Is there a way (in Fluent NHibernate) to cascade delete from tables which have no direct relationship with each other? I have the situation below:
What I would like to happen is for Authorizations to be cascade deleted when a CustomerProduct is deleted (where auth.Customer = cp.Customer and auth.Product = cp.Product).
Authorization did have a direct relationship with CustomerProduct up until recently but it's been broken away from that so I can't solve the issue that way.
I was hoping to do something like (from CustomerProduct mappings):
mapping.HasMany<Authorization>(x => x.Authorizations)
.KeyColumn("ProductID")
.KeyColumn("CustomerID")
.Cascade.AllDeleteOrphan();
But obviously that's not going to work as there's no Authorizations member in CustomerProduct (at least I think that's why it doesn't work ^^).
This should be solved in the business layer, since there is a piece of business logic that knows how to remove the relation of a customer to a product.
Related
I have more experience with SQL databases than I do with Symfony and am hoping someone can clarify the association mappings on how Doctrine connects the database to Symfony.
Taking a one-to-many mapping between Category and Product as an example:
I have very little need to record productIDs as a long string in each category record and I assume that having it is an unnecessary overhead. If I really needed to get a list of all products in a category record in the future though then I assume I could just manually query it still?
By extension, to get the above, I would need a unidirectional many-to-one association. If this is the case though, then would I still (and how would I?) be able to control such things as on delete cascade if required?
I think you are not totally understanding how this works in Doctrine. I hope this helps:
If you do a one-to-many between your Category and Product (one category has many products) with doctrine then it means that all you need is a category_id column in your product table (product is in this case the owning side of the relationship). You can make the relationship bi-directional without any consequences for the category table. Doctrine will allow you to get the products for a category easily by doing:
$category->getProducts();
In the background a query will be performed where all products with matching category_id column are resolved from your database and added to the products collection in the Category entity.
Check the example in the docs. It is exactly like yours, but then a one-to-many between product and features.
To prevent all products from loading when querying your category you can mark the inverse side as fetch="EXTRA_LAZY".
If you still have questions after this, just leave a comment.
Update:
So to make it very clear: doctrine does not add a column inside the category table. In your case the products property only exist in the object model not in the database model.
I have a design problem with regards to Entity Framework model relationship
I have this model in the edmx
Business Rule:
A Participant can have multiple Roles so I create a relationship table ParticipantRoles that has 1-to-Many relationship on the Participant and the Role table
The Problem:
In order to get the Participant's Role value, I have to drill down through Participant->ParticipantRole->Role (see JSON output below)
The Question:
In EF, how to design the table relationship to bypass the ParticipantsRole table. I want to access the Role in something like this Particant.Role and not Participant.ParticipantsRole.Role
You say A Participant can have multiple Roles. And of course, a Role can have multiple Participants. So basically this is a many-to-many association.
Entity Framework will only map pure many-to-many associations (without connecting class) when the junction table only has two foreign keys. In your case, if the table ParticipantsRole only would have had a primary key consisting of ParticipantId and RoleId at the time of generating the model the class ParticipantsRole would not have been created. You would have had Participant.Roles and Role.Participants as navigation properties.
However, the model has been generated with ParticipantsRole and you want to get rid of it. (Or not, I'll get back to that).
This is what you can do:
Remove ParticipantRoles from the class diagram.
Modify the database table ParticipantRoles so it only has the two FK columns, that both form the primary key.
Update the model from the database and select ParticipantsRole in the Add tab.
This should give you a model with a pure many-to-many association.
However, think twice before you do this. M2m associations have a way of evolving into 1-m-1association (as you've got now). The reason is that sooner or later the need is felt to record data about the association, so the junction table must have more fields and stops being a pure junction table. In your case I can imagine that one day participant's roles must have a fixed order, or one marked as default. It can be a major overhaul to change a m2m association into 1-m-1 in a production environment. - Something to consider...
I have three table -
1. Anomaly
2. Markup
3. Anomaly_Markup
Mapping -
public AnomalyMap()
{
Table("anomaly");
Id(x => x.Id).Column("ID").CustomType("decimal");
HasManyToMany<DMMarkupData>(x => x.DMMarkupData)
.Table("anomaly_markup")
.ParentKeyColumn("ANOMALY_ID")
.ChildKeyColumn("MARK_UP_ID")
.Cascade.All()
.LazyLoad();
}
public MarkupDataMap()
{
Table("markup");
Id(x => x.Id).Column("ID");
}
Condition :
Save data by Anomaly - Anomaly contains MarkupData. It saves data. It is working functionality with me.
