I'm building an API and I have modeled the entities I need inside it. By example
User
Name
Email
City
Company
Name
Website
I'm using Blueprint to specify the API itself and I need to create endpoints for CRUD operations in pretty much every entity. The task seems very redundant to me - besides some tuning that is needed in some specific entities, most of the basic skeleton looks like the same.
I wonder if there is any tool that allows me to write down my entities, its fields and types and generates this basic skeleton.
I was about to start creating one and then I stopped to look around if there already is one but I did not find anything yet...
API Blueprint contains a tool to write, use, reuse, compose, inherit your data structures, and it's MSON.
Basically it's a way to describe your data structures within an API Blueprint. We do also provide an html renderer for that, and it's the Attributes Kit. Try also to have a look to its Playground.
You can find an useful tutorial on official website, as well more information.
Hopefully it should be enough to get started.
Cheers,
V.
I am part of a studentproject and we are to develop a product for a company using Java EE. As "lead architect" in the project I am responsible for composing a good design which should be flexible for further extensions.
Background info: We are to develop a website with a drag and drop GUI with possibilites to connect data sources with data manipulations to perform on that specific data. The GUI should be generic and possible to integrate with upcoming products. This means that we cannot code to an implementation in the presentation layer. Instead we will use an interface to define what kind of data manipulations that are possible for all kinds of products. However, each product might also sport product specific data manipulations (thus extending the interface with more methods).
The problem I have with the scenario above is that I dont see how we could pass on these "product specific data manipulations" to the GUI and say that, in addition to the generic interface, we also possess these data manipulation actions...
Now I had a discussion with some of the more experienced programmers from the company and they told me that there is a common solution to this problem - more specifically known as the "Observer pattern". They draw something like [1] on the whiteboard and explained that it would be possible to "register" to a third party (getApplicationContext) that in turn could convey our product specific interface. This is a common problem to get rid of those nasty circular dependencies, they explained.
I have now had a look on the observer pattern and how it works and I still dont really get how I am supposed to solve the design problem. Could someone possibly try to explain how it would turn out in my specific scenario? I have no real problem understanding how it works with "subjects" and "observers".
Here is an UML diagram of the design where we are using a reference of the specific product. This is what is undesirable and something we would like to get around.
(maybe I got this all wrong...)
I am sorry but I cant change the picture to the correct one as I am a new user... Here is a link to an updated UML diagram:
It seems what you are looking for is the Model View Controller design pattern. The Observer pattern is just a part of this design pattern. There is a short description for doing this with Java Servlets and JavaServer Pages from Java EE on the wikipedia article.
I am working on a packaged product that is supposed to cater to multiple clients with varying requirements (to a certain degree) and as such should be built in a manner to be flexible enough to be customizable by each specific client. The kind of customization we are talking about here is that different client's may have differing attributes for some of the key business objects. Also, they could have differing business logic tied in with their additional attributes as well
As an very simplistic example: Consider "Automobile" to be a business entity in the system and as such has 4 key attributes i.e. VehicleNumber, YearOfManufacture, Price and Colour.
It is possible that one of the clients using the system adds 2 more attributes to Automobile namely ChassisNumber and EngineCapacity. This client needs some business logic associated with these fields to validate that the same chassisNumber doesnt exist in the system when a new Automobile gets added.
Another client just needs one additional attribute called SaleDate. SaleDate has its own business logic check which validates if the vehicle doesnt exist in some police records as a stolen vehicle when the sale date is entered
Most of my experience has been in mostly making enterprise apps for a single client and I am really struggling to see how I could handle a business entity whose attributes are dynamic and also has a capacity for having dynamic business logic as well in an object oriented paradigm
Key Issues
Are there any general OO principles/patterns that would help me in tackling this kind of design?
I am sure people who have worked on generic / packaged products would have faced similar scenarios in most of them. Any advice / pointers / general guidance is also appreciated.
My technology is .NET 3.5/ C# and the project has a layered architecture with a business layer that consists of business entities that encompass their business logic
This is one of our biggest challenges, as we have multiple clients that all use the same code base, but have widely varying needs. Let me share our evolution story with you:
Our company started out with a single client, and as we began to get other clients, you'd start seeing things like this in the code:
if(clientName == "ABC") {
// do it the way ABC client likes
} else {
// do it the way most clients like.
