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  • Abstract Factory Method and Polymorphism

    - by Scotty C.
    Being a PHP programmer for the last couple of years, I'm just starting to get into advanced programming styles and using polymorphic patterns. I was watching a video on polymorphism the other day, and the guy giving the lecture said that if at all possible, you should get rid of if statements in your code, and that a switch is almost always a sign that polymorphism is needed. At this point I was quite inspired and immediately went off to try out these new concepts, so I decided to make a small caching module using a factory method. Of course the very first thing I have to do is create a switch to decide what file encoding to choose. DANG! class Main { public static function methodA($parameter='') { switch ($parameter) { case 'a': $object = new \name\space\object1(); break; case 'b': $object = new \name\space\object2(); break; case 'c': $object = new \name\space\object3(); break; default: $object = new \name\space\object1(); } return (sekretInterface $object); } } At this point I'm not really sure what to do. As far as I can tell, I either have to use a different pattern and have separate methods for each object instance, or accept that a switch is necessary to "switch" between them. What do you guys think?

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  • Trying to Integrate Five9 and Apptivio [on hold]

    - by David Mitchell
    Five9 is a calling system application and Apptivio will be used to store client information for purchased products. Specifically what I need is an example code that will allow me to access Five9's CRM system using the access key and transfer a persons first and last name, for example, to Apptivio. The issue is I have never dealt with this type of system and I cannot find any information for it other than the Web2Campaign that was sent to me by Five9. Lets say this is the code from Five9 F9key=first_name&F9key=last_name&first_name=jon&last_name=smith Once this information is placed into Five9 I must update Apptivio with this information. I am lost as to how to send this information to Apptivio.

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  • Service Layer - how broad should it be, and should it also be on the local application?

    - by BornToCode
    Background: I need to build a desktop application with some operations (CRUD and more) (=winforms), I need to make another application which will re-use some of the functions of the main application (=webforms). I understood that using service layer is the best approach here. If I understood correctly the service should be calling the function on the BL layer (correct me if I'm wrong) The dilemma: In my main winform UI - should I call the functions from the BL, or from the service? (please explain why) Should I create a service for every single function on the BL even if I need some of the functions only in one UI? for example - should I create services for all the CRUD operations, even though I need to re-use only update operation in the webform? YOUR HELP IS MUCH APPRECIATED

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  • Creating a shared library that might be used with desktop applications and web projects

    - by dreza
    I have been involved in a number of MVC.NET and c# desktop projects in our company over the last year or so while also managing to kept my nose poked into other projects (in a read-only learning capacity of course). From this I've noticed that across the various projects and teams there is a-lot of functionality that has been well designed against good interfaces and abstractions. Because we tend to like our own work at times, I noticed a couple of projects had the exact same class, method copied into it as it had obviously worked on one and so was easily moved to a new project (probably by the same developer who originally wrote it) I mentioned this fact in one of our programmer meetings we have occasionally and suggested we pull some of this functionality into a core company library that we can build up over time and use across multiple projects. Everyone agreed and I started looking into this possibility. However, I've come across a stumbling block pretty early on. Our team primarily focuses on MVC at the moment and we have projects mainly in 2.0 but are starting to branch to 3.0. We also have a number of desktop applications that might benefit from some shared classes and basic helper methods. Initially when creating this DLL I included some shared classes that could be used across any project type (Web, Client etc) but then I started looking at adding some shared modules that would be useful in our MVC applications only. However this meant I had to include a reference to some Microsoft Web DLL's in order to leverage some of the classes I was creating (at this stage MVC 2.0). Now my issue is that we have a shared DLL that has references to web specific libraries that could also possibly be used in a client application. Not only that, our DLL referenced initially MVC 2.0 and we will eventually move onto MVC 3.0 for all projects. But alot of the classes in this library I expect to still be relevant to MVC 3 etc Our code within this DLL is separated into it's own namespaces such as: CompanyDLL.Primitives CompanyDLL.Web.Mvc CompanyDLL.Helpers etc etc So, my questions are: Is it OK to do a shared library like this, or if we have web specific features in it should we create a separate web DLL only targeted at a specific framework or MVC version? If it's OK, what kind of issues might we face when using the library that references MVC 2 in a MVC 3 project for example. I would be thinking that we might run into some sort of compatibility issue, or even issues where the developers using the library doesn't realize they need MVC 2.0 libraries. They might only want to use some of the generic classes etc The concept seemed like a good idea at the time, but I'm starting to think maybe it's not really a practical solution. But the number of times I've seen copied classes and methods across projects because they are proven tested code is a bit unnerving to be perfectly honest!

