I'm creating a webservice layer over a legacy SQL Server based system. It's a pretty large and complicated business application which has a large number of stored procedures that perform SELECT statements . Most of these stored procedures join a number of tables and produce a single resultset for easy consumption by the client.
In building my webservice I want to take advantage of EF, and using a Code First approach 80% of my use cases can be achieved by mapping direclty to tables. However I have a number of use cases where I need the cross tbale views of data as provided by the stored procedures. As I see it I have 3 options:
Create new POCOs that represent the stored procedure returns and link these to the existing stored procedures (let SQL do the join and re-use exisitng code)
Create new POCOs that look like the stored procedure return, but populate themselves by association with othe EF entities (let EF do the jons)
Do the joins somehow in LINQ
What do people think is best practice in situations like this, which I guess most of us are coming up against everyday?
Thanks,
Andy
many a good book out there. anything from Julie Lerman... this is more recent http://www.apress.com/9781430257882
With Navigation properties, you can do most things without old fashioned joins.
So 4) do it in Linq,and let EF do the Joins.
Use Navigation properties. you can do many logical joins and even avoid the join keyword.
this blog shows how easy and why LINQ with no join syntax results in Joins at the db level.
http://blog.staticvoid.co.nz/2012/7/17/entity_framework-navigation_property_basics_with_code_first
Related
Our database has about 500 tables we'd like to use in our EF model. Of those I'd be happy to start with 50 or fewer just to get our feet wet after working in plain ADO.net for years.
The problem is, our SQL server contains many thousands of other tables that exist in our database that have been created through the years and many that are dynamically generated. Believe it or not:
select count(*) from INFORMATION_SCHEMA.TABLES
73261
So that's a lot of tables. I have found that pretty much every tool I've tried to design, build or template EF models or entities either hangs or does not return a list of tables. Even SQL Server Object Explorer in VS2012 won't list the tables and instead shows the Tables folder with a little "x" over the icon. So I can't even select a subset of tables.
What options do I have for using EF? Is there a template where I can explicitly define the tables that I want to use entities for? Even with 50 tables, I don't want to hand code each one in an empty EDMX.
Using a Database / Code First approach and avoiding connecting Visual Studio to the database at all (i.e. don't create an edmx, or connect with server explorer) would allow you to do this easily. It does not give you any of the Model First advantages, but I think it sounds like your project would be better served with a Database / Code First approach anyway as:
You have an existing Model, and are not looking to push changes from your EDMX to the DB
You are looking to implement this on a subset of your database
This link has a good summation ( Code-first vs Model/Database-first ) with the caveat that in you case a Database/Code First approach does not have you pushing changes from code to the Database, so the last two bullets under code first apply less, and yours is a Database/Code First hybrid.
With 70k tables I think that any GUI is going to be tricky. When I am saying Database / Code First, I am trying to convey that you are not using the code to create / define and update your Database. Someone may be able to answer this more succinctly / accurately?
I now this is an old question. But for those who land here on a google search. The only tool I have found that actually works with thousands of tables is The Sharp Factory.
It is an ORM. Pretty simple to use. So if you are looking for an ORM that can work with a large number of tables and does not require you to write "POCOS" or "Mappings" or SQL then this is the tool.
You can find it here: The Sharp Factory
I have some tables which should add to my database every year and name of databases contains the year (like sell2005) and iv'e written some ef queries on these tables ,and queries can only be on a single entity (like sell2005) but what should i do when sell2006 or sell2007 add ? how can i manage them with that single query which iv'e written before?
thank you.
There is no easy way. EF is simply not tool for this scenario. For EF you must have "single table" so you must either use partitioning with one real database table partitioned by year or you must build a view on top of these tables.
The problem is that in EF you have strict relation between classes and tables. You cannot have single class mapped to multiple tables even if they are exactly same (except inheritance which is not solution for you). So the workaround would require to have multiple SSDL/MSL mappings - one for each table and construct correct context instance with correct mapping for every query. As I know dynamic changes of mapping are not possible (except modifying SSDL/MSL files before using them).
I'm trying to display the results of a sproc in my MVC 3 web app.
However, the sproc calls into 4 tables on one database and joins them with 5 views (single table views only, thank goodness) on another database. Each (SQL Server) db is on a separate server but that shouldn't matter.
I've read this: http://blogs.msdn.com/b/swiss_dpe_team/archive/2008/02/04/linq-to-sql-returning-multiple-result-sets.aspx
and this:
http://www.codeproject.com/KB/dotnet/linqToSql5.aspx
and still cannot determine whether I should use the dataContext classes or just embed the straight SQL.
