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  • How can I handle dynamic calculated attributes in a model in Django?

    - by bullfish
    In Django I calculate the breadcrumb (a list of fathers) for an geographical object. Since it is not going to change very often, I am thinking of pre calculating it once the object is saved or initialized. 1.) What would be better? Which solution would have a better performance? To calculate it at _init_ or to calculate it when the object is saved (the object takes about 500-2000 characters in the DB)? 2.) I tried to overwrite the _init_ or save() methods but I don't know how to use attributes of the just saved object. Accessing *args, **kwargs did not work. How can I access them? Do I have to save, access the father and then save again? 3.) If I decide to save the breadcrumb. Whats the best way to do it? I used http://www.djangosnippets.org/snippets/1694/ and have crumb = PickledObjectField(). Thats the method to calculate the attribute crumb() def _breadcrumb(self): breadcrumb = [ ] x = self while True: x = x.father try: if hasattr(x, 'country'): breadcrumb.append(x.country) elif hasattr(x, 'region'): breadcrumb.append(x.region) elif hasattr(x, 'city'): breadcrumb.append(x.city) else: break except: break breadcrumb.reverse() return breadcrumb Thats my save-Method: def save(self,*args, **kwargs): # how can I access the father ob the object? father = self.father # does obviously not work father = kwargs['father'] # does not work either # the breadcrumb gets calculated here self.crumb = self._breadcrumb(father) super(GeoObject, self).save(*args,**kwargs) Please help me out. I am working on this for days now. Thank you.

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  • Define tables from a part of my ER Diagram.

    - by M R Jafari
    I have a ER-Diagram (Show in http://www.4freeimagehost.com/show.php?i=f82997ca4d5d.png). In the diagram you see 2 entities and a 1:N relataion together. Project has 2 columns as ProjectID, ProjectName. Employee has 3 colums as EmployeeID, EmployeeName and ProjectID. A project has ONLY 1 project-manager and project-manager is a employee. What columns add them?

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  • Should I use custom exceptions to control the flow of application?

    - by bonefisher
    Is it a good practise to use custom business exceptions (e.g. BusinessRuleViolationException) to control the flow of user-errors/user-incorrect-inputs??? The classic approach: I have a web service, where I have 2 methods, one is the 'checker' (UsernameAlreadyExists()) and the other one is 'creator' (CreateUsername())... So if I want to create a username, I have to do 2 roundtrips to webservice, 1.check, 2.if check is OK, create. What about using UsernameAlreadyExistsException? So I call only the 2. web service method (CrateUsername()), which contains the check and if not successfull, it throws the UsernameAlreadyExistsException. So the end goal is to have only one round trip to web service and the checking can be contained also in other web service methods (so I avoid calling the UsernameAlreadyExists() all the times..). Furthermore I can use this kind of business error handling with other web service calls completely avoiding the checking prior the call.

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  • Using hashing to group similar records

    - by Neil Dobson
    I work for a fulfillment company and we have to pack and ship many orders from our warehouse to customers. To improve efficiency we would like to group identical orders and pack these in the most optimum way. By identical I mean having the same number of order lines containing the same SKUs and same order quantities. To achieve this I was thinking about hashing each order. We can then group by hash to quickly see which orders are the same. We are moving from an Access database to a PostgreSQL database and we have .NET based systems for data loading and general order processing systems, so we can either do the hashing during the data loading or hand this task over to the DB. My question firstly is should the hashing be managed by DB, possibly using triggers, or should the hash be created on-the-fly using a view or something? And secondly would it be best to calculate a hash for each order line and then to combine these to find an order-level hash for grouping, or should I just use a trigger for all CRUD operations on the order lines table which re-calculates a single hash for the entire order and store the value in the orders table? TIA

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  • Revisions: algorithm and data structure

    - by SODA
    Hi, I need ideas for structuring and processing data with revisions. For example, I have a database of objects (e.g. cars). Each object has a number of properties, which can be arbitrary, so there's no a set schema to describe these objects. These objects are probably saved as key-value pairs. Now I need to change property of an object. I don't want to completely rewrite it - I want to be able to go back and see history of changes to these properties, that's why I want to add new property and keep the old one (so I guess a timestamp would do the job of telling which property is the latest). At the same time I want to be able to get info about any object in a snap, with only latest versions of each of the properties. Any ideas what would be the best approach? At least please point me in the right direction. Thanks!

