OK, I want to make sure I cover my situation and everything I've tried thoroughly. I'm pretty sure what I need/want can be done, but I haven't quite found the perfect combination for success.
I'm utilizing Entity Framework 4 RTM and its POCO support. I'm looking to query for an entity (Config) that contains a many-to-many relationship with another entity (App). I turn off lazy loading and disable proxy creation for the context and explicitly load the navigation property (either through .Include() or .LoadProperty()). However, when the navigation property is loaded (that is, Apps is loaded for a given Config), the App objects that were loaded already contain references to the Configs that have been brought to memory. This creates a circular reference.
Now I know the DataContractSerializer that WCF uses can handle circular references, by setting the preserveObjectReferences parameter to true. I've tried this with a couple of different attribute implementations I've found online. It is needed to prevent the "the object graph contains circular references and cannot be serialized" error. However, it doesn't prevent the serialization of the entire graph, back and forth between Config and App.
If I invoke it via WcfTestClient.exe, I get a stackoverflow (ha!) exception from the client and I'm hosed. I get different results from different invocation environments (C# unit test with a local reference to the web service appears to work ok though I still can drill back and forth between Configs and Apps endlessly, but calling it from a coldfusion environment only returns the first Config in the list and errors out on the others.) My main goal is to have a serialized representation of the graph I explicitly load from EF (ie: list of Configs, each with their Apps, but no App back to Config navigation.)
NOTE: I've also tried using the ProxyDataContractResolver technique and keeping the proxy creation enabled from my context. This blows up complaining about unknown types encountered. I read that the ProxyDataContractResolver didn't fully work in Beta2, but should work in RTM.
For some reference, here is roughly how I'm querying the data in the service:
var repo = BootStrapper.AppCtx["AppMeta.ConfigRepository"] as IRepository<Config>;
repo.DisableLazyLoading();
repo.DisableProxyCreation();
//var temp2 = repo.Include(cfg => cfg.Apps).Where(cfg => cfg.Environment.Equals(environment)).ToArray();
var temp2 = repo.FindAll(cfg => cfg.Environment.Equals(environment)).ToArray();
foreach (var cfg in temp2)
{
repo.LoadProperty(cfg, c => c.Apps);
}
return temp2;
I think the crux of my problem is when loading up navigation properties for POCO objects from Entity Framework 4, it prepopulates navigation properties for objects already in memory. This in turn hoses up the WCF serialization, despite every effort made to properly handle circular references.
I know it's a lot of information, but it's really standing in my way of going forward with EF4/POCO in our system. I've found several articles and blogs touching upon these subjects, but for the life of me, I cannot resolve this issue. Feel free to simply ask questions and help me brainstorm this situation.
PS: For the sake of being thorough, I am injecting the WCF services using the HEAD build of Spring.NET for the fix to Spring.ServiceModel.Activation.ServiceHostFactory. However I don't think this is the source of the problem.
EDIT: The ProxyDataContractResolver class works correctly if I don't have the circular references. (i.e.: I make the setter of App.Configs to be private, which prevents serialization of the property.) It blows up, it appears, when it hits Configs via the App object -- they don't seem to be recognized as the same type as the top level Configs.
EDIT2: It appears that either EF or WCF doesn't recognize that the entities are indeed equal. i.e.: 'Config' is the same as a particular 'Config.Apps[x].Configs[y]'. The entity keys are properly set in the CSDL for each model and I've overridden the Equals() function to compare entities based on their 'Id' property. This fits the symptoms as no circular reference error is thrown, yet it is indeed a circular reference (and blows up WcfTestClient.exe) AND the ProxyDataContractResolver blows up when it hits the 'Config.Apps[x].Configs[y]' level of Configs. (It doesn't know how to map a Config proxy. The ProxyDataContractResolver works otherwise. It's like it knows how to handle the initial round of entities, but the second level it considers as different entities.)
Wow, I can be wordy. Sorry folks!
You might want to check out my blog post on this specific scenario - please email me if it doesn't help fix your current predicament! I've included a sample solution as well.