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  • Code Line Delimiter [closed]

    - by John Isaiah Carmona
    Possible Duplicate: Why are statements in many programming languages terminated by semicolons? I just found out that R Programming Language, which is somewhat belong to the C family (I'm not sure about this but it uses {} instead of begin end), uses a new line as a delimiter for a new line of code instead of the semi-colon ;. Why is some programming language designed to use a new line instead of a symbol like semi-colon which I think will make the code more readable? Phyton total = item_one + \ item_two + \ item_three C total = item_one + item_two + item_three;

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  • How to handle status columns in designing tables

    - by altsyset
    How to handle multiple statuses for a table entry, for example an item table may have an active, inactive, fast moving, and/or batch statuses. And I wanted to handle them in single column with VARCHAR type. Also I might set each of those attributes as a boolean with different columns. But I am not sure what consequences this might lead to. So if you have experienced such situations which one would be the best way to handle it?

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  • Why don't languages include implication as a logical operator?

    - by Maciej Piechotka
    It might be a strange question, but why there is no implication as a logical operator in many languages (Java, C, C++, Python Haskell - although as last one have user defined operators its trivial to add it)? I find logical implication much clearer to write (particularly in asserts or assert-like expressions) then negation with or: encrypt(buf, key, mode, iv = null) { assert (mode != ECB --> iv != null); assert (mode == ECB || iv != null); assert (implies(mode != ECB, iv != null)); // User-defined function }

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  • How stable are Single Page Application (SPA) build with Microsoft .Net for enterprise application [on hold]

    - by Husrat Mehmood
    Imagine a situation where you have your data loading to your application via REST Api,you are building a responsive application(ajax request) for an Enterprise. What potential problems might I run into for a single page application(SPA) using Microsoft Asp.Net Web application build using MVC template? Are there advantages to just designing a multi-page application using asp.net mvc 5 remember I am using SPA for an Enterprise Application where there are role based views for the users.?

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  • Concurrency pattern of logger in multithreaded application

    - by Dipan Mehta
    The context: We are working on a multi-threaded (Linux-C) application that follows a pipeline model. Each module has a private thread and encapsulated objects which do processing of data; and each stage has a standard form of exchanging data with next unit. The application is free from memory leak and is threadsafe using locks at the point where they exchange data. Total number of threads is about 15- and each thread can have from 1 to 4 objects. Making about 25 - 30 odd objects which all have some critical logging to do. Most discussion I have seen about different levels as in Log4J and it's other translations. The real big questions is about how the overall logging should really happen? One approach is all local logging does fprintf to stderr. The stderr is redirected to some file. This approach is very bad when logs become too big. If all object instantiate their individual loggers - (about 30-40 of them) there will be too many files. And unlike above, one won't have the idea of true order of events. Timestamping is one possibility - but it is still a mess to collate. If there is a single global logger (singleton) pattern - it indirectly blocks so many threads while one is busy putting up logs. This is unacceptable when processing of the threads are heavy. So what should be the ideal way to structure the logging objects? What are some of the best practices in actual large scale applications? I would also love to learn from some of the real designs of large scale applications to get inspirations from!

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  • Best Option for Creating A Small Church Website

    - by Jim
    I've been asked to create a website for a small church. Their prior site was hosted on geocities which is no longer. They are not looking for anything robust, just an informational site with a calendar and maybe a contact form. The church would also like to be able to administer the site with little technical know-how. Cost is also an issue. Given these requirements, something like sites.google.com seems like a good option. However, my main concern is that Sites will suffer the same fate as geocities. It is definitely not a flagship Google product. Are there other good alternatives that fit the requirements?