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  • Automatically reporting javascript errors to the developer

    - by Cine
    As most production environments we have setup something to send us a notification if there is an error in our web application. The problem is ofcourse that this only covers errors on the server side. My question to the community is: What are you doing about client side errors, especially in javascript? And what about other quality of service issues, such as slow processing and other things that might be due to the client machine?

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  • How big is too big (for NTFS)

    - by BCS
    I have a program and as it's done now, it has a data directory with something like 10-30K files in it and it's starting to cause problems. Should I expect that to cause problems and my only solution to tweak my file structure or does that indicate other problems?

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  • Database: relational/not relational/object oriented... What to choose?

    - by Damian
    I'm porting a website that I made for app engine to run on a dedicated server. It is coded in java and I'm looking for a database to replace google datastore. My first thougt was MySql because everybody uses it, but i dont like SQL and I think I would feel more comfortable using OODB or anything else. With google datastore I could modify my models and don't worry about the database definition at all. I know using MySql that isn't possible. And I don't want to miss that. And if I use a OODB, which should I use? What about performance compared to MySql? Well, any idea or tip will really help me since I know nothing about databases.

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  • friendship database schema

    - by Daniel Hertz
    I'm creating a db schema that involves users that can be friends, and I was wondering what the best way to model the ability for these friends to have friendships. Should it be its own table that simply has two columns that each represent a user? Thanks!

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  • Haskell: Pattern Matching with Lists

    - by user1670032
    I'm trying to make a function that takes in a list, and if one of the elements is negative, then any elements in that list that are equal to its positive counterpart should be changed to 0. Eg, if there is a -2 in a list, then all 2's in that list should be changed to 0. Any ideas why it only works for some cases and not others? I'm not understanding why this is, I've looked it over several times. changeToZero [] = [] changeToZero [x] = [x] changeToZero (x:zs:y:ws) | (x < 0) && ((-1)*(x) == y) = x : zs : 0 : changeToZero ws changeToZero (x:xs) = x : changeToZero xs *Main changeToZero [-1,1,-2,2,-3,3] [-1,1,-2,2,-3,3] *Main changeToZero [-2,1,2,3] [-2,1,0,3] *Main changeToZero [-2,1,2,3,2] [-2,1,0,3,2] *Main changeToZero [1,-2,2,2,1] [1,-2,2,0,1]

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  • How should I use color in my application? Single, Theme, or Chaos?

    - by CodeSlave
    How should I be using color in my application? I have over a 100 different forms (windows) in my application, and the default windows grey seems like a bad choice to me. One school of thought says pick one neutral color, and use the same one everywhere. Another school of thought says pick a set of neutral colors, and use them same ones within a group of form (e.g., shipping screens might be light green, receiving screens light orange, user administration screens light blue, etc.). The final school of thought says make every form different. We've got millions of colors, why not use them? What should I do and why?

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  • Cocoa framework development: sharing between projects

    - by e.James
    I am currently developing a handful of similar Cocoa desktop apps. In an effort to share code between them, I have identified a set of core classes and functions that can be common across all of these applications. I would like to bundle this common code into a framework which all of my current applications (and any future ones) can link against. Now, here's the hard part: I'm going to be developing this framework as I go, so I need each of my desktop apps to have a reference to it, but I want to be able to edit the framework source code from within each of the app projects and have the framework automatically rebuilt as required. For example, let's say I have the Xcode project for DesktopAppNumberOne open, and I decide that one of my framework classes needs to be changed. I would like to: Open and edit the source file for that framework class without having to open the framework project in Xcode. Hit "build" on DesktopAppNumberOne, and see the framework rebuilt first (because one of its sources has changed), then see parts of DesktopAppNumberOne rebuilt (because one of the frameworks it links against has changed). I can see how to do this with only one app and one framework, but I'm having trouble figuring out how to do it with multiple apps that share a single framework. Has anyone had success with this approach? Am I perhaps going about this the wrong way? Any help would be appreciated.

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  • Initialization of components with interdependencies - possible antipattern?

