We Keep Coding

The table does not have a primary key defined error

I have two tables that are basically link tables.
So one looks like this;
QueueId
TaskId
the two columns link to a Queues table and a Tasks table.
There is no primary key and i don't believe I need one.
I so try to import it into my .EDMX and I get the warning that
the table does not have a primary key defined but that it's been inferred as a read only table.
Also, the table doesn't show up in the Diagram and there is no model created for it.
I added a primary key and then got errors in my code.
I deleted all tables and did it all again and still the same thing happens with this one table.
The second table that is virtually identical has the same error but does appear in the diagram.
How do I get the first table to show in the diagram and not be read only because I need to delete the associations from time to time.
Thanks

Entity Framework doesn't need association table in the model to work with it.
There should be two navigation properties on either side of the relation - Task has ICollection<Queue> and Queue has ICollection<Task>. To remove association between specific task and queue you either find queue and remove that thask from it's collection, or do the reverse.

How to have more than 1 many-to-many relationship

My problem is simple but I can't seem to get EF to understand my database schema (Oracle).
Problem
I want to model more than 1 M-M relationship see diagram below:
As you can see I have a book and a journal - and I want to store a URI against both of these, by way of using a linking table (junction table, intersection table, you get it!). In this case it happens to be "www.google.com" that I want to store against Journal 16 and Book 75, they would be stored in the linking table in the follwoing format marked out in blue. For completeness I have added a green example for link with an ID of 5.
So you can see how the data knits together, I think you'll agree it's nothing too crazy.
Anyway, when I try and update EF model, it complains (in Visual Studio) with an error along the lines of.
Problem in mapping fragments starting at line 210:Foreign key constraint 'REF_URI_JOURNAL_FK1' from table REF_URI (REF_ID) to table JOURNALs (REF_ID): The columns of table REF_URI are mapped to AssociationSet BOOK_URISet's End BOOKs but the key columns of table JOURNALs are not mapped to the keys of the EntitySet BOOKs corresponding to this End.
Yeh - not really getting that error message!
I can get EF to work with 1 M-M relationship, e.g.
and it all works "hunky dory", but when I added a second M-M relationship it fell over with that error message above e.g.
Anyone know how I can get round this?

For two many-to-many relationships your need two linking tables (junction tables, intersection tables) REFBOOK_URI and REFJOURNAL_URI. I think that is what the exception is saying in a cryptic fashion. If you only had one table it would mean that if Journal 123 links to URI 789 then also Book 123 must also link to URI 789 because the REF_ID column in the link table would be a non-nullable foreign key to both the Journal and the Book table.

C# Entity Framework: Update Query Does not work

I have this simple code : (update value)
I'm trying to update column "c"
using (MaxEntities ctx = new MaxEntities())
{
aa orders = (from order in ctx.aa
select order).First();
orders.c = 22;
ctx.SaveChanges();
}
this is the table :
CREATE TABLE [dbo].[aa](
[a] [int] NULL,
[b] [int] NOT NULL,
[c] [int] NOT NULL
) ON [PRIMARY]
and values inside :
but i get an exception :
The property 'c' is part of the object's key information and cannot be modified.
I'm new to EF.
any help will be much appreciated.

The property 'c' is part of the object's key information and cannot be modified.
That's why you can't edit it. Maybe you need to add id column as a key with identity specified

As explained in another answer EF must uniquely identify every entity. If you don't have PK in the database, EF will infer some key. Key is considered as fixed so if EF inferred c as part of the key (and it did it because it uses all non-nullable non-binary columns) you cannot change its value. Moreover EF takes all tables without primary key as readonly so even if you remove c from the key in the designer and modify c value you will get another exception when you execute SaveChanges.
The reason for the second exception is in the way how EF describes model and the database. When EF inferred key, it did it only for description of your entities and for context's internal needs but not for description of the database. When EF tries to save changes it builds UPDATE statement from database description and without information about real database PK columns it will not be able to identify correct record for update (every update in EF can affect only single record - EF checks ROWCOUNT). This can be solved by cheating EF and updating its database description = by describing some column in the table description as primary key. This leads to multiple problems:
You must have some unique column in the database otherwise this method will not work.
You must edit EDMX manually (as XML) to add this change
You must not use default MS EDMX designer for updating your model from database because it will delete your change
Simple advice: Either use database tables with primary keys or don't use Entity framework.

Primary key missing here. Add primary key in table and it work.

