I know that one way to use a context is via the using statement.
I use it like so within my controllers
[ApiController]
public class MyController : ControllerBase
{
[HttpPost]
public ActionResult PostActionHere(ActionRequestClass request)
{
using (var context = new MyEntityFrameworkContext())
{
....
// use context here
context.SaveChanges()
....
}
}
}
I would like to start injecting it into my controller. Mainly because I think it is easier to read and is more uniform with .NET Core dependency injection.
[ApiController]
public class MyController : ControllerBase
{
private MyEntityFrameworkContext _myDb;
public MyController(MyEntityFrameworkContext myDb)
{
_myDb = myDb;
}
[HttpPost]
public ActionResult PostActionHere(ActionRequestClass request)
{
....
// use context here
_myDb.SaveChanges()
....
}
}
Within my startup.cs:
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<MyEntityFrameworkContext >(options =>
options.UseSqlServer(Configuration.GetConnectionString("MyEntityFrameworkDatabase")));
}
What I am worried about is that injecting it I lose the disposal properties that come with the using statement. Is that true? Feel free to suggest alternate approaches.
injecting it I lose the disposal properties that come with the using statement. Is that true?
No:
The AddDbContext extension method registers DbContext types with a
scoped lifetime by default.
Configuring a DbContext
And when the scope (here the HttpRequest) ends, the Scoped Lifetime object will be Disposed.
I am using Razorpages in ASP.NET Core
I have a simple detailsModel that brings in the different DbContext from Entity Framework (EF) using the constructor parameters.
this means that my DbContexts are available when performing different actions using the OnGetVerb and OnPostVerb.
I have created a helper class that I want to use to execute the actions as I need to call this code from other places as well, but when I call the helper class the DbContext is not available in the helper class.
await new Helpers.ApproveOrder().Approve(id);
This is my code
public class DetailsModel : PageModel {
public Context1 _context1;
public Context2 _context2;
public Context3 _context3;
public IMemoryCache _cache;
public DetailsModel(Context1 context1, Context2 context2, Context3 context3, IMemoryCache memoryCache) {
_context1 = context1;
_context2 = context2;
_context3 = context3;
_cache = memoryCache;
}
public async Task<IActionResult> OnGetApproveAsync(int id) {
await new Helpers.ApproveOrder().Approve(id);
return Redirect("~/");
}
}
how can I fix this so that my dbContexts are also available in my helper class
With EF Core, DbContext is registered as Scoped by EF service extension. This is desirable because DbContext is not thread-safe and therefore it should be created per request.
ServiceStack IOC treats any Scoped registration in Startup as singleton, which contradicts with the point above.
One possible solution is to not use EF Core's service extension, but that seems to bring a lot of boilerplate code and reduce maintainability. Is there any better way?
--
UPDATE
I'd like to provide sample code for clarity
I added a private Guid to the DbContext class so that I can tell whether we have the new instance.
public class BloggingContext : DbContext
{
private readonly Guid _instance;
public BloggingContext(DbContextOptions<BloggingContext> options)
: base(options)
{
_instance = Guid.NewGuid();
}
public DbSet<Blog> Blogs { get; set; }
}
With .NET Core MVC, the controller code looks like
public class BlogsController : Controller
{
private readonly BloggingContext _context;
public BlogsController(BloggingContext context)
{
_context = context;
}
// skip for readability
}
For each request hitting the controller, the _instance inside BloggingContext returns an unique value. However, when using within a ServiceStack service, _instance always returns the same value.
public class BlogService : ServiceStack.Service
{
private readonly BloggingContext _context;
public BlogService(BloggingContext context)
{
_context = context;
}
// skip for readability
}
This behaviour is consistent with ServiceStack documentation about .NET Core Container Adapter that scoped dependencies registered in .NET Core Startup is singleton within ServiceStack. However, it is not desirable because we want DbContext to be created per request.
