As someone who hasn't used either technology on real-world projects I wonder if anyone knows how these two complement each other and how much their functionalities overlap?
LINQ to SQL forces you to use the table-per-class pattern. The benefits of using this pattern are that it's quick and easy to implement and it takes very little effort to get your domain running based on an existing database structure. For simple applications, this is perfectly acceptable (and oftentimes even preferable), but for more complex applications devs will often suggest using a domain driven design pattern instead (which is what NHibernate facilitates).
The problem with the table-per-class pattern is that your database structure has a direct influence over your domain design. For instance, let's say you have a Customers table with the following columns to hold a customer's primary address information:
StreetAddress
City
State
Zip
Now, let's say you want to add columns for the customer's mailing address as well so you add in the following columns to the Customers table:
MailingStreetAddress
MailingCity
MailingState
MailingZip
Using LINQ to SQL, the Customer object in your domain would now have properties for each of these eight columns. But if you were following a domain driven design pattern, you would probably have created an Address class and had your Customer class hold two Address properties, one for the mailing address and one for their current address.
That's a simple example, but it demonstrates how the table-per-class pattern can lead to a somewhat smelly domain. In the end, it's up to you. Again, for simple apps that just need basic CRUD (create, read, update, delete) functionality, LINQ to SQL is ideal because of simplicity. But personally I like using NHibernate because it facilitates a cleaner domain.
Edit: #lomaxx - Yes, the example I used was simplistic and could have been optimized to work well with LINQ to SQL. I wanted to keep it as basic as possible to drive home the point. The point remains though that there are several scenarios where having your database structure determine your domain structure would be a bad idea, or at least lead to suboptimal OO design.
Two points that have been missed so far:
LINQ to SQL does not work with Oracle
or any database apart from SqlServer. However 3rd parties do offer better support for Oracle, e.g. devArt's dotConnect, DbLinq, Mindscape's LightSpeed and ALinq. (I do not have any personal experience with these)
Linq to NHibernate lets you used
Linq with a Nhiberate, so it may
remove a reason not to use.
Also the new fluent interface to Nhibernate seems to make it less painful to configure Nhibernate’s mapping. (Removing one of the pain points of Nhibernate)
Update
Linq to Nhiberate is better in Nhiberate v3 that is now in alpha. Looks like Nhiberate v3 may ship towards the end of this year.
The Entity Frame Work as of .net 4 is also starting to look like a real option.
#Kevin: I think the problem with the example you are presenting is that you are using a poor database design. I would have thought you'd create a customer table and an address table and normalized the tables. If you do that you can definately use Linq To SQL for the scenario you're suggesting. Scott Guthrie has a great series of posts on using Linq To SQL which I would strongly suggest you check out.
I don't think you could say Linq and NHibernate complement each other as that would imply that they could be used together, and whilst this is possible, you're much better off choosing one and sticking to it.
NHibernate allows you to map your database tables to your domain objects in a highly flexible way. It also allows you to use HBL to query the database.
Linq to SQL also allows you to map your domain objects to the database however it use the Linq query syntax to query the database
The main difference here is that the Linq query syntax is checked at compile time by the compiler to ensure your queries are valid.
Some things to be aware of with linq is that it's only available in .net 3.x and is only supported in VS2008. NHibernate is available in 2.0 and 3.x as well as VS2005.
Some things to be aware of with NHibernate is that it does not generate your domain objects, nor does it generate the mapping files. You need to do this manually. Linq can
do this automatically for you.
Fluent NHibernate can generate your mapping files based on simple conventions. No XML-writing and strongly typed.
I've recently worked on a project, where we needed to change from Linq To SQL to NHibernate for performance reasons. Especially L2S's way of materializing the objects seems slower than NHibernate's ditto and the change management is quite slow too. And it can be hard to turn the change management off for specific scenarios where it is not needed.
If you are going to use your entities disconnected from the DataContext - in WCF scenarios for example - you're may have a lot of trouble connecting them to the DataContext again for updating the changes. I have had no problems with that with NHibernate.
The thing I will miss from L2S is mostly the code generation that keeps relations up-to-date on both ends of the entities. But I guess there are some tools for NHibernate to do that out there too...
Can you clarify what you mean by "LINQ"?
LINQ isn't an data access technology, it's just a language feature which supports querying as a native construct. It can query any object model which supports specific interfaces (e.g. IQueryable).
Many people refer to LINQ To SQL as LINQ, but that's not at all correct. Microsoft has just released LINQ To Entities with .NET 3.5 SP1. Additionally, NHibernate has a LINQ interface, so you could use LINQ and NHibernate to get at your data.
