I have a problem with the following Linq query using Entity Framework:
from o in ctx.Entity
where o.EntityID = entityid
select o;
Simple enough right? Well the 'Entity' set is the parent class of a whole lot of other classes. The generated SQL for this simple query is about 20K worth of characters with a slew of 'case' and 'union'. In addition of taking a while for the framework to compile the query, it takes a while to execute too.
So how can I improve the SQL generated by the framework in case of queries using classes with heritage? Or what other technique can I use to avoid this problem?
AD
The reason it is doing that is because of the relationships of Entity with other tables in your database. To cut down on that, you need to read up on how to better control the explicit/lazy loading of references that EF is doing for you
http://blogs.msdn.com/jkowalski/archive/2008/05/12/transparent-lazy-loading-for-entity-framework-part-1.aspx
No post like this would be complete without a plug for nhibernate, which is more powerful/robust/performant/and easier to use ;-) but hopefully that link will help you out
Related
Hi i write because i have configured the Audit for one single table for all my entities and its working fine for the general tables in my model, but with the Many-To-Many tables i don't know how can i do for setup the "AssociationEntryRecord"? the event is fired by EF when i do one change in this tables but i don't know how saved!
Could you please help me with this questions, thanks in advance for your help & the library...
For configuring the Entity Framework event provider use the fluent API provided by Audit.EntityFramework.Configuration.Setup()
You can include the associations as follows:
Audit.EntityFramework.Configuration.Setup()
.ForAnyContext(config => config
.IncludeIndependantAssociations());
And about your sample code (what you should have included as textual code and not as an image):
The first line is not needed, since the UseEntityFramework() will
override the DataProvider
The primary key value can be calculated as: entity.TablePk = entry.PrimaryKey.FirstOrDefault().Value.ToString();
Mates, I want to update a role description using my application
I don´t know what is the better way to connect to the database and run a UPDATE statement.
Would it be Entity Framework? LINQ? None of this 2 options..
Please, suggestions.
I would say that Entity Framework would be currently the best solution for you. Not only it is strongly supported by Microsoft (well Silverlight was as well) but:
If you start with it, you can use designer. It's graphical UI will guide you when generating the model (based on database) or generating the database schema when starting with model.
Read some tutorials abut it:
http://msdn.microsoft.com/en-us/data/ee712907
And later take a look how to use some more profesionla techniques as Repository pattern or unit of work
http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application
Not Linq ..well yes linq, but linq is the querying framework where as entity framework is the object relational mapper. So Both actually. You could do this in various other ways but those two technologies work very well together from my experience.
In Visual studio you would create a new ADO.NET project template which you then hook up to your database. and then you can update the tables and do a whole bunch of stuff. Linq is build into .NET so technically you can query any objects using linq ( which makes it so much fun ) and because your entity is an object you just reference it ( first declare it ) and then play with it
FooModel foo = new FooModel(); // Entity
var fooQuery = from _ in foo.DescriptionTable // Linq query
where _.Description == SelectedDesc // table selection query
select _;
foo.Add(fooQuery); // add to database
foo.SaveChanges(); // save changes
Something like that. There is a bit more to it that would project specific but you would have to give more details.
It is most certainly worth learning both technologies and have doubt you will find them very useful. Both can get very complex but for what you need it for you just need the basics down and then you can explore from there.
We are looking for a way of automatically filtering all CRUD operations by a tenant ID in Entity Framework.
The ideas we thought of were:
Using table valued user defined functions
Using stored procedures (but we don't really want to, as we're using an ORM to avoid doing so)
Some how modifying the templates used to generate the SQL to add a where clause on each statement.
Some how modifying the templates used to generate the LINQ in the controllers (we may use MVC).
Any tips?
-thanks
Alex.
Using table valued user defined functions
Table valued function are only available in .NET 4.5 Beta (and not available in code first). Using them will still not help you because you will have to use the function in every LINQ query so it is the same as using where clause.
Using stored procedures (but we don't really want to, as we're using an ORM to avoid doing so)
It can be useful for some special complex queries but generally it is not what you want.