Please drop me some feedback either way, I'd really like to hear from more people on this particular issue - especially with the implementation problems on the client end of things.
hrmm, I may not have fully understood the issue, but everytime I run into circular references with WCF the answer is to change [DataContract] on the offending classes to [DataContract(IsReference = true)].
This is a huge help compared to all the drek of messing with the contract resolvers that was needed pre WCF 3.5 SP1.
Hope this helps.
Faced the same issue today and used Value Injecter to solve it. It's as simple as:
var dynamicProxyMember = _repository.FindOne<Member>(m=>m.Id = 1);
var member = new Member().InjectFrom(dynamicProxyMember) as Member;
We couldnt afford disabling ProxyCreation
Try setting myContext.ContextOptions.ProxyCreationEnabled = false;
If the problem is solved (like mine) then you've not followed the steps mentioned in: http://msdn.microsoft.com/en-us/library/ee705457.aspx
This solved the problem for me.
You can use the ApplyDataContractResolverAttribute and a ProxyDataContractResolver along with the CyclicReferencesAwareAttribute. At first this produces error like this one - as if there is no DataContractResolver specified at all:
Type 'System.Data.Entity.DynamicProxies.Whatever_E6......A9' with data contract name 'Whatever_E6......A9:http://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.
It will work with one simple change.
In the ApplyCyclicDataContractSerializerOperationBehavior, the constructors for the DataContractSerializer must also pass in the DataContractResolver. This is left out of all the versions I have seen online.
Example:
public class ApplyCyclicDataContractSerializerOperationBehavior : DataContractSerializerOperationBehavior
{
private readonly Int32 _maxItemsInObjectGraph;
private readonly bool _ignoreExtensionDataObject;
public ApplyCyclicDataContractSerializerOperationBehavior(OperationDescription operationDescription, Int32 maxItemsInObjectGraph, bool ignoreExtensionDataObject, bool preserveObjectReferences)
: base(operationDescription)
{
_maxItemsInObjectGraph = maxItemsInObjectGraph;
_ignoreExtensionDataObject = ignoreExtensionDataObject;
}
public override XmlObjectSerializer CreateSerializer(Type type, String name, String ns, IList<Type> knownTypes)
{
return new DataContractSerializer(type, name, ns, knownTypes,
_maxItemsInObjectGraph,
_ignoreExtensionDataObject,
true,
null /*dataContractSurrogate*/,
DataContractResolver); // <-----------------------------
}
public override XmlObjectSerializer CreateSerializer(Type type, XmlDictionaryString name, XmlDictionaryString ns, IList<Type> knownTypes)
{
return new DataContractSerializer(type, name, ns, knownTypes,
_maxItemsInObjectGraph,
_ignoreExtensionDataObject,
true,
null /*dataContractSurrogate*/,
DataContractResolver); // <-----------------------------
}
}
Related
I am developing a website for a beauty salon. There is an admin part of the website, where the esthetician can add a new care. A care is linked to a care category (all cares related to hands, feets, massages, ...). To solve this I wrote this code into the CareRepository in the .NET API :
public async Task<Care?> AddAsync(Care care)
{
// var dbCareCategory = await this._careCategoryRepository.GetByNameAsync(care.CareCategoryName);
if (string.IsNullOrEmpty(care.CareCategoryName) || string.IsNullOrWhiteSpace(care.CareCategoryName))
return null;
var dbCareCategory = await this._instituteDbContext.CareCategories
.Where(careCategory => Equals(careCategory.Name, care.CareCategoryName))
.Include(careCategory => careCategory.Cares)
.FirstOrDefaultAsync();
if (dbCareCategory == null || dbCareCategory.Cares.Contains(care))
return null; // TODO : improve handling
dbCareCategory.Cares.Add(care);
await this._instituteDbContext.SaveChangesAsync();
return care;
}
My problem here is that I am a bit struggling with the best practice to have, because in order to add a care to a category, I have to get the category first. At the first place, I called the CareCategoryRepository to get the care (commented line). But then, EF was not tracking the change, so when I tried to add the care, it was not registered in the database. But once I call the category from the CareRepository, EF tracks the change and saves the Care in the database.
