I am currently writing a .net application with c# and want to check a number of rules and based on passing or failing the rules, perform an action. So I am looking to implement a generic solution that I can reuse adhering to good oop principles. This has lead me to the conclusion that I need to write a rules engine.
I have good knowledge of c# but this is the first time I have needed to write a rules engine so as part of my research in to the design and development of such, I am looking for any tips regarding the creation of such an engine. What would be great further would be any examples out there that I could look at? Any c#/.net rules engine applications? What layer in a typical 3 tier architecture should such reside at? I had a quick look on the codeplex and google code but none jumped out at me! So some direction would be great.
Actually .NET has a top-notch rules engine meant to be used with workflows (as it is designed to be) but can be used outside of workflows easily: You should see "Windows Workflow Foundation Rules Engine" and inspect the System.Workflow.Activities.Rules namespace.
Learning how to use rules outside of workflows takes only a bit of googling.
Edit: If you want to inspect the architecture, here is two open-source prebuilt engines:
NxBRE
.NET Application Block for Validation and Business Rules
Building and implementing your own rules engine can be a very difficult task with many things to consider. The biggest problem you will face is trying to decide which rules to fire and when. Not giving this the proper care can lead to performance problems within the implementation. I would highly recommend focusing in on the business problem and providing your subject matter experts (SME’s) with the ability to define and maintain their own rules. There are many good commercial products that do this; the one I have successfully implemented multiple times is www.inrule.com. They have a nice set of products that can help solve simple and complex problems. Hopefully this helps.
Related
I'm looking into NRules.Net to implement my pricing engine. After some testings, I don't really understand the benefits of using a .net rules engine vs using a rich domain model...
Rules are still plain CS classes (there is nothing dynamic)
I have to deal with a black-box (the rule engine) which does not allow me to understand what is going on
In the end, why shall I go for a .net rule engine? Is there anything I'm missing?
Thanks
Seb
A rules engine allows you to reason about a Rule as a concept of its own and gives you an elaborate language to play with rules.
You can compose rules dynamically, classify and manipulate lists of rules with different priorities, manage conflicting rules, express them with a convenient DSL that business people might understand, create transformations to make an object comply with a rule, etc.
Without an abstraction of what a Rule is, you can't do all this in a conscious, consistent way.
Not all domains need it but if that general concept often comes up in discussions with your domain experts, a rules engine is probably worth having a look at.
Background
There are a lot of good resources on how to use MVVM/MVP to separate your layers so that the designer and coder can work separately. This isn't a PRISM question, but I have also checked several Prism tutorials ( including this excellent 4+ hours series by Microsoft' Mike Taulty, and many more)
These tutorials/books/videos explain the internal workings, such as how to pass messages across view models, how to modularize the application, the best security practices and so on.
However, no one talks about how to actually *logically divide*an application (WPF or ASP.Net MVC) so that multiple people can work on it.
Question
How do you generally go about assigning responsibilities to your development team?
Assuming that you use a high level UML tool, once a high level diagram is ready but no code has been written, how do you ensure that
1- The developer(s) working on the UI will know and be able to access the class library functions that the class-library developers will write?
2- Two libraries that will be written for two different purposes by two different developers will inter operate?
I hope I am not being confusing here. The question is just for a few good rules of thumb. That as two people working on two projects ( WPF/Silverlight or ASP.Net MVC) in a solution will take two different ways , how do the methods/classes/functions written by one fit together with the others?
Thank you
However, no one talks about how to actually *logically divide*an application (WPF or ASP.Net MVC) so that multiple people can work on it.
You don't really need to divide an application so that multiple people can work on it: you can also use a Team Foundation Server. There's also a free version available for 5 users or fewer.
Tutorial: Getting Started with TFS in VS2010
As I understand of your question(s), you want to have an infrastructure in your project that people with different skills can work separately. If I were right, "Domain Driven Design" would be the best infrastructure you can choose.
Domain-driven design (DDD) is an approach to develop software for complex needs by connecting the implementation to an evolving model. The premise of domain-driven design is the following:
Placing the project's primary focus on the core domain and domain logic.
Basing complex designs on a model of the domain.
Initiating a creative collaboration between technical and domain experts to iteratively refine a conceptual model that addresses particular domain problems.
The term was coined by Eric Evans in his book of the same title.
There is a great project that can help you: Microsoft Spain - Domain Oriented N-Layered .NET 4.0 Sample App is based on simple scenarios easy to understand which is well documented.
Concepts like modularity, layering, etc. are discussed in the project very carefully which I believe can fulfill your expectation.
Obviously, you need a source control like Team Foundation Server or other alternatives that provide control over changes to source code among multiple developers.
That as two people working on two projects ( WPF/Silverlight or
ASP.Net MVC) in a solution will take two different ways , how do the
methods/classes/functions written by one fit together with the others?
You need maintain some common library for public functions. And the two developers need to make code review every 2 or 3 weeks. So they could find their difference and learn from each others.
I am creating an interface where users can build their own business rules out of domain specific objects at runtime, have those rules persisted in the database and then used by the application. Some of these are complex predicates and others require combinations of domain objects in what seems fairly complicated relations. So far I have looked into GoF, dynamics with eval, and CodeDom. Does anyone have suggestion on what should be used?
Actually, you can just develop your application with WF rules engine API without using WF. http://blogs.microsoft.co.il/blogs/bursteg/archive/2007/08/09/WF-Rules-Engine-without-Workflow.aspx This will save you from a lot of work.
Kaizen, depending on the scope and kind of your dynamic rules you could eventually use a workflow engine, like MS WF to define the rules as workflow activities for example... in this way you isolate the logic and do not need a full rebuild of the application when you need to change anything in the workflow.