By LINQ, I'm assuming you mean LINQ to SQL because LINQ, by itself, has no database "goings on" associated with it. It's just an query language that has a boat-load of syntac sugar to make it look SQL-ish.
In the very basic of basic examples, NHibernate and LINQ to SQL seem to both be solving the same problem. Once you get pass that you soon realize that NHibernate has support for a lot of features that allow you to create truly rich domain models. There is also a LINQ to NHibernate project that allows you to use LINQ to query NHibernate in much the same way as you would use LINQ to SQL.
First let´s separate two different things:
Database modeling is concerned about the data while object modeling is concerned about entities and relationships.
Linq-to-SQL advantage is to quickly generate classes out of database schema so that they can be used as active record objects (see active record design pattern definition).
NHibernate advantage is to allow flexibility between your object modeling and database modeling. Database can be modeled to best reflect your data taking in consideration performance for instance. While your object modeling will best reflect the elements of the business rule using an approach such as Domain-Driven-Design. (see Kevin Pang comment)
With legacy databases with poor modeling and/or naming conventions then Linq-to-SQL will reflect this unwanted structures and names to your classes. However NHibernate can hide this mess with data mappers.
In greenfield projects where databases have good naming and low complexity, Linq-to-SQL can be good choice.
However you can use Fluent NHibernate with auto-mappings for this same purpose with mapping as convention. In this case you don´t worry about any data mappers with XML or C# and let NHibernate to generate the database schema from your entities based on a convention that you can customize.
On the other hand learning curve of Linq-to-SQL is smaller then NHibernate.
Or you could use the Castle ActiveRecords project. I've been using that for a short time to ramp up some new code for a legacy project. It uses NHibernate and works on the active record pattern (surprising given its name I know). I haven't tried, but I assume that once you've used it, if you feel the need to drop to NHibernate support directly, it wouldn't be too much to do so for part or all of your project.
As you written "for a person who have not used either of the them"
LINQ to SQL is easy to use so any one can use it easily
It also support procedures, which helps most of the time.
Suppose you want to get data from more than one table then write a procedure and drag that procedure to designer and it will create everything for you,
Suppose your procedure name is "CUSTOMER_ORDER_LINEITEM" which fetch record from all these three table then just write
MyDataContext db = new MyDataContext();
List<CUSTOMER_ORDER_LINEITEMResult> records = db.CUSTOMER_ORDER_LINEITEM(pram1, param2 ...).ToList<CUSTOMER_ORDER_LINEITEMResult>();
you can use you records object in foreach loop as well, which is not supported by NHibernate
Related
I'm not so good at both Linq and SQL. But I have worked more with SQL and less with LINQ. I've gone through many articles which favors LINQ. I don't want to go the SQL way (i.e. writing stored procedures and operating data etc.)
I want to start with LINQ for every operation related with data. Here are the reasons why I want to do this:
I want to have complete control of my database via application and not by writing stored procs (as I'm not so good at writing store procedure)
I want to create my project as an easy maintainability view
Want faster development
For that, I know that:
I need to add a dbml file, drag and drop tables into that
Use dbContext class, and so on
But I want to know, is there a way:
I can avoid creating dbml file and still be able to access the database?
Do I need to use Linq to Entities for the same?
Will it be a good way to avoid using dbml file? Since for every database changes I need to drop and drop tables every time
Also I've come across many posts where linqToSql is considered deprecated and not a .net future?
I have so many doubts, but I think that's obvious when starting with a new technology?
I found this useful article which is good for beginners:
[http://weblogs.asp.net/scottgu/archive/2010/08/03/using-ef-code-first-with-an-existing-database.aspx][1]
after doing some more research I came to conclusion that:
1)i can avoid creating dbml file and still be able to access database??
ANS Yes but instead of dbml now edmx files will be created.
2)Do I need to use Linq to Entities for the same?
ANS Yes you can go with linq to entities.
3)Will it be good way avoid using dbml file? since for every database changes I need to drop and drop tables every time
ANS it is not required to drop and create again the tables. their are options where you can update selected part of your database and you are not avoiding dbmls. it will created edmx file and that will almost similar to dbmls in many ways.
4) Also I've come across many posts where linqToSql is considered deprecated and not a .net future?
ANS yes in future development it will be depreciated. it supports only sql server as backend.
I hope I'm right. Please do tell me in case any other suggestions.
