In my MS SQL Server 2008 database I have self-referenced table with categories for hierarchy (ID and ParentID). Table have a self Foreign Key constraint and "Instead of Delete" trigger to perform deleting the full node with its children.
To manage data I'm using Entity Framework (4.3), with the model generated from DB with self-tracking entities and ObjectContext (generated by VS template). EDM also have self-referenced association on "category" entity.
I am faced with problem when trying to delete any parent row that has at least one child row.
After I call:
Entity.MarkAsDeleted();
Context.SaveChanges();
In SQL Server Profiler I see that EF first generates an update statement to set ParentID of child row(s) to null and then deletes parent row! Of course cascade rule in DB doesn't work and child nodes remains both in EF context and DB.
I've tried to set association rule "On delete" to "Cascade" and to "None" but it doesn't make sense...
How can I perform a cascade delete in a self-referenced table with EF, or at least how to prevent EF from updating parent IDs of child rows?
PS: here I found exactly the same problem without answer (MSDN)
Related
Some of my entities have navigation properties as they have a foreign key to another entity in the database. In my code, I've set the primary keys of the navigation properties to link the entities with each other.
The problem is that entity framework sees this as a new entity and tries to add it to the database with next error as a result:
Cannot insert explicit value for identity column in table 'xxx' when IDENTITY_INSERT is set to OFF.
Obviously, because the entity is new and not acquired from the database.
Is there a way in EF to remove the tracking of the entity?
I am using VS2012 and the Entity designer to generate both the database and the models. I have a very basic scenario of Table1 to Table1and2JoinTable to Table2. Something like Students, Classes, StudentClasses. You can have many students in many classes. I would like to have a cascading delete. So if you delete a student any rows in the StudentClass join table are deleted for that student id. Same for deleting a class any rows in the StudentClass are deleted for that class id. After setting up the many to many association in the designer and setting the cascade delete options you get the following error when you attempt to generate the database:
Error 132: End 'Student' on relationship 'Model1.StudentClass' cannot have operation specified since its multiplicity is ''. Operations cannot be specified on ends with multiplicity ''.
Here is a small example:
Here is the association created:
And the resulting error messages:
Here is a portion of the SQL code for generating the database tables:
-- Creating foreign key on [Students_Id] in table 'StudentClass'
ALTER TABLE [dbo].[StudentClass]
ADD CONSTRAINT [FK_StudentClass_Student]
FOREIGN KEY ([Students_Id])
REFERENCES [dbo].[Students]
([Id])
ON DELETE NO ACTION ON UPDATE NO ACTION;
-- This should be ON DELETE CASCADE ON UPDATE NO ACTION;
GO
-- Creating foreign key on [Classes_Id] in table 'StudentClass'
ALTER TABLE [dbo].[StudentClass]
ADD CONSTRAINT [FK_StudentClass_Class]
FOREIGN KEY ([Classes_Id])
REFERENCES [dbo].[Classes]
([Id])
ON DELETE NO ACTION ON UPDATE NO ACTION;
-- This should be ON DELETE CASCADE ON UPDATE NO ACTION;
GO
I know how to work around this by just editing the database script and add in the on delete cascade option. But, I don't want to do this because I am going to come back to the designer many times as the project grows and I don't want to have to remember this step every time.
Has anyone figured out how to resolve this?
It seems to be an edmx restriction, which I don't really understand. Code-first is perfectly capable of generating a junction table with two cascading ON DELETE constraints, but model-first and database-first do not allow the same configuration in the edmx. Normally, cascade actions are configured on the 'one' end of an association. Maybe it is too complex to check the validity of cascade actions on '*' ends (only when both ends are '*').
For the cascaded delete to happen with a context based on an edmx model, you have to load a parent and its children and then delete the parent.
var cls = db.Classes.Include(c => c.Students).Single(c => c.Id = 1);
db.Classes.Remove(cls);
db.SaveChanges();
The executed SQL statements show that the Class is fetched from the database in a JOIN statement with Student. Then the StudentClasss and the Class are deleted respectively.
Obviously, this is much more expensive than enabling cascaded delete in the database.
The work-around to modify the DDL each time after is was generated is not attractive, of course. But I think the only alternative is to make StudentClass part of the model and configure cascaded delete on the 'one' ends of the new associations. Or go code-first.
First of all make sure that you have an ON DELETE CASCADE specified in your Foreign Keys on database side.
I had similar problem and just adding ON DELETE CASCADE solve it instead of setting End1OnDelete and End2OnDelete properties.
I have a junction table with and idenity primary key columns to realize a many to many relationship. Visual Studio automatically detects it as a many to many relationship and the junction table is not an entity.
How can i realize it that also this table is generated as an entity? I need this for breeze.js .
You just need to add additional columns (or properties) to that table (or model).
You said that your table has acolumn named ID and it's the primary key withe IsIdentity set to true. It must works, I'm using this approach...
There must be a problem or missing with your table definition. However, if all are OK, just add a nullable column in your table and update your model from database. The problem will go away.
I have the following entities structure-
ParameterDefinition-->ParameterGroup-->Parameter
ParameterDefinition-->ParameterOperations
Also there is a map table with 2 FKs- Parameter & ParameterOperation (many to many entity).
The problem is that when i try to delete ParameterDefinition it first tries to delete ParameterGroup which can't be done because FK constraint to Parameter.
All my associations are set On Delete- Cascade.
How can i solve this so first it will start from the Map Entity , than other entities according the FKs ?
From everything I've read, you have to both set your FKs in the database to cascade on delete. The EDMX file won't pick this up when you update it, so you also have to set cascade on delete on the FKs in the EDMX file. Did you set the cascade on delete option at both the database level and the EDMX level? I'm reading it as you've only done this at the EDMX level, but I could be wrong.
I'm not a big fan of setting all my FKs to cascade on delete, so I just had to delete things in the correct order.
I'm trying to use migrations to add a parent table to an existing child table. For eg. I currently have User table, now I want to add a Department table that has a 1 to many relationship: Department has many User.
My questions, in automatic update, can I somehow seed the parent table before adding the FK so I can update all the children to this default seeded Department? If automatic update cannot do this, how do I accomplish this in code?
What I currently did: Made the FK nullable, created the Parent and seeded it, then update all child User FK to the parent. But now I cant change the FK not nullable because throws this error: Automatic migration was not applied because it would result in data loss.
Switching from nullable to non-nullable is considered data loss because after the migration, there is no way to tell which rows (if any) were null. If you are ok with this, you can call Update-Database with the -Force flag.
Another option would be to add a code-based migration that would:
Add the Departments table
Insert a default department
Add the required FK column to User with a default value of the inserted department