Some how modifying the templates used to generate the SQL to add a where clause on each statement.
Too complex and on completely different level of abstraction.
Some how modifying the templates used to generate the LINQ in the controllers (we may use MVC).
Close to ideal solution. You simply need to wrap access to your entity set into some code which will look like:
public class MultiTenantAccess<T> where T : IMultitenant
{
private IDbSet<T> set;
...
public IQueryable<T> GetQuery(int tenantID)
{
return set.Where(e => e.TenantID == tenantID);
}
}
Sometimes this is core for something called Generic repository but it is really just a wrapper around EF set. You will always use GetQuery to query your data store instead of using DbSet directly.
you may also separate the tenants data into different databases
or into same database, but with different schemas? You can read more about this in an old MSDN article called "Multi-Tenant Data Architecture"
I just starting learning, testing ADO.net Entity Data Models with MySql - everything is going fantastic except i've noticed one thing..
In my MySql table i've created an Enum column type. When ASP.net creates the Model classes the enums are treated as strings and not as Enums - is there a way to fix this?
UserStatus column in MySql is an Enum that has 2 potential properties, Enabled and Disabled - however asp.net treats as string value:
user.UserStatus = "Enabled";
Was hoping to see something along these lines...
user.UserStatus = UserStatuses.Enabled;
Thanks!!
Loren
There's no such thing as an enum sql type, at least not a standard type, which means it's non-standard and you'll have a hard time finding any framework that properly supports it properly.
To make matters worse, Entity Framework does not currently support Enum types in code either. There are some hacks and workarounds, but you will find them to be painful and not worth it. For all intents and purposes, a MySQL enum is a string object. You may have to issue some custom sql to get the enum types to populate your listbox though.
Oh, and FYI: 8 Reasons why MySQL's ENUM data type is evil
I am using LINQ to SQL with C#.
Is there a method through which we can generate entity class files from the table schema?
By dragging tables onto the graphical designer classes are generated but they are not the real class files(i mean actual files with the extension cs).
I am aware of that we can code the class files first and then create the schema manually or programmatically, but i wanted to know if the reverse is possible, may be using some third-party tools. I feel it will be very convenient to use LINQ that way.
Thanks in advance.
I'm not as familiar with LINQ to SQL as I am with Entity Framework (v4), but EF certainly would fit your requirements. You can download the POCO templates for EF from Microsoft, right through VS2010 in the Extension Manager (Tool > Extension Manager, click on Online Gallery, and search for POCO). The link is not just the download for the template, but a walkthrough on how to get started.
I also have started a series of blog posts that include some nice T4 templates for an Entity Framework EDMX model that auto generate DTO classes for all of your entity classes, whether you're using the default code generation model, or Microsoft's POCO template. The auto generated DTOs are handy for use in UI or service layers, and save you from having to bring in dependencies on Entity Framework in consuming layers. It's also very easy to get DTOs from your entity objects.
var people = from p in context.People select p;
return people.ToDtos();
Might be worth a look (shameless self promotion).
If you need/want to stick with LINQ to SQL, do a google search for "linq to sql POCO", it seems some people have had a degree of success with this, but most of the search results seem to be from 2008 and earlier, so I'm not sure about currency / relevancy.
All the classes generated when you drag tables to the designer are created as partial classes. There is no reason you can't just create a file for each one and use that to make the necessary modifications.
Absolutely you can, if you use the T4 template for L2S - http://l2st4.codeplex.com/
You still use the .DBML file, but you need to set the "build action" to "none" on the file to turn off the compilation of the default code that gets generated. Then you add the .tt file and the .ttinclude file from your codeplex download.
The T4 template has a line of code in it that you can modify to suit your purposes:
FilePerEntity = false, // Put each class into a separate file
Oddly, Entity Framework 4 is using this approach too with the dual methods of generating the code from the model file, but with EF, the T4 template is included with VS2010. With Linq-to-sql, you have to download the T4 template separately. The nice part with using T4 is you can add other customizations as you go. However, initially the code that's generated is identical as what you got from the .DBML designer.