I have something like a Customer object with up to 50000 order in an ICollection<Orders>.
Assume the Custome being in the local cache, the orders not. How can i delete the Cutomer and all of its related orders without loading all of the Customer orders into the cache and marking them with setDeleted()?
What is the best practice here. I assume extending the public SaveResult SaveChanges(JObject saveBundle) method is the best way. Any other possibilities here on the client side like a flag delete_all_navigation_too()?
Thanks
I must suppose that you do not have and do not want cascade delete on your database. Personally, I'm "terrified" of deletes in general and try to avoid them. I prefer a soft delete (marking a record as inactive). But not everyone agrees or can follow suit
I would consider adding a Web API method (say "DeleteCustomerAndOrders") to your controller to do it. You can call any API method from your client, not just a Breeze method.
In recommending this, I'm assuming that this kind of thing is a relative rarity in your app. You don't need a general purpose deleter, a deleter that takes an array of parent object IDs, a deleter that will delete some child objects and not others, ... etc., etc.
Follow this path and you will have moved the problem from the client to the server. That's good: you didn't have to load the orders on the client. Now you have to get rid of them on the server. If you're using Entity Framework, you face the same challenge of deleting the orders without loading them. Check out Alex James' solution: Bulk-deleting in LINQ to Entities.
Simplest approach that I can come up with is to create a cascade delete constraint on the database so that when a customer is deleted all of its orders get deleted as well. Then simply delete the customer on the client and call 'SaveChanges'. In addition, since Breeze does not yet support client side 'cascaded' deletes ( we are considering this one), you will need to iterate over any client side orders that are already loaded and 'detach' them.
Related
Scenario:
(with an ASP.NET web app - Core or MVC)
I have a database with Users and Items for each user.
That means the UserId is a foreign key in the Items table.
From the browser I login as a User. I get my Items as a list of ItemViewModels, which are mapped (AutoMapper) to ItemViewModels via a simple api GET request.
I want to update one of the items (which should belong to me - the logged in user) via a simple API call. So I send the modified item back to the server via a PUT request as an ItemViewModel.
First approach:
The simplest approach would be to include the Item's database ID, ItemId, in the ItemViewModel - so when I receive the item to be updated as an ItemViewModel, I can map it back to the existing item in the database.
This however sounds pretty unsafe to me, as anyone could modify the PUT request with any ItemId and affect items which don't belong to the user who executed the request. Is there anything I'm missing about this approach?
Second approach:
Don't pass the database PK ItemId in the ItemViewModel.
Instead use an additional form of identification: let's say that user X has 10 items. And they are numbered from 1 to 10 using a property named UserItemId(which also exists in the database).
I can then pass this UserItemId in the ItemViewModel and when I get it back I can map it to an existing Item in the database (if all was ok with the request) or discard it and reject the request if the UserItemId didn't match anything from the logged in user's items.
Is anyone using this approach?
Pros:
The user only has access to it's own items and can't affect anyone else's since it doesn't know the actual Item ID (primary key), and any modifications are restricted to it's items.
Cons:
A great deal of extra management must be implemented on the server side for this approach to work.
Any other approaches ?
Please consider that the case mentioned above applies to all entities in the database which a client side implementation can CRUD, so it's not just the simple case described above.
The proposed solution should work for the entire app data.
I know this question has been asked here and here but the first one doesn't have a satisfying answer and I don't think the second one really applies to my situation, since it just deals with the UserId.
Thanks.
EDIT
Please consider the Item above as an aggregate root which contains multiple complex subItems each with a table in the db. And the question applies for them as much as for the main Item. That means that each subItem is passed as a ViewModel to the client.
I should mention that regarding further securing the update request:
For the first approach I can easily check if the user is allowed to change the item. But I should do this for all subItems too.
For the second approach I can check if the user can update the Item as follows: I get the userItemId of the incoming ViewModel -> I get all the logged in user's items from the database and try to find a match with the same userItemId, if I get a hit then I proceed with the update.
I think your application is not secure, if you only hide the Id.
You must check, before changing the database entity, if the user is allowed to change the entity.
In your case you should check, if your Id from the authenticated user is the UserId in your item.
If your ViewModel ist similar or identical for your API you could use a FilterAttribute in your controller.
I have an entity like this:
EntityA {id, someCollectionOfEntityB}
I load entityA from server with an expand on someCollectionOfEntityB.
I have one item in the collection.
Then on the server-side this item is deleted from DB by some third-party application.
Later my client application makes another call to fetch EntityA with an expand. This time the expand finds no records and therefore the collection is empty.
Yet, on the client-side, the item that was deleted from DB is still in the collection.