This might not be the best solution but could be an alternative...
Having spent a year building a rules engine and fighting on approaches I can tell you its not easy. Especially when you focus on what your goal is. If its to get users to write the rules for the system, you really need to focus hard on that area. Whats easy for a developer is perhaps much harder for most business users. We built a rules authoring platform in Excel that was compiled into C# and run dynamically ... problem was users found the spreadsheets and flow of logic too complicated and hired ASp.NET contractors to do build the rules.
BizTalk has an engine that I believe can be used for .NEt apps
http://www.microsoft.com/biztalk/en/us/business-rule-framework.aspx
Have fun!
How often do the rules change? Building a system that let's the business build (and version) their own rules is significantly more challenging than building a system that lets a programmer update the rules dynamically.
When a similar requirement came up in a past project, the business admitted that while yes, the rules will change; they won't change so often that it has to be them making the updates.
We ended up using IronPython for the dynamic parts and storing the code in the database and the system would pull up the appropriate rules on load. The rest of the app was written in C#. A win for us and for the business.
I have to create a workflow in C# capable of moving an object (persisted as a database record) through an approval workflow where people are required to perform some sort of action or validation.
We initially looked at Windows Workflow Foundation but shied away from it because it seemed so infrastructure-heavy (and besides we don't really like Microsoft products). We looked at ObjectFlow because it's lightweight, but I'm having trouble figuring out how to persist & resume workflow states. It almost seems like it's too lightweight.
Does anyone have a particular favorite framework for doing workflow? I'm open to ideas (even to WWF, if you can explain why it's your favorite).
Now at the end of 2022 I recommend Elsa Workflows library which is free and open source.In this case state machine workflows works. I have used it in multiple projects witch success. It is flexible, has a web workflow designer and acceptable documents
As the question #gsharp linked to says, WF 4 isn't entirely easy to use. However, ObjectFlow has an easy fluent interface that is light and built with solid design principles. Given the apparent lack of decent workflow frameworks, I decided to pitch in and extend ObjectFlow with an IStatefulWorkflow that contains a .Yield() method capable of yielding workflow processing to the calling method so that it's state can be persisted.
The end result of my work will be a new release at codeplex in a couple weeks. Until then, you can follow my progress at github.
Have you looked at Drools.Net?
Drools.NET is a Business Rules Engine (BRE) based on Charles Forgy's Rete algorithm. Developers can now exploit a powerful Rule Engine through a completely managed .NET code base! Drools.NET is based on Jboss Rules, and comes with all the features of that Rules Engine.
I have recently developed a C# Workflow library that leverages the fluent syntax and provides compile time validation between workflow steps. A Workflow's steps can be consolidated in a single location providing maintainable code. The library is very light weight and performant.
https://www.nuget.org/packages/NetWorkflow
https://github.com/Tmarndt1/NetWorkflow
I'm going to have to write a big system in January with ASP.NET MVC3 / C#, and need to know how to write a system that will WORK. I do have a bit of experience with ASP.NET MVC and C# but would not call myself an expert. It needs to be extensible so that I can extend it later with new features. How would one go about this? Is there books that explains this topic in detail or should I use trial and error?
In short I need to know good design practice in my code thats extend-able for the future.
Regards
RaVen
The System will be a community portal with forums ratings etc. Cant say more than that << Company Policy>>, The forums I can manage because of plenty open source options... But the rest is up to me.
SOLID == Great Success
Follow SOLID principles in any project and you'll do well.
With regards to core infrastructure/architechure, SharpArchitecture is a good place to start. It is by no means the perfect solution...BUT they give you a good framework to play with and you can have a working system quickly while learning the concepts that work and don't work over time. Take a look and see what you think. It uses NHibernate, Castle and MVC.
Test Driven development will ensure quality for your project. Be strict with yourself, red green refractor. One of MVCs strengths is that it's easier to test.
Professional ASP.NET MVC 2 is a good starting point, though, I would assume that they'll come out with an MVC 3 edition as well. The NerdDinner tutorial contains a lot of ideas on how to structure your application.
Basic advice: work with the MVC architecture, not against it. Understand your application, especially your data model, and layer that onto your application structure. Typically you'll have a controller per model, but not always.
If you want more detailed advice, you'll need to be more specific about your project. I'd suggest coming up with specific questions about various details of your design as you have them, rather than a single question covering the whole project. The latter probably won't get the kind of response you desire.
you can use my "awesome" demo as a start
http://awesome.codeplex.com
If it's going to have to be extensible, make sure you write tests. You'll save yourself sleepless nights in the long run when you fix something, but ended up breaking the entire system.
As far as how to make things "WORK" - that depends on your ability. Read, and look to improve things, but don't get caught in premature optimization or it will leave you dead in the water.
Based upon your edit and your abilities, it might be wiser to select an open source CMS written in ASP.NET MVC and support it. Your skills are good enough, it sounds like, to learn how to write modules and be part of a larger community. You do not sound like you really want to write the whole thing because you are timid about your skills, deadlines, etc. Whilst learning the ins and outs of a well written piece of software, one day you may choose to write your own or contribute to a core piece of the software. There are several to choose from see my comment above under your question.
edit: I also think this will allow you to just start and not worry about every design paradigm people will throw at you for success.
WhoCanHelpMe is a nice reference application. It's built upon S#arp Architecture which is a good starting point for an MVC-application using domain driven design. That will also help you on the way with wiring IoC and db-stuff.
Remember that not every example and framework will fit your requirements, so do as jFar said, think SOLID and make your own decisions based on principals.
You should also look into MEF for extensibility.