we use Azure Caching directly (and not through one of the available Entity Framework wrappers). Apparently, for distributed caching, we need to serialize the objects. Unfortunately, this causes issues with lazy-loaded DbContext-based proxies used for navigation properties.
I see we can use a custom serializer in order to map proxies to empty collections (if not loaded) or to normal objects (if loaded), but I am not sure about the implementation. One possible implementation can be based on the one used by WCF, but I am not sure Azure works the same way.
The ideal solution (and that's why I point to ProxyDataContractResolver) would be one where, when serialization happens:
IF the navigation property has been already loaded the data would be serialized as if it were a normal Collection,
and if they are not loaded, they won't be serialized (I would like lazy loading to work back after deserialization for the latter case, but it's acceptable if it doesn't).
Has anyone manually fixed that problem in an elegant way?
Thanks in advance!
I will presume that if you are wanting to cache EF objects, you don't require lazy loading or change tracking on those entities.
I believe that both of those are enabled through object proxies that will cause serialization issues (since you don't want to serialize the proxy).
If you disable the property DbContext.Configuration.ProxyCreationEnabled then serialization of the actual object, not the proxy, should work fine. This is typically required when returning POCO objects over WCF but is likley the same for other serializations scenarios such as this.
If you detach the EF entity from the DbContext before serializing it, that disables lazy loading, so your custom serializer won't try to serialize anything that isn't already part of the entity's graph.
Then when you get it back from the cache, if you attach it to a new (identical) DbContext, that should reenable lazy loading.
(Caveat: once you detach the entity from the context, any new queries that include that same object will create a new, attached, copy, so you will need to code with some care to avoid running into trouble with multiple potentially-different versions of the same object running around. But that said, this should let you do what you want.)
Related
I'm trying to figure out how to cache EF query results in an Azure AppFabric cache. Currently I'm using the LoreSoft EntityFramework extensions to deal with the caching (http://bit.ly/LWSywm). It works perfectly with an in memory cache, but not so much with AppFabric across multiple VM's. The issue is that I've got virtual properties in my EF objects, and they're being serialized as Dynamic Proxy objects, which of course can't be deserialized on a different VM, or even after a single VM restarts the application.
I only have a few queries I need to cache, so I'd rather not load every single related object manually across the whole project. Is there any way I can serialize an EF object with virtual properties? I don't need the virtual properties to magically start lazy loading again after I deserialize them. I've tried turning off lazy loading the DbContext before serializing the results, but that doesn't work. The only way I've found to get a serializable EF object is the remove all virtual properties.
By the way I've looked at the Julie Lerman article here: http://bit.ly/LWToZT
Seems like a cool project, but I'm not entirely sure it's going to solve my problem of not being able to serialize EF objects. Don't want to go down that road if I'm just going to end up where I started.
Any ideas most appreciated!
You can configure your dbcontext (or object context) to not use proxy objects. Obviously, this means no change tracking and no lazy loading. If you don't eager load an object's navigation properties, they will simply be null instead of references to proxies. It's worth noting that you can toggle this on and off throughout the context's lifetime, so it's not an all or nothing decision.
If you are using DbContext, the syntax is:
context.Configuration.ProxyCreationEnabled = false;
We have had a similar problem. We had a service that returned data that was read from a database using EF. This data needed to be cached in Appfabric.
In our case the services returned DTO objects, so we mapped the EF objects to DTO objects, and then stored the DTO objects in Appfabric cache.
Let's say I have an entity called Product and this entity is loaded every time user hits the product information page. Usually I'd save the object in Zend_Cache (memcache) for an hour to avoid hitting the db for each request but as far as I understand that's not possible with Doctrine2 entities because of the Proxy objects.
So my question is, how can I avoid loading the same entity from the database for each request?
[EDIT]
I tried using Doctrine Cache like this
$categoryService = App_Service_Container::getService('\App\Service\Category');
$cache = $categoryService->getEm()->getConfiguration()->getResultCacheImpl();
$apple = $cache->fetch('apple');
But I get the following error
Warning: require(App/Entity/Proxy/_CG_/App/Entity/Category.php)
[function.require]: failed to open stream: No such file or directory
in /opt/vhosts/app/price/library/Doctrine/Common/ClassLoader.php on
line 163
This is same for Zend Cache as well as you can't serialize the entity because of the Proxy class
You've got several options:
Use Doctrine's built-in result caching
Try just sticking entity in memcache via Zend_Cache. When you pull it out, you may need to merge() the Product back into the EM so proxies can be dereferenced. If you fetch-join any associations you need to display the product info, and you're only doing reads, this shoudl work fine.
Don't cache the entity at all. Cache whatever output you generate instead.
EDIT: If you don't care about the hydration overhead, you're using mysql, and your Products and associated tables don't change very often, you might prefer to just rely on the mySQL query cache. It's a fairly blunt object, but useful enough to mention.
You might want to try implementing __sleep or __wakeup methods for your entity class, as Doctrine 2 has special requirements and limitations concerning serialization/deserialization of entities (which is what happens when storing them in Zend_Cache).
There is this guidance.
General information about limitations including serialization.
I find this extremely strange since i just messed around with this myself and didn't have any issues with the proxy object being stored in the database. So im guessing your configuration is not setup 100% ?
If you find the issue with your configuration then be very aware of what timdev said you MUST merge the object back into the EntityManager else you will have weird bugs down the line.
A fourth solution available for you is also to retrieve the data as an array instead of an object, but then of course you lose all the functionality connected to your module which might not be exactly want you wanted.
