I've used the Entity Framework Power Tools Beta 2 to reverse engineer my model classes.
However no primary keys have been declared in the data annotations.
Is there a way to do this?
By default, the mapping done via fluent.
If you want to change that, you can customize the TT files used to generate the model. Where you would remove it from the mapping.tt and then add the data annotation to entity.tt. Rowan Miller made a great post about that.
Related
As per my understaning, 3 layered model is of UI, BLL and DAL. Now am assuming that writing insertData() funcationality, in this case i'll bind all UI-controls value to Business Entity and pass to the BLL --> DAL(since busines entity accessible to all 3 layers). let DAL replace with Linq to SQL, and now i have confusion , Linq to SQL will create classes (equalent to Business enitity) also i ahve business entity on the otherhand in my projects solution,
Q1) Do i need to have both B-entity and L2S classes?
Q2) is it possible to remove business entity and L2S classes to use in the same way? if so how?
Q3) better idea?
Thanks for help.
Yogesh
It is possible to use POCOs (your BLL layer classes) with Linq to SQL; Google around for "Linq to SQL POCO" (here is one blog post).
If you are starting a new project, it may also be worth looking in to the Entity Framework instead of Linq to SQL (or if you can use non-MS libraries, maybe even NHibernate; The 3.0 release just came out, I believe it supports Linq).
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'm reading the book "ASP.NET 3.5 Social Networking - Andrew Siemer" and I got confused when he uses Repositories to access the data.
Here is the idea of his code:
public interface IAccountRepository
{
Account GetAcountByID(int acId);
void SaveAccount(Account account);
List<Account> GetAllAccounts();
}
public class AccountRepositoryLINQ : IAccountRepository
{
Account GetAcountByID(int acId){
..... LINQ query .....
...... return.....
}
void SaveAccount(Account account){
..... LINQ .....
}
List<Account> GetAllAccounts(){
..... LINQ query .....
...... return.....
}
}
The class "Account" is the one generated automatically on the "LINQ to SQL Classes".
Some of the problems I see:
1º
I code my business layer, GUI, etc... and later in time the table Accounts in the database is changed (example: change the name of one column), then I need to rebuild the "LINQ to SQL Classes" and all my code layers will need to be recoded because my "Account" object changed.
2º
If I need to have other repositories (MySQL, Oracle, XML, other), what "Account" class will I use?
What to do?
Shouldn't I use a custom Account class? This will be used in all application layers.
How do the mapping from LINQ to my custom Account class?
Using simple "myClass.Name = linqClass.Name;" ???
Isn't this consuming machine resources if I need to "map" all the classes?
There isn't a easiest/lightest way to do it?
Is this the correct approach? Is there other ways?
Good instinct..
My suggestion is to abstract away the LinqToSQL objects, and create a set of Business Domain Objects. Then the Repository can query for the needed data and map them to the Domain objects that your application uses, and return those. Now your Data Access layer is decoupled from your application, and you can now do all of the things you listed.
The mapping can be a pain, so look at tools like Automapper to accomplish this.
I have a love hate relationship with LINQ to SQL classes myself, but I thought I'd play devils advocate :-), firstly addressing the points you made:-
1º I code my business layer, GUI,
etc... and later in time the table
Accounts in the database is changed
(example: change the name of one
column), then I need to rebuild the
"LINQ to SQL Classes" and all my code
layers will need to be recoded because
my "Account" object changed.
The general approach is that you'd add behaviour to the partial classes generated by LINQ to SQL, these files won't be replaced when you refresh a table from the data context. If you change the name of the column and don't want to change the rest of your code just update the class in the designer to use the old column name?
Even if you used POCOs for persistence with NHibernate for instance you'd still need to change the mapping so I don't really see this as an issue.
2º If I need to have other repositories (MySQL, Oracle, XML, other),
what "Account" class will I use?
Personally I'd call YAGNI on this one, if you really anticipate needing support for multiple databases LINQ to SQL might not be the best solution to start with in any case (simply to keep your infrastructure consistent across the application), tools like NHibernate would have far better support for such situations.
Moving on to adding a custom account class, mapping code can be taken care of by tools like AutoMapper, though this might mean you give up things like lazy loading (which may or may not be a big deal to you).
In the end it can be quite empowering to have full control over your entities (e.g. not having to use a parameterless constructor, control over instatiation etc, simple user types that map to one or two columns) and if you feel that your application might benefit from this it's probably the way to go, but you will pay the price in the repository implementation which will be complicated by mapping code and handling whether things need to be updated / deleted / inserted.
