Context: The structure of the code is that a WCF service (server-size) talks to a domain model, which talks to the data layer. I have a need that work assignments (for real people) need to be created when certain values change in an entity.
Currently, I have placed that logic in the WCF service, but it makes me feel kind of icky. I then proceeded to move the logic into a Repository, but that made me feel icky too. Now I don't have anywhere to put it.
What I do not have is a Domain Service to itermediate between the WCF service and the domain repository! Is this something I should create and place this logic there? Do you have any other ideas?
Your domain model is what should understand that there are special actions that need to be taken when these property values change. The details of the actions should be separated out - possibly into workflows using Windows Workflow Foundation. That allows for easy customization, asynchronous processing, and even human workflows (a person needing to approve something before the workflow is complete).
Of course, if you feel the need, it's easy to create a workflow service using WCF. There are even templates for it, and that's the direction in which the forthcoming Dublin fnctionality is aimed.
Related
I am new to DDD and this is the first project for me to apply DDD and clean architecture,
I have implemented some code in the domain layer and in the application layer but currently, I have a confusion
now I have an API which is placeOrder
and to place the order I need to grab data from other microservices, so I need to grab production details from product service and address details from user profile microservice
my question is, should these data are pulled into the domain layer or in the application layer?
is it possible to implement a domain service that has some interfaces that represent the product service API and use that interface in the domain layer and it will be injected later using dependency injection or should I implement the calling of this remote API in the application layer?
please note that, calling product service and address service are prior steps to create the order
Design is what we do when we want to get more of what we want than we would get by just doing it. -- Ruth Malan
should these data are pulled into the domain layer or in the application layer?
Eric Evans, introducing chapter four of the original DDD book, wrote
We need to decouple the domain objects from other functions of the system, so we can avoid confusing the domain concepts with other concepts related only to software technology or losing sight of the domain altogether in the mass of the system.
The domain model doesn't particularly care whether the information it is processing comes from a remote microservice or a cache. It certainly isn't interested in things like network failures and re-try strategies.
Thus, in an idealized system, the domain model would only be concerned with the manipulation of business information, and all of the "plumbing" would be somewhere else.
Sometimes, we run into business processes where (a) some information is relatively "expensive" to acquire and (b) you don't know whether or not you need that information until you start processing the work.
In that situation, you need to start making some choices: does the domain code return a signal to the application code to announce that it needs more information, or do we instead pass to the domain code the capability to get the information for itself?
Offering the retrieve capability to the domain code, behind the facade of a "domain service" is a common implementation of the latter approach. It works fine when your failure modes are trivial (queries never fail; or abort-on-failure is an acceptable policy).
You are certainly going to be passing an implementation of that domain service to the domain model; whether you pass it as a method argument or as a constructor argument really depends on the overall design. I wouldn't normally expect to see a domain entity with a domain service property, but a "use case" that manipulates entities might have one.
That all said, do keep in mind that nobody is handing out prizes for separating domain and application code in your designs. "Doing it according to the book" is only a win if that helps us to be more cost effective in delivering solutions with business value.
I'm working on my first "real" DDD application.
Currently my client does not have access to my domain layer and requests changes to the domain by issuing commands.
I then have a separate (flattened) read model for displaying information (like simple CQRS).
I'm now working on configuration, or specifically, settings that the user configures. Using a blog application as an example, the settings might be the blog title or logo.
I've developed a generic configuration builder that builds a strongly typed configuration object (e.g. BlogSettings) based on a simple key value pair collection. I'm stuck on whether these configuration objects are part of my domain. I need access to them from the client and server.
I'm considering creating a "Shared" library that contains these configuration objects. Is this the correct approach?
Finally where should the code to save such configuration settings live? An easy solution would be to put this code in my Domain.Persistence project, but then, if they are not part of the domain, should they really be there?
Thanks,
Ben
User configurable settings belong to domain if they are strongly typed and modeled based on ubiquitous language, i.e. 'BlogSettings'. The only difference between settings and other domain objects is that conceptually settings are 'domain singletons'. They don't have a life cycle like other Entities and you can only have one instance.
Generic configuration builder belongs to Persistence just like the code that is responsible for saving and reading settings.
Having found this question, I feel obliged to suggest an answer because I don't like the accepted one.
First off I don't see why this has to be a singleton.
