I'm doing some exercises on Data Access Layer in ASP.NET webforms. It looks to me as if everything I'm trying to do with DataSets, I can do with the Entity Framework. So today, does it make sense to learn DataSets? So many steps with DataSets just to get the same result as EF.
Do you need to know how to ride a bicycle in order to drive a car? Nope. Does it hurt to know both? Nope.
If you're going to use EF you don't need to know datasets; EF is an abstraction built on top of traditional ADO.NET. At the same time, knowing how the underlying ADO connections/readers/etc work doesn't hurt, it helps you understand what is going on underneath.
However, knowing SQL Server, TSQL, and a bit (or more) about how the SQL optimizer works is more important than knowing ADO.NET if you're going to use EF (or any other OR mapper). Although much of that is also "hidden" by OR mappers it is still important to know what goes on "behind the scenes" to avoid making mistakes that can hurt performance etc.
What I find really powerful in ADO.NET Entities or LINQ to SQL, is the ability to model complex queries. I really don't need the mappings that Entities or LINQ to SQL are doing for me - I just need the ability to model complex expressions that can be translated into T-SQL.
My question is - am I abusing too much? Can I use the Entity Framework for modeling queries and just that? Should I? I know I can write my own custom LINQ to SQL provider, but that is just not possible to handle in the time spans I have.
What is the best approach to model complex T-SQL queries? How do you handle conditional group byes, orders, joins, unions etc in the OOP world? Using StringBuilders for this kind of job feels too ugly and harder to maintain given the possibilities we have with Expression Trees.
When I use StringBuilder to model a complex SQL Query I feel kind of guilty! I feel the same way as when I have to hard code any number into my code that is different than 0 or 1. Feeling that makes you ask yourself if there is a better and cleaner way of doing it...
I must mention that I am using C# 4.0, but I am not specifically looking for an answer in this language, but rather in the domain of CLR 4. Are there any real enterprise libraries that can help with constructing complex SQL at runtime?
If you find it easier (not to mention less error prone) to compose a query in LINQ rather than T-SQL, then why not?
There is no law written that says you can't use EF or L2S to help you write T-SQL, and then just go off and execute the T-SQL directly yourself.
In fact I think this makes a lot of sense.
Don't feel guilty!
I am new to CSLA and Entity Framework. I am creating a new CSLA / Silverlight application that will replace a 12 year old Win32 C++ system. The old system uses a custom DCOM business object library and uses ODBC to get to SQL Server. The new system will not immediately replace the old system -- they must coexist against the same database for years to come.
At first I thought EF was the way to go since it is the latest and greatest. After making a small EF model and only 2 CSLA editable root objects (I will eventually have hundreds of objects as my DB has 800+ tables) I am seriously questioning the use of EF.
In the current system I have the need many times to do fine detail performance tuning of the queries which I can do because of 100% control of generated SQL. But it seems in EF that so much happens behind the scenes that I lose that control. Article like http://toomanylayers.blogspot.com/2009/01/entity-framework-and-linq-to-sql.html don't help my impression of EF.
People seem to like EF because of LINQ to EF but since my criteria is passed between client and server as criteria object it seems like I could build queries just as easily without LINQ. I understand in WCF RIA that there is query projection (or something like that) where I can do client side LINQ which does move to the server before translation into actual SQL so in that case I can see the benefit of EF, but not in CSLA.
If I use raw ADO.NET, will I regret my decision 5 years from now?
Has anyone else made this choice recently and which way did you go?
In your case, I would still choose EF over doing it all by hand.
Why? EF - especially in .NET 4 - has matured considerably. It will allow you to do most of your database operations a lot easier and with a lot less code than if you have to all hand-code your data access code.
And in cases where you do need the absolute maximum performance, you can always plug in stored procedures for insert, update, delete which EF4 will then use instead of the default behavior of creating the SQL statements on the fly.
EF4 has a much better stored proc integration, and this really opens up the best of both worlds:
use the high productivity of EF for the 80% cases where performance isn't paramount
fine tune and handcraft stored procs for the remaining 20% and plug them into EF4
See some resources:
Using Stored Procedures for Insert, Update and Delete in an Entity Data Model
Practical Entity Framework for C#: Stored Procedures (video)
You seem to have a mix of requirements and a mix of solutions.
I normally rate each requirement with an essential, nice to have, not essential. And then see what works.
I agree with what #marc_s has said, you can have the best of both worlds.
The only other thing I would say is that if this solution is to be around for the next 5 years, have you considered Unit Testing?
There's plenty of examples on how to set this up using EF. (I personally avoid ADO.Net just because the seperating of concerns is so complicated for Unit Tests.)
There is no easy solution. I would pick a feature in your project that would take you a day or so to do. Try the different methods (raw sql, EF, EF + Stored Procs) and see what works!
Take an objective look at CSLA - invoke the 'DataPortal' and check out the call stack.
Next, put those classes on a CI build server that stores runtime data and provides a scatter plot over a series of runs.
Next, look at the code that gets created. Ask yourself how you can use things like dependecy injection in light of classes that rely on static creators with protected/private constructors.