A good middle ground might be to simply code to an interface (e.g. IAccount) this should define the properties and method you expect from an account. Your repository would then become
IAccount GetById(int accountId);
You'll then give yourself freedom over what the implementation is (i.e. whether it's implemented by a LINQ to SQL class or a projection / mapping) and if you do opt for a custom class in future it'd be a simple case of moving the implementation to that class and altering the repository implementation.
In the end it's down to the application, if you think it's going to end up a huge application with extremely complex business logic by all means I would opt for a segregated domain layer that at least tries to be persistence ignorant. If, however, it isn't and opting for the repository pattern is simply a means to achieve good testability and a simple abstraction above your data access. I don't see why explicitly referencing LINQ to SQL classes and using them as a simple domain layer is such a big deal.
I personally use a combination of NHibernate and FluentNHibernate and seperate my domain(business objects) from all other things. I use messages from my other layers, like a GUI, to my domain which has a handler which injects repositories inside that hydrate the object(s) in question and perform the business logic, the interfaces in the repositories above are a nice way to decouple if you want to use other implementations of repositories or data access.
I'm trying to find a way to generate Linq to SQL classes with bi-directional serialization attributes. Basically I want a DataMember tag (with an appropriate order) on every association property, not just the ones where the class is the primary key (like the Visual Studio generator and SQL Metal do). I checked MyGeneration, but didn't really find anything that worked for me. I thought the T4 Toolbox was going to be my solution, it would be quite easy to modify it to add the attributes, but I get an exception on the calling side of my WCF service, and I've gotten no response back on the issue. I'm about to try installing CodeSmith and using PLINQO, but I'd prefer something free.
I'm pretty close to just writing my own T4 generator, but before I do that, I was hoping to find an pre-built solution to this rather simple problem first.
I ended up writing my own code generator for our L2S classes. We actually generate two sets of classes. One is a "lightweight" set of entities for client application use. These classes have no L2S plumbing. But they have the full datamember attributes with proper order. Then we have our L2S entities, which are strictly for backend use. This has worked out quite well.
Be careful using PLINQO. I've looked at that product extensively. In fact, much of my code generator is based on the code PLINQO generates. However, they have a "major flaw" (their words) in how they have implemented many to many relationships.
You might want to also look at a product named "Reegenerator".
Randy
This turned out to be the solution to my problem. I had just resigned myself to start researching my own generator when I stumbled upon that. It has a bidirectional serialization option and it works great! Here's a link to the author's bog, which contains a great video example of how to get started.
What if you need to create POCO objects from a dbml file? Do you use a generator and who? You write the POCO's manually?
Say you like to make your objects Persistent Ignorant and share to clients, then create a DAO pattern for the communication between Client - DAO - L2S Objects, this is a question for disconnected design using Linq 2 SQL. Supposed that the POCO's using the client should be as much as primitive as they can be without dependencies (EntityRef<>, EntitySet<>, Attributes, etc.), and ofcourse you could cast the L2S object into the POCO with the appropriate DATA.
Any help and any corrections on the concept would be really helpful!
I would be tempted to say "wait until EF in .NET 4.0", which has much improved POCO support (compared to EF current) and hopefully a POCO T4 template in VS2010.
At the moment SqlMetal will emit rich objects; while LINQ-to-SQL can work on POCO types, you would have to write the POCOs yourself, or use xslt / T4 / whatever on the dbml.
SqlMetal can emit an XML mapping file from an input DBML file via the /map[:file] switch. This removes attributes from the generated class files, which is a step closer to POCO - you just have to remember to initialize your data context instances from the XML mapping file.
Removing EntitySet<T> and EntityRef<T> references is harder, and I'm not sure it's something I would recommend as you would lose a lot of useful functionality. However, it is possible - you need to manually manipulate the DBML file that you pass to SqlMetal by removing all <Association> elements. You could do this using LINQ to XML as a custom step in your build process, for example.
This would basically disable associations in the output mapping file and classes, as SqlMetal will only generate EntitySet / EntityRef code for <Association> mappings. You lose the ability to manage parent-child relationships automatically though.
That would give you a pretty close POCO pattern - the only other thing you would get is the INotifyPropertyChanging implementation, but I think you could justify hanging onto that as it is fairly generic.
If that doesn't meet your needs then you could look at doing your own code generation - check out T4 templates for LINQ to SQL which works in VS 2008 and is based on SqlMetal, but you have the option to totally customize the output to suit your needs as it uses T4 for template specification and output generation.
We also use Linq2Sql and need to write own model classes from L2S results. After lot of googling I've found T4 POCO Templates for Linq2Sql and EF which uses .dbml or .edmx files as a source and create own POCO entities.
Link to download at the bottom of the article or duplicated here.
We used it as a base and then customized it for our needs.