I assume this is because when calling from another repository, it is a different db context that tracks the changes of my entity. Please correct me if my assumption is wrong.
So, I am wondering, what is the best practice in this case ?
Keep doing what I am doing here, there is no issue to be calling the category entities from the care repository.
Change my solution and put the AddCare method into the CareCategoryRepository, because it makes more sense to call the categories entities from the CareCategoryRepository.
Something else ?
This solution works fine, however I feel like it may not be the best way to solve this.
The issue with passing entities around in web applications is that when your controller passes an entity to serve as a model for the view, this goes to the view engine on the server to consume and build the HTML for the view, but what comes back to the controller when a form is posted or an AJAX call is made is not an entity. It is a block of data cast to look like an entity.
A better way to think of it is that your Add method accepts a view model called AddCareViewModel which contains all of the fields and FKs needed to create a new Care entity. Think about the process you would use in that case. You would want to validate that the required fields are present, and that the FKs (CareCategory etc.) are valid, then construct a Care entity with that data. Accepting an "entity" from the client side of the request is trusting the client browser to construct a valid entity without any way to validate it. Never trust anything from the client.
Personally I use the repository pattern to serve as a factory for entities, though this could also be a separate class. I use the Repository since it already has access to everything needed. Factory methods offer a standard way of composing a new entity and ensuring that all required data is provided:
var care = _careRepository.Create(addCareViewModel.CareCategoryId,
/* all other required fields */);
care.OptionalField = addCareViewModel.OptionalField; // copy across optional data.
_context.SaveChanges(); // or ideally committed via a Unit of Work wrapper.
So for instance if a new Care requires a name, a category Id, and several other required fields, the Create method accepts those required fields and validates that they are provided. When it comes to FKs, the repository can load a reference to set the navigation property. (Also ensuring that a valid ID was given at the same time)
I don't recommend using a Generic Repository pattern with EF. (I.e. Repository()) Arguably the only reason to use a Repository pattern at all with EF would be to facilitate unit testing. Your code will be a lot simpler to understand/maintain, and almost certainly perform faster without a Repository. The DbContext already serves all of those needs and as a Unit of Work. When using a Repository to serve as a point of abstraction for enabling unit testing, instead of Generic, or per-entity repositories, I would suggest defining repositories like you would a Controller, with effectively a one-to-one responsibility.
If I have a CareController then I'd have a CareRepository that served all needs of the CareController. (Not just Care entities) The alternative is that the CareController would need several repository references, and each Repository would now potentially serve several controllers meaning it would have several reasons to change. Scoping a repository to serve the needs of a controller gives it only one reason to change. Sure, several repositories would potentially have methods to retrieve the same entity, but only one repository/controller should be typically responsible for creating/updating entities. (Plus repositories can always reference one another if you really want to see something as simple as Read methods implemented only once)
If using multiple repositories, the next thing to check is to ensure that the DbContext instance used is always scoped to the Web Request, and not something like Transient.
For instance if I have a CareRepository with a Create method that calls a CareCategoryRepository to get a CareCategory reference:
public Care Create(string name, int careCategoryId)
{
if (string.IsNullOrEmpty(name)) throw new ArgumentNullException(nameOf(name));
var care = new Care { Name = name };
var careCategory = _careCategoryRepository.GetById(careCategoryId);
care.CareCategory = careCategory;
_context.Cares.Add(care);
}
We would want to ensure that the DbContext reference (_context) in all of our repositories, and our controller/UnitOfWork if the controller is going to signal the commit with SaveChanges, are pointing at the exact same single reference. This applies whether repositories call each other or a controller fetches data from multiple repositories.
