). Is there a way of doing this, or am I going about the whole thing wrong?

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  • MySQL - Calculating fields on the fly vs storing calculated data

    - by Christian Varga
    Hi Everyone, I apologise if this has been asked before, but I can't seem to find an answer to a question that I have about calculating on the fly vs storing fields in a database. I read a few articles that suggested it was preferable to calculate when you can, but I would just like to know if that still applies to the following 2 examples. Example 1. Say you are storing data relating to a car. You store the fuel tank size in litres, and how many litres it uses per 100km. You also want to know how many KMs it can travel, which can be calculated from the tank size and economy. I see 2 ways of doing this: When a car is added or updated, calculate the amount of KMs and store this as a static field in the database. Every time a car is accessed, calculate the amount of KMs on the fly. Because the cars economy/tank size doesn't change (although it could be edited), the KMs is a pretty static value. I don't see why we would calculate it every single time the car is accessed. Wouldn't this waste cpu time as opposed to simply storing it in a separate field in the database and calculating only when a car is added or updated? My next example, which is almost an entirely different question (but on the same topic), relates to counting children. Let's say we have a app which has categories and items. We have a view where we display all the categories, and a count of all the items inside each category. Again, I'm wondering what's better. To perform a MySQL query to count all the items in each category every single time the page is accessed? Or store the count in a field in the categories table and update when an item is added / deleted? I know it is redundant to store anything that can be calculated, but I worry that calculating fields or counting records might be slow as opposed to storing the data in a field. If it's not then please let me know, I just want to learn about when to use either method. On a small scale I guess it wouldn't matter either way, but apps like Facebook, would they really count the amount of friends you have every time someone views your profile or would they just store it as a field? I'd appreciate any responses to both of these scenarios, and any resource that might explain the benefits of calculating vs storing. Thanks in advance, Christian

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