Why ? And how do I change this behaviour ?
[EDIT]
I have used the following strategy, but it does not solve the problem:
query.queryOptions = new breeze.QueryOptions({ mergeStrategy: breeze.MergeStrategy.OverwriteChanges });
In the end, I'm looping through the entities in the collection and I detach each one of them before querying the server again.
I don't think this is a very neat way to solve this issue. So I'd love to hear from the breeze team on this matter :)
Having an entity in cache, that entity has related entities in the form of a top 20.
Now a user action can update the top 20 on the server, and I thus would like to redownload the entire entity. Server sends the correct data with top 20, but in Breeze, I end up with a top 40... And I can't figure out how to avoid this behavior.
Thanks for the tip
Update: I do not use odata webapi and iqueryable, as it offers too much power to clients for my app. So I don't want to use EntityQuery.fromEntityKey, which seems to do what I want. I'd prefer to keep using a "normal" query, to which I add a parameter.
Update 2: To add more clarity as to why I want to prevent merge, when I recompute the top 20, I delete all related entries in the db and recreate them, so they have new Id's. So I am now considering an update, which might actually solve my issue BUT I would still like to know if merge can be prevented.
The Breeze EntityManager caches entities by primary key. So presumably your 2nd query is returning a completely new set of entities with each query. If this is the case, and you really only want the "latest" 20, the simplest fix would be to simply empty the EntityManager cache for this entity type before each query. Something like:
var entities = myEntityManager.getEntities(myEntityType);
entities.forEach(function(e) {
myEntityManager.detachEntity(e);
// or
// e.entityAspect.setDetached();
});
I am not sure what is exactly your qustion, but if you want to have different results on entity queries you may do it by creating 2 different controllers with different action names, or just with different parameters - overloaded methods. Then in your datacontext you can have 2 different queries.
You use .withParameters() propriety on the query to call the controller method with parameters.
Then in the controller method you can query and filter with LINQ, in any way you want. This way you can have different results based on the query/controller you chose to call.
Documentation: http://www.breezejs.com/documentation/querying-depth
I'm having trouble understanding how one would access the sub entities of an aggregate root. From answers to my previous question I now understand that I need to identify the aggregate roots of my model, and then only setup repositories which handle these root objects.
So say I have an Order object that contains Items. Items must exist within and Order so the Order is the aggregate root. But what if I want to include as part of my site an OrderItem details page? The URL to this page may be something like /Order/ItemDetails/1234, where 1234 is the ID of the OrderItem. Yet this would require that I retrieve an Item directly by ID, and because it is not an aggregate root I should not have a OrderItemRepository that can retrive an OrderItem by ID.
Since I want to work with OrderItems independent of an Orders does that imply that OrderItem is not actually an aggregate of Order but another aggregate root?
I don't know your business rules, of course, but I can't think of a case where you would have an orderitem that doesn't have an order. Not saying you wouldn't want to "work with one" by itself, but it still has to have an order, imo, and the order is sort of in charge of the relationship; e.g. you would represent all this by adding or deleting items from an order.
In situations like this, I usually will still require access to the items through the order. It's pretty easy to setup, in URLs I would just do /order/123/item/456. Or, if item ordering is stored / important (which it normally is stored at least indirectly via the order of entry), you could do /order/123/item/1 to retrieve the first item on the order.
In the controller, then, I just retrieve the order from the OrderRepository and then access the appropriate item from there.
All that said, I do agree w/ Arnis that you don't always have to follow this pattern at all. It's a case-by-case thing that you should evaluate the tradeoffs before doing it.
In Your case, I would retrieve OrderItem directly by URL /OrderItem/1234.
I personally don't try to abstract persistence (I don't use repository pattern). Also - I don't follow repository per aggregate root principle. But I do isolate domain model from persistence.
Main reason for that is - it's near-impossible to abstract persistence mechanisms completely. It's a leaky abstraction (e.g. try specifying eager/lazy loading for ORM that lives underneath w/o polluting repository API).
Another reason - it does not matter that much in what way You report data. Reporting part is boring and relatively unimportant. Real value of application is what it can do - automation of processes. So it's much more important how Your application behaves, how it manages to stay consistent, how objects interact etc.
When thinking about this problem, it's good to remember Law of Demeter. The point is - it should be applied only if we explicitly want to hide internals. In Your case - we don't want to hide order items.
So - exploiting fact that we know that entity Ids are globally unique (as opposed to unique only in Order context) it's just a short-cut and there is nothing wrong with retrieving them directly.
Interestingly enough - this can be pushed forward.
Even behavior encapsulation can and should be loosened up too.