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  • Strategy to use two different measurement systems in software

    - by Dennis
    I have an application that needs to accept and output values in both US Custom Units and Metric system. Right now the conversion and input and output is a mess. You can only enter in US system, but you can choose the output to be US or Metric, and the code to do the conversions is everywhere. So I want to organize this and put together some simple rules. So I came up with this: Rules user can enter values in either US or Metric, and User Interface will take care of marking this properly All units internally will be stored as US, since the majority of the system already has most of the data stored like that and depends on this. It shouldn't matter I suppose as long as you don't mix unit. All output will be in US or Metric, depending on user selection/choice/preference. In theory this sounds great and seems like a solution. However, one little problem I came across is this: There is some data stored in code or in the database that already returns data like this: 4 x 13/16" screws, which means "four times screws". I need the to be in either US or Metric. Where exactly do I put the conversion code for doing the conversion for this unit? The above already mixing presentation and data, but the data for the field I need to populate is that whole string. I can certainly split it up into the number 4, the 13/16", and the " x " and the " screws", but the question remains... where do I put the conversion code? Different Locations for Conversion Routines 1) Right now the string is in a class where it's produced. I can put conversion code right into that class and it may be a good solution. Except then, I want to be consistent so I will be putting conversion procedures everywhere in the code at-data-source, or right after reading it from the database. The problem though is I think that my code will have to deal with two systems, all throughout the codebase after this, should I do this. 2) According to the rules, my idea was to put it in the view script, aka last change to modify it before it is shown to the user. And it may be the right thing to do, but then it strikes me it may not always be the best solution. (First, it complicates the view script a tad, second, I need to do more work on the data side to split things up more, or do extra parsing, such as in my case above). 3) Another solution is to do this somewhere in the data prep step before the view, aka somewhere in the middle, before the view, but after the data-source. This strikes me as messy and that could be the reason why my codebase is in such a mess right now. It seems that there is no best solution. What do I do?

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  • Dependency Injection Confusion

    - by James
    I think I have a decent grasp of what Dependency Inversion principle (DIP) is, my confusion is more around dependency injection. My understanding is the whole point of DI is to decouple parts of an application, to allow changes in one part without effecting another, assuming the interface does not change. For examples sake, we have this public class MyClass(IMyInterface interface) { public MyClass { interface.DoSomething(); } } public interface IMyInterface { void DoSomething(); } How is this var iocContainer = new UnityContainer(); iocContainer.Resolve<MyClass>(); better practice than doing this //if multiple implementations are possible, could use a factory here. IMyInterface interface = new InterfaceImplementation(); var myClass = new MyClass(interface); It may be I am missing a very important point, but I am failing to see what is gained. I am aware that using an IOC container I can easily handle an objects life cycle, which is a +1 but I don't think that is core to what IOC is about.

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  • Should I close database connections after use in PHP?

    - by Sprottenwels
    I wonder if I should close any unnecessary database connection inside of my PHP scripts. I am aware of the fact that database connections are closed implicitly when the block stops executing and 'manually' closing the connections could kinda bloat the codebase with unnecessary code. But shouldn't I do so in order to make by code as readable and as easy understandable as possible, while also preventing several possible issues during run time? Also, if I would do, would it be enough to unset() my database object?

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  • Query something and return the reason if nothing has been found

    - by Daniel Hilgarth
    Assume I have a Query - as in CQS that is supposed to return a single value. Let's assume that the case that no value is found is not exceptional, so no exception will be thrown in this case. Instead, null is returned. However, if no value has been found, I need to act according to the reason why no value has been found. Assuming that the Query knows the reason, how would I communicate it to the caller of the Query? A simple solution would be not return the value directly but a container object that contains the value and the reason: public class QueryResult { public TValue Value { get; private set; } public TReason ReasonForNoValue { get; private set; } } But that feels clumsy, because if a value is found, ReasonForNoValue makes no sense and if no value has been found, Value makes no sense. What other options do I have to communicate the reason? What do you think of one event per reason? For reference: This is going to be implemented in C#.

