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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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• Storing users in a database

  - by EMcKenna

  Im wondering whats the best way of storing different types of users in my database. I am writing an application that has 4 main user types (admin, school, teacher, student). At the moment I have a table for each of these but i'm not sure thats the best way of storing user information. For instance... Allowing students to PM other student is simple (store sender and receiver student_id) but enabling teachers to PM students requires another table (sender teacher_id, sender student_id). Should all users be stored in one users table with a user_type field? If so, the teacher / student specific information will still have to be stored in another table. users user_id, password_hash, user_type students user_id, student_specific_stuff... teachers user_id, teacher_specific_stuff... How do I stop a user who has a user_type = student from being accidentally being entered into the teachers table (as both have a user_id) Just want to make sure I get the database correct before i go any further. Thanks...

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• Doctrine: Relating a model to itself using a link table, like "This event is related to to the following other events"

  - by mattalexx

  So in English, the relationship would sound like "This event is related to to the following other events". My first instinct is to create an EventEvent model, with a first_event_id field and a second_event_id field. Then I would define the following two relationships in the Event model: $this->hasMany('Event as FirstRelatedEvents', array('local' => 'first_event_id', 'foreign' => 'second_event_id', 'refClass' => 'EventEvent')); $this->hasMany('Event as SecondRelatedEvents', array('local' => 'second_event_id', 'foreign' => 'first_event_id', 'refClass' => 'EventEvent')); But I would rather not have to use two relationships on the Event model. Is there a better way to do this?

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• How to hire a good ui designer

  - by Mark

  I have a webapp that can probably look better. Looking on jobs.stackoverflow, all I see for UI jobs are full-time positions. Is it possible to hire a good UI designer for freelance work? Where would I begin? And anyone know how much I would be looking at?

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• data structure book recommendation

  - by Pennf0lio

  Hi, Are there books you know that covers data structure? how data should be properly structured (eg, in array or database). thanks!

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• Handling Session ID with Spring

  - by Max

  Hi, I'm trying to build a Spring server for GWT (you can think of it as of Javascript AJAX client). But I can't decide on one point of architecture. How should session be created and used? The obvious easiest way - is to use HTTP sessions (cookies and stuff). Looks fine, but I think that sending session ID separate from the headers would be better (SOAP style). So, what is better: getMyPetsName(String sessionID, int petID) or getMyPetsName(int petID) + session ID through HTTP header (cookies or something). Another question is, if I use the first way (which I like more) - how do I handle session in Spring? I'm really newbie in Spring, and googling did not help. What I mean is: String getMyPetsName(String sessionID, int petID) { Session s = someWayToGetItById(sessionID); } Thanks in advance.

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• Looking for Programming Language that allows you to change true and false.

  - by Maushu

  For my curiosity sake I'm looking for a dynamic object oriented language that allows you to change true to false and vice versa. Something like this: true = false, false = true; This should also affect any conditional statements, therefore 42 == 42 should return False. Basically, with this premise, nothing in the language would be safe from the programmer. Is there any language like this?

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• How to organize and manage multiple database credentials in application?

  - by Polaris878

  Okay, so I'm designing a stand-alone web service (using RestLET as my framework). My application is divided in to 3 layers: Data Layer (just above the database, provides APIs for connecting to/querying database, and a database object) Object layer (responsible for serialization from the data layer... provides objects which the client layer can use without worrying about database) Client layer (This layer is the RestLET web service... basically just creates objects from the object layer and fulfills webservice request) Now, for each object I create in the object layer, I want to use different credentials (so I can sandbox each object...). The object layer should not know the exact credentials (IE the login/pw/DB URL etc). What would be the best way to manage this? I'm thinking that I should have a super class Database object in my data layer... and each subclass will contain the required log-in information... this way my object layer can just go Database db = new SubDatabase(); and then continue using that database. On the client level, they would just be able to go ItemCollection items = new ItemCollection(); and have no idea/control over the database that gets connected. I'm asking this because I am trying to make my platform extensible, so that others can easily create services off of my platform. If anyone has any experience with these architectural problems or how to manage this sort of thing I'd appreciate any insight or advice... Feel free to ask questions if this is confusing. Thanks! My platform is Java, the REST framework I'm using is RestLET, my database is MySQL.

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• Patterns: Local Singleton vs. Global Singleton?

