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• Does Ruby on Rails "has_many" array provide data on a "need to know" basis?

  - by Jian Lin

  On Ruby on Rails, say, if the Actor model object is Tom Hanks, and the "has_many" fans is 20,000 Fan objects, then actor.fans gives an Array with 20,000 elements. Probably, the elements are not pre-populated with values? Otherwise, getting each Actor object from the DB can be extremely time consuming. So it is on a "need to know" basis? So does it pull data when I access actor.fans[500], and pull data when I access actor.fans[0]? If it jumps from each record to record, then it won't be able to optimize performance by doing sequential read, which can be faster on the hard disk because those records could be in the nearby sector / platter layer -- for example, if the program touches 2 random elements, then it will be faster just to read those 2 records, but what if it touches all elements in random order, then it may be faster just to read all records in a sequential way, and then process the random elements. But how will RoR know whether I am doing only a few random elements or all elements in random?

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• which Server I have to buy?

  - by sri

  Hello, Recently i have registered startup (home office). My intension is to have virtual(company) server for LAMP website development(virtual). Initially thinking, 2-5 people will be logging virtually to the server. a. but not sure where to shop or what to shop. b. Should I go for my own Server or i have to share some server. c. If i have to go My Server, should I go with rack or tower model. d. which brand and model i have to buy. d. If I have to go with shared(cloud), not sure which is the best place It will be great help, if some one provide in site. Thanks in advance. Sri

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• Sorting out POCO, Repository Pattern, Unit of Work, and ORM

  - by CoffeeAddict

  I'm reading a crapload on all these subjects: POCO Repository Pattern Unit of work Using an ORM mapper ok I see the basic definitions of each in books, etc. but I can't visualize this all together. Meaning an example structure (DL, BL, PL). So what, you have your DL objects that contain your CRUD methods, then your BL objects which are "mapped" using an ORM back to your DL objects? What about DTOs...they're your DL objects right? I'm confused. Can anyone really explain all this together or send me example code? I'm just trying to put this together. I am determining whether to go LINQ to SQL or EF 4 (not sure about NHibrernate yet). Just not getting the concepts as in physical layers and code layers here and what each type of object contains (just properties for DTOs, and CRUDs for your core DL classes that match the table fields???). I just need some guidance here. I'm reading Fowler's books and starting to read Evans but just not all there yet.

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• MVC2 IModelBinder and parsing a string to an object - How do I do it?

  - by burnt_hand

  I have an object called Time public class Time{ public int Hour {get;set;} public int Minute {get;set;} public static Time Parse(string timeString){ //reads the ToString()'s previous output and returns a Time object } override protected string ToString(){ //puts out something like 14:50 (as in 2:50PM) } } So what I want is for the automatic model binding on the Edit or Create action to set this Time instance up from a string (i.e. feed the Parse method with the string and return the result). The reason I am doing this is that I will have a DropDownList with selectable times. The value of each option will be the parser readable string. Can anyone provide an example BindModel method from the IModelBinder interface?

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• ibatis domain modelling

  - by josh

  Hi team; I am working on the domain model for a project. I have a class named user that has a class named UserType as one of the properties. I know when i want to select all users, i will use joins to pick up all corresponding usertypes. How do i do inserts? Do i have to write a handler for userType? or can i do something like INSERT INTO users(... usertype_id ...) VALUES(... #{usertype.usertype_id}...) Please help; I have spent the whole day trying to figure this out. Am using ibatis 3.0 and am new to ibatis. Regards Josh

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• Where should configuration be placed?

  - by James P.

  I have an application structured as follows: dao domain main services utils I've made a class that reads the application configuration from an XML file. The question is where should it be placed? In the utilities package?

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• Typed DefaultListModel to avoid casting

  - by Thomas R.

  Is there a way in java to have a ListModel that only accepts a certain type? What I'm looking for is something like DefaultListModel<String> oder TypedListModel<String>, because the DefaultListModel only implements addElement(Object obj) and get(int index) which returns Object of course. That way I always have to cast from Object to e.g. String and there is no guarantee that there are only strings in my model, even though I'd like to enforce that. Is this a flaw or am I using list models the wrong way?