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  • ASP.NET MVC 3 (C#) Software Architecture

    - by ryanzec
    I am starting on a relatively large and ambitious ASP.NET MVC 3 project and just thinking about the best way to organize my code. The project is basically going to be a general management system that will be capable of supporting any type management system whether it be a blogging system, cms, reservation system, wikis, forums, project management system, etc…, each of them being just a separate 'module'. You can read more about it on my blog posted here : http://www.ryanzec.com/index.php/blog/details/8 (forgive me, the style of the site kinda sucks). For those who don't want to read the long blog post the basic idea is that the core system itself is nothing more than a users system with an admin interface to manage the users system. Then you just add on module as you need them and the module I will be creating is a simple blog post to test it out before I move on to the big module which is a project management system. Now I am just trying to think of the best way to structure this so that it is easy for users to add in there own modules but easy for me to update to core system without worrying about the user modifying the core code. I think the ideal way would be to have a number of core projects that user is specifically told not to modify otherwise the system may become unstable and future updates would not work. When the user wants to add in there own modules, they would just add in a new project (or multiple projects). The thing is I am not sure that it is even possible to use multiple projects all with their own controllers, razor view template, css, javascript, etc... in one web application. Ideally each module would have some of it own razor view templates, css, javascript, image files and also need access to some of the core razor view templates, css, javascript, image files which would is in a separate project. It is possible to have 1 web application run off of controllers, razor view templates, css, javascript, image files that are store in multiple projects? Is there a better was to structure this to allow the user to easily add in module with having to modify the core code?

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  • How to name setter that does data conversion?

    - by IAdapter
    I'm struggling with how to name this method, I don't like the "set" prefix, because I feel it should be reserved for normal "dumb" setters and some tools might not like it (i did not check it in checkstyle, pmd, etc., but I got a feeling they won't like it.) for example (in java, but I feel its language agnostic) public void setActionListenerClicked(boolean actionListenerClicked) { this.actionListenerClicked = actionListenerClicked ? "1" : "0"; } The only purpose of this method is ONLY to set, this method is needed and cannot be joined with any other (because of framework used). P.S. I DO know that question is similar to How to name multi-setter?, but I feel its not the same question.

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  • Layout Columns - Equal Height

    - by Kyle
    I remember first starting out using tables for layouts and learned that I should not be doing that. I am working on a new site and can not seem to do equal height columns without using tables. Here is an example of the attempt with div tags. <div class="row"> <div class="column">column1</div> <div class="column">column2</div> <div class="column">column3</div> <div style="clear:both"></div> </div> Now what I tried with that was doing making columns float left and setting their widths to 33% which works fine, I use the clear:both div so that the row would be the size of the biggest column, but the columns will be different sizes based on how much content they have. I have found many fixes which mostly involve css hacks and just making it look like its right but that's not what I want. I thought of just doing it in javascript but then it would look different for those who choose to disable their javascript. The only true way of doing it that I can think of is using tables since the cells all have equal heights in the same row. But I know its bad to use tables. After searching forever I than came across this: http://intangiblestyle.com/lab/equal-height-columns-with-css/ What it seems to do is exactly the same as tables since its just setting its display exactly like tables. Would using that be just as bad as using tables? I honestly can't find anything else that I could do. edit @Su' I have looked into "faux columns" and do not think that is what I want. I think I would be able to implement better designs for my site using the display:table method. I posted this question because I just wasn't sure if I should since I have always heard its bad using tables in website layouts.

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  • I need an approach to the problem of preventing inserting duplicate records into the database

    - by Maurice
    Apologies is this question is asked on the incorrect "stack" A webservice that I call returns a list of data. The data from the webservice is updated periodically, so a call to the webservice done in one hour could return the same data as a call done in an hour. Also, the data is returned based on a start and end date. We have multiple users that can run the webservice search, and duplicate data is most likely to be returned (especially for historical data). However I don't want to insert this duplicate data in the database. I've created a db table in which the data is stored (most important columns are) Id int autoincrement PK Date date not null --The date to which the data set belongs. LastUpdate date not null --The date the data set was last updated. UserName varchar(50) --The name of the user doing the search. I use sql server 2008 express with c# 4.0 and visual studio 2010. Entity Framework is used as the ORM. If stored procedures could be avoided in the proposed solution, then that will be a plus. Another way of looking interpreting what I'm asking a solution for is as follows: I have a million unique records in my table. A user does a new search. The search results from the user contains around 300k of the data that is already in the db. An efficient solution to finding an inserting only the unique records is needed.