LINQ is a way to query and project collection of data. For example, you can use LINQ to query and shape data from a database or from an array. LINQ by it self has nothing to with the under lying database.
You use an ORM (Object Relational Mapper) technology to project data stored in tables of a database as collections of objects. Once you have the collection of objects, you can use LINQ to query them.
Now, you have many ORM technologies to select from, such as Entity Framework, NHibernate, Linq2Sql. If you don’t like to maintain a dbml file, have a look at code first approach offered by Entity Framework.
Then there are things called LINQ data providers. They would take a LINQ query, transform it to a SQL targeting a particular database, execute the query and get the results back as a set of objects. Many of the ORMs above has built in LINQ data providers as a part of them and would work behind the scene in fetching the data.
I would advise you to look up on some patterns such Repository and Unit of work for your data layer. When used correctly, these patterns will isolate your data access code from your applications upper layers. This will help you to change your data access technology is it becomes obsolete, without affecting the rest of the application.
LINQ is an awesome technology and you should definitely try it
I have composed the above answer based on my own experience and I am sure there are many SO users with better understanding of the above technologies than myself who may wish to add their own opinion
Good luck
I have a legacy VB6 app which I am rewriting in .Net. I have not used an ORM package before (being the old fashioned type who likes to know what SQL is being used), but I have seen good reports of NNibernate and I am tempted to use it for this project. I just want to check I won't be shooting myself in the foot.
Because my new app will initially run alongside the existing one, any ORM I use must work with the existing database schema. Also, I need to use SQL server text searching. From what I gather, LINQ to SQL does not support Text searching, so this will rule it out.
The app uses it's own method of allocating IDs for new objects - will NHibernate allow this or does it expect to use it's own mechanisms?
Also I have read that NHibernate does caching. I need to make sure that rows inserted outside of NHibernate are immediately accessible when accessing the database from NHibernate and vice versa.
There are 4 or 5 main tables and 10 or so subsidiary tables. although a couple of the main tables have up to a million rows, the app itself will normally be only returning a few. The user load is low so I don't anticipate performance being a problem.
At the moment I'm not sure whether it will be ASP.NET or win forms but either way I will be expecting to use data binding.
In terms of functionality, The app is not particulatly complicated - the budget to re-implement it is about 20 man days, so if I am going to use ORM it has to be something that will start paying for itself pretty quickly. Similarly I want the app to be simple to deploy and not require some monster enterprise framework.
Any thoughts on whether this is a suitable project for NHibernate would be much appreciated.
While ORMs are good, I personally wouldn't take on the risk of trying to use any ORM on a 20 day project if I had to absorb the ORM learning curve as I went.
If you have ADO.NET infrastructure you are comfortable with and you can live without ORM features, that is the much less risky approach to take.
You should learn ORMs and Linq (not necessarily Linq To Sql) eventually, but it's much more enjoyable when there is no immediate time pressure.
This sounds more like a risk management issue and that requires you to make a personal decision about how willing you are to see the project fail due to embracing new (to you) technologies.
You might also check out LLBL Gen Pro. It is a very mature ORM that handles a lot of different scenarios.
I have successfully fitted an NHibernate domain model to a few legacy database schemas - it's not yet proved impossible, but it is sometimes not without its difficulties. The easiest schemas to map are those where all primary keys and foreign keys are single column ones, but with so few tables you should be able to do the mapping relatively quickly even if this is not true of yours.
I strongly recommend, particularly given your timescale, that you use Fluent NHibernate to do your mappings - the time to learn the XML mapping file syntax may be too big an ask. However, you will need to use an XML mapping file for your full-text indexing stuff (assuming that's what you meant), writing these as named SQL queries. (See nhibernate.info documentation for details.)
Suggest you spend a day or two trying to create a model for a couple of your tables, and writing code to interact with them. There'll always be people on SO ready to answer any questions you have.
You may also want to take a look at Linq to NHibernate - we've found it helpful in terms of abstracting even more of our database access stuff away behind a simple interface. But it's Fluent NHibernate that will give you the biggest and quickest win in terms of "cheating" on the NHibernate learning curve.
I was just reading about Linq to SQL being discontinued. For a while I put off learning Linq at all. Even on asp.net, when I last checked, their data access tutorials were using table adapters and bll classes. Then there are linq tutorials. Now that I have read this and that the Entity Framework is the new way to go, does that mean all the Linq "stuff" I have been reading about for a year and a half, how great it is, etc., is all this just gone? No one ever seems to settle on the right way to do things or at least some standard way with MS products. And I understand that you can't say one way is right for everything. But, in this particular case I do not understand why there cannot be some settling on data access.
