My question has to do with the WCF and typed factory facilities that is provided by Windsor. I am quite new to the IoC container concepts and especially facilities but started looking into it after evaluating a project we wrote a while back. The program is n-layered and not very unit testable because dependency injection is not implemented everywhere. The issue is that since it is n-layered, to do a proper DI would end up making the top layer responsible for creating an instance of something that will get used like 5 layers down; so I turned to IoC.
However, after reading many a SO article and other sites I am now stuck with a couple of issues. One of the main issues initially was to decouple a class from a physical implementation of a WCF service and I did it as follows:
service = ManagerService.IoC.Resolve<IGridSubmitWorkService>(new { binding = new BasicHttpBinding(), remoteAddress = new EndpointAddress(WorkerAddress) });
result = service.SubmitWorkUnit(out errorString, aWorkUnit);
ManagerService.IoC.Release(service);
However, I found multiple mentions as to how you should not be using IoC.Resolve<>() and should rather use factories and WCF facilities to remove the dependency on your IoC container and that it is a service locator pattern which some people consider to be an anti-pattern.
My issue is this: The above three lines of code solves almost all my problems but to follow the proper patterns I have to instead create a WCF facility, a typed factory (that will deal with providing me instances of the class where this code is used) and a new interface for the factory and this feels like over-engineering and adding unnecessary complication to the code just for the sake of pleasing a pattern.
Question 1: Is there something fundamental I am missing here?
Question 2: As you can see from the code, I am calling a non-empty constructor for the web service. Will this still be as simple if I implement a WCF facility?
Question 3: Can you point me to a decent tutorial on using WCF facilities since I found the explanations on the Windsor wiki to be very brief and not really useful?
Thanks
Q1. Yes I think there is something important being missed. In your three line example, all you have done is replaced one implementation dependency (your GridSubmitWorkService) with another one (ManagerService.IoC). To illustrate, why not make it even simpler with the following?
service = new GridSubmitWorkService(binding,remoteAddress);
result = service.SubmitWorkUnit();
This is even simpler again but it has the hardwired implementation dependency. The point is that constructor and property injection allow you to write clean components that do not have to understand how the plumbing is done. In both your code and my code that principle is violated - the components are managing their own plumbing and in a large application, that becomes very painful, very quickly. This is why ServiceLocator is considered by many to be an anti-pattern.
The name of your service locator itself gives the game away. It's called IoC - abbreviation for Inversion of Control. But when you look at the structure of these two bits of code you can clearly see that nothing has been inverted - the code is doing pretty much the same thing in both cases, but your example is just a little more abstract and convoluted.
Also no-one offering IoC is trying to force you to stick to a pattern. If you don't see the benefit or the benefits simply aren't there for your app, then please don't use the pattern.
Q2. Any decent DI container is based on constructor injection. Using the Windsor WCF facility is very straight-forward and it supports a variety of hosting methods so things like bindings and addresses are handled properly anyway.
Q3. There is plenty of information around ranging from forums to questions here on stackoverflow.com, in addition to the Windsor docs and wikis. I suggest putting a specific question if there is something you are unable to resolve.
I tried out EF back in .NET 3.5 SP1, and I was one of the many who got frustrated and decided to learn LINQ to SQL instead. Now that I know EF is the "chosen" path forward, plus EF 4.0 has some exciting new features, I'd like to migrate my app to EF 4.0.
Can anyone suggest any good resources that are specifically targeted towards 4.0 and L2S migration? NOTE: I can find plenty of blogs and articles related to migrating from L2S to EF on .NET 3.5, but I feel like many of those were obviously dated and unhelpful to someone using 4.0.
I'd really like as much deep, under-the-hood stuff as I can get; I want to really come away feeling like I know EF 4.0 the way I currently know L2S 3.5.
TIA!
I have done loads of this very type of conversion and FWIW, I would say there are more similarities than differences. I don't think there is any definitive documentation that will make you feel like an expert in EF4, beyond the stuff that is already out there...
http://msdn.microsoft.com/en-us/library/ex6y04yf(VS.100).aspx
What I can give you are the more obvious "gotchas." Specifically, Linq2Sql wanted to combine the business layer and the data layer a lot more obviously. It really pushed you to create your own partial classes. I could go on and on about way, but the most specific reason is the way the one-to-one mapper will create public parent and child properties for all relations.