    - by Rosarch
    I'm writing a game that has many components. Many of these are dependent upon one another. When creating them, I often get into catch-22 situations like "WorldState's constructor requires a PathPlanner, but PathPlanner's constructor requires WorldState." Originally, this was less of a problem, because references to everything needed were kept around in GameEngine, and GameEngine was passed around to everything. But I didn't like the feel of that, because it felt like we were giving too much access to different components, making it harder to enforce boundaries. Here is the problematic code: /// <summary> /// Constructor to create a new instance of our game. /// </summary> public GameEngine() { graphics = new GraphicsDeviceManager(this); Components.Add(new GamerServicesComponent(this)); //Sets dimensions of the game window graphics.PreferredBackBufferWidth = 800; graphics.PreferredBackBufferHeight = 600; graphics.ApplyChanges(); IsMouseVisible = true; screenManager = new ScreenManager(this); //Adds ScreenManager as a component, making all of its calls done automatically Components.Add(screenManager); // Tell the program to load all files relative to the "Content" directory. Assets = new CachedContentLoader(this, "Content"); inputReader = new UserInputReader(Constants.DEFAULT_KEY_MAPPING); collisionRecorder = new CollisionRecorder(); WorldState = new WorldState(new ReadWriteXML(), Constants.CONFIG_URI, this, contactReporter); worldQueryUtils = new WorldQueryUtils(worldQuery, WorldState.PhysicsWorld); ContactReporter contactReporter = new ContactReporter(collisionRecorder, worldQuery, worldQueryUtils); gameObjectManager = new GameObjectManager(WorldState, assets, inputReader, pathPlanner); worldQuery = new DefaultWorldQueryEngine(collisionRecorder, gameObjectManager.Controllers); gameObjectManager.WorldQueryEngine = worldQuery; pathPlanner = new PathPlanner(this, worldQueryUtils, WorldQuery); gameObjectManager.PathPlanner = pathPlanner; combatEngine = new CombatEngine(worldQuery, new Random()); } Here is an excerpt of the above that's problematic: gameObjectManager = new GameObjectManager(WorldState, assets, inputReader, pathPlanner); worldQuery = new DefaultWorldQueryEngine(collisionRecorder, gameObjectManager.Controllers); gameObjectManager.WorldQueryEngine = worldQuery; I hope that no one ever forgets that setting of gameObjectManager.WorldQueryEngine, or else it will fail. Here is the problem: gameObjectManager needs a WorldQuery, and WorldQuery needs a property of gameObjectManager. What can I do about this? Have I found an anti-pattern?

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  • Online graphing and data visualization frameworks

    - by Marques
    I have been looking around at web applications and websites with rich graphs, charts, and data visualization and for the most part have been able to determine which frameworks or tools websites are using. However I was looking over 'resumup.com' and couldn't determine what they are using. Does anyone know off hand or can you tell? It doesn't seem like any javascript framework i've seen unless its custom...is it some sort of flash or flex framework? Any help would be greatly appreciated. Thanks, Marques

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  • Is there a programming language that performs currying when named parameters are omitted?

    - by Adam Gent
    Many functional programming languages have support for curried parameters. To support currying functions the parameters to the function are essentially a tuple where the last parameter can be omitted making a new function requiring a smaller tuple. I'm thinking of designing a language that always uses records (aka named parameters) for function parameters. Thus simple math functions in my make believe language would be: add { left : num, right : num } = ... minus { left : num, right : num } = .. You can pass in any record to those functions so long as they have those two named parameters (they can have more just "left" and "right"). If they have only one of the named parameter it creates a new function: minus5 :: { left : num } -> num minus5 = minus { right : 5 } I borrow some of haskell's notation for above. Has any one seen a language that does this?

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  • c# multi threaded file processing

    - by user177883
    There is a folder that contains 1000 of small text files. I aim to parse and process all of them while more files are being populated in to the folder. My intention is to multithread this operation as the single threaded prototype took 6 minutes to process 1000 files. I like to have reader and writer thread(s) as following : while the reader thread(s) are reading the files, I d like to have writer thread(s) to process them. Once the reader is started reading a file, I d like to mark it as being processed, such as by renaming it, once it s read, rename it to completed. How to approach such multithreaded application ? Is it better to use a distributed hash table or a queue? Which data structure to use that would avoid locks? Would you have a better approach to this scheme that you like to share?

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  • database is normalized but the following is a problem please help

    - by user287745
    but the prob is there are relations ships which are so huge that after normalizing they have like a 20 primary keys( composite keys) which are really foreign keys but have to be declared as primary keys to identify the relationship uniquely. so please help? is it correct and i apologize to the expert community for not accepting answers, i was not aware that accepting is possible, the TICK MARK is that visible :-)

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  • If we make a number every millisecond, how much data would we have in a day?