}
Eventually we got wise to the fact that this makes really ugly and unmanageable code. If another client wanted theirs to behave like ABC's in one place and CBA's in another place, we were stuck. So instead, we turned to a .properties file with a bunch of configuration points.
if((bool)configProps.get("LastNameFirst")) {
// output the last name first
} else {
// output the first name first
}
This was an improvement, but still very clunky. "Magic strings" abounded. There was no real organization or documentation around the various properties. Many of the properties depended on other properties and wouldn't do anything (or would even break something!) if not used in the right combinations. Much (possibly even most) of our time in some iterations was spent fixing bugs that arose because we had "fixed" something for one client that broke another client's configuration. When we got a new client, we would just start with the properties file of another client that had the configuration "most like" the one this client wanted, and then try to tweak things until they looked right.
We tried using various techniques to get these configuration points to be less clunky, but only made moderate progress:
if(userDisplayConfigBean.showLastNameFirst())) {
// output the last name first
} else {
// output the first name first
}
There were a few projects to get these configurations under control. One involved writing an XML-based view engine so that we could better customize the displays for each client.
<client name="ABC">
<field name="last_name" />
<field name="first_name" />
</client>
Another project involved writing a configuration management system to consolidate our configuration code, enforce that each configuration point was well documented, allow super users to change the configuration values at run-time, and allow the code to validate each change to avoid getting an invalid combination of configuration values.
These various changes definitely made life a lot easier with each new client, but most of them failed to address the root of our problems. The change that really benefited us most was when we stopped looking at our product as a series of fixes to make something work for one more client, and we started looking at our product as a "product." When a client asked for a new feature, we started to carefully consider questions like:
How many other clients would be able to use this feature, either now or in the future?
Can it be implemented in a way that doesn't make our code less manageable?
Could we implement a different feature that what they are asking for, which would still meet their needs while being more suited to reuse by other clients?
When implementing a feature, we would take the long view. Rather than creating a new database field that would only be used by one client, we might create a whole new table which could allow any client to define any number of custom fields. It would take more work up-front, but we could allow each client to customize their own product with a great degree of flexibility, without requiring a programmer to change any code.
That said, sometimes there are certain customizations that you can't really accomplish without investing an enormous effort in complex Rules engines and so forth. When you just need to make it work one way for one client and another way for another client, I've found that your best bet is to program to interfaces and leverage dependency injection. If you follow "SOLID" principles to make sure your code is written modularly with good "separation of concerns," etc., it isn't nearly as painful to change the implementation of a particular part of your code for a particular client:
public FirstLastNameGenerator : INameDisplayGenerator
{
IPersonRepository _personRepository;
public FirstLastNameGenerator(IPersonRepository personRepository)
{
_personRepository = personRepository;
}
public string GenerateDisplayNameForPerson(int personId)
{
Person person = _personRepository.GetById(personId);
return person.FirstName + " " + person.LastName;
}
}
public AbcModule : NinjectModule
{
public override void Load()
{
Rebind<INameDisplayGenerator>().To<FirstLastNameGenerator>();
}
}
This approach is enhanced by the other techniques I mentioned earlier. For example, I didn't write an AbcNameGenerator because maybe other clients will want similar behavior in their programs. But using this approach you can fairly easily define modules that override default settings for specific clients, in a way that is very flexible and extensible.
Because systems like this are inherently fragile, it is also important to focus heavily on automated testing: Unit tests for individual classes, integration tests to make sure (for example) that your injection bindings are all working correctly, and system tests to make sure everything works together without regressing.
PS: I use "we" throughout this story, even though I wasn't actually working at the company for much of its history.
PPS: Pardon the mixture of C# and Java.
That's a Dynamic Object Model or Adaptive Object Model you're building. And of course, when customers start adding behaviour and data, they are programming, so you need to have version control, tests, release, namespace/context and rights management for that.
A way of approaching this is to use a meta-layer, or reflection, or both. In addition you will need to provide a customisation application which will allow modification, by the users, of your business logic layer. Such a meta-layer does not really fit in your layered architecture - it is more like a layer orthoganal to your existing architecture, though the running application will probably need to refer to it, at least on initialisation. This type of facility is probably one of the fastest ways of screwing up the production application known to man, so you must:
Ensure that the access to this editor is limited to people with a high level of rights on the system (eg administrator).
Provide a sandbox area for the customer modifications to be tested before any changes they are testing are put on the production system.
An "OOPS" facility whereby they can revert their production system to either your provided initial default, or to the last revision before the change.
Your meta-layer must be very tightly specified so that the range of activities is closely defined - George Orwell's "What is not specifically allowed, is forbidden."
Your meta-layer will have objects in it such as Business Object, Method, Property and events such as Add Business Object, Call Method etc.
There is a wealth of information about meta-programming available on the web, but I would start with Pattern Languages of Program Design Vol 2 or any of the WWW resources related to, or emanating from Kent or Coplien.
We develop an SDK that does something like this. We chose COM for our core because we were far more comfortable with it than with low-level .NET, but no doubt you could do it all natively in .NET.
