C# - Are Repositories Useful Without Domain Driven Design?
Mar 9, 2011
Assuming my application did not warrant a full blown DDD setup, would Repositories still be useful? I like the way they shield from implementation details (such as use of Entity Framework) underneath. However Repositories tend to be tied to Aggregate Roots (the concept is still a holy grail to me) by definition.
I suppose the question could also be put as such: if I have a typical 3-tier application, with a business layer facade consisting of "logical grouping" classes based on functionality (rather than aggregate roots as in DDD) such as TradingManager and ContactsManager, would it make sense to also create "logical grouping" repositories. Or perhaps a Data Access Object, which I believe is like a Repository without the aggregate root requirement. Of course I will still have a Model (EF POCOs) that will be passed up and down between the layers.
Also, is what I just described would be considered as a Transaction Script approach? It's certainly not DDD, and not Active Record. I'm not even sure if Active Record exists with EF4 like it does with Nhibernate.
I am trying to understand how others structure n-layered applications when they do not follow DDD.
I want to know what is the advantages of using aggregates in c# for design patterns.
suppose i have tree tables
Member(M_Id,M_Info)
Bid(B_Id,B_Info,M_Id,Item_Id)
Item(Item_Id,Item_Info)
"One member can place more than one bid on more than one item."
so there is one to many bidirectional association between Bid and Member table.
And one to many association between bid and item table Now According to defination of aggregates in this case Item table is the root of aggregate item and item has aggregation with bid table.
and bid table holds unidirectional reference to member table and hence only bid table has access over member table.
But ultimately this will also map in database same as without using aggregate then what is use of aggregates?
I'm doing some asp.net mvc coding using DDD. I have objects representing the business entities and service repositories that handle fetching and adding them. I'm new to this and as my application grows I begin to see a lot of secondary code that must run as a result of adding, deleting or changing my domain objects/data.
I'd like to make an event driven system where one action triggers other parts of code to run. For instance when I delete a user I want to be able to subscribe a number of other things to this action so they all are run when a delete takes place.
How have you coded your applications to handle these situations? How can I establish a reliable and coherent OO system for my problem? I already know about events and delegates but I'm more interested in coding techniques and nice practices.
the best practice for a designing a simple CRUD application with some screens updating various tables (like admin pages to maintain static data for an application). the simplest way would be to drag a data grid/gridview, bind it to a dataset and use a data adapter for CRUD operations. but if this application needs to be scalable, lets say to add any extra UI/business logic in future, then is there any design pattern that can with this? should I be using an object data source control and bind it to business objects instead? or are there any better ways of doing it? should I build a complete layered application or will that be overengineering for this requirement?
All the users of my system get a common Id (SystemUserId). There are predefined roles/groups in the system. One user can be belong one or more of these groups. We are populating the menu/dashboard at runtime according to logging credentials.All common details (properties) of group are stored in main table (SystemUser) and specialized details are stored in relavant tables.(Teacher/Student). My solution already has classes called, SystemUser, Teacher & Student.
Problem:My system should support new group addition. (eg-: Auditor)This should support new properties to be added to SystemUser/Teacher/Student or any other new group added by the Customer at runtime.
Could someone explain what happens to the Repositories that are created when they are no longer needed? Are they automatically disposed of, or should we dispose of them manually?
Using EF4 as the DAL, to keep the program efficient I have been building repositories for the Model that abstract the data needed for specific views or actions. I have also used the Iinterface for the methods and call them in the Controller to pass them to the View. At some point the program needs to pass a behavior or request that requires the creation of a new repository and the process may repeat itself over and over again. What happens to the repositories that created for previous views, but are no longer needed? Should the dispose be written into each repository, or does garbage collection take care of this? How should this handled?
I've been reading up on MVC 2 and the recommended patterns, so far I've come to the conclusion (amongst much hair pulling and total confusion) that:
Model - Is just a basic data container Repository - Provides data access Service - Provides business logic and acts as an API to the Controller
The Controller talks to the Service, the Service talks to the Repository and Model. So for example, if I wanted to display a blog post page with its comments, I might do:
post = PostService.Get(id); comments = PostService.GetComments(post); Or, would I do:
post = PostService.Get(id); comments = post.Comments;
If so, where is this being set, from the repository? the problem there being its not lazy loaded.. that's not a huge problem but then say I wanted to list 10 posts with the first 2 comments for each, id have to load the posts then loop and load the comments which becomes messy.All of the example's use "InMemory" repository's for testing and say that including db stuff would be out of scope. But this leaves me with many blanks, so for a start can anyone comment on the above?