If you attempt to use any type of serialization against this model, you will like run into circular reference problems as a serializer moves from a parent to a child and then back to the parent as the Linq2Sql serialization behavior automatically includes all children in the graph. This can also be really annoying when you try to grab a customer record to check the "Name" property and automatically get all the related order records included in the graph. You can set these parent and child navigation properties to be either "public" or "internal" which means if you want access to them, but don't want the serializers to automatically create circular references, you pretty much have to access them in partial classes.
Once you start down the partial class path you generally just continue the pattern and eventually will start to add helper methods for accessing your data into your individual entity classes. Also, with the Linq2Sql DataContext being more lightweight, you often find people using some kind of Singleton pattern or Repository pattern for their context. You don't see this as much at all with EF 3.5 / 4.
So let's say you have some environment similar to the one described and you want to start converting. Well, you need to find out when your DataContext is going to be create/destroyed...some people will just start each Business Layer method with a using() statement and let the context pretty much live for the lifetime of the method. Obviously this means you can get into some hairy situations that require adding .ToList() or some other extension method to the ends of your questions you can have a fully in-memory collection of your objects to pass to a child method or whatever and even then you can have problems with attempting to update entities on a context that they weren't originally retrieved from.
You'll also need to figure out how to much of the BusinessLogic incorporated in your Linq2Sql partial classes out into another layer if it doesn't deal explicitly with the data operations. This will not be painless as you figure out when you need/don't need your context, but it is for the best..
Next, you will want to deal with the object graph situation. Because of the difference in the way lazy-loading works (they made this configurable in EF 4.0 to make it behave more like Linq2Sql for those who wanted it) you will probably need to check any implied uses of child objects in the graph from your Linq2Sql implementation and verify that it doesn't now require an explicit .Include() or a .Load() to get the child objects in the graph.
Finally, you will need to decide on a serialization solution in general. By default, the DataContracts and DataMember attributes that are generated as part of an EF model work great with WCF, but not at all great with the XmlSerializer used for things like old .asmx WebServices. Even in this circumstance you might be able to get away with it if you never need to serialize child objects over the wire. Since that usually isn't the case, you are going to want to move to WCF if you have a more SOA, which will add a whole new host of opportunies, yet headaches.
In order to deal with the partial classes situation, and the hefty DataContext and even the serialization issues, there are a number of new code-generation templates available with EF 4.0. The POCO-Entity template has a lot of people excited as it creates POCO classes, just as you'd expect (the trouble is that excludes any class or member attributes for WCF etc etc). Also, the Self-Tracking Entities model pretty much solves the context issue, because you can pass your entities around and let them remember when and how they were updated, so you can create/dispose your contexts much more freely (like Linq2Sql). As another bonus, this template is the go-to template for WCF or anything that builds on WCF like RIA Services or WCF Data Services, so they have the [DataContract], [DataMember], and [KnownType] attributes already figured out.
Here is a link to the POCO template (not included out of the box):
(EDIT: I cannot post two hyperlinks, so just visit the visualstudio gallery website and search for "ADO.NET C# POCO Entity Generator")
Be sure to read the link on the ADO.net team blog about implementing this. You might like the bit about splitting your context and your entities into separate projects/assemblies if you fall into the WebService vs. WCF Service category. The "Add Service Reference..." proxy generation doesn't do namespaces the same way "Add Web Reference..." used to, so you might like to actually reference your entity class assembly in your client app so you can "exclude types from reference libraries" or whatever on your service references so you don't get a lot of ambiguous references from multiple services which use the same EF model and expose those entities...
I know this is long and rambling, but these little gotchas were waaay more of an issue for me than remembering to use context.EntityCollection.AddObject() instead of context.EntityCollection.InsertOnSubmit() and context.SaveChanges() instead of context.SubmitChanges()...
For EF Code First, it's mostly about reverse engineering the existing tables into EF classes. EF Power Tools now does this for you:
http://msdn.microsoft.com/en-us/data/jj200620.aspx
The rest is the obvious work of modifying your existing code to use those generated classes to talk to the database instead of LINQ to SQL.
I have encountered this topic lately and couldn't understand why they are needed.