I have a base abstract context which has a couple hundred shared objects, and then 2 "implementation" contexts which both inherit from the base and are designed to be used by different tenants in a .net core application. A tenant object is injected into the constructor for OnConfiguring to pick up which connection string to use.
public abstract class BaseContext : DbContext
{
protected readonly AppTenant Tenant;
protected BaseContext (AppTenant tenant)
{
Tenant = tenant;
}
}
public TenantOneContext : BaseContext
{
public TenantOneContext(AppTenant tenant)
: base(tenant)
{
}
}
In startup.cs, I register the DbContexts like this:
services.AddDbContext<TenantOneContext>();
services.AddDbContext<TenantTwoContext>();
Then using the autofac container and th Multitenant package, I register tenant specific contexts like this:
IContainer container = builder.Build();
MultitenantContainer mtc = new MultitenantContainer(container.Resolve<ITenantIdentificationStrategy>(), container);
mtc.ConfigureTenant("1", config =>
{
config.RegisterType<TenantOneContext>().AsSelf().As<BaseContext>();
});
mtc.ConfigureTenant("2", config =>
{
config.RegisterType<TenantTwoContext>().AsSelf().As<BaseContext>();
});
Startup.ApplicationContainer = mtc;
return new AutofacServiceProvider(mtc);
My service layers are designed around the BaseContext being injected for reuse where possible, and then services which require specific functionality use the TenantContexts.
public BusinessService
{
private readonly BaseContext _baseContext;
public BusinessService(BaseContext context)
{
_baseContext = context;
}
}
In the above service at runtime, I get an exception "No constructors on type 'BaseContext' can be found with the constructor finder 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder'". I'm not sure why this is broken....the AppTenant is definitely created as I can inject it other places successfully. I can make it work if I add an extra registration:
builder.RegisterType<TenantOneContext>().AsSelf().As<BaseContext>();
I don't understand why the above registration is required for the tenant container registrations to work. This seems broken to me; in structuremap (Saaskit) I was able to do this without adding an extra registration, and I assumed using the built in AddDbContext registrations would take care of creating a default registration for the containers to overwrite. Am I missing something here or is this possibly a bug in the multitenat functionality of autofac?
UPDATE:
Here is fully runable repo of the question: https://github.com/danjohnso/testapp
Why is line 66 of Startup.cs needed if I have lines 53/54 and lines 82-90?
As I expected your problem has nothing to do with multitenancy as such. You've implemented it almost entirely correctly, and you're right, you do not need that additional registration, and, btw, these two (below) too because you register them in tenant's scopes a bit later:
services.AddDbContext<TenantOneContext>();
services.AddDbContext<TenantTwoContext>();
So, you've made only one very small but very important mistake in TenantIdentitifcationStrategy implementation. Let's walk through how you create container - this is mainly for other people who may run into this problem as well. I'll mention only relevant parts.
First, TenantIdentitifcationStrategy gets registered in a container along with other stuff. Since there's no explicit specification of lifetime scope it is registered as InstancePerDependency() by default - but that does not really matter as you'll see. Next, "standard" IContainer gets created by autofac's buider.Build(). Next step in this process is to create MultitenantContainer, which takes an instance of ITenantIdentitifcationStrategy. This means that MultitenantContainer and its captive dependency - ITenantIdentitifcationStrategy - will be singletons regardless of how ITenantIdentitifcationStrategy is registered in container. In your case it gets resolved from that standard "root" container in order to manage its dependencies - well, this is what autofac is for anyways. Everything is fine with this approach in general, but this is where your problem actually begins. When autofac resolves this instance it does exactly what it is expected to do - injects all the dependencies into TenantIdentitifcationStrategy's constructor including IHttpContextAccessor. So, right there in the constructor you grab an instance of IHttpContext from that context accessor and store it for using in tenant resolution process - and this is a fatal mistake: there's no http request at this time, and since TenantIdentitifcationStrategy is a singleton it means that there will not ever be one for it! So, it gets null request context for the whole application lifespan. This effectively means that TenantIdentitifcationStrategy will not be able to resolve tenant identifier based on http requests - because it does not actually analyze them. Consequently, MultitenantContainer will not be able to resolve any tenant-specific services.
Now when the problem is clear, its solution is obvious and trivial - just move fetching of request context context = _httpContextAccessor.HttpContext to TryIdentifyTenant() method. It gets called in the proper context and will be able to access request context and analyze it.
