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Thanks for sharing your experience using both approaches in two different environments.
Keld Ølykke wrote: I find it pretty annoying in Java. They clearly made this better choice...
These two statements seem to conflict with each other. If the one approach is "pretty annoying" is it really "better?" And this is reason I raise the question: I have the same conflict internally. Which approach is "better" seems to come down to where you approach the problem from. One day I look at the problem from one perspective and one way seems "better." The next day I look at the code and say "How crappy! This way is better!" What I optimize for changes the context enough to change the answer.
Keld Ølykke wrote: Another question, is whether to use enums or classes as arguments, but ... that is another question 
Yes. Yes it is. 
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I'm looking for a CMS (Umbraco) doc type etc. structure for agile (mostly) project collaboration and eventually management. My initial idea is for a content type structure as follows:
Project Home
Project Area
Feature
Documents like overview and description, as well as miscellaneous artefacts.
User stories, Use Cases, Narative specs, etc.
Unclassified Project Documents, with attachements etc.
Then, for the User Stories, I integrate with YouTrack for fine grained, micro-tracking and developer assignment. Time tracking as well, that aggregates up to the Feature (or Story) on Umbraco.
That's my basic prototype. Any suggestions, warnings, anecdotes, or any other feedback would be great. This is a first iteration before demo'ing to the boss and team, and Umbraco is fairly flexible if not too customised.
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The fourth result in that list is my duplicate of this question on StackOverflow. The range of results is simply too broad. I am looking for feedback from people who have implemented such a structure, particularly on Umbraco.
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I am editing this post to remove the sample code as I no longer think it would be a good design.
After more research, it appears that the Data Access Object Design Pattern is a good solution to separate a Data Access API from the business objects.
Example: http://www.tutorialspoint.com/design_pattern/data_access_object_pattern.htm
Comments are welcome.
Thanks!
Carlos.
Original Question: What is the best Design Pattern to separate data access from the business layer?
modified 14-Feb-14 12:03pm.
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Why is it necessary to separate the data layer from the business layer? Are you thinking of changing the data repository? Is there another reason?
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Just to counter the other inference in the other response there are good reasons for having a data layer.
It helps to start with a data model. A data model represents data in the application and although it will often be one to one with database tables/objects that isn't always the case.
Once you have that then your data base layer is created to expose that data model.
This is common enough that there are already generic frameworks for it. NHibernate is one and there are others.
In my experience it is a bad idea to use inheritance as you have suggested. Data models seldom represent inheritance and implementing it like that even when it seems like such models are there is often a problem. This of course is compounded by a poor design where inheritance is used rather than a better choice of attributes and/or composition.
You data layer should not expose anything about the database itself. Often it will be better to have helper classes that do the real work and your exposed classes use those to do the real work.
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Carlos Merighe wrote: ANY COMMENTS OR SUGGESTIONS?
STOP SHOUTING!
Carlos Merighe wrote: PLEASE BE SPECIFIC.
STOP POSTING TEXT IN ALL-CAPS!
You weren't specific with wich type of comment you expected, so my apologies, I'm grumpy, ignore it if you're not in a good mood.
What's the difference between Oracle and SQL? Does Oracle not use SQL? Did you mean "SQL Server" or "MySQL"?
Second, you don't want two different implementations to load data from a DataProvider that shares an interface; one can handle both scenario's using a db-agnostic interface (the IDbCommands) - there may be variations in the queries, but the infrastructure would be the same. Any ORM worth it's money would provide the same functionality. ORM's are sweet, they keep code nicely readable.
Alternatively, if you want to dive into some examples created from your dataset - take a look at some code-generators like MyGeneration[^]; there's usually multiple templates to create 3-tier applications (and more) - some templates generating complete websites. A benefit is that the code is generated from data that you're (often) familiar with, making it easier to recognize some of the parts (compared to those abstract examples in the books).
Bastard Programmer from Hell 
If you can't read my code, try converting it here[^]
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I agree with the comment regarding a shared interface.
But inserting large number of records into Oracle works very differently from SQL/Informix. SQL's bulk loader does not share a common interface with Oracle. It is not important to discuss their interfaces here. Besides, that is a design test at this point.