Secondly, there is something about settings that is very important: they are usually hierarchical, and they almost always have to have the concept of defaults. Sometimes those defaults are at the item level. Other times you might prefer to replicate a whole set of defaults. Also, consider the fact that settings can use the concept of inheritance: maybe an agency has a setting, but it permits agents the ability to do their own.
We're trying to implement the Gatekeeper Design pattern as recommended in Microsoft Security Best Practices for Azure, but I;m having some trouble determining how to do that.
To give some background on the project, we're taking an already developed website using the traditional layered approach (presentation, business, data, etc.) and converting it over to use Azure. The client would like some added security built around this process since it will now be in the cloud.
The initial suggestion to handle this was to use Queues and have worker roles process requests entered into the queue. Some of the concerns we've come across are how to properly serialize the objects and include what methods we need run on that object as well as the latency inherent in such an approach.
We've also looked setting up some WCF services in the Worker Role, but I'm having a little trouble wrapping my head around how exactly to handle this. (In addition to this being my first Azure project, this would also be my first attempt at WCF.) We'd run into the same issue with object serialization here.
Another thought was to set up some web services in another web role, but that seems to open the same security issue since we won't be able to perform IP-based security on the request.
I've searched and searched but haven't really found any samples that do what we're trying to do (or I didn't recognize them as doing so). Can anyone provide some guidance with code samples? Thanks.
Please do not take this the wrong way, but it sounds like you are in danger of over-engineering a solution based on the "requirement" that 'the client would like some added security'. The gatekeeper pattern that is described on page 13 of the Security Best Practices For Developing Windows Azure Applications document is a very big gun which you should only fire at large targets, i.e., scenarios where you actually need hardened applications storing highly sensitive data. Building something like this will potentially cost a lot of time & performance, so make sure you weigh pro's & con's thoroughly.
Have you considered leveraging SQL Azure firewall as an additional (and possibly acceptable) security measure? You can specify access on an IP address level and even configure it programmatically through stored procedures. You can block all external access to your database, making your Azure application (web/worker roles) the only "client" that is allowed to gain access.
To answer one of your questions specifically, you can secure access to a WCF service using X.509 certificates and implement message security; if you also need an SSL connection to protect data in transit you would need to use both message and transport security. It's not the simplest thing on earth, but it's possible. You can make it so only the servers that have the correct certificate can make the WCF request. Take a look at this thread for more details and a few more pointers: http://social.msdn.microsoft.com/Forums/en-US/windowsazuresecurity/thread/1f77046b-82a1-48c4-bb0d-23993027932a
Also, WCF makes it easy to exchange objects as long as you mark them Serializable. So making WCF calls would dramatically simplify how you exchange objects back and forth with your client(s).
I'm currently looking at developing an application, and have a choice between doing a standard ASP.NET web application or integrating it into SharePoint. Our client would like it to be SharePoint if possible, as they are under pressure to put all new development into it, but standard ASP.NET is still an option.
It is an application to manage and view data in a database with about 10 tables, including an approval workflow when certain new items are added. Referential integrity of the data is important.
I have experience of developing ASP.NET applications, but very little with SharePoint. Does anyone have any criteria they would apply to deciding between the two?
So far I am thinking along the lines of:
Referential integrity of the data is important and SP doesn't seem to handle this very well without writing lots of custom code
SharePoint doesn't seem very scaleable with the suggested limit of 2000 items in a list
The application has an approval workflow, which does seem to be something SP does well
On the wholem, it seems like we would end up writing lots of custom code and not really using any of the out of the box SP features. So my thinking is why not just write a standard ASP.NET application.
Are there any other key things we should consider?
By now, you may have already found this link: http://blogs.msdn.com/sanjaynarang/archive/2009/06/19/should-i-build-my-application-in-sharepoint-vs-asp-net.aspx. If not, it's a decent starting place with some good questions to ask.
What follows is my take as a long-time .NET developer (for as long as the platform has been around) and a SharePoint architect (since 2003). That's basically my way of saying that I've been on both sides of the fence.
In my opinion, SharePoint is a platform, not a product. As ASP.NET provides valuable web-based services to the core .NET framework, SharePoint supplies additional services and capabilities on top of ASP.NET. The platform removes the need for writing common code pieces that are a part of so many ASP.NET apps: security code, user profile management, personalization, UI/UX baseline, etc. When you get into the plumbing, you get even more: rich caching support that requires minimal configuration, customization modularity via Features, and more.
