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DbContext with read-only set properties

I was reading this article http://blogs.msdn.com/b/adonet/archive/2011/01/27/using-dbcontext-in-ef-feature-ctp5-part-2-connections-and-models.aspx and was trying to figure out how to create private setters (the section in the article DbContext with read-only set properties is right before the summary). How would you create private setters? I was playing around with different methods but nothing seemed to work. I am doing this because I need to group the original table based on a query I have because the original table is a heap and I need a primary key for the entity. So anytime a client asks for this table it is already grouped. Not even sure if this is the correct way to do that. Thanks.
EDIT: sorry for being vague. I am doing code first. For example there exists a SQL Table with JobNbr, Qty and Date and I need to group by JobNumber, sum on Qty and take the oldest expiration date, and that will be my entity since this table has no primary key. The way I am doing it now gives me the error below from a method I created in the DbContext class. I do have a EntityTypeConfiguration class. Do I do this in that class?
EDIT: : you might be wondering why I am doing this. Basically I need to get data from the heap and save it in another database. My original approach was database.SqlQuery() to get grouped rows from the heap, but sometimes I have too many parameters for execute_sql. So I decided to create an entity for the grouped query without tracking changes (since all I am doing is reading from the table and saving to another DB). See my post here with the issue I am having https://stackoverflow.com/questions/22106030/entity-framework-6-this-database-sqlquery-character-limitation-with-sp-executes. The only way I know to get around it is to create an entity (even though in this case the entity is a query and not a table).
The entity or complex type
' cannot be
constructed in a LINQ to Entities query.

Save a List of object in ASP.NET MVC

I have a question about Saving a list of object in ASP.NET MVC.
First I'm not using EntityFramework or Nh like ORM tool, just use Ado.net
suppose I have an object Product, and I want to collect all the products data via javascript and batch update the product list in one call.
my question is when should I differentiate which item is inserted, updated, or deleted?
one strategy is that I have a enum property on the DTO object and
also on the javascript ViewModel, and when I add an item into the
viewModel, I marked this object to add, and if I changed one Item, I
marked it to updated. so when this request come to the action, I can
know which items to be insert or update.
pros: it's easy on server side, don't need to differentiate the object status from server side.
cons: if I want to publish this action to webapi that will be called by third party, that may need third party user to
differentiate the state of the object.
differentiate the data from server side, just give me a list of object, on the server side, first retrive the current data from database, compare the data, then check which record to be inserted or updated.
pros: all the compare are done from server side.
cons: proformance issue
what ever the data passed from client, just remove the current data and insert the new data
I hope someone could give me an advice, what's the best practice to handle this situation, I think it's quite common but I can't find a best solution.

I've seen option 1 where added/deleted/modified items are maintained in javascript arrays and posted back to server. But for some reason, I didn't like it maybe because of writing client side code to maintain state.
So, I had used second option and thanks to LINQ for making my task easier. Assuming list has some unique id, below is pseudo code. Note: newly added items should have unique random id's, otherwise there might be chance of treating them as already existing item. In my case its GUID, so there was no chance of overriding.
var submittedIds = vmList.Select(a=>a.Id).ToList();
var dbIds = dbList.Select(d=>d.Id).ToList();
//Added items
var newIds = submittedIds.Except(dbIds).ToList();
//loop over newIds and construct list object to contain newly added items
//Deleted items
var deletedIds = dbIds.Except(submittedIds).ToList();
//Modified items
var modifiedIds = dbIds.Intersect(submittedIds).ToList();//if the values don't change, update statement won't do any harm here
This approach gives reasonable performance unless you are dealing with huge lists.
I think third option is not good. For ex: if you plan to implement audit features on your tables, it will give you wrong functionality. If a new record is inserted, you will have entries for all records as deleted and then one inserted which is wrong because only one is inserted.

3rd strategy is suitable for simple situations e.g. when you want to update a Purchase Order items, an Order will not have too much OrderLineItems. However, you have to take care concurrency issue.
I think your first strategy is best suitable in general case. It's also easy to implement. When you want to publish your service to a 3rd party, it's usual that a client must follow the service definition and requirement.
Update
For 1st strategy: If you don't want your clients have to specify status for their data, then do it for them. You can separate the SaveOrder service into smaller services: CreateOrder, UpdateOrder, DeleteOrder.

How can I denormalize my clr entity, but keep my db tables normalized?