PS. This digging has been highly educational for me since I had absolutely no idea about autofac's multi-tenant concept, so thank you very much for such an interesting question! :)
PPS. And one more thing: this question is just a perfect example of how important well prepared example is. You provided very good example. Without it no one would be able to figure out what the problem is since the most important part of it was not presented in the question - and sometimes you just don't know where this part actually is...
I have been trying for three days to figure out this NHibernatefacility thing with Castle and wcf and it's really getting frustrating.
After solving a good dozen of errors, i have come to this one which seems pretty obvious but i can't solve.
This is my global.asax's Application_Start
container.AddFacility<AutoTxFacility>();
container.Register(Component.For<INHibernateInstaller>().ImplementedBy<NHibernateInstaller>());
container.AddFacility<NHibernateFacility>();
container.AddFacility<WcfFacility>();
container.Register(
Component.For<IAuthService>().ImplementedBy<AuthService>().LifestylePerWcfOperation(),
Component.For<IUserRepository>().ImplementedBy<UserRepository>().LifestylePerWcfOperation(),
Component.For<IActionWebService>().ImplementedBy<ActionWebService>().Named("ActionWebService").LifestylePerWcfOperation(),
Component.For<ISession>().LifeStyle.PerWcfOperation().UsingFactoryMethod(x => container.Resolve<ISessionManager>().OpenSession()));
This works for the first request. After that, it comes up with this error.
The factory was disposed and can no longer be used.
Object name: 'this'.
the error is happening in my userrepository in this line
[Transaction]
public virtual User GetUserByCredentials(string email, string password)
{
using (var tx = session())
{
return tx.QueryOver<User>().Where(x => x.Email == email && x.Password == password).SingleOrDefault();
}
}
I am having a feeling this has to do with the LIfestyle. I have tried multiple combinations but unsuccessful. I don't know what to do at this point. I got into this Castle thing with all the facilities (that are supposed to make life easier) and it's really complicated due to the lack of documentation. I haven't been able to find a descent guide to implement all of this together, not to mention something that is not 4 years old.
Help Please!
Sorry for not finding this question previously.
The most likely reason you're getting this error message is that you are re-registering the ISession. The point of the facility is to provide that support for you.
I also read in your comment that you have set the ISession to singleton. That should never ever be done, because any single fault on it an you will crash and burn and you'll have to throw away the full container (which most often is the composition root of the application, so you have to reboot the application).
The point of the facility is to give you AOP-based transactions, and then you need to have your transactions as close to the GUI or command layer as possible. Child operation, such as reading should not be wrapped in singular transactions with [Transaction] because they do not denote the transactional boundary for your operation.
Instead, look at your surface API and see where you have methods being called that are supposed to run with ACID; this is where you put the attributes.
In your case, it seems that your transactional boundaries are around the WCF calls. What you'd need to do is to replace the lifestyle that the ISession is registered with.
If you have a look at the c'tor for NHibernateFacility, you'll find an option to pass transient lifestyle; if all of your components depending on ISession are transient you'll be good to go with Transient lifestyle on ISession, because it is guaranteed to only live for as long as the object taken from the composition root/container lives.
The 'real' fix is to extend the facility, from my github, with an enum in the c'tor taking a PerWCFOperation value, and having the facility register ISessionManager and Func with those, similar to how it does with the three existing lifestyles.
I try to get above configuration working, but with no luck.
Step 1)
I started a new solution with a WCF Service Application project.
Step 2)
In this project, I added an edmx file and create a very simple model:
Entity Parent with Id and DisplayName
Entity Child with Id and ChildDisplayName
Association from Parent to Child, 1-to-m, resulting in NavigationProperties on both entities.
I generatedthe database without any problems. After generation, I inserted one Parent object with two related Child objects manually to the database.
Step 3)
I added the code generation, using the ADO.NET Self-Tracking Entity Generator.
I know that this should be done in diffrent assemblies, but to make it straight and easy, I put it all to the same project (the WCF project)
Step 4)
I just changed the IService Interface to create a simple get
[OperationContract]
Parent GetRootData(Int32 Id);
In the corresponding implementation, I take an Page object from the context and return it:
using (PpjSteContainer _context = new PpjSteContainer() )
{
return _context.ParentSet.Include("Child").Single(x => x.Id == Id);
}
Problem:
If I now run this project (the Service1.svc is start page), VS2010 automatically generates the test client to invoke the service. But once I invoke the service, I get an StackOverflowException! Debugging on the server side looks ok until it returns the object graph.