Can you explain why I should use them in my projects and how they can ease my life.
Examples will be great, and where from I can learn this topic little more.
At least you have framed the question from the correct perspective =)
The usual reasons for using a code generator are given as productivity and consistency because they assume that the solution to a consistent and repetitive problem is to throw more code at it. I would argue that any time you are considering code generation, look at why you are generating code and see if you can solve the problem through other means.
A classic example of this is data access; you could generate 250 classes ( 1 for each table in the schema ) effectively creating a table gateway solution, or you could build something more like a domain model and use NHibernate / ActiveRecord / LightSpeed / [pick your orm] to map a rich domain model onto the database.
While both the hand rolled solution and ORM are effectively code generators, the primary difference is when the code is generated. With the ORM it is an implicit step that happens at run-time and therefore is one-way by it's nature. The hand rolled solution requires and explicit step to generate the code during development and the likelihood that the generated classes will need customising at some point therefore creating problems when you re-generate the code. The explicit step that must happen during development introduces friction into the development process and often leads to code that violates DRY ( although some argue that generated code can never violate DRY ).
Another reason for touting code generation comes from the MDA / MDE world ( Model Driven Architecture / Engineering ). I don't put much stock in this but rather than providing a number of poorly expressed arguments, I'm simply going to co-opt someone elses - http://www.infoq.com/articles/8-reasons-why-MDE-fails.
IMHO code generation is the only solution in an exceedingly narrow set of problems and whenever you are considering it, you should probably take a second look at the real problem you are trying to solve and see if there is a better solution.
One type of code generation that really does enhance productivity is "micro code-generation" where the use of macros and templates allow a developer to generate new code directly in the IDE and tab / type their way through placeholders (eg namespace / classname etc). This sort of code generation is a feature of resharper and I use it heavily every day. The reason that micro-generation benefits where most large scale code generation fails is that the generated code is not tied back to any other resource that must be kept in sync and therefore once the code is generated, it is just like all the other code in the solution.
#John
Moving the creation of "basic classes" from the IDE into xml / dsl is often seen when doing big bang development - a classic example would be developers try to reverse engineer the database into a domain model. Unless the code generator is very well written it simply introduces an additional burden on the developer in that every time they need to update the domain model, they either have to context-switch and update the xml / dsl or they have to extend the domain model and then port those changes back to the xml / dsl ( effectively doing the work twice).
There are some code generators that work very well in this space ( the LightSpeed designer is the only one I can think of atm ) by acting as the engine for a design surface but often
these code generators generate terrible code that cannot be maintained (eg winforms / webforms design surfaces, EF1 design surface) and therefore rapidly undo any productivity benefits gained from using the code generator in the first place.
Well, it's either:
you write 250 classes, all pretty much the same, but slightly different, e.g. to do data access; takes you a week, and it's boring and error-prone and annoying
OR:
you invest 30 minutes into generating a code template, and let a generation engine handle the grunt work in another 30 minutes
So a code generator gives you:
speed
reproducability
a lot less errors
a lot more free time! :-)
Excellent examples:
Linq-to-SQL T4 templates by Damien Guard to generate one separate file per class in your database model, using the best kept Visual Studio 2008 secret - T4 templates
PLINQO - same thing, but for Codesmith's generator
and countless more.....
Anytime you need to produce large amounts of repetetive boilerplate code, the code generator is the guy for the job. Last time I used a code generator was when creating a custom Data Access Layer for a project, where the skeleton for various CRUD actions was created based on an object model. Instead of hand-coding all those classes, I put together a template-driven code generator (using StringTemplate) to make it for me. The advandages of this procedure was:
It was faster (there was a large amount of code to generate)
I could regenerate the code in a whim in case I detected a bug (code can sometimes have bugs in the early versions)
Less error prone; when we had an error in the generated code it was everywhere which means that it was more likely to be found (and, as noted in the previous point, it was easy to fix it and regenerate the code).
Using GUI builders, that will generate code for you is a common practice. Thanks to this you don't need to manually create all widgets. You just drag&drop them and the use generated code. For simple widgets this really saves time (I have used this a lot for wxWidgets).
Really, when you are using almost any programming language, you are using a "code generator" (except for assembly or machine code.) I often write little 200-line scripts that crank out a few thousand lines of C. There is also software you can get which helps generate certain types of code (yacc and lex, for example, are used to generate parsers to create programming languages.)
