I am using NHibernate with a SQL CE desktop database, and I'm getting an odd error when I try to do an update. SQL CE is throwing Error 25026: "A foreign key value cannot be inserted because a corresponding primary key value does not exist."
The exception occurs when performing a cascading update of a collection property of an entity object. The entity object is an Owner, and the collection property is Projects (IList), the projects for a particular Owner. In my database, the primary key of the Owners table is a three-character string (the owner's initials), with a corresponding foreign key in the Projects table.
Here's why I am puzzled: NHibernate can fetch all of the records for a particular owner (for example, "DCV"). And in my code, I can add a new Project object to Owner.Projects with no problem. I take the owner ID value directly from the Owner object fetched from the database, so I know the primary key exists in the Owners table. But when I do an ISession.SaveOrUpdate() on my Owner object, I get the foreign key error described above.
Am I dealing with some idiosyncracy of NHibernate, or some mundane error in my code or mappings? Any thoughts that would help me troubleshoot this problem greatly appreciated!
David Veeneman
Foresight Systems
I found the answer. It has to do with how NHibernate handles one-to-many associations. From the NHibernate Documentation, Sec. 6.4, One-To-Many Associations:
Very Important Note: If the
column of a association
is declared NOT NULL, NHibernate may
cause constraint violations when it
creates or updates the association. To
prevent this problem, you must use a
bidirectional association with the
many valued end (the set or bag)
marked as inverse="true". See the
discussion of bidirectional
associations later in this chapter.
If you are having this problem, remove the foreign key constraint temporarily and run your code, outputting NHibernate's SQL to the console. You will see that NHibernate first inserts the new record without the foreign key, then calls up the record, then inserts the foreign key into the record. The first operation is what generates the foreign key error.
The solution, as the NHibernate documentation points out, is to make the relation bidirectional.
Related
Lets say you have two entity named Parent and Child.
Child entity is DEPENDENT of Parent entity.
A weak key of child entity is the NAMEOFCHILD.
Is it possible for the Parent entity to have NAMEOFCHILD as a foreign key?
This idea has not been talked about in class. I was wondering is this possible in SQL?
If so, should i just add
FOREIGN KEY (NAMEOFCHILD) source CHILD
in my table?
In the database schema, yes (if Child.NAMEOFCHILD has a unique index). In entity framework, no. EF doesn't support associations to unique indexes (yet). But this is just on the technical level. Whether it's meaningful is another question.
Also, beware of painting yourself in a corner. When both foreign keys are not nullable you'd never be able to insert data, because you can't insert two records at a time and sequential inserts always cause foreign key violations. You would be able to design the database schema but never get any data in.
I'm setting up a project with Doctrine 2.1.5. I have got few tables without primary keys. I added some primary keys temporarily to generate Entities and Repositories.
But I will delete the fake primary key columns and remove the reference from Doctrine Entity as well.
Also I will be defining few columns as composite primary key in those table Entities (but not in tables).
Will there be any consequences (eg: wrong result from query or failing query) when joining those entity classes Because of 1. not having PK in database 2.adding fake composite primary key in entity classes?
Lots of tutorial and blogs mentions that needs to have primary key. But, never anything mentioned (which I can find) that the above solution is not a problem. (or it is a problem).
An answer from real experience would be great. But everyone welcome.
Thanks in advance for help.
P
Using the usual example for one-to-many ORM objects "Artist" and "Art", I have an Art table with a column called ArtistID that is labeled as a foreign key of "Artist" (it uses, surprise, the primary key of the Artist table). When I then have a specific Artist (called "thisArtist") and attempt to EntityDelete("thisArtist"), I get an error:
The DELETE statement conflicted with the REFERENCE constraint "FK_Art_Artists". The conflict occurred in database "ArtistTracker", table "dbo.Art", column 'ArtistID'.
I feel pretty confident that I am doing something dumb, either with my setup of relations or perhaps with my syntax. Has anyone encountered this? I don't see an example of how to EntityDelete() a specific Artist if it has foreign key constraints on entries in an Art table.