I have these two related tables Client (ClientId, Name) and ClientDescription (ClientDescriptionId, (FK) ClientId, Description). That is to say each Client can have many associated descriptions. Now, when displaying the a list of ClientDescriptions, I also need to know what the Name of it's associated Client is.
Now you'll probably say that I allready have this information, since I can simply follow my navigation property back to the associated Client and use its Name. I can't do that because I'm autogenerating a grid in Ria services, and this just gives me a count for navigation properties, and I haven't found a way to flatten this down in my metadata file. Hence why I want a property.
The whole idea is that I want to be able to add a new field to my database, update my entity classes from the database and regenerate my domain service, and the new field should just pop up in my grid. I shouldn't have to update my xaml just because my database happen to have an extra field.
So, what I would like to do is add a ClientName field to the entity (clr object), but keep my database clean (no such denormalization in the db).
So, I generated my edmx, and added a new property named ClientName. Set it to StoreGeneratedPattern.Computed, and compiled. I then get a nasty little error
Error 3004: Problem in mapping fragments starting at line NN: No mapping specified for properties (etc..)
The solution apparently is to generate my database from my edmx. (Or that's what answers to questions about that error seems to yield.) But this generates an actual DB-field, which I don't want, so that answer doesn't apply to my case.
So my question is: How can I denormalize my clr entity, but keep my db tables normalized?
Edit: I guess this question can be generalized a bit. The issue would be the same if ClientDescription contained a few numeric fields that I wanted to do some calculations on, and I wanted the result available as a field and the algorithm should be in c# rather than in my database.

To answer your more generalized question:
Entities are generated by the Entity Framework with a partial keyword.
This means that the code of an entity can be split in multiple source files in the same namespace and assembly. One will contain the generated code from the Entity Framework, the other will contain custom properties and methods.
If for example, your entity has the database fields Price and Amount you could add a property in the partial class TotalPrice which would return Price * Amount.
Then the algorithm will be C# and your database won't know about the extra property.

Entity Framework: subset entity of larger entity

Sooo basically I have a table called Comment. On that table I have three fields,
ID
Title
Text
I've created an Entity object for the table already and it maps all three fields, but what I want now is another Entity called CommentHeader that will map only ID and Title. I want to only load the titles of all the comments and not the text for speed reasons. So what's the best way for going about this?
I'm not looking for a Select statement with a var object. I can figure that one out on my own and I really don't like that solution because I'd much rather abstract it behind an Entity object.
I've tried the obvious solution, which was to just copy the original Entity object and delete Text from it. That resulted in an error because only one Entity can map to one table without conditions. It sounds to me like I have no choice but to use a Select statement. I just wanted to make sure before I did something stupid.
(By the way this example only has three fields for simplicity's sake. Assume that the header could have considerably more fields in it. This is the primary reason I don't want to just use a select with a var object, because it's not just one field but could be a whole bunch of fields).

The easiest way probably would be to create a view ("CommentHeaders") in the database that only selects ID and title from the Comment table. Then update your model and add the view, which will create a new entity based on those columns.

LINQ-to-SQL + One-to-Many + DataBinding deleting

I use LINQ-to-SQL to load data from a database that has two tables in a one-to-many relationship (one Recipe has many Ingredients).
I load a Recipe and LINQ retrieves Ingredient objects into an EntitySet that is binded into a ListBox.
If I want to delete some Ingredients off a Recipe, I get a "An attempt was made to remove a relationship between a Recipe and a Ingredient. However, one of the relationship's foreign keys (Ingredient.RecipeID) cannot be set to null.
I SOLVED this problem using the well known solution by adding 'DeleteOnNull="true"' to the DBML file. But adding this setting only removes the problem when we are deleting Ingredient objects that were retrieved from the DB.
The problem is with the Ingredient objects that were created in code (added to a Recipe) and added to the EntitySet collection of Ingredients and then deleted BEFORE SubmitUpdates is called. Then, the same exception happens again. This usually happens on a new, unsaved recipe when user is adding ingredients to it, makes a mistake and erases an ingredient off a recipe. I added the DeleteOnNull to both 'Association Name="Recipe_Ingredient"' lines in DBML.
How am I supposed to remove such objects? The only solution I see at the moment is that I would load the ingredients into a collection not under the DataContext and then when saving, delete all ingredients off a recipe and add then again from that cache..

try
{
// Needed for existing records, but will fail for new records
yourLINQDataContext.Ingredients.DeleteOnSubmit(ingredient);
}
catch (Exception)
{
// Swallow
}
yourRecipeObject.Ingredients.Remove(ingredient);