Perhaps there is a better way to return my results than LINQ to SQL (15 columns, 3 different data types)? I need to update the tables as well. The user will have the ability to update each value if they choose. Is this a task best suited for the entity framework classes?
I plan on using the repository pattern so I can change data access technology if I must but would rather make the correct decision the 1st go 'round.
I was hoping for a resource that was more up-to-date than say, NerdDinner and more robust than the movie apps for MVC3 that abound, particularly implementing the sproc results inside a view. Any suggestions would surely be appreciated. Thanks.
Once you plan to "update" data then you are going to handle it all through stored procedures. Both Linq-to-sql or Entity framework will not help you with this because they are not able to persist changes to something created from arbitrary query. You should very carefully check if you are even able to track the data back to the correct record in the correct table. Generally result of a stored procedure is mostly for viewing the data but once you want to modify the data you must work with each table directly or again use some stored procedure which will do the task. Working with tables from multiple databases can be pretty complex in entity framework (EF doesn't support objects from multiple databases in one entity model).
Also what you mean by 15 columns, 3 different data types? Stored procedures support in both Linq-to-sql and Entity framework will return enumeration of one flattened data type containing 15 properties.
I'm not aware of anything that linq-to-sql can do that Entity Framework can't really, so EF seems to be a better solution in this case. You can add a stored procedure to your Entity Framework model as well, so you can just have it call the procedure and deal with whatever comes back.
Since the end goal will involve accessing the same Databases with either technology and they will be using sql to retrive the data either way its really a subjective anwser.
I would use whatever technology you are most comfortable and focus more on the implementation. Both data access platforms are based off of ado.net technologies and are for the most part equally powerful.
Regardless of the technology I would evaluate how the data is accessed and make implementation decisions based on that.
I am working on creating a service layer for a large sql server database (2008 R2) that is currently the backend for a winforms POS application with strongly typed datasets.
I think WCF is the way to go, and at first glance it seemed EF 4 was a good choice but now I'm having my doubts. Here is what I have found:
The stored procedure mapping isn't that great. I have hundreds of stored procs that I want to reuse. Most of them wouldn't return an 'entity' so the stored procs would have to be mapped to a complex type. Many of the procs use dynamic sql or temp tables so EF can't figure out what complex type to crete. Many of the procs return multiple result sets. I've read that EF extensions have a way to map stored procs with multiple result sets, but only for entities, so that doesn't help me.
Large models are a problem. There doesn't seem to be a good way to handle large entity models. The workaround of creating smaller models isn't that desirable and splitting the model loses design support, am I missing something?
EF mappings only go so far. The stored procs that I want to reuse return projections or information from many tables into a result set. There doesn't seem to be a way to map these results into entities, am I wrong? I've read about combining results from 2 table into 1 entity, but that only works if the tables have the same primary key.
Are people using EF in large scale existing databases? If not what would you recommend?
I've used EF on large scale databases, but as you say, the support for SPs as you have got is not great. That's not specifically a failing of EF per-se - ORMs in general work on the same principle and have the same "limitation".
If you have lots of SPs and are mapping them to datasets, you'll have to do lots of work even without SPs in terms of no longer referencing datasets and referencing your domain model types through your system, so you'd need to have some way to map your SPs to your domain model and back anyway.
I want to know, do I use stored procedure with Entity Framework or just user Linq-to-Entities queries?
Consider I want have a customer's orders. So one solution achieved by using stored procedure that uses joins on two table and for example return order IDs.
Another solution achieved by using Linq-to-Entities queries. This solution have a preference over first solution and that is, we can user navigation properties to easily move in customer order information. but in stored procedure since it only return ID's it's a little bit to access order information.
So which is better, considering second solution preference?
Both solutions work - and since you didn't define what "better" means to you, we cannot possibly tell you which solution is "better".
Using stored procedures with Entity Framework is definitely possible - especially with EF4. Stored procedure have their benefits - you don't have to give the user direct table access, you can possibly let a DBA tweak those stored procs for top performance, and you can do things like delete a Customer by just calling a stored proc with the CustomerID to delete (instead of having to first load the whole customer, just to delete it).
So stored procedures definitely have benefits - the downside to many folks is that they have to write those in T-SQL, and now suddenly part of your application is in your C# code, while another part is in stored procedure's T-SQL code.
So again: as vague as you asked, there's no real good answer to this. Both approaches are valid and both work - it's a bit of a personal preference, which one you want to use.