If I remove the Include("Child") everything is ok, but of course the Child objects are missing now.
I have no idea what I'm missing. I read a lot of howto's and guides, but all do it the way I did it (at least that's what I think)...
I tried the School example here, but this does not work for me as it seems the database generation and the coding in the example does not match.
So, I would much appreciate if someone could guide me how to make this work.
P.S.
Yes, all Entity-Classes are marked "[DataContract(IsReference = true)]"
Lazy-Loading is set to "false" in the edmx file
Edit:
I changed the WCF to be hosted in a console app and no longer in IIS. Of course then I had to write my own little test client.
Funny enough, now everything's working.
I of course have no idea why, but at least for my testing this is a solution...
Have a look here. Basically you have to make the serializer aware of cycles in the navigation properties.
I have two .NET 3.5 WCF services build with VS2008.
I have two WCF clients in Silverlight to consume these services. The clients are generated with the 'Add Service Reference'. I am using Silverlight 4.
ONE of the proxies is generated with Specified properties for each property. This is a 'message-in' class for my service method :
// properties are generated for each of these fields
private long customerProfileIdField;
private bool customerProfileIdFieldSpecified;
private bool testEnvField;
private bool testEnvFieldSpecified;
Now my other service (still with a Silverlight client) does NOT generate Specified properties.
Now I don't care about 'tenets of good SOA'. I just want to get rid of these damn properties because in the context of what I'm doing I absolutely hate them.
There has to be some difference between the two services - but I don't want to have to completely rip them apart to find out the difference.
A similar question before had the answer 'you cant do it' - which is definitely not true because I have it - I just don't know what I did differently.
Edit: I am now in a situation where I regenerate my Silverlight 4 proxy to my 3.5 WCF service (all on the same localhost machine) that sometimes I get 'Specified' properties and sometimes I don't. I no longer think (as I suspected originally) that this is due solely to some endpoint configuration or service level [attribute]. Theres certain triggers in the message itself that cause Specified to be generated (or not). There may be many factors involved or it may be something very simple.
try this in your WCF service where the property is declared
[DataMember(IsRequired=true)]
public bool testEnvField { get; set; }
IsRequired=true will negate the need for the testEnvFieldSpecified property
These extra Specified properties are generated for value types which are being specified as optional in either the contract or the attribute markup.
As value types have a value by default, the extra Specified flags are being added for these properties, to allow the client (and server) to distinguish between something explicitly not specified or explicitly specified - which may well be set to the default value. Without it, integers would always end up being 0 (and being serialized) even if you don't set them (because of the mapping to int) in your client code. So when you do, you need to also make sure that you set the Specified flag to true, otherwise these properties will not get serialized.
So to prevent these flags being generated for value types, you would have to change the contract to make these value type properties mandatory, instead of optional.
Hope that makes sense.
OK I've found one thing so far that will cause Specified properties to be generated:
The presence of an XTypedElement in the message.
These are used by Linq2XSD. I was returning an element from a Linq2XSD model.
This triggered Specified properties to be generated EVERYTHING in all my classes :
public XTypedElement Foo { get; set; }
This however didn't :
public XElement Foo { get; set; }
Still curious as to why this is, and if there are any other things that trigger this.
NOTE: I realize this is an old question. I'm adding this here because this question comes up as a top result on Google, and it's helpful information for whoever comes looking.
Try adding this line into your operation contract declaration:
[XmlSerializerFormat]
It should look something like this:
namespace WebServiceContract
{
[ServiceContract(Namespace = "http://namespace")]
[XmlSerializerFormat] //This line here will cause it to serialize the "optional" parameters correctly, and not generate the extra
interface InterfaceName
{
/*...Your web service stuff here...*/
}
}
I found that if I put a DataTable in a service DataContract then the generated client will use xml serializer and thus generate the *IsSpecified members.