It seems that you're looking for something that I was looking for myself just a few days back when I asked "How do I design backing data types for a databound WPF dialog with Ok/Cancel buttons?".
The answer is an intriguing post from Paul Stovell describing a sample IEditable adapter for Linq to Sql. This will let you create your desired "Apply/Cancel" semantics in a generalized manner without completely dissociating yourself from the underlying ORm-generated classes through a full custom-written layer.
It's a pretty slick trick, overall, that will essentially let you sidestep the problems you're fighting right now. :)
On a different note, I'm curious as to why your recipe to ingredient relationship is 1:n instead of m:n. Is it for simplicity's sake? I use garlic in a lot of recipes. :)

// Create new entities
Cart c = new Cart();
CartEntry ce = new CartEntry();
ce.Cart = c;
// Delete the entry
c.CartEntries.Remove(ce);
dc.Cartentries.Attach(ce);
dc.CartEntries.DeleteOnSubmit(ce);
// Insert the cart into database
dc.Carts.InsertOnSubmit(c);
dc.SubmitChanges();
Explaination of the issue: Both entities, c and ce, are not related to a data context - they are not being tracked. EntitySet.Remove() (first delete line) only removes the relation between c and ce. While c can exist without associated cart entries, ce can't exist without an assiciated cart because of a foreign key constraint. When submitting changes to the database, the disconnected ce is dealt with as well, causing a constraint violation and the exception.
In order to get rid of that untracked and disconnected cart entry you need to attach it to your data context (causing it to be tracked) and then mark it for delete on submit. The moment you submit your changes the cart entry will be deleted properly and not cause the exception.
For more details on that issue check this out:
http://msdn.microsoft.com/en-us/library/bb546187%28v=VS.100%29.aspx

you need to decouple the save code from the events in your GUI, it seems like you're a little to eager to save things to the db before the dust has settled and you're queuing and removing things from the db that never got there in the first place, it would be best if you could identify a point when the user will "commit" their changes, and at that moment, process the full condition of the GUI - this will save you a bunch of spaghetti code.
I would also be curious to know if your entities have autonumber IDs or if you're using some other ID mechanism. You're probably sending DELETEs to the database for the as-yet-uncommitted Ingredient records, if those include NULL IDs, I think the linq could get nasty.
Have you hooked up a textwriter to your DataContext.Log to see what sorts of SQL is generated just before you get your exeception?

Thank you for your answer, I will examine the posts and see what I can do. I must say I'm surprised to even see this problem occuring, it seems quite natural to me that one could add records to the LINQ-provided "cache" of data, then decide to erase some of them and then commit. Change tracking should be able to handle that. I just starting with LINQ so I might be doing a stupid mistake somewhere in the code (wouldn't be the first).
On the other note: You are quite correct that garlic can belong to many recipes (not my coctail recipes thought!). I actually model that with an Article object/table. But for a recipe, you need quantities. So in my model, you have a Recipe that has 1:n Ingredients, each of them having a Quantity, a 1:1 link to an Article (which has a Name, an AlcoholContent and some data to establish an interchangeability hierarchy) and a 1:1 link to an Unit (for the quantity to make sense).
So in a sense, Ingredient table makes a M:N relationship between Recipe and Article, and at the same time adding some additional information to each individual linked pair.

I had exactly the same problem. I had a parent / child hierarchy, and when adding and removing the child entity without saving to the database I received the "An attempt was made to remove a relationship" exception.
I discovered that this problem only arose when I set an object style property of the child to another linq-sql entity before saving. eg
1. This creates the error
RetailAccountCustomerCard racc = new RetailAccountCustomerCard();
Card addedCard = _idc.Cards.Where(c => c.CardId == card.CardId).ToList().First();
racc.Card = addedCard;
this.CurrentCustomer.RetailAccountCardsBindingList.Add(racc);
// Some code triggered by the user before saving to the db
CurrentCustomer.RetailAccountCardsBindingList.Remove(racc);
2. This doesn't create the error
RetailAccountCustomerCard racc = new RetailAccountCustomerCard();
racc.CardId = card.CardId; // note that I have set the Id property not the object
this.CurrentCustomer.RetailAccountCardsBindingList.Add(racc);
// Some code triggered by the user before saving to the db
CurrentCustomer.RetailAccountCardsBindingList.Remove(racc);
Strangely enough, the error that arises in 1. specifies the problem is to do with the relationship is on the RetailAccountCustomerId property of RetailAccountCustomerCard. IT HAS NOTHING to do with the Card object I added. It seems that simply setting any object property of the new entity triggers the problem.
NB. Example 1 works fine in terms of saving, it only causes a problem if the the new entity is deleted before saving.

I am running into a similar issue, as a workaround, I need to call DataContext.GetChanges(), then everything seems to have caught on again :)
Another problem you could have it that you are binding to columns and not entity properties, and hence the referential collections are not updated (already stated by someone else, but enforcing the fact).