E.g. - it makes more sense to have orderItem.EditComments("asdf") than order.EditOrderItemComments(order.OrderItems[0], "asdf").
Entity Framework 4, POCO objects and ASP.Net MVC2. I have a many to many relationship, lets say between BlogPost and Tag entities. This means that in my T4 generated POCO BlogPost class I have:
public virtual ICollection<Tag> Tags {
// getter and setter with the magic FixupCollection
}
private ICollection<Tag> _tags;
I ask for a BlogPost and the related Tags from an instance of the ObjectContext and send it to another layer (View in the MVC application). Later I get back the updated BlogPost with changed properties and changed relationships. For example it had tags "A" "B" and "C", and the new tags are "C" and "D". In my particular example there are no new Tags and the properties of the Tags never change, so the only thing which should be saved is the changed relationships. Now I need to save this in another ObjectContext. (Update: Now I tried to do in the same context instance and also failed.)
The problem: I can't make it save the relationships properly. I tried everything I found:
Controller.UpdateModel and Controller.TryUpdateModel don't work.
Getting the old BlogPost from the context then modifying the collection doesn't work. (with different methods from the next point)
This probably would work, but I hope this is just a workaround, not the solution :(.
Tried Attach/Add/ChangeObjectState functions for BlogPost and/or Tags in every possible combinations. Failed.
This looks like what I need, but it doesn't work (I tried to fix it, but can't for my problem).
Tried ChangeState/Add/Attach/... the relationship objects of the context. Failed.
"Doesn't work" means in most cases that I worked on the given "solution" until it produces no errors and saves at least the properties of BlogPost. What happens with the relationships varies: usually Tags are added again to the Tag table with new PKs and the saved BlogPost references those and not the original ones. Of course the returned Tags have PKs, and before the save/update methods I check the PKs and they are equal to the ones in the database so probably EF thinks that they are new objects and those PKs are the temp ones.
A problem I know about and might make it impossible to find an automated simple solution: When a POCO object's collection is changed, that should happen by the above mentioned virtual collection property, because then the FixupCollection trick will update the reverse references on the other end of the many-to-many relationship. However when a View "returns" an updated BlogPost object, that didn't happen. This means that maybe there is no simple solution to my problem, but that would make me very sad and I would hate the EF4-POCO-MVC triumph :(. Also that would mean that EF can't do this in the MVC environment whichever EF4 object types are used :(. I think the snapshot based change tracking should find out that the changed BlogPost has relationships to Tags with existing PKs.
Btw: I think the same problem happens with one-to-many relations (google and my colleague say so). I will give it a try at home, but even if that works that doesn't help me in my six many-to-many relationships in my app :(.
Let's try it this way:
Attach BlogPost to context. After attaching object to context the state of the object, all related objects and all relations is set to Unchanged.
Use context.ObjectStateManager.ChangeObjectState to set your BlogPost to Modified
Iterate through Tag collection
Use context.ObjectStateManager.ChangeRelationshipState to set state for relation between current Tag and BlogPost.
SaveChanges
Edit:
I guess one of my comments gave you false hope that EF will do the merge for you. I played a lot with this problem and my conclusion says EF will not do this for you. I think you have also found my question on MSDN. In reality there is plenty of such questions on the Internet. The problem is that it is not clearly stated how to deal with this scenario. So lets have a look on the problem:
Problem background
EF needs to track changes on entities so that persistance knows which records have to be updated, inserted or deleted. The problem is that it is ObjectContext responsibility to track changes. ObjectContext is able to track changes only for attached entities. Entities which are created outside the ObjectContext are not tracked at all.
Problem description
Based on above description we can clearly state that EF is more suitable for connected scenarios where entity is always attached to context - typical for WinForm application. Web applications requires disconnected scenario where context is closed after request processing and entity content is passed as HTTP response to the client. Next HTTP request provides modified content of the entity which has to be recreated, attached to new context and persisted. Recreation usually happends outside of the context scope (layered architecture with persistance ignorace).
Solution
So how to deal with such disconnected scenario? When using POCO classes we have 3 ways to deal with change tracking:
Snapshot - requires same context = useless for disconnected scenario
Dynamic tracking proxies - requires same context = useless for disconnected scenario
Manual synchronization.
Manual synchronization on single entity is easy task. You just need to attach entity and call AddObject for inserting, DeleteObject for deleting or set state in ObjectStateManager to Modified for updating. The real pain comes when you have to deal with object graph instead of single entity. This pain is even worse when you have to deal with independent associations (those that don't use Foreign Key property) and many to many relations. In that case you have to manually synchronize each entity in object graph but also each relation in object graph.