I would like to start a debate on traditional repositories versus one built on the UnitOfWork pattern. In a traditional repository, we wrap inserts, updates and deletes in a transaction, but selects don't really need them. In addition, nhibernate configuration is typically done once per application due to BuildSessionFactory being rather expensive. We often have several repositories of this type (one per aggregate chain). We also need to have projected, ahead of time, exactly what kinds of queries we'll need in order to build the interfaces and concretes correctly. In a single UnitOfWork repository we have the ability to manage both the current session and transaction, perform several operations, and then commit any changes all at once. In such a repository we may opt to put our configuration in the constructor since (typically speaking) no more than one Action is called per request anyway, initializing it in the application doesn't seem like much of an overall gain in speed. I must admit, I'm very temped to use the UnitOfWork pattern, as the following code looks really nice to me:
Csharp Code: using (IUnitOfWork worker = new UnitOfWork()){// session and transaction are now both set // save changes to three itemsworker.SaveOrUpdate(item1);worker.SaveOrUpdate(item2);worker.SaveOrUpdate(item3); // grab a fourth var item4 = worker.Criteria<Foo>().Add(Expression.Eq("title", title)).UniqueResult<Foo>(); // delete the fourthworker.Delete(item4); // all pending operations are commited or rolled back as a single unit (if one fails, all are rolled back), and then disposed, along with the session}
My proposed UnitOfWork class is rather simple. It implements IDisposable where I use a try-catch-finally in Dispose() to attempt a tx.Commit(), doing a tx.Rollback on failure, and a cleaning everything up in the finally clause. It also exposes common things like SaveOrUpdate, Delete, GetAll, Get, and even a Critera<T>() for custom on-the-spot queries. So what are your thoughts on this? I'd really like to hear about your experience with this pattern.
In a typical business application, a session is started and persisted across several pages. It is commited only when the transaction is complete. A good example of this is a tax preparation application. Once the session is started, it is persisted through session, cookies, or both. Nothing is written to file, or database, until the entire profile is complete and the refund/return is calculated. In such an ennvironment, is makes a great deal of sense to work with the structure imposed by domain driven design, and using a single repository to simple commit the session. However, there are times when this doesn't translate correctly, even when domain driven design is used.
An example of this is my forum project. While the entities themselves are good targets for domain driven design, I am not sure about the repositories. The basic structure is that a Category has many Forums, a Forum has many Threads, and a Thread has many posts. There are other things in there, but that's enough to describe what I want to get across. If a user has navigated to /Thread/Edit/42, and they have rights to edit it, all I am concerned about is fetching that record and displaying it. On postback, all I want is to be able to save it..................
Are there advantages in creating complex types in EF4 Entities and then use the complex properties in the repositories; instead of creating the aggregates in the the repository themselves? I.e. If the customer repository consists of properties of 3 entities: customers, addresses, email would it make sense to create a complex type consisting of the address and email properties, and add them as a complex property of the customer entity then just call the customer entity and the complex property in the repository, rather than just creating the repository class and aggregate the entities in the repository.What are there advantages or disadvantages in doing this in a MVC3 application?
I have a few repositories in my project. All repositories inherit from an abstract interface repository containing the public datacontext variable and a Save function for the entire DB.
In my controllers I want to make changes to the the db and in one of my functions I'm working with two different repositories. Calling the Save function on each of the repositories I'm using can cause a situation in which one of the calls to Save succeeds and and the other fails resulting in a need of rolling back the changes of the Save function that failed.
What is the best way to work against multiple repositories and access to the DB to avoid such a situation?
I'm got 2 model objects. Category and CategoryItem. I try to add a CategoryItem to Category in my Controller but It wont save to database, and I know why because I don't know how to call the submitChanges on the add while using repository, I dont got the DBContext right there is you know what I mean?.. here I will show you with code.
As a new developer I'm getting thoroughly confused by naming and structural conventions for developing c# code using best practice.I appreciate it's perhaps applicable to each domain I am developing for but I've seen the code of many different open source projects and there seems to be a common theme. The successful projects have well thought out structure for maintenance and extensibility.The terms context, service, repository and controllers are used often and I wondered if these are open to interpretation or is there a consensus or convention on what, where or how these get used.
In an e-commerce platform I've seen there are order services, order contexts, customer repositories and product controllers for example. What should they do based on these names? Does a controller do something different to a service? When should you use a context? Is there a convention for namespaces? It's mind boggling when you try and push from a spoon fed newbie developer and try to move on.What software/tools should I really be looking at to develop quality code? Unit Testing, Continous Integration, Resharper, Mocking tools, DOI Containers, nHibernate.