Should every application be built in SharePoint? I'd never push for that. With my current client, we use a mix of SharePoint-based and custom ASP.NET applications. Whether an application gets built in SharePoint vs. written from the ground-up in ASP.NET is a function of what we're doing. We conduct the same sort of exercise you are. If SharePoint's features and functionality can be brought to bear to reduce development time, it goes in SharePoint. If the need is too specific or we feel we'd be working around SharePoint, we go the custom app route.
You have some very specific concerns for your application, so let me take a crack at them with the little I understand about your requirements:
REFERENTIAL INTEGRITY: based on what you're saying, it sounds like your data model is pretty specific. Building your information architecture to natively leverage site columns, content types, and lists probably doesn't make sense. That doesn't throw SharePoint out, though. There's absolutely no reason why you couldn't build the data model you want (presumably in SQL Server) and then consume it with components that reside in SharePoint. If you're using MOSS, some of the BDC WebParts might work for you straightaway. If not, you'd still be writing controls and/or pages to work with the data, correct? There's nothing wrong with using SharePoint as your presentation layer for access to SQL directly or (in a more scalable, n-tier fashion) go against business services somewhere else.
2000 ITEM LIMIT: this is a common concern and one that is misunderstood. There is no 2000 list item limit; the actual measurement is 2000 items per view (and that's with out of the box views, by the way) or "container" (such as a folder). You can store many more times that (millions, if you like) in a list if you partition with folders, build your own view to page, etc. Again, given your data structure and the likely need you have to dodge SharePoint's lists, this wouldn't be an issue if you simply consumed data from SQL Server.
WORKFLOW: SharePoint is nice as a workflow host, and the OOTB workflows are handy. I'm assuming you're looking at MOSS (versus straight WSS), but just in case: the approval workflow comes with MOSS. If you're constrained to WSS, you only have one workflow available to you: the three-state workflow.
At the end of the day, SharePoint is .NET and built on top of ASP.NET. Much of the code you'd have to write in a SharePoint app you'd need to write in a custom .NET anyway. I'd look at things from the perspective of understanding whether the experience and features SharePoint affords you (as a developer) can help speed your development cycle and/or improve the user experience (something we, as developers, sometimes forget).
David in Dakota does have an excellent point, though, in that the dev experience for SharePoint is different from straight ASP.NET. The need (or rather, best practice) to deploy via Features, understand specific SharePoint concerns (e.g., lifetime and disposal of SharePoint objects), etc., mean that there will be ramp-up time if you do build in SharePoint. There are quite a few good resources out there (including folks here on StackOverflow) that can help, but you'll need to factor some learning into the equation of whether or not SharePoint makes sense.
One more parting thought: Microsoft is slowly shifting many of its own products and platforms to leverage SharePoint as their UI/UX layer, and the trend is picking up some steam. PerformancePoint, Project Server, Team Foundation Server, and Commerce Server all use SharePoint as their presentation tier. The trend will probably continue, though I don't know how far. If you use any of these products (or their on your technology roadmap), a SharePoint investment now might pay off later.
Despite all of my writing about and advocating for SharePoint, I don't think it's the right tool in every scenario. I still build WinForms apps, smart clients, command line apps, and more quite a bit. It just comes down to weighing "what I get" for "what I spend" (in both time and money).
I hope this helps!
Your evaluation is quite accurate. (It would help to have more detail about every feature your application needs but that's not really practical for this medium.)
The problems you mention have been largely solved but you would need to understand and implement the solutions. For example, there is a CodePlex project that can assist with referential integrity and there are recommendations on how to manage the number of items in a list. But using SharePoint is never going to give you the freedom of writing an ASP.NET application from scratch.
Another thing to consider is how you and/or the client expect the application will evolve in the future. If it will need more collaboration-style features or features such as version history on list items and integration with the Office client then SharePoint may be the better option.
You should also think about the complexity of deploying and updating your application on SharePoint.
My company is in need of a task management system to handle scenarios as simple as "Purchase a computer for X" to "Relocate a person to another country". The simple scenarios are a single tasks handled by a single person, whereas bigger tasks can be broken down into multiple sub tasks delegated to multiple people during the workflow. Additionally the clients and vendors need their own views into the process.
We are evaluating different solutions from a custom application built on Workflow Foundation to SharePoint to BPM products like Metastorm and BPM.Net.