It seems to me more like a configuration error. Either Proxies have not been generated or there is something wrong with the proxy directory and namespace.
Depending on your configuration, proxies can be either generated automatically or manually. Does your proxies have been indeed generated under App/Entity/Proxy ? Is this indeed the right directory?
FYI proxies can be manually generated by executing doctrine orm:generate-proxies <dest-dir>
Seconding what timdev says: Doctrine has built-in caching, you want to use it.
I also wonder from your question if you are experiencing any performance issues or if you are a victim of overly eager optimisation.
I wish to unit test my business logic is loading the correct data by loading an entity via the business logic and comparing it to an entity loaded directly from the dbcontext.
Assert.AreEqual fails I'm guessing because the entities are loaded as tracked.
I thought that I could possibly use AsNoTracking(), but it didn't work.
Is there a way of "unwrapping" the entity from entity framework to a POCO?
I've read about disabling proxycreation, but is this the only option?
I'm hoping there is something similar (although I realise a completely different concept), to ko.utils.unwrapObservable() in the knockout javascript library.
It is strange integration test (it is not unit test at all because it uses database) - it should be enough to simply define static expectation instead of loading it again from the database. Dynamic tests are more error prone and can hide issues.
To make it work you must override Equal to compare data not references. Disabling proxy creation will not work because you will still have different reference from your business logic and different reference from tested context (unless you share the context but in such case the test will be even more strange).
I am using the Service Layer --> Repository --> Entity Framework (Code-First) w/POCO objects approach, and I am having a hard time with updating entities.
I am using AutoMapper to map my Domain Objects to my View Models and that works good for getting the data, no how do I get that changes back into the database?
Using pure POCO objects, I would assume that there is no sort of change tracking, so I see my only option is to handle it myself. Do you just make sure that your View Models have the EXACT same properties as your Domain Objects? What if I just change a field or two on the View Model? Won't the rest of the fields on the Domain Object get overwritten in the database with default values?
With that said, what is the best approach?
Thanks!
Edit
So what I am stumbling on is this, lets take for example a simple Customer:
1) The Controller has a service, CustomerService, that calls the services GetCustmoerByID method.
2) The Service calls into the CustomerRepository and retrieves the Customer object.
3) Controller uses AutoMapper to map the Customer to the ViewModel.
4) Controller hands the model to the View. Everything is great!
Now in the view you do some modifications of the customer and post it back to the controller to persist the changes to the database.
I would assume at this point the object is detached. So should the model have the EXACT same properties as the Customer object? And do you have to make hidden fields for each item that you do not want to show, so they can persist back?
How do you handle saving the object back to the database? What happens if your view/model only deals with a couple of the fields on the object?
If you're using EF Code First, i.e: the DbContext API, then you still do have change tracking which is taken care of by your context class.
after making changes to your objects, all you have to do is call SaveChanges() on your context and that will persist the changes to your database.
EDIT:
Since you are creating a "copy" of the entity using AutoMapper, then it's no longer attached to your context.
I guess what you could do is something similar to what you would in ASP.NET MVC (with UpdateModel). You can get the original entity from your context, take your ViewModel (which may contain changed properties) and update the old entity, either manually (just modified properties), or using AutoMapper. And then persist the changes using context.SaveChanges().
Another solution would be to send the model entity as [part of] the ViewModel. This way, you'll have your entity attached to the container and change tracking will still work.
Hope this helps :)
You are absolutely right that with a detached object you are responsible for informing the context about changes in your detached entity.
The basic approach is just set the entity as modified. This works for scalar and complex properties but it doesn't work for navigation properties (except FK relations) - for further reading about problems with navigation properties check this answer (it is related to EFv4 and ObjectContext API but same problems are with DbContext API). The disadvantage of this approach is that all fields in DB will be modified. If you just want to modify single field you still have to correctly fill others or your database record will be corrupted.
There is a way to explicitly define which fields have changed. You will set the modified state per property instead of whole entity. It is little bit harder to solve this on generic approach but I tried to show some way for EFv4 and for EFv4.1.
I agree with #AbdouMoumen that it's much simpler to use the model entities at the view level. The service layer should provide an API to persist those entities in the data store (db). The service layer shouldn't dumbly duplicate the repository lawyer (ie: Save(entity) for every entity) but rather provide a high level save for an aggregate of entities. For instance, you could have a Save(order) in the service layer which results in updating more basic entities like inventory, customer, account.
In ADO.net EF, when should you call the context.Attach() and the context.Detach() methods and how do these calls affect the data being returned or being inserted?
This is one of those questions where, "If you have to ask, you probably should not be doing it." The Entity Framework will implicitly attach entities in cases where it is obvious that this needs to happen. You really only ever need to explicitly attach and detach entities in cases where you are using more than one ObjectContext at once. Because this can be quite confusing, due to the implicit attachment which happens in the course of normal Entity Framework operations, I strongly recommend that people new to the Entity Framework use only one ObjectContext at a time. If you do this, you should never need to explicitly call Attach or Detach.
Calling, say, Attach does not really affect the data returned, insofar as it's scaler properties are concerned. But if it refers to other entities which are already loaded into the context into which it is attached, then these properties will be pre-populated without explicit loading. That said, entities returned from a query are already attached, so you cannot attach them.
Attaching Objects (Entity Framework)
http://msdn.microsoft.com/en-us/library/bb896271.aspx
Detaching Objects (Entity Framework)
http://msdn.microsoft.com/en-us/library/bb738611.aspx