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• What is the best practice in regards to building composite dtos off of an aggregate root with domain

  - by Chance

  I'm trying to figure out the best approach/practice for assembling a composite data transfer object off of an aggregate root and would love to hear people's thoughts on this. For example, lets say I have a root that has a few domain objects as children. I want to assemble a specific view dto, based on some business logic, that either has attributes or full dto's of it's objects. What I'm struggling with is trying to figure out where that assembly should happen. I can see it going on the domain object of the aggregate root as there is some business logic associated with it. The benefits of this approach from what I've deduced thus far is that it should reduce the inevitable business logic from bleeding outisde of the domain object. It also allows for private methods that take care of tasks that could become more complex from an external builder. The downsides being that the domain object becomes much more entrenched in the application's workflow and represents much more than just the domain object. It also could become very large in the scenario where you need multiple composite Dtos. Alternatively, I could also see it belonging to some form of transfer object assembler where there is a builder for each domain object. The domain objects would still be responsible for GetDto() and UpdateFromDto(dto). Outside of that, the builder would handle the construction and deconstruction of composite dtos. The downside is kind of mentioned above, where I fear this will easily lead to developers unfamiliar with DDD bleeding a ton of business logic into the assembler which is what I want to desperately avoid. Any thoughts would be greatly apperciated.

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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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• C# Event Handlers Using an Enum

  - by Jimbo

  I have a StatusChanged event that is raised by my object when its status changes - however, the application needs to carry out additional actions based on what the new status is. e.g If the new status is Disconnected, then it must update the status bar text and send an email notification. So, I wanted to create an Enum with the possible statuses (Connected, Disconnected, ReceivingData, SendingData etc.) and have that sent with the EventArgs parameter of the event when it is raised (see below) Define the object: class ModemComm { public event CommanderEventHandler ModemCommEvent; public delegate void CommanderEventHandler(object source, ModemCommEventArgs e); public void Connect() { ModemCommEvent(this, new ModemCommEventArgs ModemCommEventArgs.eModemCommEvent.Connected)); } } Define the new EventArgs parameter: public class ModemCommEventArgs : EventArgs{ public enum eModemCommEvent { Idle, Connected, Disconnected, SendingData, ReceivingData } public eModemCommEvent eventType { get; set; } public string eventMessage { get; set; } public ModemCommEventArgs(eModemCommEvent eventType, string eventMessage) { this.eventMessage = eventMessage; this.eventType = eventType; } } I then create a handler for the event in the application: ModemComm comm = new ModemComm(); comm.ModemCommEvent += OnModemCommEvent; and private void OnModemCommEvent(object source, ModemCommEventArgs e) { } The problem is, I get a 'Object reference not set to an instance of an object' error when the object attempts to raise the event. Hoping someone can explain in n00b terms why and how to fix it :)

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• Controlling CodeModel's code output formatting: putting lines between namespace declarations

  - by devoured elysium

  I'm making some experiments with Visual Studio's CodeModel. I tried creating a file with two namespaces in there through VS's Code Model: CodeModel codeModel = projItem.ContainingProject.CodeModel; codeModel.AddNamespace("Namespaces.FirstNamespace", "namespacestest.cs"); codeModel.AddNamespace("Namespaces.SecondNamespace", "namespacestest.cs"); the output of such code is: //file namespacestest.cs namespace Namespaces.FirstNamespace { } namespace Namespaces.SecondNamespace { } Which is almost what I'm looking for. The only catch here is that I'd like to control the spacing: having at least one line between the first and the second namespace. Does by chance anyone know of a way of achieving this? This is what I want: //file namespacestest.cs namespace Namespaces.FirstNamespace { } namespace Namespaces.SecondNamespace { } Thanks

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• ASP.Net 4.0 Database Created Pages

  - by Tyler

  I want to create asp.net 4.0 dynamic pages loaded from my MS SQL server. Basically, its a list of locations with informations. For example: Location1 would have the page www.site.com/location/location1.aspx Location44 would have the page www.site.com/location/location44.aspx I dont even know where to start with this, url writting maybe?

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• Of Models / Entities and N-tier applications

  - by Jonn

  I've only discovered a month ago the folly of directly accessing entities / models from the data access layer of an n-tier app. After reading about ViewModels while studying ASP.NET MVC, I've come to understand that to make a truly extensible application the model that the UI layer interacts with must be different from the one that the Data Access layer has access to. But what about the Business layer? Should I have a different set of models for my business layer as well? For true separation of concern, should I have a specific set of models that are relevant only to my business layer so as not to mess around with any entities (possibly generated by for example, the entity framework, or EJB) in the DAL or would that be overkill?

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• Zend without Database

  - by dbemerlin

  Hi, i googled for an hour now but maybe my Google-Fu is just too weak, i couldn't find a solution. I want to create an application that queries a service via JSON requests (all data and backend/business logic is stored in the service). With plain PHP it's simple enough since i just make a curl request, json_decode the result and get what i need. This already works quite well. A request might look like this: Call http://service-host/userlist with body: {"logintoken": "123456-1234-5678-901234"} Get Result: { "status": "Ok", "userlist":[ {"name": "foo", "id": 1}, {"name": "bar", "id": 2} ] } Now we want to get that into the Zend Framework since it's a hobby project and we want to learn about Zend. The problem is that all information i could find use a Database. Is there even a way to create a Zend Project that does not use a Database? And how can i write a model that represents the actions instead of objects and object-relations?