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  • I've been told that Exceptions should only be used in exceptional cases. How do I know if my case is exceptional?

    - by tieTYT
    My specific case here is that the user can pass in a string into the application, the application parses it and assigns it to structured objects. Sometimes the user may type in something invalid. For example, their input may describe a person but they may say their age is "apple". Correct behavior in that case is roll back the transaction and to tell the user an error occurred and they'll have to try again. There may be a requirement to report on every error we can find in the input, not just the first. In this case, I argued we should throw an exception. He disagreed, saying, "Exceptions should be exceptional: It's expected that the user may input invalid data, so this isn't an exceptional case" I didn't really know how to argue that point, because by definition of the word, he seems to be right. But, it's my understanding that this is why Exceptions were invented in the first place. It used to be you had to inspect the result to see if an error occurred. If you failed to check, bad things could happen without you noticing. Without exceptions every level of the stack needs to check the result of the methods they call and if a programmer forgets to check in one of these levels, the code could accidentally proceed and save invalid data (for example). Seems more error prone that way. Anyway, feel free to correct anything I've said here. My main question is if someone says Exceptions should be exceptional, how do I know if my case is exceptional?

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  • How to have operations with character/items on binary with concrete operations on C++?

    - by Piperoman
    I have the next problem. A item can have a lot of states: NORMAL = 0000000 DRY = 0000001 HOT = 0000010 BURNING = 0000100 WET = 0001000 COLD = 0010000 FROZEN = 0100000 POISONED= 1000000 A item can have some states at same time but not all of them Is impossible to be dry and wet at same time. If you COLD a WET item, it turns into FROZEN. If you HOT a WET item, it turns into NORMAL A item can be BURNING and POISON Etc. I have tried to set binary flags to states, and use AND to combine different states, checking before if it is possible or not to do it, or change to another status. Does there exist a concrete approach to solve this problem efficiently without having an interminable switch that checks every state with every new state? It is relatively easy to check 2 different states, but if there exists a third state it is not trivial to do.

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  • How to had operation with character/items on binary with concrete operations on C++?

    - by Piperoman
    I have the next problem. A item can had a lot of states: NORMAL = 0000000 DRY = 0000001 HOT = 0000010 BURNING = 0000100 WET = 0001000 COLD = 0010000 FROZEN = 0100000 POISONED= 1000000 A item can had some states at same time but not all of them Is impossible to be dry and wet at same time. If you COLD a WET item, it turns into FROZEN. If you HOT a WET item, it turns into NORMAL A item can be BURNING and POISON Etc. I have try to set binary flags to states, and use AND to set operation to combine different states, checking before if is possible or not to do it, or change to another status. Exist a concrete patron to solve this problem efficiently without had a interminable switch that check every states with everynew states? It is relative easy to check 2 different states, but if exist a third state it is not trivial to do.

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  • Whats a good structure to save and retrieve locations of images?

    - by Goot
    I got a java-ee application, where I collect informations about movies. Im my backend I provide data like the name, description, genre and a random uuid. I also got lots of related files, which are stored on a file server. Including some screenshots, the dvd or bluRay cover and video trailers. My current approach is: When saving the files to the fileserver, I retrieve the movies random uuid (which is the primary key btw.). I then rename the files screenshot_[UUID]_1, screenshot_[UUID]_2 ... etc. Now, there are lots of other ways to handle this, like saving all filenames in a database or creating a dir structure on the fileserver for every uuid and, e.g., return all images in the "[uuid]/screenshots" folder via REST. I expect about 30k requests a day, so the service has to be pretty performant. Whats the best way to solve this?

