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What are the pros/cons of choosing between static and instance data access classes in a web app?

Answer 1

A:

My general feeling is: Why instantiate if you don't have to?

I use static classes when there wont be any use for multiple instances and there isn't a need for instance members. As for the DAL, the point is that there is only one. Why instantiate it if there is no value in it?

Look at this link, which shows that static method calls are faster than instance class method calls.

This link shows that an advantage of using a static class is that the compiler can check to make sure that no instance members are accidentally added.

This link shows that a static class can be used as a convenient container for sets of methods that just operate on input parameters and do not have to get or set any internal instance fields. For a DAL, this is exactly what you have. There is no reason to create any internal instance fields, and therefore, no reason to instantiate.

Gabriel McAdams 2010-01-20 01:10:05

There is a lot of value in instantiating. I personally feel the exact opposite: Only go static if there is a compelling reason for the type/data/method/etc to be treated statically.

Reed Copsey 2010-01-20 01:14:03

My general feeling is: Why make it static when you don't need to?

yodaj007 2010-01-20 01:15:29

@yoda and @Reed: You seem to feel that my answer is incorrect. In your opinion, what are the downsides to static classes?

Gabriel McAdams 2010-01-20 01:24:16

Major downside (and I've seen it happen many times): as things get more complex over time, you end up with big monolithic methods because all your state has to be passed as method args, since you can't (practically) use static fields to store state in a multi-threaded app. As the complexity and depth grows, people get lazy and instead of encapsulating something in a new method, everything gets stuffed inline, copied, pasted, looped, etc. Same thing can happen with instance methods, but it's much easier to refactor with instance fields/properties.

nitzmahone 2010-01-20 01:54:15

@Nitz: That sounds like a downside to bad development practices, and the lack of code-reviews.

Gabriel McAdams 2010-01-20 01:57:11

@Gabriel McAdams: Static classes have quite a few downsides for anything but very simple utility classes (ie: System.Math). They tend to be more difficult in threaded scenarios, since you need extra locking. They're more difficult to test, and to mock out when you need to do complex testing (very important for a DAL). They're less flexible, since they break polymorphism. Basically, a static class locks you into a fixed, rigid design - in most cases, creating a class non-static is much cleaner. Worst case, if you really want static, consider a singleton...

Reed Copsey 2010-01-20 16:39:56

Answer 2

+2 A:

Static based approaches really typically have one, and only one, main advantage: they're easy to implement.

Instance based approaches win for:

Threading and Concurrency - You don't need any/as much synchronization, so you get better throughput
Scalability - Same issues as above
Perf. - Same issues as above
Testability - This is much easier to test, since mocking out an instance is easy, and testing static classes is troublesome

Static approaches can win on:

Memory - You only have one instance, so lower footprint
Consistency/Sharing - It's easy to keep a single instance consistent with itself.

In general, I feel that instance-based approaches are superior. This becomes more important if you're going to scale up beyond a single server, too, since the static approach will "break" as soon as you start instancing it on multiple machines...

Reed Copsey 2010-01-20 01:13:25

I'd appreciate knowing why the downvotes...?

Reed Copsey 2010-01-20 16:32:17

I think the pros far outweigh the cons, at least in my opinion. And as for Memory consumption, I think that is probably a negligible downside in most applications.

Kevin Babcock 2010-01-28 15:55:51

@Kevin Babcock: I personally almost always try to use instance based approachs. If I want/need static, I usually go to a singleton, since that's easier to adapt to a multiton or to an instance approach later (since you're still working with instances...)

Reed Copsey 2010-01-28 16:34:18

Answer 3

A:

I have been using a static DAL for years, and I agree with your concerns. Threading and concurrency is the most challenging and in my case I store different connection objects in thread static structures. It has proven to be very scalable and performs well, even more so now that I am converting PropertyInfo into PropertyDescriptor which gives me the same benefits of reflection with better performance. In my DAL I simply have to write:

 List<Entity> tableRows = SQL.Read(new SearchCriteria(), new Table());

Everything spawns off the SQL static class, and that makes my code a lot simpler.

Otávio Décio 2010-01-20 01:15:23

What kind of concurrency issues have you run into with your approach?

Kevin Babcock 2010-01-28 15:56:38

The way I have it set up I run one connection object per thread. One concurrency issue I had to deal with was when you insert a new object, get its generated primary key (from a sequence or identity) and populate the object's PK value - if you are not careful you end up doing many inserts and getting the wrong sequence messing up the FK relationship.

Otávio Décio 2010-01-28 20:40:24

Answer 4

A:

For me the main reason is that I don't need to keep the state of that DAL object. The state of the objects it uses don't span the scope of the method they are embeded. This way why would you keep multiple instances of an object, if they are all the same?

With the latest versions of the ADO.NET, seems to be best practice to create and destroy the connection to the database within the scope of your call, and let the ConnectionPool take care of the whole connection reusability issue anyway.

Again with the latest versions of the .NET Framework, TransactionScope (which would be one reason to manage your connections yourself) move up to the business level, which allow you to join multiple calls to the DAL within the same Scope.

So I can't see a compeling case to create and destroy (or cache) instances of the DAL.

Wagner Silveira 2010-01-20 01:55:47

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What are the pros/cons of choosing between static and instance data access classes in a web app?

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