  - by Mike Rosenblum

  There is a pattern that I use from time to time, but I'm not quite sure what it is called. I was hoping that the SO community could help me out. The pattern is pretty simple, and consists of two parts: A singleton factory, which creates objects based on the arguments passed to the factory method. Objects created by the factory. So far this is just a standard "singleton" pattern or "factory pattern". The issue that I'm asking about, however, is that the singleton factory in this case maintains a set of references to every object that it ever creates, held within a dictionary. These references can sometimes be strong references and sometimes weak references, but it can always reference any object that it has ever created. When receiving a request for a "new" object, the factory first searches the dictionary to see if an object with the required arguments already exits. If it does, it returns that object, if not, it returns a new object and also stores a reference to the new object within the dictionary. This pattern prevents having duplicative objects representing the same underlying "thing". This is useful where the created objects are relatively expensive. It can also be useful where these objects perform event handling or messaging - having one object per item being represented can prevent multiple messages/events for a single underlying source. There are probably other reasons to use this pattern, but this is where I've found this useful. My question is: what to call this? In a sense, each object is a singleton, at least with respect to the data it contains. Each is unique. But there are multiple instances of this class, however, so it's not at all a true singleton. In my own personal terminology, I tend to call the factory method a "global singleton". I then call the created objects "local singletons". I sometimes also say that the created objects have "reference equality", meaning that if two variables reference the same data (the same underlying item) then the reference they each hold must be to the same exact object, hence "reference equality". But these are my own invented terms, and I am not sure that they are good ones. Is there standard terminology for this concept? And if not, could some naming suggestions be made? Thanks in advance...

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• Entity framework and database logic.

  - by Xavier Devian

  Hi all, i have a question that's being around for several years. As all you know entity framework is an ORM tool that tries to model the database to an object oriented access model. All the samples I've seen are quering directly to the database tables. So, which is the role of the views in the database now?. The views were used to model the database in a more friendly way, that is, several physical tables, one logic table. This was great for example in hidding the complex relational model on stored procedures as queryng the views inside them was much easier than reproducing the query joins over and over on each stored procedure. So the question is, why is entity framework so good if stored procedures can not take benefit of it?

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• How should rules for Aggregate Roots be enforced?

  - by MylesRip

  While searching the web, I came across a list of rules from Eric Evans' book that should be enforced for aggregates: The root Entity has global identity and is ultimately responsible for checking invariants Root Entities have global identity. Entities inside the boundary have local identity, unique only within the Aggregate. Nothing outside the Aggregate boundary can hold a reference to anything inside, except to the root Entity. The root Entity can hand references to the internal Entities to other objects, but they can only use them transiently (within a single method or block). Only Aggregate Roots can be obtained directly with database queries. Everything else must be done through traversal. Objects within the Aggregate can hold references to other Aggregate roots. A delete operation must remove everything within the Aggregate boundary all at once When a change to any object within the Aggregate boundary is committed, all invariants of the whole Aggregate must be satisfied. This all seems fine in theory, but I don't see how these rules would be enforced in the real world. Take rule 3 for example. Once the root entity has given an exteral object a reference to an internal entity, what's to keep that external object from holding on to the reference beyond the single method or block? (If the enforcement of this is platform-specific, I would be interested in knowing how this would be enforced within a C#/.NET/NHibernate environment.)

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• Building out a well-structured service layer

  - by Chris Stewart

  First, I want to say that it has been awhile since I've gotten into the kind of detail I am at currently. Lately, I've been very much in the SharePoint world and my entire thought process was focused there for quite some time. I'm very glad to be creating databases again, writing "lower level" code to deal with data access, and so forth. I'm working on a very simple web application and taking the opportunity to reacquaint myself with the way I used to structure my projects and various layers of code. For instance, I might have created something like this the last time I went about building something basic from scratch: - MyProject/ -- Domain/ --- Impl/ ---- Person -- Model/ --- IPersonRepository --- Impl/ ---- PersonRepository : IPersonRepository -- Services --- IPersonService --- Impl/ ---- PersonService : IPersonService That would have been the project I did the real work in, and then referenced in the ASP.NET project. My approach was very much inspired by what I saw from the CodeCampServer project as at that time ASP.NET MVC was still very new and it was the only open project I could find actively being developed, and by solid people at that. What ways are you going about structuring your projects and code, when it comes to a general problem you're working on? Certainly various problems can put constraints on this, but assume it's a basic problem without specific needs that affect the structure and layout of your code.

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• An appropriate C API for inspecting attribute values

  - by uk82

  There are two obvious ways in C to provide outside access to internal attribute values (A) provide a generic interface that accepts a list of attributes that changes over time (some added / some die) or (B) a specific interface for each and every attribute. Example A: int x_get_attribute_value(ATT att) { if (a) return a_val; if (b) return b_val; } Example B: A_Enum x_get_a_type_attribute() {} B_Enum x_get_b_type_attribute() {} I recall that Eclipse's API is very much like A (I could be wrong). What I can't do is come up with a compelling argument against either. A is clean - any user will no where to go to find out a property value. It can evolve cleanly without leaving dead interfaces around. B has type checking to a degree - this is C enums! Is there a big hitter argument that pushes the balance away from opinion?

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• Are we using IoC effectively?