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  • Managing accounts on a private website for a real-life community

    - by Smudge
    I'm looking at setting-up a walled-in website for a real-life community of people, and I was wondering if anyone has any experience with managing member accounts for this kind of thing. Some conditions that must be met: This community has a set list of real-life members, each of whom would be eligible for one account on the website. We don't expect or require that they all sign-up. It is purely opt-in, but we anticipate that many of them would be interested in the services we are setting up. Some of the community members emails are known, but some of them have fallen off the grid over the years, so ideally there would be a way for them to get back in touch with us through the public-facing side of the site. (And we'd want to manually verify the identity of anyone who does so). Their names are known, and for similar projects in the past we have assigned usernames derived from their real-life names. This time, however, we are open to other approaches, such as letting them specify their own username or getting rid of usernames entirely. The specific web technology we will use (e.g. Drupal, Joomla, etc) is not really our concern right now -- I am more interested in how this can be approached in the abstract. Our database already includes the full member roster, so we can email many of them generated links to a page where they can create an account. (And internally we can require that these accounts be paired with a known member). Should we have them specify their own usernames, or are we fine letting them use their registered email address to log-in? Are there any paradigms for walled-in community portals that help address security issues if, for example, one of their email accounts is compromised? We don't anticipate attempted break-ins being much of a threat, because nothing about this community is high-profile, but we do want to address security concerns. In addition, we want to make the sign-up process as painless for the members as possible, especially given the fact that we can't just make sign-ups open to anyone. I'm interested to hear your thoughts and suggestions! Thanks!

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  • Versioning APIs

    - by Sharon
    Suppose that you have a large project supported by an API base. The project also ships a public API that end(ish) users can use. Sometimes you need to make changes to the API base that supports your project. For example, you need to add a feature that needs an API change, a new method, or requires altering of one of the objects, or the format of one of those objects, passed to or from the API. Assuming that you are also using these objects in your public API, the public objects will also change any time you do this, which is undesirable as your clients may rely on the API objects remaining identical for their parsing code to work. (cough C++ WSDL clients...) So one potential solution is to version the API. But when we say "version" the API, it sounds like this also must mean to version the API objects as well as well as providing duplicate method calls for each changed method signature. So I would then have a plain old clr object for each version of my api, which again seems undesirable. And even if I do this, I surely won't be building each object from scratch as that would end up with vast amounts of duplicated code. Rather, the API is likely to extend the private objects we are using for our base API, but then we run into the same problem because added properties would also be available in the public API when they are not supposed to be. So what is some sanity that is usually applied to this situation? I know many public services such as Git for Windows maintains a versioned API, but I'm having trouble imagining an architecture that supports this without vast amounts of duplicate code covering the various versioned methods and input/output objects. I'm aware that processes such as semantic versioning attempt to put some sanity on when public API breaks should occur. The problem is more that it seems like many or most changes require breaking the public API if the objects aren't more separated, but I don't see a good way to do that without duplicating code.

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  • MVVM- Expose Model object in ViewModel