Manual synchronization is proposed as solution by MSDN documentation: Attaching and Detaching objects says:
Objects are attached to the object
context in an Unchanged state. If you
need to change the state of an object
or the relationship because you know
that your object was modified in
detached state, use one of the
following methods.
Mentioned methods are ChangeObjectState and ChangeRelationshipState of ObjectStateManager = manual change tracking. Similar proposal is in other MSDN documentation article: Defining and Managing Relationships says:
If you are working with disconnected
objects you must manually manage the
synchronization.
Moreover there is blog post related to EF v1 which criticise exactly this behavior of EF.
Reason for solution
EF has many "helpful" operations and settings like Refresh, Load, ApplyCurrentValues, ApplyOriginalValues, MergeOption etc. But by my investigation all these features work only for single entity and affects only scalar preperties (= not navigation properties and relations). I rather not test this methods with complex types nested in entity.
Other proposed solution
Instead of real Merge functionality EF team provides something called Self Tracking Entities (STE) which don't solve the problem. First of all STE works only if same instance is used for whole processing. In web application it is not the case unless you store instance in view state or session. Due to that I'm very unhappy from using EF and I'm going to check features of NHibernate. First observation says that NHibernate perhaps has such functionality.
Conclusion
I will end up this assumptions with single link to another related question on MSDN forum. Check Zeeshan Hirani's answer. He is author of Entity Framework 4.0 Recipes. If he says that automatic merge of object graphs is not supported, I believe him.
But still there is possibility that I'm completely wrong and some automatic merge functionality exists in EF.
Edit 2:
As you can see this was already added to MS Connect as suggestion in 2007. MS has closed it as something to be done in next version but actually nothing had been done to improve this gap except STE.
I have a solution to the problem that was described above by Ladislav. I have created an extension method for the DbContext which will automatically perform the add/update/delete's based on a diff of the provided graph and persisted graph.
At present using the Entity Framework you will need to perform the updates of the contacts manually, check if each contact is new and add, check if updated and edit, check if removed then delete it from the database. Once you have to do this for a few different aggregates in a large system you start to realize there must be a better, more generic way.
Please take a look and see if it can help http://refactorthis.wordpress.com/2012/12/11/introducing-graphdiff-for-entity-framework-code-first-allowing-automated-updates-of-a-graph-of-detached-entities/
You can go straight to the code here https://github.com/refactorthis/GraphDiff
I know it's late for the OP but since this is a very common issue I posted this in case it serves someone else.
I've been toying around with this issue and I think I got a fairly simple solution,
what I do is:
Save main object (Blogs for example) by setting its state to Modified.
Query the database for the updated object including the collections I need to update.
Query and convert .ToList() the entities I want my collection to include.
Update the main object's collection(s) to the List I got from step 3.
SaveChanges();
In the following example "dataobj" and "_categories" are the parameters received by my controller "dataobj" is my main object, and "_categories" is an IEnumerable containing the IDs of the categories the user selected in the view.
db.Entry(dataobj).State = EntityState.Modified;
db.SaveChanges();
dataobj = db.ServiceTypes.Include(x => x.Categories).Single(x => x.Id == dataobj.Id);
var it = _categories != null ? db.Categories.Where(x => _categories.Contains(x.Id)).ToList() : null;
dataobj.Categories = it;
db.SaveChanges();
It even works for multiple relations
The Entity Framework team is aware that this is a usability issue and plans to address it post-EF6.
From the Entity Framework team:
This is a usability issue that we are aware of and is something we have been thinking about and plan to do more work on post-EF6. I have created this work item to track the issue: http://entityframework.codeplex.com/workitem/864 The work item also contains a link to the user voice item for this--I encourage you to vote for it if you have not done so already.
If this impacts you, vote for the feature at
http://entityframework.codeplex.com/workitem/864
All of the answers were great to explain the problem, but none of them really solved the problem for me.
I found that if I didn't use the relationship in the parent entity but just added and removed the child entities everything worked just fine.
Sorry for the VB but that is what the project I am working in is written in.
The parent entity "Report" has a one to many relationship to "ReportRole" and has the property "ReportRoles". The new roles are passed in by a comma separated string from an Ajax call.
The first line will remove all the child entities, and if I used "report.ReportRoles.Remove(f)" instead of the "db.ReportRoles.Remove(f)" I would get the error.
report.ReportRoles.ToList.ForEach(Function(f) db.ReportRoles.Remove(f))
Dim newRoles = If(String.IsNullOrEmpty(model.RolesString), New String() {}, model.RolesString.Split(","))
newRoles.ToList.ForEach(Function(f) db.ReportRoles.Add(New ReportRole With {.ReportId = report.Id, .AspNetRoleId = f}))