  - by Juliet

  So my company uses Castle Windsor IoC container, but in a way that feels "off": All the data types are registered in code, not the config file. All data types are hard-coded to use one interface implementation. In fact, for nearly all given interfaces, there is and will only ever be one implementation. All registered data types have a default constructor, so Windsor doesn't instantiate an object graph for any registered types. The people who designed the system insist the IoC container makes the system better. We have 1200+ public classes, so its a big system, the kind where you'd expect to find a framework like Windsor. But I'm still skeptical. Is my company using IoC effectively? Is there an advantage to new'ing objects with Windsor than new'ing objects with the new keyword?

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• Architecting ASP.net MVC App to use repositories and services

  - by zaladane

  Hello, I recently started reading about ASP.net MVC and after getting excited about the concept, i started to migrate all my webform project to MVC but i am having a hard time keeping my controller skinny even after following all the good advices out there (or maybe i just don't get it ... ). The website i deal with has Articles, Videos, Quotes ... and each of these entities have categories, comments, images that can be associated with it. I am using Linq to sql for database operations and for each of these Entities, i have a Repository, and for each repository, i create a service to be used in the controller. so i have - ArticleRepository ArticleCategoryRepository ArticleCommentRepository and the corresponding service ArticleService ArticleCategoryService ... you see the picture. The problem i have is that i have one controller for article,category and comment because i thought that having ArticleController handle all of that might make sense, but now i have to pass all of the services needed to the Controller constructor. So i would like to know what it is that i am doing wrong. Are my services not designed properly? should i create Bigger service to encapsulate smaller services and use them in my controller? or should i have an articleCategory Controller and an articleComment Controller? A page viewed by the user is made of all of that, thee article to be viewed,the comments associated with it, a listing of the categories to witch it applies ... how can i efficiently break down the controller to keep it "skinny" and solve my headache? Thank you! I hope my question is not too long to be read ...

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• Database Table Schema and Aggregate Roots

  - by bretddog

  Hi, Applicaiton is single user, 1-tier(1 pc), database SqlCE. DataService layer will be (I think) : Repository returning domain objects and quering database with LinqToSql (dbml). There are obviously a lot more columns, this is simplified view. http://img573.imageshack.us/img573/3612/ss20110115171817w.png This is my first attempt of creating a 2 tables database. I think the table schema makes sense, but I need some reassurance or critics. Because the table relations looks quite scary to be honest. I'm hoping you could; Look at the table schema and respond if there are clear signs of troubles or errors that you spot right away.. And if you have time, Look at Program Summary/Questions, and see if the table layout makes makes sense to those points. Please be brutal, I will try to defend :) Program summary: a) A set of categories, each having a set of strategies (1:m) b) Each day a number of items will be produced. And each strategy MAY reference it. (So there can be 50 items, and a strategy may reference 23 of them) c) An item can be referenced by more than one strategy. So I think it's an m:m relation. d) Status values will be logged at fixed time-fractions through the day, for: - .... each Strategy.....each StrategyItem....each item e) An action on an item may be executed by a strategy that reference it. - This is logged as ItemAction (Could have called it StrategyItemAction) User Requsts b) - e) described the main activity mode of the program. To work with only today's DayLog , for each category. 2nd priority activity is retrieval of history, which typically will be From all categories, from day x to day y; Get all StrategyDailyLog. Questions First, does the overall layout look sound? I'm worried to see that there are so many relationships in all directions, connecting everything. Is this normal, or does it look like trouble? StrategyItem is made to represent an m:m relationship. Is it correct as I noted 1:m / 1:1 (marked red) ? StrategyItemTimeLog and ItemTimeLog; Logs values that both need to be retrieved together, when retreiving a StrategyItem. Reason I separated is that the first one is strategy-specific, and several strategies can reference same item. So I thought not to duplicate those values that are not dependent no strategy, but only on the item. Hence I also dragged out the LogTime, as it seems to be the only parameter to unite the logs. But this all looks quite disturbing with those 3 tables. Does it make sense at all? Or you have suggestion? Pink circles shows my vague attempt of Aggregate Root Paths. I've been thinking in terms of "what entity is responsible for delete". Though I'm unsure about the actual root. I think it's Category. Does it make sense related to User Requests described above?

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• Are bad data issues that common?

  - by Water Cooler v2

  I've worked for clients that had a large number of distinct, small to mid-sized projects, each interacting with each other via properly defined interfaces to share data, but not reading and writing to the same database. Each had their own separate database, their own cache, their own file servers/system that they had dedicated access to, and so they never caused any problems. One of these clients is a mobile content vendor, so they're lucky in a way that they do not have to face the same problems that everyday business applications do. They can create all those separate compartments where their components happily live in isolation of the others. However, for many business applications, this is not possible. I've worked with a few clients, one of whose applications I am doing the production support for, where there are "bad data issues" on an hourly basis. Yeah, it's that crazy. Some data records from one of the instances (lower than production, of course) would have been run a couple of weeks ago, and caused some other user's data to get corrupted. And then, a data script will have to be written to fix this issue. And I've seen this happening so much with this client that I have to ask. I've seen this happening at a moderate rate with other clients, but this one just seems to be out of order. If you're working with business applications that share a large amount of data by reading and writing to/from the same database, are "bad data issues" that common in your environment?