Next, take a look at how many responsibilities the 'CSLA' classes take on.
Finally ask yourself if creating objects with different constructors per environment make sense, and ask yourself how you will unit test those.
We have used Entity Framework on 2 projects both with several 100 tables.
Our experiance is mainly positive. We have had large productivity gains, compare with using Enterprise Library and stored procedures.
However, when I suggest using EF on stackoverflow, I often get negative comments.
On the negative side we have found that there is a steep learning curve for certain functionality.
Finally, to the question: What problems have people had with EF, why do they prefer other ORMS?
Like you, my experience with the EF is mostly positive. The biggest problem I've had is that very complex queries can take a long time to compile. The visual designer is also much less stable and has fewer features than the framework itself. I wish the framework would put the GeneratedCode attribute on code it generates.
I recently used EF and had a relatively good experience with it. I too see a lot of negative feedback around EF, which I think is unfortunate considering all that it offers.
One issue that surprised me was the performance difference between two strategies of fetching data. Initially, I figured that doing eager loading would be more efficient since it would pull the data via a single query. In this case, the data was an order and I was doing an eager load on 5-8 related tables. During development, we found this query to be unreasonably slow. Using SQL profiler, we watched the traffic and analyzed the resulting queries. The generated SQL statement was huge and SQL Server didn't seem to like it all that much.
To work around the issue, I reverted to a lazy-loading / on-demand mode, which resulted in more queries to the server, but a significant boost in performance. This was not what I initially expected. My take-away, which IMHO holds true for all data access implementations, is that I really need to perf test the data access. This is true regardless of whether I use an ORM or SQL procs or parameterized SQL, etc.
I use Entity Framework too and have found the following disadvantages:
I can't work with Oracle that is really necessary for me.
Model Designer for Entity Framework. During update model from database storage part is regenerated too. It is very uncomfortably.
Doesn't have support for instead of triggers in Entity framework.
Which approach is better: 1) to use a third-party ORM system or 2) manually write DAL and BLL code to work with the database?
1) In one of our projects, we decided using the DevExpress XPO ORM system, and we ran across lots of slight problems that wasted a lot of our time. Amd still from time to time we encounter problems and exceptions that come from this ORM, and we do not have full understanding and control of this "black box".
2) In another project, we decided to write the DAL and BLL from scratch. Although this implied writing boring code many, many times, but this approach proved to be more versatile and flexible: we had full control over the way data was held in the database, how it was obtained from it, etc. And all the bugs could be fixed in a direct and easy way.
Which approach is generally better? Maybe the problem is just with the ORM that we used (DevExpress XPO), and maybe other ORMs are better (such as NHibernate)?
Is it worth using ADO Entiry Framework?
I found that the DotNetNuke CMS uses its own DAL and BLL code. What about other projects?
I would like to get info on your personal experience: which approach do you use in your projects, which is preferable?
Thank you.
My personal experience has been that ORM is usually a complete waste of time.
First, consider the history behind this. Back in the 60s and early 70s, we had these DBMSes using the hierarchical and network models. These were a bit of a pain to use, since when querying them you had to deal with all of the mechanics of retrieval: follow links between records all over the place and deal with the situation when the links weren't the links you wanted (e.g., were pointing in the wrong direction for your particular query). So Codd thought up the idea of a relational DBMS: specify the relationships between things, say in your query only what you want, and let the DBMS deal with figuring out the mechanics of retrieving it. Once we had a couple of good implementations of this, the database guys were overjoyed, everybody switched to it, and the world was happy.
Until the OO guys came along into the business world.
The OO guys found this impedance mismatch: the DBMSes used in business programming were relational, but internally the OO guys stored things with links (references), and found things by figuring out the details of which links they had to follow and following them. Yup: this is essentially the hierarchical or network DBMS model. So they put a lot of (often ingenious) effort into layering that hierarchical/network model back on to relational databases, incidently throwing out many of the advantages given to us by RDBMSes.
My advice is to learn the relational model, design your system around it if it's suitable (it very frequently is), and use the power of your RDBMS. You'll avoid the impedance mismatch, you'll generally find the queries easy to write, and you'll avoid performance problems (such as your ORM layer taking hundreds of queries to do what it ought to be doing in one).
There is a certain amount of "mapping" to be done when it comes to processing the results of a query, but this goes pretty easily if you think about it in the right way: the heading of the result relation maps to a class, and each tuple in the relation is an object. Depending on what further logic you need, it may or may not be worth defining an actual class for this; it may be easy enough just to work through a list of hashes generated from the result. Just go through and process the list, doing what you need to do, and you're done.
Perhaps a little of both is the right fit. You could use a product like SubSonic. That way, you can design your database, generate your DAL code (removing all that boring stuff), use partial classes to extend it with your own code, use Stored Procedures if you want to, and generally get more stuff done.
That's what I do. I find it's the right balance between automation and control.
I'd also point out that I think you're on the right path by trying out different approaches and seeing what works best for you. I think that's ultimately the source for your answer.
Recently I made the decision to use Linq to SQL on a new project, and I really like it. It is lightweight, high-performance, intuitive, and has many gurus at microsoft (and others) that blog about it.