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• Django complex queries

  - by Josh K

  I need to craft a filter for an object that checks date ranges. Right now I'm performing a very inefficient loop which checks all the objects. I would like to simplify this to a database call. The logic is you have a start and an end date objects. I need to check if the start OR the end is within the range of an appointment. if (start >= appointment.start && start < appointment.end) || (end > appointment.start && end <= appointment.end) I could do this in SQL, but I'm not as familiar with the Django model structure for more complex queries.

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• Good design of mapping Java Domain objects to Tables (using Hibernate)

  - by M. McKenzie

  Hey guys, I have a question that is more in the realm of design, than implementation. I'm also happy for anyone to point out resources for the answer and I'll gladly, research for myself. Highly simplified Java and SQL: Say I have a business domain POJO called 'Picture' with three attributes. class Picture int idPicture String fileName long size Say I have another business domain POJO called "Item" with 3 attributes Class Item int idItem String itemName ArrayList itemPictures These would be a normal simple relationship. You could say that 'Picture' object, will never exist outside an 'Item' object. Assume a picture belongs only to a specific item, but that an item can have multiple pictures Now - using good database design (3rd Normal Form), we know that we should put items and pictures in their own tables. Here is what I assume would be correct. table Item int idItem (primary key) String itemName table Picture int idPicture (primary key) varchar(45) fileName long size int idItem (foreign key) Here is my question: If you are making Hibernate mapping files for these objects. In the data design, your Picture table needs a column to refer to the Item, so that a foreign key relation can be maintained. However,in your business domain objects - your Picture does not hold a reference/attribute to the idItem - and does not need to know it. A java Picture instance is always instantiated inside an Item instance. If you want to know the Item that the Picture belongs to you are already in the correct scope. Call myItem.getIdItem() and myItem.getItemPictures(),and you have the two pieces of information you need. I know that Hibernate tools have a generator that can auto make your POJO's from looking at your database. My problem stems from the fact that I planned out the data design for this experiment/project first. Then when I went to make the domain java objects, I realized that good design dictated that the objects hold other objects in a nested way. This is obviously different from the way that a database schema is - where all objects(tables) are flat and hold no other complex types within them. What is a good way to reconcile this? Would you: (A) Make the hibernate mapping files so that Picture.hbm.xml has a mapping to the POJO parent's idItem Field (if it's even possible) (B) Add an int attribute in the Picture class to refer to the idItem and set it at instantiation, thus simplifying the hbm.xml mapping file by having all table fields as local attributes in the class (C) Fix the database design because it is wrong, dork. I'd truly appreciate any feedback

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• How to properly reserve identity values for usage in a database?

  - by esac

  We have some code in which we need to maintain our own identity (PK) column in SQL. We have a table in which we bulk insert data, but we add data to related tables before the bulk insert is done, thus we can not use an IDENTITY column and find out the value up front. The current code is selecting the MAX value of the field and incrementing it by 1. Although there is a highly unlikely chance that two instances of our application will be running at the same time, it is still not thread-safe (not to mention that it goes to the database everytime). I am using the ADO.net entity model. How would I go about 'reserving' a range of id's to use, and when that range runs out, grab a new block to use, and guarantee that the same range will not be used.

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• Social Media Java Design Problem

  - by jboyd

  I need to put something together quickly that will take blog posts and place them on social media sites, the requirements are as follows: Blog Entries are independent records that already exist, they have a published date and a modified date, the blog entry application cannot be changed, at least not substantially A new blog entry, or update needs to be sent to social media sites I currently do not need to update or delete social media communications if the blog entry is edited, or deleted, though I may need to later My design problems here are as follows: how do I know the status of each update how can I figure out what blog entry updates and postings have already been sent out? how can I quickly poll the blog entry table for postings that haven't yet been sent out? Avoiding looking at each Entry record from the DB as an object and asking if it's been sent already. That would be too slow. I cannot hook into any Blog Entry update code, my only option would be to create a trigger that an update queues something to be processed I'm looking for general guiding principles here, the biggest problem I'm having is coming up with any reasonable way to figure out if a blog entry should be sent to our social media sites in the first place

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• How would you organize this in asp.net mvc?