Or, is Linq To SQL just the ORM portion of Linq? What exactly would I learn now if I wanted to use an ORM? I have read several things on StackOverflow, but none that really help me know what to do.
It seems that nHibernate may be better than any of the Microsoft choices. Yes, I know there are others (subsonic, and others were mentioned in various SO questions.)
Thank you.
No.
LINQ to SQL is built on top of LINQ, which is one of the fundamental added language features in .NET 3.5 Framework.
Technically other ORMs can implement their own LINQ systems, e.g., NHibernate already has LINQ to NHibernate going. This is on top of the ones provided in the framework, such as LINQ to XML, LINQ to Objects etc.
The Entity Framework certainly doesn't mean that LINQ is going away - the Entity Framework is a LINQ provider itself!
LINQ is a whole collection of technologies, and more than that - it's a pattern which you can implement for your own data provider as well.
LINQ to SQL is just one example of that pattern. For what it's worth, I think LINQ to SQL is being de-emphasized rather than actually going away, but we'll see...
Personally I find LINQ to Objects the most useful LINQ provider in the first place :)
Linq to sql is just one of many linq providers out there (there is linq to db4o, linq to starcounter, linq to objects, linq to ado and many, many more). The entity framework has its own linq provider, called linq to enteties. Your year of reading about linq is not lost.
Linq is much more than Linq-to-SQL. Things like Linq-to-Objects and Linq-to-XML are part of the technology, for example.
I doubt they are going away! Fingers crossed. ;-)
LINQ hasn't gone away. LINQ to SQL hasn't either, but it is not Microsoft's strategic platform for data access, that would be Entity Framework. EF uses LINQ to Entities so if you've spent time learning about LINQ, it'll still be valid and useful.
LINQ isn't a product-specific technology, though. It is easy to leverage the power and flexibility in collections of (almost) all kinds. eg.
List<MyType> myList = new List<MyType>();
// populate the list here
var filteredResults = from o in myList
where o.property == "hello world"
select o;
is (conceptualy) valid, even if the code example here is flawed.
LINQ is a library for processing sequences of data. And it is pretty awesome.
These sequences of data may be anything that implements IEnumerable, or it may be whatever sequences are provided by adapters.
Linq to SQL is an adapter which allows a SQL database to provide sequences of data that are compatible with LINQ.
There is also a Linq to XML which is an adapter that lets you treat an XML document as a sequence of data, allowing LINQ to process it.
LINQ is just the query language, and it is extremely good at what it does. It has nothing to do with databases or SQL. It is definitely worth learning just to be able to process in-memory collections easily.
I'm thinking of using SqlMetal to auto-generate LinqToSql code for a simple and small database. The database will have only tables with some primary and foreign keys (i.e., no views, stored procedures, functions, etc.). I'd like to do all joins, grouping, sorting, and advanced data manipulation using Linq.
I have experience with LinqToObjects and LinqToXml, but I've never used a proper ORM or LinqToSql.
Some questions:
How steep is the learning curve for SqlMetal/LinqToSql, given my prior experience?
Is SqlMetal reliable for simple databases?
What kind of surprises, if any, might I encounter?
How would I automate my project so that the LinqToSql code gets regenerated every time I build or, better yet, rebuild my project? (I will be using Visual Studio 2008.)
Can you recommend a good tutorial for getting me up to speed quickly on using SqlMetal and LinqToSql?
The answer to your title question is yes it is a fine solution for database with tables only (and to a point can grow when your database grows to include other database constructs like views and stored procedures).
Pretty shallow. The main difference you'll find is that certain methods that work on Linq2Objects don't work for Linq2SQL. You have to be careful when mixing objects and Linq2SQL together. You'll know you hit this when you get an exception saying something to the effect of "The only thing we support is Contains".
Quite.
You'll probably find that in certain situations Linq2SQL doesn't generate the most efficient SQL.
Sometimes things can get tricky with transactions.
There is no update statement. Every time you want to update a set of records you have to select them, update each one and then SubmitChanges().
Unless you're only doing selects you need to have a primary key on your table. Without a primary key you can't delete or update.
Linq2SQL doesn't directly support many-to-many relationships.
A simple solution would be to setup a prebuild task that generates your Linq2SQL DataContexts every time you build.
As to your goal of using Linq2SQL for everything, be ready for some nasty LINQ queries (and nasty debugging cycles). The join syntax is verbose and depending on the complexity of your queries can quickly become harder to maintain than the SQL equivalent. Grouping isn't as easy as GROUP BY.
