I have two databases that I am accessing. The first is against a contact database which I connected to using EF Model First; creating the edmx. I have since begun to learn the virtue of CODE First when working with Entity Framework, so I decided I would, in the same project, write the Product database using Code First techniques, allowing the database to be generated from the code I am writing.
Everything compiles fine. The problem occurs when I hit my harness and it attempts to create the Product database and retreive a list of values from one of the tables...
I get the folowing error "Could not find the conceptual model type for 'Core.Data.Account'", when I attempt to enumerate the ProductLines property (Line3 below).
1. using (var ctx = new ProductDb())
2. {
3. var lines = ctx.ProductLines.ToList();
4. this.litOne.Text = lines.Count.ToString();
5. }
After some research it appears that this message may be occuring because of multiple entities with the same name (regardless of namespace), however there is nothing in the ProductDb context with the name "Account".
There is a class in the OTHER context created by the Model First approach named "Account". But how/why would that make a difference? They each point to different databases i.e. different connection strings. Why would the ProductDb be attempting to create a table called Account, when it should be completely unaware of it's exstence?
thoughts?
Thank you as always!,
- G
I bumped into the same problem, but the other way around: first a DbContext + generated database and then generated an edmx off the database (just for a little presentation). It appeared to be a restriction in EF: EF currently has a restriction that POCO classes can't be loaded from an assembly that contains classes with the EF attributes.
The only thing you can do for now is keep the contexts in separate assemblies.
Related
I really don't know where else to search for a solution to this problem. Basically, I've read twice (or more) all documentation and all pages I found on the web about Core Data Migration.
I had to change some names on the Entities (to readability) and also had to change the domain values used in my entities. AFAIK, in this case, I have to make a custom migration because I have to analyze the Input and generate a new Output:
I've created the new Model Version (v7)
I've updated the Model
Renamed existent Entities, Attributes and Relationships.
Added/Removed some Attributes
I've created the Mapping Model (v6 to v7)
I've configured the Mapping Model using Expressions
I've created two NSEntityMigrationPolicy (one for each entity)
The migration is going well for the entities and fields values, but none of the relationships are getting restored during the process.
During the process, the expression:
FUNCTION($manager, "destinationInstancesForEntityMappingNamed:sourceInstances:" , "RecentCallToRecentRecord", $source.recents)
is returning nothing.
I have debugged my custom NSEntityMigrationPolicy to check if the Source and Destination Entities are bound as expected and something very weird is happing. During the execution of createDestinationInstancesForSourceInstance:entityMapping:manager:error: everything is OK, after calling the superclass, I can navigate from Source to Destination (and the other way around). But during the execution of createRelationshipsForDestinationInstance:entityMapping:manager:error: this objects navigation does not work anymore.
Thanks in advance for any help.
Environment : EF 6, SQL 2012
Setup: Database First, LazyLoading disabled
The question might appear more generic but will try to explain it in the best possible way.
I have a large application using ASP.NET MVC and grouped the entity based on the logical functionality. Hence we built multiple EDMX files
There is scenario in which we have to use the similar entity in two EDMX file.
School has relation to Teachers and Students.In first EDMX file, i used school and Teachers.In Second EDMX file, i used school and students
But only one Entity class getting created. If i run the custom tool on second EDMX context file, then the entity(school.cs) on my first edmx getting disappeared and it appears on the second one..
Why this strange behaviour occurs?
Here is the code in my first EDMX file
As you see here, i m not accessing school entity and also i disabled Lazyloading. But it complains that it couldnt find school file. Note: Courses has navigation property to school. But i didnt include it here.. Why its occuring so?
var courses= DB.courses
.AsNoTracking()
.Select(e =>
new CourseDTO()
{
CourseID= e.CourseID,
Name= e.CourseName,
Desc= e.Desc,
isActive= e.isActive
})
.OrderBy(e => e.CourseID);
The problem is, I m able to include one entity in the EDMX file only..
In first EDMX, it has navigation property to Teachers
In second EDMX , it has navigation property related to Students. But only Entity file exists at a time.. With only one Entity file, the code breaks
Note: This is just sample..Not my original application
Thanks #GertArnold. Meanwhile, i tried to create folders and kept the EDMX file inside it. Means i created seperate folder for each logical group and then included edmx file inside it. This in turn made the edmx file entities have different name space(i mean the entity classes) and also it enabled to have the same entity across multiple EDMX files. It sounds to have resolved my problem.