I believe if there's no PK at all, EF uses all of the fields/columns as part of the key info.Here's a nice explanation: by #SteveWilkes of why. But what do your entities look like? The other possibility is that it doesn't have a property because the association is inside a different entity, if this is a foreign key.
EDIT
This got me thinking. There are just going to be situations where you have to work with legacy tables having no PK, even if you would never create such a thing. What about views? EF is a mapper - it has to uniquely identify that record so it infers and defines this key. Yes, you could use stored procedures, but could you also hack the XML and remove the keys from the table definition?
AND EDIT AGAIN
After posting this, I see #Ladislav Mrnka already said a similar idea (cheating EF and updating its database description), so it has been done (WARNING: Consume at your own risk - never tried). Quick google got me this blog with clear instructions:
Close the model designer in Visual Studio if it is still open and re-open the .edmx file in an XML editor
Find the edmx:StorageModels -> Schema -> Entity Container -> EntitySet element that refers to the table in question
On the EntitySet element, rename the store:Schema attribute to Schema
Remove the store:Name attribute altogether
Remove the opening and closing DefiningQuery tags and everything in between them
Save and close the .edmx file
But really, who doesn't like a PK? Can you not add an id?

Table-per-type inheritance insert problem

I followed this article on making a table-per-type inheritance model for my entities, but I ran into some issues. Below I'm posting steps to reproduce the problem I'm having in a minimal environment to rule out other factors.
First, I created a new MS SQL Server 2008 R2 database with the following two tables:
Users
Id : bigint (PK and set it as the identity column)
Name : nvarchar(25) NOT NULL (whatever, some random property
Customers
Id : bigint (PK, identity column, and FK on Users.Id)
Title : nvarchar(25) NOT NULL (also whatever, some random property)
Next, I generated the .edmx entity model from the database, and followed the link at the top verbatim. That is to say, I deleted the association between User and Customer, set User as the base class of Customer, deleted the Id property from the Customer entity, and made sure that the Customer.Id column was mapped to the inherited User.Id property. I then ran the following small program:
using (var db = new EF_Test.testEntities())
{
var cust = db.Users.CreateObject<Customer>();
db.Users.AddObject(cust);
db.SaveChanges();
}
I get the following error when I make that last call:
"A value shared across entities or associations is generated in more than one location. Check that mapping does not split an EntityKey to multiple store-generated columns."
With the following inner exception:
"An item with the same key has already been added."
Any ideas on what I could be missing?

A quick google on the error message turned up the following solution, maybe it helps you:
http://social.msdn.microsoft.com/Forums/en/adodotnetentityframework/thread/4bfee3fd-4124-4c1d-811d-1a5419f495d4
I think that I figured it out. The
table for the Party sub type had its
key column set to autogenerate a key
value and since it's derived, the EF
wanted to set that value explicitly.
So have you tried removing the "identity" setting from the customer table? So it doesn't autogenerate the primary key?
Hope this helps.

I finally found the source of my troubles. For those still interested, in the Customers table, the Id column should not have been set to the identity column of the table (PK and the FK dependency are fine though).

Why you don't want to make a foreign key (UserId) as a separate column? Maybe it can help you.
Also try to use model first approach and generate db after model creation as it is described in the following article.

MVC Entity Model not showing my table

I have a database with multiple tables, and some basic relationships. Here is an example of the problem I am having:
My Database:
**Org**
ID
Name
etc
**Detail1**
ID
D1name
**Org_Detail1**
Org_ID
Detail1_ID
**Detail2**
ID
D2Name
**Org_Detail2**
Org_ID
Detial1_ID
BooleanField
My problem is, the Org_detail1 table is not showing up in the entity model, but the Org_Details2 table does.
I thought it may have been because the Org_Detail1 table only contains two ID fields that are both primary keys, while the Org_Details2 table contains 2 primary key ID fields as well as a boolean field.
If I add a dummy field to Org_detail1 and update it, it still won't show up and wont allow me to add a new entity relating to the Org_Detail1 table. The table won't even show up in the list, but it is listed under the tables.
Is there any solution to get this table to appear in my model?

Seems like I may just need to completely delete the model and recreate it. Adding dummy fields is the only solution I've found.

Not sure this is an MVC problem.
Does a Detail1 collection turn up in your Org entity and an Org collection show up in your Detail1 entity. This is the normal behaviour for Entity framework for a many to many intersecting table with no other tangible data.
If not then maybe the foreign key constraints are not defined.