Guys, but the business layer is not inheriting from the data implementation, such as the Oracle-specific implementation class. The business object Bonus does not know where the data is coming from. Removing the inheritance would mean that a client would be able to access the Name property for the business object, which makes no sense to me. Example:
Bonus obj = new Bonus( new LevelBonus_SQL() );
obj.Name = "some name";
obj.Load(); //It will load from SQL, but the business Bonus object does not know
PROBLEM: Remove the inheritance and I can no longer access obj.Name.
modified 13-Feb-14 17:28pm.
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Carlos A Merighe wrote: PROBLEM: Remove the inheritance and I can no longer access obj.Name.
I use the following model when I create my own layers. Following is pseudo code.
class CustomerPrimitive
{
String name
String address
String telephone.
}
class CustomerDb
{
create(CustomerPrimitive)
update(CustomerPrimitive)
delete(Id id)
List<CustomerPrimitive> query(CustomerPrimitiveQuery)
}
Keep in mind that the 'Primitive' is a Data Model Object and not necessarily a direct table representation. The 'Primitive' must NOT have any significant functionality and must NOT have and database specific code in it.
The database specific code goes in the 'Db' classes. You can add abstractions on top of the above but I haven't found them useful (and I have done it.)
The 'Primitive' types should be in their own space (package, namespace, whatever) which is entirely separate from the 'Db' types.
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Ditch the term "Load"; how about "LoadByName" or "LoadById"? Throw an InvalidOperation if a property is set in a non-loaded (but created) object. Personally, I'd have that argument in the constructor, removing the possibility to create an empty class.
Bastard Programmer from Hell
If you can't read my code, try converting it here[^]
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Have a look at my article[^]
Carlos Merighe wrote: it appears that the Data Access Object Design Pattern is a good solution to separate a Data Access API from the business objects.
I would even say it is mandatory. It makes you think in smaller problems, which in turn makes you build simple and easy solutions to those problems. If you pile up everything into one problem/solution you'll end up with a huge mess.
Also it enforces re-usability, which leads to robust and stable code.
Carlos Merighe wrote: What is the best Design Pattern to separate data access from the business layer?
The one that fits you best. I'm not saying that so I can give you an easy answer. There is no "best" solution. Try out different solutions and see what best fits your needs and coding styles. Depending on the technology you can go old school as in my article or go the new way with LINQ or other technologies. Note that if you're in a company you probably want to use their way of working.
hope this helps.
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You could also use the Unit of Work / Repository pattern for your purposes.
Thanks
JD
http://www.seitmc.com/seitmcWP
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i need design pattern which will do continuous monitoring and evaluating and then further evaluating after certain time period. Working on Windows platform. Need help how or which design pattern to use or what approach to use .
Thanks,
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i want which particular is more suitable to scenario which i described.
-- modified 11-Feb-14 3:22am.
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What do you mean which language? Design patterns are concepts, they are language neutral.
Veni, vidi, abiit domum
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bymistake i typed it - "which language" .. i have edited it.. please see it.. I know design patterns concept.. looking for specific pattern suitable for my requirement.
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You first need to do the requirements analysis and design of your application. You can then look at all design patterns and implement where they are most appropriate.
Veni, vidi, abiit domum
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There is no specific design pattern for what you're trying to do. But here are some general pointers:
1. Observer pattern allows you to monitor an object by subscribing to an event and then taking an action when that event occurs.
2. Visitor pattern allows you to perform operations on an element's structure.
3. The Command pattern can be used to encapsulate the command you wish to perform on the monitored objects.
4. To do a periodic or continuous or repetitive task, you usually implement a Timer.
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Hi All,
I need to design a system where-in there is lot of decision making and also system needs to be adaptable as and when required.
Looking into above criteria adapter n visitor design pattern come to my mind but not sure. Please suggest design pattern as per above requirement.
I need to develop system in C++ and on Windows platform.
Thanks,
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You should gather the requirements of the system and work out the overall design of it first. Then as you take each part and refine its design, you will see where patterns become appropriate for the actual implementation.
Veni, vidi, abiit domum
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manisha.k.chaubey wrote: I need to design a system where-in there is lot of decision making and also system needs to be adaptable as and when required.
Sounds like a human brain. Good luck with that design.
Other than that actually restricting the domain would be the place to start. Additionally focus on what the users want.
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There is no "do-it-all" design pattern. Each pattern is suited for a specific programming task.
What you need to do here is to build a complex Rules Engine that takes in a set of rules (criteria) and emits a set of ordered steps/actions that need to be performed for the specified rules.
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