The basic architecture is something like this: Types are described in a COM type library. All types derive from a root type called Object. A COM DLL implements this root Object type and provides generic access to derived types' properties via IDispatch. This DLL is wrapped in a .NET PIA assembly because we anticipate that most developers will prefer to work in .NET. The Object type has a factory method to create objects of any type in the model.
Our product is at version 1 and we haven't implemented methods yet - in this version business logic must be coded into the client application. But our general vision is that methods will be written by the developer in his language of choice, compiled to .NET assemblies or COM DLLs (and maybe Java too) and exposed via IDispatch. Then the same IDispatch implementation in our root Object type can call them.
If you anticipate that most of the custom business logic will be validation (such as checking for duplicate chassis numbers) then you could implement some general events on your root Object type (assuming you did it something like the way we do.) Our Object type fires an event whenever a property is updated, and I suppose this could be augmented by a validation method that gets called automatically if one is defined.
It takes a lot of work to create a generic system like this, but the payoff is that application development on top of the SDK is very quick.
You say that your customers should be able to add custom properties and implement business logic themselves "without programming". If your system also implements data storage based on the types (ours does) then the customer could add properties without programming, by editing the model (we provide a GUI model editor.) You could even provide a generic user application that dynamically presents the appropriate data-entry controls depending on the types, so your customers could capture custom data without additional programming. (We provide a generic client application but it's more a developer tool than a viable end-user application.) I don't see how you could allow your customers to implement custom logic without programming... unless you want to provide some kind of drag-n-drop GUI workflow builder... surely a huge task.
We don't envisage business users doing any of this stuff. In our development model all customisation is done by a developer, but not necessarily an expensive one - part of our vision is to allow less experienced developers produce robust business applications.
Design a core model that acts as its own independent project
Here's a list of some possible basic requirements...
The core design would contain:
classes that work (and possibly be extended) in all of the subprojects.
more complex tools like database interactions (unless those are project specific)
a general configuration structure that should be considered standard across all projects
Then, all of the subsequent projects that are customized per client are considered extensions of this core project.
What you're describing is the basic purpose of any Framework. Namely, create a core set of functionality that can be set apart from the whole so you don't have to duplicate that development effort in every project you create. Ie, drop in a framework and half your work is done already.
You might say, "what about the SCM (Software Configuration Management)?"
How do you track revision history of all of the subprojects without including the core into the subproject repository?
Fortunately, this is an old problem. Many software projects, especially those in the the linux/open source world, make extensive use of external libraries and plugins.
In fact git has a command that's specifically used to import one project repository into another as a sub-repository (preserving all of the sub-repository's revision history etc). In fact, you can't modify the contents of the sub-repository because the project won't track it's history at all.
The command I'm talking about is called 'git submodule'.
You may ask, "what if I develop a really cool feature in one client's project that I'd like to use in all of my client's projects?".
Just add that feature to the core and run a 'git submodule sync' on all the other projects. The way git submodule works is, it points to a specific commit within the sub-repository's history tree. So, when that tree is changed upstream, you need to pull those changes back downstream to the projects where they're used.
The structure to implement such a thing would work like this. Lets say that you software is written specifically to manage a car dealership (inventory, sales, employees, customers, orders, etc...). You create a core module that covers all of these features because they are expected to be used in the software for all of your clients.
But, you have recently gained a new client who wants to be more tech savvy by adding online sales to their dealership. Of course, their website is designed by a separate team of web developers/designers and webmaster but they want a web API (Ie, service layer) to tap into the current infrastructure for their website.
What you'd do is create a project for the client, we'll call it WebDealersRUs and link the core submodule into the repository.
The hidden benefit of this is, once you start to look as a codebase as pluggable parts, you can start to design them from the start as modular pieces that are capable of being dropped in to a project with very little effort.
Consider the example above. Lets say that your client base is starting to see the merits of adding a web-front to increase sales. Just pull the web API out of the WebDealersRUs into its own repository and link it back in as a submodule. Then propagate to all of your clients that want it.
What you get is a major payoff with minimal effort.
Of course there will always be parts of every project that are client specific (branding, ect). That's why every client should have a separate repository containing their unique version of the software. But that doesn't mean that you can't pull parts out and generalize them to be reused in subsequent projects.
While I approach this issue from the macro level, it can be applied to smaller/more specific parts of the codebase. The key here is code that you wish to re-use needs to be genericized.
OOP comes into play here because: where the functionality is implemented in the core but extended in client's code you'll use a base class and inherit from it; where the functionality is expected to return a similar type of result but the implementations of that functionality may be wildly different across classes (Ie, there's no direct inheritance hierarchy) it's best to use an interface to enforce that relationship.