    - by Roger Travis
    I'm a bit confused here... I'm being offered to get into a project, where would be an array of certain sensors, that would give off reading every millisecond ( yes, 1000 reading in a second ). Reading would be a 3 or 4 digit number, for example like 818 or 1529. This reading need to be stored in a database on a server and accessed remotely. I never worked with such big amounts of data, what do you think, how much in terms of MBs reading from one sensor for a day would be?... 4(digits)x1000x60x60x24 ... = 345600000 bits ... right ? about 42 MB per day... doesn't seem too bad, right? therefor a DB of, say, 1 GB, would hold 23 days of info from 1 sensor, correct? I understand that MySQL & PHP probably would not be able to handle it... what would you suggest, maybe some aps? azure? oracle? ... Thansk!

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  • How to implement Gradient Opacity (Mask) using html css javascript

    - by brz dot net
    I have to show 25% right screen in such way that the text looks appeared from right. For this I need to set opacity from 0 to 100 at 25% right side screen means rightmost opacity would be 0 and at 75% the opacity would be 100. For this, I took a Div and set opacity but It looks bad because of border. I need to gray out text. It looks a block. Let me know how I can implement cross browser compatible gradient opacity mask for right screen text. What is the best way to do this?

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  • How to make some functions of a class as private for third level of inheritance.

    - by Shantanu Gupta
    I have created a class say A which has some functions defined as protected. Now Class B inherits A and class C inherits B. Class A has private default constructor and protected parameterized constructor. I want Class B to be able to access all the protected functions defined in Class A but class C can have access on some of the functions only not all the functions and class C is inheriting class B. How can I restrict access to some of the functions of Class A from Class C ? Class A { private A(){} protected A(int ){} protected calc(){} protected allow(){} } Class B : A {} // calc() and allow() should be accessible here CLass C:B { // calc() should not be accessible here but allow() should be accessible here. }

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  • Event feed implementation - will it scale?

    - by SlappyTheFish
    Situation: I am currently designing a feed system for a social website whereby each user has a feed of their friends' activities. I have two possible methods how to generate the feeds and I would like to ask which is best in terms of ability to scale. Events from all users are collected in one central database table, event_log. Users are paired as friends in the table friends. The RDBMS we are using is MySQL. Standard method: When a user requests their feed page, the system generates the feed by inner joining event_log with friends. The result is then cached and set to timeout after 5 minutes. Scaling is achieved by varying this timeout. Hypothesised method: A task runs in the background and for each new, unprocessed item in event_log, it creates entries in the database table user_feed pairing that event with all of the users who are friends with the user who initiated the event. One table row pairs one event with one user. The problems with the standard method are well known – what if a lot of people's caches expire at the same time? The solution also does not scale well – the brief is for feeds to update as close to real-time as possible The hypothesised solution in my eyes seems much better; all processing is done offline so no user waits for a page to generate and there are no joins so database tables can be sharded across physical machines. However, if a user has 100,000 friends and creates 20 events in one session, then that results in inserting 2,000,000 rows into the database. Question: The question boils down to two points: Is this worst-case scenario mentioned above problematic, i.e. does table size have an impact on MySQL performance and are there any issues with this mass inserting of data for each event? Is there anything else I have missed?

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  • Are these jobs for developer or designers or for client himself? for a web-site projects [closed]

    - by jitendra
    Are these jobs for developer or for designers or for client himself? for a web-site projects. Client is asking to do all things to XHTML CSS PHP coder.. Spell checking grammar checking Descriptive alt text for big chart , graph images, technical images To write Table summary and caption Descriptive Link text Color Contrast checking Deciding in content what should be H2 ,H3, H4... and what should be <strong> or <span class="boldtext"> Meta Description and keywords for each pages Image compression To decide Filenames for images,PDf etc To decide Page's <title> for each page

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  • Service Layer Pattern - Could we avoid the service layer on a specific case?

    - by lidermin
    Hi, we are trying to implement an application using the Service Layer Pattern cause our application needs to connect to other multiple applications too, and googling on the web, we found this link of a demonstrative graphic for the "right" way of apply the pattern: martinfowler.com - Service Layer Pattern But now we have a question: what if our system needs to implement some business logic, only for our application (like some maintenance data for the system itself) that we don't need to share with other systems. Based on this graphic: As it seems, it will be unnecesary to implement a service layer just for that; it will be more practical to avoid the service layer, and just go from User Interface to the Business Layer (for example). What should be the right way in this case to implement the Service Layer Pattern? What do you suggest us for a scenario like the one I told you? Thanks in advance.

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