Is it possible to create multiple order detail lines using manager.createEntity(entityName) and save the whole bundle using a single manager.saveChanges().
Can anyone point me to an example?
Any help appreciated.
Regards, Paul
You'll see numerous descriptions of entity graph save in the documentation. It's simple really:
create the entities
make sure they are related which is as simple as assigning the parent to the pertinent navigation property of each child.
call entityManager.saveChanges() to save the entire lot of pending changes as a single transaction.
There is a particularly apt test, "can save new Order and its OrderDetails in one transaction", in the saveNorthwindTests.js file in the DocCode sample
Related
I'm wondering if there is some sort of way to set up something similar to a spreadsheet in Xcode. I'm trying to create a 'tapping game' or a 'clicker game' and storing so many variables in regular coding would be really tough.
Having this 'table' would enable me to keep track of multipliers and upgrade levels instead of clogging my coding with it.
Preferably, I could then just tell my code what to pull and what to look for off of the table. The table would be an 'engine' of sorts and it would not be UI. The table would do all of the work behind scenes, then show it through UI based on labels and buttons.
As traxido is saying, without more details we can't point you to a concrete example/solution. Base on the title the answer is yes. It's not a ui component though. It doesn't even need to be one.
What you want is a data structure to hold your data in a way that's convenient to access (save and retrieve). You could create a class which is a composite of other data structures like arrays and dictionaries and possibly other data structures. You might end up having many questions before you're through.
So: the answer is yes. Try it yourself and ask new questions if you get stuck.
Provide the code and error messages and I bet you quickly get answers.
Yes, you can.
Create a shared or singleton instance and retain all the data in instances of it.
(or) create a custom data structure and overide set or get methods to autoprocess the exiting data everytime you add or delete data element
Ex: If you want to maintain an array thats is always sorted. MySortedArray is the custom structure that inherits NSMutableArray and maintain a protected NSMutableArray instance. Overide addObject method to ensure sorting it whenever a new object is added.
I've looked all over SO, youtube, and the Apple docs and am having real trouble understanding the distinction--if any--between parent/child and to-one/to-many inverse relationships in Core Data. Nothing I've found appears to address the subject directly and explicitly.
I need to know this because I want to load a table view with data from one entity, called ListActivity, grouped into sections defined by another entity called ListCategory, as shown here. Also not real confident of my naming convention:
Can someone please clearly explain the difference--and when to use each case--or point me to something that can?
Thanks!
Edit for clarification:
For comparison, here is a screenshot of my entities with ListCategory specified via the menu in the Data Model Inspector as the Parent Entity for ListActivity:
Relationship is used go down in an object graph (i.e activities in a category) while an inverse relationship is used to go up in an object graph (i.e category to which an activity belong to).
While naming convention looks fine. better use "activities" instead of "listActivities" and "category" instead of "toCategory".
Generate classes for them and you'll better know how these will work out.
I need to write a form for creating a new entity and with it, up to 3 relations (which are new entities).
I can either have it dynamically attach/delete them dynamically (which could be useful) or have all 3 always be related to the entity, and for them to have an 'active' boolean on them, which would be just as appropriate.
At what point should I be doing this? I need them rendered as checkboxes on the form.
So far I've tried attaching them to the entity prior to passing it to the form, but choice fields can't be passed unmapped entities, so that's no good.
I've also tinkered with a DataTransformer for this, although then, as far as I can see, I would have to create new entities in the DataTransformer, which seems wrong, and I can't get to work anyway- I don't have access to the entity within it and even hacking around that, the relationship fails to bind properly (Doctrine tries to save the relationships first).
In Symfony1 terms, I could just embed a couple of forms for each additional relation I needed, using new objects, and it'd just work, so surely there's still a relatively easy way around this?
A friend also recommended looking into the ResizeFormEventListener, but this, as far as I understand, is for 'resizing' a form based on the returned data, whilst I never want the form to change, I want 3 checkboxes always.
What's the best way to approach this problem?
I'm not sure on exact details without playing with it - but based on how i've done similar things, i'd be looking to use a 'collectiontype' and then adding the three department types into that.
Being fairly new to CoreData (Started playing with it 2 hours ago ;) ) I keep wondering if there is an easier way to do things.
I'm currently using a DataModel to create my persistant objects code.
However when I keep adjusting things like number of attributes sotred, the name of the fields etc... and that leads to having the update the code of my NSManagedObjects.
I found that you can create the classes with the attributes already implemented, however, I haven't figured out how to update the code of an existing class other than adding it by hand or creating a new object and overwriting the existing one? (or how do other developers do it)
I'm aware that the answer is surely: "there is no better way" but I still have to ask.
Check out mogenerator.
This command line utility will generate two class files. A machine generated _MyClass header and implementation, with all code for your model. It will also create a subclass MyClass where you can add your own customizations.
Each time you regenerate your code, only the machine generated _MyClass files will be updated. All your changes to MyClass will be preserved.
If you can not use mogenerator, you can use the native code generation. Make sure you regenerate the code every time. However, that will erase any changes.
So, you have two very viable options.
Write a category on the entity class. You can do just about everything you want with a category.
Subclass from the entity, and put all your code in there.
Personally, I prefer using categories unless I absolutely must inherit... which is extremely rare.
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}))