I'm not really aware of blogs/books that will help me push on from being a proficient web developer into someone who can develop extensible, quality and testable code. There are big gaps in authors assumptions. You are either a newbie or a software architect. I want to push from being a junior developer with a long term aim of being a software architect. I realise it's all about patterns and practices but where are the training materials? I work on my own so don't have the opportunity of learning from others.
My feeling says it's not posible but anyway I am curious if there is at least a workaround for accomplish this.Basically I am working at my client site and my machine is not connected to the domain.What I want to do is running a web application locally under a domain account, and using the webdev server.The webapp uses the default authentication, windows authentication that is.I tried using impersonation with domainuser & password but I got the following error Could not create Windows user token from the credentials specified in the config file. Error from the operating system 'Logon failure: unknown user name or bad password.I have to mention that the username and the password are correct.
We have a ASP.NET site that partially depends on forms authentication for login credentials, however the implementation of IPrincipal is completely custom.
But, when running the site on a particular server (which is somewhat semi-hardened when it comes to security), the app crashes when invoking IPrincipal.IsInRole() with the following messsage:
System.SystemException: The trust relationship between the primary domain and the trusted domain failed.
This indicates a communication error between the web-server and the DC, however since our application doesn't at all utilizes Windows authentication, I don't see why it needs to communicate with the DC.
This is my implementation:
[code]...
EDIT:
I was finally enable to reproduce this error on my dev-machine (i revoked my machine from the DC yesterday, but didn't reproduce it until today)
HttpContext.User is actually a WindowsPrincipal by default it seems, and the error in my code was that I only replace it with CustomPrincipal upon login. Hence, unathenticated users still get the WindowsPrincipal which then fails horribly if you have trust issues on your AD.
I tried changing the default principal by invoking this on appstart
Im returning the username from sharepoint site as a string. This is done successfully with the below code but I also get the domain with it. How can I only return the username and not the domain either through sharepoint or programmatically removing it? domain/username
My feeling says it's not posible but anyway I am curious if there is at least a workaround for accomplish this.Basically I am working at my client site and my machine is not connected to the domain.What I want to do is running a web application locally under a domain account, and using the webdev server.The webapp uses the default authentication, windows authentication that is.I tried using impersonation with domainuser & password but I got the following error Could not create Windows user token from the credentials specified in the config file. Error from the operating system 'Logon failure: unknown user name or bad password.I have to mention that the username and the password are correct.
I have two domain servers X and Y.My Asp.net Web application is hosted on Domain X.But my scope is required to authorize the user of Domain Y on the Web application hosted on Domain X server.I am using Windows Authetication mode in application
I have a main domain "mydomain.com" and then a sub domain "forums.mydomain.com". If a user visits "forums.mydomain.com" without being logged in, they are redirected to "mydomain.com/login.aspx".
The two scenarios are:
If they are redirected to the login page with "mydomain.com/login.aspx?ReturnUrl=http://forums.mydomain.com", then they are succesfully logged into the forums but NOT the main site.
If they are simply redirected to the login page with "mydomain.com/login.aspx" with no returnUrl, they are correctly logged into both the main site and the forums.
can't connect to sql 2005 express sp1 and vs is also sp1. 2) Which my guess is because of the database connection not being able... design view is not able to pull in the application for design, it's as if there is no theme and css just white background and black print.
I have a domain: http://www.mydomain.com. This domain is redirected to http://mydomain.anotherDomain.com.
I user forms authorization, so when the user navigates to Default.aspx he is redirected to Login.aspx. Pretty standard stuff.
On FireFox the user can log in on both on http://www.mydomain.com and http://mydomain.anotherDomain.com.
But with Explorer http://www.mydomain.com doesn't work. I only get the Login.aspx page.
Can it have anything to do with that on http://www.mydomain.com I can't see the filename ('Default.aspx', 'Login.aspx')? How can I enable so the filename is included in the redirected domain?
I have an intranet web application. There are 2 user groups, group A belongs to the domain and group B does not. If I set the IIS to enable anonymous access, Request.ServerVariables("LOGON_USER") always return nothing. If I disable anonymous access and set Integrated Windows authenication, a Windows login prompt will come up if group B's users want to access the website.
How can I setup IIS so that when domain user access the website, it will direct to the main page with Session("user_name") = Request.ServerVariables("LOGON_USER"). If a user is not a domain user, the website will direct him/her to a login.aspx instead of having the Windows authenication prompt, then set Session("user_name") = txtUserName.Text, and finally redirect to the website main page ?