The key here is to think of your code generator's input as the actual source code, and think of the stuff it spits out as just part of the build process. In which case, you are writing in a higher-level language with fewer actual lines of code to deal with.
For example, here is a very long and tedious file I (didn't) write as part of my work modifying the Quake2-based game engine CRX. It takes the integer values of all #defined constants from two of the headers, and makes them into "cvars" (variables for the in-game console.)
http://meliaserlow.dyndns.tv:8000/alienarena/lua_source/game/cvar_constants.c
Here is the short Bash script which generated that code at compile-time:
http://meliaserlow.dyndns.tv:8000/alienarena/lua_source/autogen/constant_cvars.sh
Now, which would you rather maintain? They are both equivalent in terms of what they describe, but one is vastly longer and more annoying to deal with.
The canonical example of this is data access, but I have another example. I've worked on a messaging system that communicates over serial port, sockets, etc., and I found I kept having to write classes like this over and over again:
public class FooMessage
{
public FooMessage()
{
}
public FooMessage(int bar, string baz, DateTime blah)
{
this.Bar = bar;
this.Baz = baz;
this.Blah = blah;
}
public void Read(BinaryReader reader)
{
this.Bar = reader.ReadInt32();
this.Baz = Encoding.ASCII.GetString(reader.ReadBytes(30));
this.Blah = new DateTime(reader.ReadInt16(), reader.ReadByte(),
reader.ReadByte());
}
public void Write(BinaryWriter writer)
{
writer.Write(this.Bar);
writer.Write(Encoding.ASCII.GetBytes(
this.Baz.PadRight(30).Substring(0, 30)));
writer.Write((Int16)this.Blah.Year);
writer.Write((byte)this.Blah.Month);
writer.Write((byte)this.Blah.Day);
}
public int Bar { get; set; }
public string Baz { get; set; }
public DateTime Blah { get; set; }
}
Try to imagine, if you will, writing this code for no fewer than 300 different types of messages. The same boring, tedious, error-prone code being written, over and over again. I managed to write about 3 of these before I decided it would be easier for me to just write a code generator, so I did.
I won't post the code-gen code, it's a lot of arcane CodeDom stuff, but the bottom line is that I was able to compact the entire system down to a single XML file:
<Messages>
<Message ID="12345" Name="Foo">
<ByteField Name="Bar"/>
<TextField Name="Baz" Length="30"/>
<DateTimeField Name="Blah" Precision="Day"/>
</Message>
(More messages)
</Messages>
How much easier is this? (Rhetorical question.) I could finally breathe. I even added some bells and whistles so it was able to generate a "proxy", and I could write code like this:
var p = new MyMessagingProtocol(...);
SetFooResult result = p.SetFoo(3, "Hello", DateTime.Today);
In the end I'd say this saved me writing a good 7500 lines of code and turned a 3-week task into a 3-day task (well, plus the couple of days required to write the code-gen).
Conclusion: Code generation is only appropriate for a relatively small number of problems, but when you're able to use one, it will save your sanity.
A code generator is useful if:
The cost of writing and maintaining the code generator is less than the cost of writing and maintaining the repetition that it is replacing.
The consistency gained by using a code generator will reduce errors to a degree that makes it worthwhile.
The extra problem of debugging generated code will not make debugging inefficient enough to outweigh the benefits from 1 and 2.
For domain-driven or multi-tier apps, code generation is a great way to create the initial model or data access layer. It can churn out the 250 entity classes in 30 seconds ( or in my case 750 classes in 5 minutes). This then leaves the programmer to focus on enhancing the model with relationships, business rules or deriving views within MVC.
The key thing here is when I say initial model. If you are relying on the code generation to maintain the code, then the real work is being done in the templates. (As stated by Max E.) And beware of that because there is risk and complexity in maintaining template-based code.
If you just want the data layer to be "automagically created" so you can "make the GUI work in 2 days", then I'd suggest going with a product/toolset which is geared towards the data-driven or two-tier application scenario.
Finally, keep in mind "garbage in=garbage out". If your entire data layer is homogeneous and does not abstract from the database, please please ask yourself why you are bothering to have a data layer at all. (Unless you need to look productive :) )
How 'bout an example of a good use of a code generator?