Linq to SQL works by creating a data layer of c# objects from your database. DevExpress XPO works in the opposite direction, creating tables for your C# business objects. The Entity Framework is supposed to work either way. I am a database guy, so the idea of a framework designing the database for me doesn't make much sense, although I can see the attractiveness of that.
My Linq to SQL project is a medium-sized project (hundreds, maybe thousands of users). For smaller projects sometimes I just use SQLCommand and SQLConnection objects, and talk directly to the database, with good results. I have also used SQLDataSource objects as containers for my CRUD, but these seem clunky.
DALs make more sense the larger your project is. If it is a web application, I always use some sort of DAL because they have built-in protections against things like SQL injection attacks, better handling of null values, etc.
I debated whether to use the Entity Framework for my project, since Microsoft says this will be their go-to solution for data access in the future. But EF feels immature to me, and if you search StackOverflow for Entity Framework, you will find several people who are struggling with small, obtuse problems. I suspect version 2 will be much better.
I don't know anything about nHibernate, but there are people out there who love it and would not use anything else.
You might try using NHibernate. Since it's open source, it's not exactly a black box. It is very versatile, and it has many extensibility points for you to plug in your own additional or replacement functionality.
Comment 1:
NHibernate is a true ORM, in that it permits you to create a mapping between your arbitrary domain model (classes) and your arbitrary data model (tables, views, functions, and procedures). You tell it how you want your classes to be mapped to tables, for example, whether this class maps to two joined tables or two classes map to the same table, whether this class property maps to a many-to-many relation, etc. NHibernate expects your data model to be mostly normalized, but it does not require that your data model correspond precisely to your domain model, nor does it generate your data model.
Comment 2:
NHibernate's approach is to permit you to write any classes you like, and then after that to tell NHibernate how to map those classes to tables. There's no special base class to inherit from, no special list class that all your one-to-many properties have to be, etc. NHibernate can do its magic without them. In fact, your business object classes are not supposed to have any dependencies on NHibernate at all. Your business object classes, by themselves, have absolutely no persistence or database code in them.
You will most likely find that you can exercise very fine-grained control over the data-access strategies that NHibernate uses, so much so that NHibernate is likely to be an excellent choice for your complex cases as well. However, in any given context, you are free to use NHibernate or not to use it (in favor of more customized DAL code), as you like, because NHibernate tries not to get in your way when you don't need it. So you can use a custom DAL or DevExpress XPO in one BLL class (or method), and you can use NHibernate in another.
I recently took part in sufficiently large interesting project. I didn't join it from the beginning and we had to support already implemented architecture. Data access to all objects was implemented through stored procedures and automatically generated wrapper-methods on .NET that returned DataTable objects. The development process in such system was really slow and inefficient. We had to write huge stored procedure on PL/SQL for every query, that could be expressed in simple LINQ query. If we had used ORM, we would have implement project several times faster. And I don't see any advantage of such architecture.
I admit, that it is just particular not very successful project, but I made following conclusion: Before refusing to use ORM think twice, do you really need such flexibility and control over database? I think in most cases it isn't worth wasted time and money.
As others explain, there is a fundamental difficulty with ORM's that make it such that no existing solution does a very good job of doing the right thing, most of the time. This Blog Post: The Vietnam Of Computer Science echoes some of my feelings about it.
The executive summary is something along the lines of the assumptions and optimizations that are incompatible between object and relational models. although early returns are good, as the project progresses, the abstractions of the ORM fall short, and the extra overhead of working around it tends to cancel out the successes.
I have used Bold for Delphi four years now. It is great but it is not available anymore for sale and it lacks some features like databinding. ECO the successor has all that.
No I'm not selling ECO-licenses or something but I just think it is a pity that so few people realize what MDD (Model Driven Development) can do. Ability to solve more complex problems in less time and fewer bugs. This is very hard to measure but I have heard something like 5-10 more efficient development. And as I work with it every day I know this is true.
Maybe some traditional developer that is centered around data and SQL say:
"But what about performance?"
"I may loose control of what SQL is run!"
Well...
If you want to load 10000 instances of a table as fast as possible it may be better to use stored procedures, but most application don't do this. Both Bold and ECO use simple SQL queries to load data. Performance is highly dependent of the number of queries to the database to load a certain amount of data. Developer can help by saying this data belong to each other. Load them as effiecent as possible.
The actual queries that is executed can of course be logged to catch any performance problems. And if you really want to use your hyper optimized SQL query this is no problem as long as it don't update the database.
There is many ORM system to choose from, specially if you use dot.net. But honestly it is very very hard to do a good ORM framework. It should be concentrated around the model. If the model change, it should be an easy task to change database and the code dependent of the model. This make it easy to maintain. The cost for making small but many changes is very low. Many developers do the mistake to center around the database and adapt everthing around that. In my opinion this is not the best way to work.
More should try ECO. It is free to use an unlimited time as long the model is no more than 12 classes. You can do a lot with 12 classes!
I suggest you to use Code Smith Tool for creating Nettiers, that is a good option for developer.