If you're serious about LINQ, pick up a copy of Linq in Action. It goes over all aspects of Linq and SqlMetal in easy to digest chapters.
Also, if you're interested, you could use SubSonic 3 which uses TT4 templates to generate your models, which is very automated in VS2008. You then use normal Linq queries to access data. This is probably the easiest way to go.
I've just started using LINQ to SQL on a mid-sized project, and would like to increase my understanding of what advantages L2S offers.
One disadvantage I see is that it adds another layer of code, and my understanding is that it has slower performance than using stored procedures and ADO.Net. It also seems that debugging could be a challenge, especially for more complex queries, and that these might end up being moved to a stored proc anyway.
I've always wanted a way to write queries in a better development environment, are L2S queries the solution I've been looking for? Or have we just created another layer on top of SQL, and now have twice as much to worry about?
Advantages L2S offers:
No magic strings, like you have in SQL queries
Intellisense
Compile check when database changes
Faster development
Unit of work pattern (context)
Auto-generated domain objects that are usable small projects
Lazy loading.
Learning to write linq queries/lambdas is a must learn for .NET developers.
Regarding performance:
Most likely the performance is not going to be a problem in most solutions. To pre-optimize is an anti-pattern. If you later see that some areas of the application are to slow, you can analyze these parts, and in some cases even swap some linq queries with stored procedures or ADO.NET.
In many cases the lazy loading feature can speed up performance, or at least simplify the code a lot.
Regarding debuging:
In my opinion debuging Linq2Sql is much easier than both stored procedures and ADO.NET. I recommend that you take a look at Linq2Sql Debug Visualizer, which enables you to see the query, and even trigger an execute to see the result when debugging.
You can also configure the context to write all sql queries to the console window, more information here
Regarding another layer:
Linq2Sql can be seen as another layer, but it is a purely data access layer. Stored procedures is also another layer of code, and I have seen many cases where part of the business logic has been implemented into stored procedures. This is much worse in my opinion because you are then splitting the business layer into two places, and it will be harder for developers to get a clear view of the business domain.
Just a few quick thoughts.
LINQ in general
Query in-memory collections and out-of-process data stores with the same syntax and operators
A declarative style works very well for queries - it's easier to both read and write in very many cases
Neat language integration allows new providers (both in and out of process) to be written and take advantage of the same query expression syntax
LINQ to SQL (or other database LINQ)
Writing queries where you need them rather than as stored procs makes development a lot faster: there are far fewer steps involved just to get the data you want
Far fewer strings (stored procs, parameter names or just plain SQL) involved where typos can be irritating; the other side of this coin is that you get Intellisense for your query
Unless you're going to work with the "raw" data from ADO.NET, you're going to have an object model somewhere anyway. Why not let LINQ to SQL handle it for you? I rather like being able to just do a query and get back the objects, ready to use.
I'd expect the performance to be fine - and where it isn't, you can tune it yourself or fall back to straight SQL. Using an ORM certainly doesn't remove the need for creating the right indexes etc, and you should usually check the SQL being generated for non-trivial queries.
It's not a panacea by any means, but I vastly prefer it to either making SQL queries directly or using stored procs.
I must say they are what you have been looking for. It takes some time getting used to it, but once you do you can't think of going back (at least for me).
Regarding linq vs. stored procedures, you can have poor performance on either if you build it wrong. I moved to linq to sql some stored procedures of a client that were awfully coded, so the time dropped from 20secs (totally unaceptable for a web app) to < 1 sec. And much much less code then the stored procedure solution.
Update 1: Also you get a lot of flexibility, as you can limit the columns of what you are getting and it will actually only retrieve that. On the stored procedure solution you have to define a procedure for each column set you are getting, even if the underlying queries are the same.
Just as an update, here are some links on the future of LINQ to SQL:
What is the Future of Linq to SQL
Has Microsoft confirmed their stance on LINQ to SQL end-of-life?
Is LINQ to SQL Dead or Alive?
As a comment in the last link states, LINQ to SQL isn't going to go away, just not "improved upon" at least by Microsoft. Take these comments and posts as you will, just be cautious in your development plans.
We switched over to LINQ2Entity over the Entity Framework environment recently. Before, we had basic SQLadapters. Since the database we are working with is rather small, I cannot comment on the performance of LINQ.
I must admit though, writing queries have become a lot easier, and the addition of Entities, does enable strong typing.