I didnt try to have them included under different namespace.. The whole idea started when i realized that even though i have two EDMX files, the associated entities(.csfiles) are created in the same physical location. I tried to create sub folders and included the EDMX files. It resolved the problem and i found it is having different name space
:):)
I have a class Country, with 227 subtypes (one for each Country).
Legacy restrictions prevent me from easily changing this.
I've double checked that in fact the high number of subtypes is causing EF to have a super slow initialisation, on the first call, the first time the DbContext is accessed it takes about 2 minutes!!
Is there any way I can maintain this high number of subtypes in Entity framework and avoid this slow spin up ??
The hang can occur by doing a simple call to Db.Users.Find(1); (for example)
What's hurting you is the initial View Generation that Entity Framework goes through during a cold query (a query against Entities that don't have Views mapped. These Models are the mapping from Entities to Tables that makes EF so efficient afterward:
The process of computing these views based on the specification of the
mapping is what we call view generation. View generation can either
take place dynamically when a model is loaded, or at build time, by
using "pre-generated views"; the latter are serialized in the form of
Entity SQL statements to a C# or VB file.
Pre-Generated Views are designed with EF tools within VS and built at compile time rather than at run-time.
You can also consider using the Entity Framework Power Tools to
generate views of EDMX and Code First models by right-clicking the
model class file and using the Entity Framework menu to select
“Generate Views”. The Entity Framework Power Tools work only on
DbContext-derived contexts and can be found at
http://visualstudiogallery.msdn.microsoft.com/72a60b14-1581-4b9b-89f2-846072eff19d.
For more information on how to use pre-generated views on Entity
Framework 6 visit http://msdn.microsoft.com/en-us/data/dn469601.
Check this Reference on Entity Framework View Generation
Everything you need to know about pre-generating views, applying them, and even moving them to their own assembly (so that View Generation builds are independent of Application release builds.
when you create the first instance of Context ,
EF validate DB Schema ,
if the model has no changes , you can skip this step by static constractor :
static ctor
{
Database.SetInitializer<BillingContext>(null);
}
I have recently changed from ObjectContext to DbContext using EntityFramwework by upgrading to EF6
Most stuff works, but saving and updating won't. Here is an example:
public void AssignToAdmin(Product product, Admin admin)
{
var pcsps = from s in context.ProductCreationSections
join pcsp in context.ProductCreationSectionAndProducts on s.ProductCreationSecitionID equals pcsp.ProductCreationSectionID
where pcsp.ProductID == product.ProductID && s.IsManagerAssigned
select pcsp;
foreach (var pcsp in pcsps.Include("AssignedAdmins"))
{
pcsp.AssignedAdmins.Add(admin);
}
}
Trying to execute the line pcsp.AssignedAdmins.Add(admin), I get the error:
Error: The relationship between the two objects cannot be defined
because they are attached to different ObjectContext objects.
There is one context for the class and it comes from Dependency Injection (the class is a Service in an MVC app).
I've tried removing/attaching and so on, but this doesn't fix it - it just gives different error messages. It's not even obvious which entity is using another context.
Any ideas of where this other context the error message refers to is coming from?
See The relationship between the two objects cannot be defined because they are attached to different ObjectContext objects
Where has admin come from?
Getting the admin object from the same context as the pcsp object should help.
Sorted it, but it was quite a major refactor.
The issue was that each service received it's own instance of 'context', so when two entities from two services were expected to work together, they wouldn't as each belonged to a different context.
One solution would have been to make the class that created the context a 'Singleton' so that it always returned the same instance, but that would have been very BAD as every page would then use the same context.
Each service got it's own instance of 'context' through Dependency Injection.
I changed the project so only the controllers got an instance of context through DI. Then, in the controller constructor, this context was passed to the services that the controller had received through dependency injection.
This way, each request only ever uses a single instance of context, but this instance is still short lived, as it is supposed to be as each request has its own context and doesn't share one.
Not sure this is the way it is supposed to work, but given the web app I was working with, this seemed to be the best solution.
I also had to go through and add a 'context.SaveChanges();' statement everywhere a change to the database was made.
Not sure why this should be when the old version of EF did this automatically, but it now works.
Thanks for the advice Derrick
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}))