Here's my current understanding of these solutions:
Workflow Foundation - Low level workflow designer and/or library with no host environment. It seems we would have to reinvent some wheels if we went this route such as fault tolerance and document management. Some of the answers on stack also cause concerns such as the lack of versioning and a complete overhaul for VS10/.NET 4.0
SharePoint - Built for document management and collaboration but trying to create advanced workflows and tasking on top of that seems like a hack. Plus all workflows have to be tied to either documents or lists. I cant envision how a list (or list of lists) can address this issue.
BPM products - Mature workflow engine at a seemingly high price. BPM.Net is the only solution for which I could find some level of technical detail but im still not sure how different developing against this product would be from developing against Workflow Foundation.
Are there any workflow engines dedicated to solving all the workflow pains that can be easily deployed with their own hosting environment and initiated through a webservice?
Are there any other options I am missing?
Thanks in advance.
****Edit**
To answer the questions below the workflow needs are pretty light. Basic routing of tasks to approvers and subcontractors.
Whats driving us too look deeper than PM software is the nature of the business not the need for advanced workflow. We are basically in the business of procuring goods and services through subcontractors for our clients which can also include full employee relocation. The interface of the package should reflect this by being customer branded as well as intuitive for this line of business.
Basically if im moving my family to the other side of the world Im not sure i'd want to interface with Jira or Sharepoint or any other PM software to facilitate this.
If you are on Microsoft stack I would definitely recommend SharePoint for this scenario. As it seems to be very simple you can go with Windows SharePoint Services edition because it is free and it has everything you need.
You are right when you say that ShartePoint workflow are bit limited. IMHO the best way to overcome that limitation is to purchase Nintex workflow to create your workflows. It is cost effective solution that can help you design workflows you need.
You can find workflow samples inside the product (as workflow templates) and on the web site.
Nothing you mentioned has much to do with workflow. You're just doing project management. If that's the case, a simple bug tracker (like FogBugz! ;) would work - but if you're going to show it externally, it may not be the most professional presentation.
The closest off the shelf solution I can think of would be Project Server - though, depending on the number of projects and project managers, the desktop Project with a sync to a webserver for client views may be enough.
If that's overkill - because your projects don't require a lot of resource scheduling, Gantt charts, or other PM artifacts - you can take something like Trac and replace "bug" with "task". ;) (Seriously though, that'd probably get you 90% of the way there.....)
Have you looked at RT? I believe it can handle all your requirements, including that it's designed to let customers interact with the system by email, rather than having to log into the website. If you've emailed IT support desks then you've probably interacted with it without knowing... You can also completely customise the web interface and allow customer access.
Can't vouch for the quality as I haven't used it, but I did watch an online-demo video of Intalio, which has BPM and workflow capabilities.
We use Basecamp to control this sort of "task management" stuff. I'm not sure if it fits your needs totally, as it's a little light on the document management side, but it has a web service (REST) API, customer / vendor facing components, and basic interaction / chat capabilities.
The best part about it is that the API is simple enough where you can offload a lot of the "management" for it to admin support personnel, like assistants and interns, by providing custom scripts. If you've got people who aren't programmers using it you'll probably have better luck with it than even something like Trac or FogBugz.
I have/am going through a similar process. We wanted a lightweight workflow for internal use by our sales team. Most of the third party apps we looked at ,K2 and Skelta BPM.Net in particular, looked way over the top for what we needed. I'm now 2 months into working with Windows Workflow Foundation 3.0 and I have to say it isn't the most pleasant coding experience I've had.
If your workflows will truely be simple then it is pretty easy to build a workflow and hook it up to some web pages for the UI. But if you need to be able to change it on the fly, or do versioning (ie the user says we want another step added, then its a whole lot of hacking to get it to work - and it only works if you limit your workflow to being really simple), then you are in for a fair bit of work. And forget about it if you use an Oracle database.
The next version of windows workflow will have it's own runtime environment, code name dublin, with will provide a WCF interface into the workflows.
If your timeframe allows you could use that.
For information on Dublin and the next version of WF see:
http://www.microsoft.com/net/dublin.aspx
My vote is for FogBugz. Unless I am missing something in your requirements, why would you want to reinvent the wheel by using a code based workflow solution where you have to code up the flows yourself when you can use a perfectly good project dependency solution like FB or even MS Project Server - which lets you create nice dependencies for resources and people.
Check FileNet
FileNet is expensive but makes a good job with content and process management, but I guess is not what you are looking for.
We use Captaris Workflow, it is pretty good but it may be expensive for your needs.