I'm having a few tables on SQL Server, which have similar structure - int Id and string Value.
This tables linked to main table via foreign key, so I'm wrote a bit of logic for mapping a string values to id's in models in MVC Razor. This feature requires that models used as dictionary implement simple IKeyValue interface with Id and Value, but after updating model from database I can loose interface implementation from models and must write it again.
Any way to automate this?
Are you modifying the auto-generated file? If so, you should not do this, for the exact reason you describe in your question -- it will get overwritten.
All of the classes in the generated file should be partial. You can take advantage of this by creating another class (in a different file, but in the same project), make sure it has the same declaration (and namespace), and have it implement the interface. This way the class will implement the interface, but will not be overwritten the next time you refresh the schema from the database.
My intent is to create a generic (not in C# meaning) database model for Windows Phone using linq to sql. User of such model should be able to pass an array of his data object types (classes marked with Table attribute) to model's contstructor, and then model should take care about adding related tables to database and provide API for CRUD operations.
But then I've found out that in order to add tables to database, your data context (class inherited from DataContext class) have to declare each table as a property! That's embarrassing. Does this fact mean that my idea is not implementable? Because I obviously cannot add properties to my DataContext-based in the runtime.
So my question is, am I right in my judgments? If yes, are there some workarounds to solve this issue?
Thanks in advance.
EDIT: better question tagging, for somebody finally notice this.
You do not need to use a strongly typed DataContext (a class inheriting from DataContext and declaring properties for each table). You can do something like the following instead
var context = new DataContext("connection string", new AttributeMappingSource());
var table = context.GetTable<T>();
where T is some type marked with the Table attribute.
In my ASP.NET application I have an EF Product class (derived from Product DB table) and I want to perform search functionality on its string fields by using inline LINQ.
Since I predict the name and amount of the fields (properties) will change I do not want to strongly couple my code with the table definition. How can I compare the values of all the fields in the table with a search string by iterating through all table fields (properties)?
I know one option is through reflection, is there any easier and more immediate way to fulfill this task?
In the end, your EF class is still just a normal .NET class. Unless EF explicitly provides some library for looping through properties (it doesn't that I know of), you'll still need to use reflection to do this.
var properties = typeof(Product).GetProperties(BindingFlags.Instance);
foreach (var property in properties)
{
...
}
I have a table called Code in my LINQ to SQL datacontext. I also have a class called Codes in my Models folder. What I want to do is save the updated object Codes to my database table Code. Is this possible?
In my controller, I would pass the edited Object to my Model. My CodesRepository file contains this:
public Codes EditCode(Codes CodeToEdit)
{
private EventsDataContext _db = new EventsDataContext();
Codes C = new Codes();
C = CodeToEdit;
_db.Codes.InsertOnSubmit(C); //error here, something about invalid arguments
//InsertOnSubmit is for adding a new object, but I don't know the syntax
// for editing an existing object.
_db.SubmitChanges();
}
This is probably not the correct way of doing this so can someone point me in the right direction? Do I even need a class called Codes or do I need to somehow just use my database table? Thanks.
Solution: I decided to change from Linq to SQL to an Entity Framework and it works much better. This way, I don't have to define my Codes class since it comes straight from the database and I was able to delete the Codes class file.
You should use DataContext.Attach when you get an object back that corresponds to en existing row in the database. For Linq-to-sql's optimistic concurrency handling to work this requires that you either have the original, unsaved object available, or that you have a TimeStamp column in the database. The latter is preferred, as it only requires one extra field to be handled (probably through a hidden field in the web form).
I'm looking at using LINQ to SQL for a new project I'm working on, but I do not want to expose the LINQ classes to my applications. For example, do an select in link returns a System.Linq.IQueryable<> collection. As well, all the classes generated to represent the database use Table, Column, EntityRef classes and attributes. It's fine if my data access layer has LINQ dependancies, but I don't want my application to.
So my thoughts are that I will have to use the LINQ to SQL generated classes as intermediate classes that are not exposed outside of my data access layer, and create my own classes which the application can use. What is the easiest/effecient way to get the data from the LINQ to SQL classes into my own classes?
I totally agree with your thinking - I would try to avoid exposing LINQ to SQL entities directly to the world.
I would definitely recommend using a "domain model" of your own, either a 1:1 mirror of the underlying LINQ to SQL entities, or a different one.
As long as you have a domain model that is quite similar to the underlying LINQ to SQL entities, you can use tools like AutoMapper to easily shuffle data between your LINQ to SQL entities and your domain model classes. It should be pretty easy and flexible to do it that way!
Rob Conery published a webcast series entitled the MVC-Storefront where he introduces a variation of the repository pattern that accomplishes what you want.
I've used ideas from the screencast on a reasonably large project and was quite pleased with the results.
There are, however, issues with the pattern, particularly around concurrency and detached scenarios that you will want to think about up front before fully committing to it.
I detailed some of my pain with concurrency in this pattern here.
I'll be interested in the responses you get because I'm considering the exact same thing. I want to use the L2S entities classes on our backend but use much lighter-weight entities for application consumption.
Randy
I would advise against using LINQ to SQL on a new project, since Microsoft will no longer be developing this project, except for maybe fine-tuning some issues. LINQ to SQL is perfectly usable and is acceptable, but I would not advise new projects to use it. If you like LINQ to SQL, you should definately look into using Entity Framework instead of LINQ to SQL.
This is my current incarnation of how I am going about doing this:
I have a DataContext class that I created by adding a LINQ to SQL class, and droping tables onto the designer. I called the class MyDataContext and put it in a namespace called Linq. My database has a table called Tag, which generated a class, also in the Linq namespace. I changed all the accessors to internal, so they would not be visible outside of the data access layer.
namespace Linq
{
[System.Data.Linq.Mapping.DatabaseAttribute(Name="MyDb")]
internal partial class MyDataContext : System.Data.Linq.DataContext
{
...
}
[Table(Name="dbo.vTag")]
internal partial class Tag
{
....
}
}
I then created a class called DataAccess which is what will be exposed to any application that references the assembly. I also created my own Tag class. The DataAccess class and my new Tag class are in a different namespace called Data to avoid collisions with the generated classes which are in the Linq namespace. I use Linq to Sql to query for an IList of Linq.Tag objects, then I use Linq to generate me a list of Data.Tag objects from the Linq.Tag objects.
I'd like to hear comments on this to see if there's a more performant way to do this, or one that requires less code. I also wasn't too happy with my use of duplicate class names (Tag) so I'm interested to hear any ideas on naming suggestions too.
namespace Data
{
public class DataAaccess
{
public IList<Tag> List_Tags()
{
using (Linq.MyDataContext dal = new Linq.MyDataContext ())
{
IList<Linq.Tag> lstTags = (from c in dal.Tags select c).ToList();
return (from tag in lstTags
select new Data.Tag()
{
ID = tag.ID,
Name = tag.Name,
Parent_ID = tag.Parent_ID
}).ToList();
}
}
}
}
What you are proposing is having two separate models. That means boilerplate code, which I've found is not necessary. I have more or less the same idea as you, but realized that this would be useless. I've suggested Entity Framework in another answer in this thread, and I want to make that point again here.
What you end up with is a model-soup, where you have to maintain two models instead of just the one. And that is definitely NOT desirable.
To go from the LINQ to SQL classes to your classes is a matter of some fairly straightfoward LINQ to Objects (or just initialisation for single objects).
More fun is going back from your model to the LINQ to SQL objects but this is fairly standard stuff (although something I'm still working out or I'd find you some specific references).