This uses t4 templates (a code generator built in to visual studio) to generate compressed css from .less files:
http://haacked.com/archive/2009/12/02/t4-template-for-less-css.aspx
Basically, it lets you define variables, real inheritance, and even behavior in your style sheets, and then create normal css from that at compile time.
Everyone talks here about simple code generation, but what about model-driven code generation (like MDSD or DSM)? This helps you move beyond the simple ORM/member accessors/boilerplate generators and into code generation of higher-level concepts for your problem domain.
It's not productive for one-off projects, but even for these, model-driven development introduces additional discipline, better understanding of employed solutions and usually a better evolution path.
Like 3GLs and OOP provided an increase in abstraction by generating large quantities of assembly code based on a higher level specification, model-driven development allows us to again increase the abstraction level, with yet another gain in productivity.
MetaEdit+ from MetaCase (mature) and ABSE from Isomeris (my project, in alpha, info at http://www.abse.info) are two technologies on the forefront of model-driven code generation.
What is needed really is a change in mindset (like OOP required in the 90's)...
I'm actually adding the finishing touches to a code generator I'm using for a project I've been hired on. We have a huge XML files of definitions and in a days worth of work I was able to generate over 500 C# classes. If I want to add functionality to all the classes, say I want to add an attribute to all the properties. I just add it to my code-gen, hit go, and bam! I'm done.
It's really nice, really.
There are many uses for code generation.
Writing code in a familiar language and generating code for a different target language.
GWT - Java -> Javascript
MonoTouch - C# -> Objective-C
Writing code at a higher level of abstraction.
Compilers
Domain Specific Languages
Automating repetitive tasks.
Data Access Layers
Initial Data Models
Ignoring all preconceived notions of code-generation, it is basically translating one representation (usually higher level) to another (usually lower level). Keeping that definition in mind, it is a very powerful tool to have.
The current state of programming languages has by no means reached its full potential and it never will. We will always be abstracting to get to a higher level than where we stand today. Code generation is what gets us there. We can either depend on the language creators to create that abstraction for us, or do it ourselves. Languages today are sophisticated enough to allow anybody to do it easily.
If with code generator you also intend snippets, try the difference between typing ctor + TAB and writing the constructor each time in your classes. Or check how much time you earn using the snippet to create a switch statement related to an enum with many values.
If you're paid by LOC and work for people who don't understand what code generation is, it makes a lot of sense. This is not a joke, by the way - I have worked with more than one programmer who employs this technique for exactly this purpose. Nobody gets paid by LOC formally any more (that I know of, anyway), but programmers are generally expected to be productive, and churning out large volumes of code can make someone look productive.
As an only slightly tangential point, I think this also explains the tendency of some coders to break a single logical unit of code into as many different classes as possible (ever inherit a project with LastName, FirstName and MiddleInitial classes?).
Here's some heresy:
If a task is so stupid that it can be automated at program writing time (i.e. source code can be generated by a script from, let's say XML) then the same can also be done at run-time (i.e. some representation of that XML can be interpreted at run-time) or using some meta-programming. So in essence, the programmer was lazy, did not attempt to solve the real problem but took the easy way out and wrote a code generator. In Java / C#, look at reflection, and in C++ look at templates
Using Linq to SQL, and a DDD style Domain Layer with de-coupled repositories, does anyone have any good ideas on how to implement a specification pattern without bleeding L2S concerns up into the domain layer, that is still understandable? :)
We have complex business logic surrounding the selection of a set of transaction data, and would like those rules/specifications to be owned by the Domain. We've also done a good job of keeping our domain persistence ignorant.
This presents a problem, because in order to implement a Specification, the domain (as far as I can tell) needs to see the types being queried (L2S types).
Any ideas?
Also, nHibernate is out of the question for reasons I don't want to explain.. :)
Have you considered mapping your generic Specifications into an Expression tree that would translate into proper L2S syntax? It seems that is the main problem you are hitting here. The Specification pattern isn't the problem, but the mapping to L2S is.
Linq-To-Sql classes can be partial. This means that you can extend them by implementing a partial that implements a common interface. That Interface can be shared between layers without the "bleeding" problem you are describing. The rest is just the details of your "IsStatisfiedBy" which should be easy to encapsulate.