    - by Angel
    I have a wpf MVVM application , I exposed my model object into my viewModel by creating an instance of Model class (which cause dependency) into ViewModel , and instead of creating seperate VM properties , I wrap the Model properties inside my ViewModel Property. My model is just an entity framework generated proxy classes. Here is my Model class : public partial class TblProduct { public TblProduct() { this.TblPurchaseDetails = new HashSet<TblPurchaseDetail>(); this.TblPurchaseOrderDetails = new HashSet<TblPurchaseOrderDetail>(); this.TblSalesInvoiceDetails = new HashSet<TblSalesInvoiceDetail>(); this.TblSalesOrderDetails = new HashSet<TblSalesOrderDetail>(); } public int ProductId { get; set; } public string ProductCode { get; set; } public string ProductName { get; set; } public int CategoryId { get; set; } public string Color { get; set; } public Nullable<decimal> PurchaseRate { get; set; } public Nullable<decimal> SalesRate { get; set; } public string ImagePath { get; set; } public bool IsActive { get; set; } public virtual TblCompany TblCompany { get; set; } public virtual TblProductCategory TblProductCategory { get; set; } public virtual TblUser TblUser { get; set; } public virtual ICollection<TblPurchaseDetail> TblPurchaseDetails { get; set; } public virtual ICollection<TblPurchaseOrderDetail> TblPurchaseOrderDetails { get; set; } public virtual ICollection<TblSalesInvoiceDetail> TblSalesInvoiceDetails { get; set; } public virtual ICollection<TblSalesOrderDetail> TblSalesOrderDetails { get; set; } } Here is my ViewModel , public class ProductViewModel : WorkspaceViewModel { #region Constructor public ProductViewModel() { StartApp(); } #endregion //Constructor #region Properties private IProductDataService _dataService; public IProductDataService DataService { get { if (_dataService == null) { if (IsInDesignMode) { _dataService = new ProductDataServiceMock(); } else { _dataService = new ProductDataService(); } } return _dataService; } } //Get and set Model object private TblProduct _product; public TblProduct Product { get { return _product ?? (_product = new TblProduct()); } set { _product = value; } } #region Public Properties public int ProductId { get { return Product.ProductId; } set { if (Product.ProductId == value) { return; } Product.ProductId = value; RaisePropertyChanged("ProductId"); } } public string ProductName { get { return Product.ProductName; } set { if (Product.ProductName == value) { return; } Product.ProductName = value; RaisePropertyChanged(() => ProductName); } } private ObservableCollection<TblProduct> _productRecords; public ObservableCollection<TblProduct> ProductRecords { get { return _productRecords; } set { _productRecords = value; RaisePropertyChanged("ProductRecords"); } } //Selected Product private TblProduct _selectedProduct; public TblProduct SelectedProduct { get { return _selectedProduct; } set { _selectedProduct = value; if (_selectedProduct != null) { this.ProductId = _selectedProduct.ProductId; this.ProductCode = _selectedProduct.ProductCode; } RaisePropertyChanged("SelectedProduct"); } } #endregion //Public Properties #endregion // Properties #region Commands private ICommand _newCommand; public ICommand NewCommand { get { if (_newCommand == null) { _newCommand = new RelayCommand(() => ResetAll()); } return _newCommand; } } private ICommand _saveCommand; public ICommand SaveCommand { get { if (_saveCommand == null) { _saveCommand = new RelayCommand(() => Save()); } return _saveCommand; } } private ICommand _deleteCommand; public ICommand DeleteCommand { get { if (_deleteCommand == null) { _deleteCommand = new RelayCommand(() => Delete()); } return _deleteCommand; } } #endregion //Commands #region Methods private void StartApp() { LoadProductCollection(); } private void LoadProductCollection() { var q = DataService.GetAllProducts(); this.ProductRecords = new ObservableCollection<TblProduct>(q); } private void Save() { if (SelectedOperateMode == OperateModeEnum.OperateMode.New) { //Pass the Model object into Dataservice for save DataService.SaveProduct(this.Product); } else if (SelectedOperateMode == OperateModeEnum.OperateMode.Edit) { //Pass the Model object into Dataservice for Update DataService.UpdateProduct(this.Product); } ResetAll(); LoadProductCollection(); } #endregion //Methods } Here is my Service class: class ProductDataService:IProductDataService { /// <summary> /// Context object of Entity Framework model /// </summary> private MaizeEntities Context { get; set; } public ProductDataService() { Context = new MaizeEntities(); } public IEnumerable<TblProduct> GetAllProducts() { using(var context=new R_MaizeEntities()) { var q = from p in context.TblProducts where p.IsDel == false select p; return new ObservableCollection<TblProduct>(q); } } public void SaveProduct(TblProduct _product) { using(var context=new R_MaizeEntities()) { _product.LastModUserId = GlobalObjects.LoggedUserID; _product.LastModDttm = DateTime.Now; _product.CompanyId = GlobalObjects.CompanyID; context.TblProducts.Add(_product); context.SaveChanges(); } } public void UpdateProduct(TblProduct _product) { using (var context = new R_MaizeEntities()) { context.TblProducts.Attach(_product); context.Entry(_product).State = EntityState.Modified; _product.LastModUserId = GlobalObjects.LoggedUserID; _product.LastModDttm = DateTime.Now; _product.CompanyId = GlobalObjects.CompanyID; context.SaveChanges(); } } public void DeleteProduct(int _productId) { using (var context = new R_MaizeEntities()) { var product = (from c in context.TblProducts where c.ProductId == _productId select c).First(); product.LastModUserId = GlobalObjects.LoggedUserID; product.LastModDttm = DateTime.Now; product.IsDel = true; context.SaveChanges(); } } } I exposed my model object in my viewModel by creating an instance of it using new keyword, also I instantiated my DataService class in VM, I know this will cause a strong dependency. So , 1- Whats the best way to expose Model object in ViewModel ? 2- Whats the best way to use DataService in VM ?

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