Delete markup - which should delete relationship from map table and markup data. I am facing this issue.
Anyone help me to find out solution, how to delete markup data ?
I see no relationship of MarkUpData with Anomaly. There must be same relationship and you should specify the control of cascade operation by using Inverse attribute in your mapping.
You can refer : How to set "cascade delete" option to "Set Null" in Fluent NHibernate?
To delete DMMarkupData just remove the object from collection and call for Save Anomaly.
From what you've posted it looks like you haven't defined a relationship on DMMarkupData -> Anomaly, so NHibernate won't know to delete it the MarkupData entries from the anomaly_markup table (despite the reverse relationship being there). You can either solve it with a database level cascade which removes entries in anomaly_markup when deleting MarkupData, or you can map the relationship in code & NHibernate and then NHibernate will do the cascade for you.
NHibernate does not manage the object graph, it only persists it. Removing the item from the list when it gets deleted is responsibility of the business logic!
(All the tricks with triggers and stuff that workaround it lead to inconsistencies and side effects within the transaction which does the change. From point of view of persistence ignorance it is not recommended. I would only do it when facing performance issues that can't be solved in another way.)
You can simplify it by using components. Provided that
you don't reference the same markup from somewhere else
you don't need to query for markup unrelated to Anomality
markups do never live outside of an Anomality
given all that, it is much easier to work with components. (I don't know how it is called in fluent, but in xml mapping it is called a "composite-element").
When using components, you don't need to delete the markup from the database. You just remove it from the list where it lives in.
I'm trying to figure out why NHibernate handles one-to-many cascading (using cascade=all-delete-orphan) the way it does. I ran into the same issue as this guy:
Forcing NHibernate to cascade delete before inserts
As far as I can tell NHibernate always performs inserts first, then updates, then deletes. There may be a very good reason for this, but I can't for the life of me figure out what that reason is. I'm hoping that a better understanding of this will help me come up with a solution that I don't hate :)
Are there any good theories on this behavior? In what scenario would deleting orphans first not work? Do all ORMs work this way?
EDIT: After saying there is no reason, here is a reason.
Lets say you have the following scenario:
public class Dog {
public DogLeg StrongestLeg {get;set;}
public IList<DogLeg> Legs {get;set;
}
If you were to delete first, and lets say you delete all of Dog.Legs, then you may delete the StrongestLeg which would cause a reference violation. Hence you cannot DELETE before you UPDATE.
Lets say you add a new leg, and that new leg is also the StrongestLeg. Then you must INSERT before you UPDATE so that the Leg has an Id that can be inserted into Dog.StrongestLegId.
So you must INSERT, UPDATE, then DELETE.
Also as nHibernate is based on Hibernate, I had a look into Hibernate and found several people talking about the same issue.
Support one-to-many list associations with constraints on both (owner_id, position) and (child_id)
Non lazy loaded List updates done in wrong order, cause exception
wrong insert/delete order when updating record-set
Why does Hibernate perform Inserts before Deletes?
Unidirection OneToMany causes duplicate key entry violation when removing from list
And here is the best answer from them:
Gail Badner added a comment - 21/Feb/08 2:30 PM: The problem arises when a new
association entity with a generated ID
is added to the collection. The first
step, when merging an entity
containing this collection, is to
cascade save the new association
entity. The cascade must occur before
other changes to the collection.
Because the unique key for this new
association entity is the same as an
entity that is already persisted, a
ConstraintViolationException is
thrown. This is expected behavior.
I'm using NHibernate (fluent) to access an old third-party database with a bunch of tables, that are not related in any explicit way. That is a child tables does have parentID columns which contains the primary key of the parent table, but there are no foreign key relations ensuring these relations. Ideally I would like to add some foreign keys, but cannot touch the database schema.
My application works fine, but I would really like impose a referential integrity rule that would prohibit deletion of parent objects if they have children, e.i. something similar 'ON DELETE RESTRICT' but maintained by NHibernate.
Any ideas on how to approach this would be appreciated. Should I look into the OnDelete() method on the IInterceptor interface, or are there other ways to solve this?
Of course any solution will come with a performance penalty, but I can live with that.
I can't think of a way to do this in NHibernate because it would require that NHibernate have some knowledge of the relationships. I would handle this in code using the sepecification pattern. For example (using a Company object with links to Employee objects):
public class CanDeleteCompanySpecification
{
bool IsSatisfiedBy(Company candidate)
{
// Check for related Employee records by loading collection
// or using COUNT(*).
// Return true if there are no related records and the Company can be deleted.
// Hope that no linked Employee records are created before the delete commits.
}
}