I recently had the same issue. Different pattern, but still LINQ to SQL (L2S). I tried two different ways to avoid the leakage.
First we tried using DTOs and a mapping layer. So we wrote super simple objects that had a one to one mapping to the tables. They were all decorated with L2S attributes. We then wrote a mapping layer to map the DTOs to our business objects. All of this was hidden via the Repository pattern from Doman Driven Design. So consumers of the business objects had no idea the L2S was under the hood.
Next, mostly for variety. We tried using the XML mapping features of L2S so the objects themselves needed no attributes. For collections we exposed IEnumerable instead of any of L2S collections. If you looked at the internals of the business classes you could still detect some usage of L2S (EntitySet or Ref). But consumers of the class had no idea. So some bits of leakage but nothing drastic.
In the end we stuck with the first pattern. The second worked and we could have replaced L2S without changing the interface of the business layer, but I was never happy with XML mapping. The first pattern had a much cleaner separation between the database and the business objects. It took more code. The first one also worked better for us because it allowed us to evolve the business objects differently than the tables. In the early days of the project the xml mapping worked because our objects were pretty much one to one with the tables.
So in the end we put a layer between L2S and the domain. It worked. It took more code, but it was really simple stuff. And it was all very testable.
If you want to avoid referencing Linq2Sql from your domain layer, you must work against interfaces that represent your entities instead of working with the actual entities themselves. You then need a mapping layer between your interfaces and your entities.
I've worked this way and found it to be a severe hindrance. I switched to NHibernate for new projects and for the older projects I simply stopped worrying about the domain referencing Linq2Sql entities directly. Overcoming that restriction is simply too much of a time-cost in my opinion.
I just started creating my data-access layer using LinqToSql. Everybody is talking about the cool syntax and I really like Linq in general.
But when I saw how your classes get generated if you drag some tables on the LinqContext I was amazed: So much code which nobody would need?!
So I looked how other people used LinqToSql, for example Rob Connery at his StoreFront Demo.
As I don't like the way that all this code is generated I created my domain layer by hand and used the generated classes as reference. With that solution I'm fine, as I can use the features provided by Linq (dereferred execution, lazy loading, ...) and my domain layer is quite easy to understand.
How are you using LinqToSql?
The created classes are not as heavy as it seems. Of course it takes quite a few lines of code, but all in all it is as lightweight as it can be for the features it's providing.
I used to create my own tables, too, but now instead I just use the LINQtoSQL DataContext. Why? Creating is simpler, the features are better, interoperability works, it is probably even faster than my own stuff (not in every aspect. Usually my own stuff was extremely fast in one thing, but the generic stuff was faster in everything else).
But the most important part: it is easier to bring new developers into the LINQ stuff than into my own. There are tutorials, example codes, documentation, everything, which I'd have to create for my code by myself. Same with using my stuff with other technology, like WCF or data binding. There are a lot of pitfalls to be taken care of.
I learned not to develop myself into a corner the hard way, it looks fast and easy at the start, is a lot more fun than learning how to use the libs, but is a real pain in the a after a few months down the road, usually even for myself.
After some time the novelty of creating my own data containers wears off, and I noticed the pain connected to adding a feature. A feature I would have had for free, if I had used the provided classes.
Next thing I had to explain my code to some other programmer. Had I used the provided classes, I could have pointed him to some web site to learn about the stuff. But for my classes, I had to train him himself, which took a long time and made it hard to get new people on a project.
LinqToSql generates a set of partial classes for your tables. You can add interface definitions to the 'other half' of these partial classes that implement your domain model.
Then, if you use the repository pattern to wrap access to the Linq queries, so that they return interface implementations of your objects (the underlying Linq objects), LinqToSql becomes quite flexible.
You can hand-write your own classes and either use the LINQ to SQL attributes to declare the mappings or an external XML file.
If you would like to stick with the existing designer and just modify the code generation process pick up my templates that let you tailor the generated code.
Use compiled queries. Linq to SQL is dog slow otherwise. Really.
We use our hand crafted domain model, along with the generated classes, plus a simple utility which utilizes reflection to convert between them when needed. We've contemplated writing a converter generator if we reach a point where reflection creates a performance bottleneck.