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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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• Why didn't C have a boolean data type prior to C99?

  - by frou

  I realise you can just #define some integers, but why didn't C have a dedicated boolean data type before C99? It's such a common occurence in programming and logic, I don't understand the absense of an explicit type and notation.

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• How I can make Recycle Bin for Database ?Application?

  - by Wael Dalloul

  Hi, I have database application, I want to allow the user to restore the deleted records from the database, like in windows we have Recycle bin for files I want to do the same thing but for database records, Assume that I have a lot of related tables that have a lot of fields. Edit: let's say that I have the following structures: Reports table RepName primary key ReportData Users table ID primary key Name UserReports table RepName primary key UserID primary key IsDeleted now if I put isdeleted field in UserReports table, the user can't add same record again if it marked as deleted, because the record is already and this will make duplication.

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• JavaScript Module Pattern - What about using "return this"?

  - by Rob

  After doing some reading about the Module Pattern, I've seen a few ways of returning the properties which you want to be public. One of the most common ways is to declare your public properties and methods right inside of the "return" statement, apart from your private properties and methods. A similar way (the "Revealing" pattern) is to provide simply references to the properties and methods which you want to be public. Lastly, a third technique I saw was to create a new object inside your module function, to which you assign your new properties before returning said object. This was an interesting idea, but requires the creation of a new object. So I was thinking, why not just use "this.propertyName" to assign your public properties and methods, and finally use "return this" at the end? This way seems much simpler to me, as you can create private properties and methods with the usual "var" or "function" syntax, or use the "this.propertyName" syntax to declare your public methods. Here's the method I'm suggesting: (function() { var privateMethod = function () { alert('This is a private method.'); } this.publicMethod = function () { alert('This is a public method.'); } return this; })(); Are there any pros/cons to using the method above? What about the others?

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• Maintaining sort order of database table rows

  - by Lox

  Say I have at database table containing information about a news article in each row. The table has an integer "sort" column to dictate the order in which the articles are to be presented on a web site. How do I best implement and maintain this sort order. The problem I want to avoid is having the the articles numbered 1,2,3,4,..,100 and when article number 50 suddenly becomes interesting it gets its sort number set to 1 and then all articles between them must have their sort number increased by one. Sure, setting initial sort numbers to 100,200,300,400 etc. leaves some space for moving around but at some point it will break. Is there a correct way to do this, maybe a completely different approach? Added-1: All article titles are shown in a list linking to the contents, so yes all sorted items are show at once. Added-2: An item is not necessarily moved to the top of the list; any item can be placed anywhere in the ordered list.

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• MCV/MVP Patterns and Applications that interface with Hardware (DAQ/PLC/etc)

  - by Ryan

  I've been reading a lot about the MCV and MVP patterns for use with UI and it seems like a really nice powerful way to handle user interfaces. I am - however - having a difficult time deciding how this could integrate into a system where data in the model is created from a Data Acquisition System or Serial/Ethernet devices. There is also the added step that 70% of application interaction is performed by a PLC instead of a live user. It seems that for apps that just read/write & manipulate information from a database this works great, but how does does hardware and automation fit into these patterns? Is it as simple as another controller (for lack of a better term) that interacts with hardware that manipulates data and writes to a model? Maybe I am over thinking this or thinking too simply, so any advice would be great. I'm not quite sure where I'm going with this, so if something doesn't make sense or I was too vague leave me a comment. Thanks!

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• Data Access Layer in ASP.Net: Where do I create the Connection?

  - by atticae

  If I want to create a 3-Layer ASP.Net application (Presentation Layer, Business Layer, Data Access Layer), where is the best place to create the Connection objects? So far I used a helper class in my Presentation Layer to create an IDbCommand from the ConnectionString in the web.config on each page and passed it on to the DAL classes/methods. Now I am not so sure, if this part shouldn't also be included in the DAL somehow, because it obviously is part of the Data Access. The DAL is in a separately compilated project, so I dont have access to the web.config and cannot access the connection string (right?). What is the best practice here?

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• If as assert fails, is there a bug?

  - by RichAmberale

  I've always followed the logic: if assert fails, then there is a bug. Root cause could either be: Assert itself is invalid (bug) There is a programming error (bug) (no other options) I.E. Are there any other conclusions one could come to? Are there cases where an assert would fail and there is no bug?

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