I know your question is general, not tied to a technology, but since you mention you actually work with .NET, I suggest you look at a new and very important technology piece that is part of .NET 4: the 'dynamic' type.
There is also a good article on CodeProject here: DynamicObjects – Duck-Typing in .NET.
It's probably worth to look at, because, if I have to implement the dynamic system you describe, I would certainly try to implement my entities based on the DynamicObject class and add custom properties and methods using the TryGetxxx methods. It also depends whether you are focused on compile time or runtime. Here is an interesting link here on SO: Dynamically adding members to a dynamic object on this subject.
Two approaches is what I feel:
1) If different clients fall on to same domain (as Manufacturing/Finance) then it's better to design objects in such a way that BaseObject should have attributes which are very common and other's which could vary in between clients as key-value pairs. On top of it, try to implement rule engine like IBM ILog(http://www-01.ibm.com/software/integration/business-rule-management/rulesnet-family/about/).
2) Predictive Model Markup Language(http://en.wikipedia.org/wiki/PMML)
How does one pass a complex object to the target Page using the NavigationService.Navigate method?
Unfortunately you can't do that. It kind of makes sense, because the idea is to provide deep linking support for pages/views, but it's definitely annoying that you can't do it. The options you have are:
For small objects, you could serialise them and pass them to the next view in the query string, although I'd recommend against that approach (different browsers have different number of maximum characters in a URL that they support, and also the object may be out of date if the user bookmarks that page and returns to it).
Store the object in a global cache, from which the view being navigated to can access it. Not nice, but it will work.
The Navigation Framework source code is a part of the Silverlight Toolkit. You could modify this to support complex objects, but I'd strongly recommend against doing so.
Use the MVVM pattern, with one view model used to manage multiple views, and therefore the object would be available to all those views.
Hope this helps...
Chris
P.S. I discuss this in my book Pro Business Applications with Silverlight 4, although only in as much depth as above as there's not a particularly nice solution to the problem :).
Can someone explain to me what interface bloat in OOP is (preferably with an example).
G'day,
Assuming you mean API and not GUI, for me I/F bloat can happen in several ways.
An API just keeps getting extended and extended with new functions without any form of segregation so you finish up with a monolithic header file that becomes hard to use.
The functions declared in an existing API keep getting new parameters added to their signatures so you have to keep upgrading and your existing applications are not backwards compatible.
Functions in an existing API keep getting overloaded with very similar variants which can lead to difficulty selecting the relevant function to be used.
To help with this you can:
Separate out the API into a series of headers and libraries so you can more easily control what parts you actually need. Any internal dependencies should be resolved automatically by the vendor so the user doesn't have to find out the dependencies by trial and error, e.g. that I need to include header file wibble.h when I only wanted to use the functions in the API declared in the shozbot.h header file.
Make upgrades to the API backwards compatible by introducing overloading where applicable. But you should group the overloaded functions into categpories, e.g. if new set of overloaded functions are added to an existing API, say our_api.h, to adapt it to a new technology, say SOA, then they are provided separately in their own header file our_api_soa.h in addition to the existing header our_api.h.
HTH
Think of an OO language where all methods are defined in Object, even though they are only meaningful for some subclasses. That would be the most extreme example.
Most Microsoft products?
Interface bloat is having too much on the screen at once, particularly elements that are little used, or are confusing in their function. Probably an easier way to describe interface bloat is to look at something that does not have it, try Basecamp from 37signals. There are only a few tabs, and a few links in the header.
Interface bloat can be remedied by collapsable panes (using Javascript, for example), or drill-down menus that hide less-often used choices until they are needed.
Interface bloat is the gradual addition of elements that turn what may been a simple, elegant interface into one littered with buttons, menus, options, etc. all over the place that ruin the original cohesive feel of the application. One example that comes to mind for me is iTunes. In it's early renditions, it was quite simple, but has, over time, added quite a lot of features that might qualify as bloat (iTunes DJ, Coverflow, Genius).
Interface bloat is sometimes caused by trying to have every feature one click away, as in this humorous example:
Too many toolbar buttons
(Although funny, this example isn't fair to Firefox because in this example the user added all those toolbars)
A UI design technique called "progressive disclosure" is one way to reduce interface bloat. Only expose the most frequently-used features as a top-level click. If you have less-frequently-used features that are still valuable enough to include in your app, group them in a logical way, e.g. behind a dropdown menu or other navigation element.
Learning by example:
http://img46.imageshack.us/img46/5127/ofilematrix.png
An extreme example of interface bloat that most C++ programmers will be familiar with is std::basic_string. Page up and page down of member functions with only small variations, most of these functions wouldn't have had to be member functions but could have been free functions in a string utility library.