  - by chobo

  I have an asp.net mvc 2.0 application that contains Areas/Modules like calendar, admin, etc... There may be cases where more than one area needs to access the same Repo, so I am not sure where to put the Data Access Layers and Repositories. First Option: Should I create Data Access Layer files (Linq to SQL in my case) with their accompanying Repositories for each area, so each area only contains the Tables, and Repositories needed by those areas. The benefit is that everything needed to run that module is one place, so it is more encapsulated (in my mind anyway). The downside is that I may have duplicate queries, because other modules may use the same query. Second Option Or, would it be better to place the DAL and Repositories outside the Area's and treat them as Global? The advantage is I won't have any duplicate queries, but I may be loading a lot of unnecessary queries and DAL tables up for certain modules. It is also more work to reuse or modify these modules for future projects (though the chance of reusing them is slim to none :)) Which option makes more sense? If someone has a better way I'd love to hear it. Thanks!

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• Can I add columns in a QListView in Qt ??

  - by Vic.

  Can I add columns in a QListView object?? here's something I found here: model->setHeaderData( 0, Qt::Horizontal, "numéro" ); model->setHeaderData( 1, Qt::Horizontal, "prénom" ); model->setHeaderData( 2, Qt::Horizontal, "nom" ); //... model->setData( model->index( line, 0 ), contact->num(), Qt::DisplayRole ); model->setData( model->index( line, 1 ), contact->prenom(), Qt::DisplayRole ); model->setData( model->index( line, 2 ), contact->nom(), Qt::DisplayRole ); Since I'm using Qt Creator 2.0.1, I figured my model would be: ui->ObjectName->model() The application builds successfully but I get a: "The program has unexpectedly finished." at runtime. Any Ideas ? Thanks.

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• Rails architecture questions

  - by justinbach

  I'm building a Rails site that, among other things, allows users to build their own recipe repository. Recipes are entered either manually or via a link to another site (think epicurious, cooks.com, etc). I'm writing scripts that will scrape a recipe from these sites given a link from a user, and so far (legal issues notwithstanding) that part isn't giving me any trouble. However, I'm not sure where to put the code that I'm writing for these scraper scripts. My first thought was to put it in the recipes model, but it seems a bit too involved to go there; would a library or a helper be more appropriate? Also, as I mentioned, I'm building several different scrapers for different food websites. It seems to me that the elegant way to do this would be to define an interface (or abstract base class) that determines a set of methods for constructing a recipe object given a link, but I'm not sure what the best approach would be here, either. How might I build out these OO relationships, and where should the code go?

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• General approach for posting business logic status messages to UI?

  - by generalt

  Hello all. I have been struggling with this question for awhile now, and I haven't reached a conclusion. I'm not typically a UI programmer, so forgive the noobishness. I'm writing a typical application with a UI layer (WPF) and a business layer. I want to post status messages to the UI from the business layer (perhaps deep within the business layer), but I don't want the business layer to have any knowledge of the UI. Is there a generally accepted pattern for this? I was thinking to have a message queue of some sort to which the business layer posts status messages, and have the view model of the UI subscribe to that queue and intercept messages from the queue and route them to the UI. Is that a good approach? Is there somewhere else I should start? Thank you.

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• Do you draw the entire object?

  - by vbman11

  Hi I'm working on learning 3d game development and I'm starting with JavaScript and the html5 canvas and I was wondering if I were to have a 3d model do I draw the entire model(front, back, etc) and let the web browser decide what to render or should I try to just draw the sides that are in view of the camera? I ask this because I can see how it would be faster to do the latter of the 2 but that can get very complex and I'll need to do quite a bit more research to find how to do that. Thanks!!

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• Adding a Categorylist to all pages with MVC4

  - by Sidriel

  I'm new with MVC4 and just MVC. I have a homecontroller and a categorycontroller. The categorycontroller sends data from the model to the categoryIndex view. That's works fine. But now I want to add the categorylist on all the available controllers. I already fixed this to add in all classes return view(db.categorys.ToList()); and add categoryIndex to the shared folder. In _layout.cshtml I'm adding a@RenderPage("~/")` and this works. But when I have to pass more than only the (db.categorys.ToList()) in the return it goes wrong. How can I fixed this problem. How do I add the categorylist too every controller and page properly?

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• Rails: How do I run a before_save only if certain conditions are met?

  - by Shpigford

  I have a before_save method that I call that renames an uploaded image. before_save :randomize_file_name def randomize_file_name extension = File.extname(screen_file_name).downcase key = ActiveSupport::SecureRandom.hex(8) self.screen.instance_write(:file_name, "#{key}#{extension}") end That method is part of my Item model. That works great when I create a new item or need to update the image associated with an item...but the problem is that if I need to update an item but NOT the image, the randomize_file_name method still gets run and renames the file in the database (though not the file itself, obviously). So, I'm thinking I need to figure out a way to only run randomize_file_name if a file is included in the form submission...but I'm not sure how to pull that off.

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