Your Artist will likely have an "arts" property, correct? And that points to an Art CFC, presumably. Your arts property probably looks like property name="arts" cfc="Art" fieldtype="one-to-many";
What's missing is to tell ORM how to handle the case where you delete the Artist. In your case, you need to add a "cascade" attribute onto the arts property, like so: property... cascade="all-delete-orphan";
Then, when you entityDelete the Artist, Hibernate will also delete any orphaned Art elements that belonged to that artist.
When creating one-to-many relationships, you almost always want to specify cascade="one-to-many" and inverse="true".
I need to use tables from a DB which I cannot alter (using linked server).
So part of my schema is a view on these table and I cannot create an FK in my DB.
When I come to creating the association in ADO.NET Entity Framework I am getting problems because a second column on the table from the external DB has an index on it and the EF is creating an Entity Key for it (it's the name descr of the record - I think they just wanted to speed the ordering on it).
When I take the Entity Key off this column in the EF entity it complains that I need it because the underlying table has a key on it.
If I leave it in I cannot map it onto anything in the table mapping of EF.
Does anyone know what I should do please?
You will have to edit the XML and remove the column from the key. Find the <EntityType> tag in the <edmx:StorageModels> section (SSDL content). Delete any <PropertyRef> in the <Key> that is not actually part of the primary key.
Once you do this, you can set "Entity Key" on the corresponding scalar property in the designer to false, and EF won't get mad. You will also not be asked to map this column in associations anymore.
I am just starting out with ADO.net Entity Framework I have mapped two tables together and receive the following error:
Error 1 Error 11010: Association End 'OperatorAccess' is not mapped. E:\Visual Studio\projects\Brandi II\Brandi II\Hospitals.edmx 390 11 Brandi II
Not sure what it is I am doing wrong.
I believe I can add some more clarity to the issue (learning as I go):
When I look at the Mapping details and look at the association, the column for operatoraccess table (from above) is blank and the drop down only includes field from the linked table.
The Entity Framework designer is terrible - I've had the same problem many times (and your problem too, Craig):
This happens when you have a many-to-one association which is improperly setup. They could very easily fix the designer to make this process simple; but instead, we have to put up with this crap.
To fix:
Click on the association, and go to the mapping details view.
Under association, click on Maps to <tablename>. Choose the table(s) which make up the many side of the relationship (ie. the table(s) which make up the *-side of the association in the designer)
Under Column, choose the table-columns which map to each entity-side Property. You get this error when one of those entries are blank.
I had the exact same problem and this is what I did to fix it.
Make sure you have an Entity Key set in your designer on the tables your making an association with. Also check that StoreGeneratedPattern is set to Identity for that Entity Key.
There's not a lot of information in your question, but, generally speaking, this means that there is an incompletely defined association. It could be that you have tried to map one table with a foreign key to another table, but have not mapped that other table. You can also get this error when you try to do table per type inheritance without carefully following the steps for implementing that feature.
Not sure of the answer, but I've just posted a similar question, which may at least help clarify the issue you are experiencing.
Defining an Entity Framework 1:1 association
I had to go back into the database itself and clarify the foreign key relationship
I had this problem in the case where I was creating both many to 0..1 and 0..1 to 0..1 associations. One entity needed associations to multiple tables, and that entity did not have foreign keys defined for those tables.
I had to do the table mappings step that is given in the accepted answer, but note that it wasn't only for many to many associations; it applied to all the types of associations I added for this entity.
In the Mapping Details view, I had to select the entity with the non-foreign key ID columns to the various tables. This is not always the "many" side of the relationship. Only there was I able to map the related entity property to the appropriate property in the original entity. Selecting the "destination" entity would not allow me to select the properties that I needed to, and the error would still exist.
So in short, I had to map using the table related to the entity that had the "non-foreign key" ID fields corresponding to the various entities' (and their tables') primary keys that I needed to associate.
Entity A
various other properties...
Id
ContactId
OrderId
etc.
Contact entity
Id
FirstName
LastName
etc.
In the mapping details, I selected Entity A's table. It then showed both ends of the association. I mapped its Entity A's Id property to its table's actual ID column (they had different names). I then mapped the Contact entity's Id field to the ContactId field on the A entity.
Simply select the many relationship table (*) from the Association>Edit Mapping & select the appropriate relationship