My solution is that I move the DbContext registration into AppHost code as below
public override void Configure(Container container)
{
container.AddScoped(c =>
{
var optionsBuilder = new DbContextOptionsBuilder<BloggingContext>();
optionsBuilder.UseSqlServer(connection);
return new BloggingContext(optionsBuilder.Options);
});
}
This code works as I expect. Every instance of BloggingContext injected into my BlogService is now unique. However, I find myself unable to use any service collection extension which is very handy in .Net Core Startup anymore. For example, I want to use Entity Framework Unit Of Work and I couldn't call
services
.AddUnitOfWork<BloggingContext>();
Instead, I have to wire up all dependencies of that library myself like
public override void Configure(Container container)
{
container.AddScoped(c =>
{
var optionsBuilder = new DbContextOptionsBuilder<BloggingContext>();
optionsBuilder.UseSqlServer(connection);
return new BloggingContext(optionsBuilder.Options);
});
container.AddScoped<IRepositoryFactory, UnitOfWork<BloggingContext>>();
container.AddScoped<IUnitOfWork, UnitOfWork<BloggingContext>>();
container.AddScoped<IUnitOfWork<BloggingContext>, UnitOfWork<BloggingContext>>();
}
You should be able to register it in .NET Core's IOC like any .NET Core App:
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<BloggingContext>(options =>
options.UseSqlite("Data Source=blog.db"));
}
Then reference like a normal dependency in your ServiceStack Services:
public class MyServices : Service
{
public BloggingContext BloggingContext { get; set; }
}
Which uses ServiceStack's .NET Core Container Adapter to resolve any dependencies not in ServiceStack's IOC, in .NET Core's IOC.
I'm building a service application using Web API, .Net Core and EntityFramework Core.
For configuring options in my DbContext I'm using these lines in "ConfigureServices" method in Startup.cs
var connection = #"Server=ISSQLDEV;Database=EventManagement;Trusted_Connection=True;";
services.AddDbContext<EMContext>(options => options.UseSqlServer(connection));
I know that if I add the context as a constructor parameter in the controller .Net will inject the context in the constructor.
But this is not the behavior I want. I don't want my web api to know anything about the dbcontext. I have a DataAccess Project with a repository class that handles all CRUD operations.
This means that I just want to say Repository.AddEvent(evt) in my controller and then repository knows how to handle that.
On the other hand, repository uses a simple dependency resolver to get the right "IDataAdapter" implementation. One of those implementations is SQLDataAdapter. This is the point I need my context.
How can I pass my context all the way to this point?
You can solve this by adding your dbcontext via constructor injection to your classes from your data access layer.
public class Startup
{
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<ApplicationDbContext>(o => o.UseSqlServer(myConnStr));
services.AddScoped<Repository>(); // 'scoped' in ASP.NET means "per HTTP request"
}
}
public class MvcController
{
private Repository repo;
public MvcController(Repository repo)
{
this.repo = repo;
}
[HttpPost]
public void SomeEndpoint()
{
this.repo.AddFoo(new Foo());
}
}
public class Repository
{
private DbContext db;
public Repository(ApplicationDbContext db)
{
this.db = db;
}
public void AddFoo(Foo obj)
{
this.db.Set<Foo>().Add(obj);
this.db.SaveChanges();
}
}
If you want to further customize how your DbContext is injected into your DI container, I suggest you look at what .AddDbContext is actually doing. See https://github.com/aspnet/EntityFramework/blob/1.0.0/src/Microsoft.EntityFrameworkCore/EntityFrameworkServiceCollectionExtensions.cs#L142-L158
I'm using StructureMap to resolve references to my repository class. My repository interface implements IDisposable, e.g.
public interface IMyRepository : IDisposable
{
SomeClass GetById(int id);
}
An implementation of the interface using Entity Framework:
public MyRepository : IMyRepository
{
private MyDbContext _dbContext;
public MyDbContext()
{
_dbContext = new MyDbContext();
}
public SomeClass GetById(int id)
{
var query = from x in _dbContext
where x.Id = id
select x;
return x.FirstOrDefault();
}
public void Dispose()
{
_dbContext.Dispose();
}
}
Anyway as mentioned I'm using StructureMap to resolve IMyRepository. So when, where and how should I call my dispose method?
WARNING: please note that my views have changed, and you should consider the following advise outdated. Please see this answer for an updated view: https://stackoverflow.com/a/30287923/264697
While DI frameworks can manage lifetime of objects for you and some could even dispose objects for you after you're done using with them, it makes object disposal just too implicit. The IDisposable interface is created because there was the need of deterministic clean-up of resources. Therefore, in the context of DI, I personally like to make this clean-up very explicit. When you make it explicit, you've got basically two options: 1. Configure the DI to return transient objects and dispose these objects yourself. 2. Configure a factory and instruct the factory to create new instances.
I favor the second approach over the first, because especially when doing Dependency Injection, your code isn't as clean as it could be. Look for instance at this code:
public sealed class Client : IDisposable
{
private readonly IDependency dependency;
public Client(IDependency dependency)
{
this. dependency = dependency;
}
public void Do()
{
this.dependency.DoSomething();
}
public Dispose()
{
this.dependency.Dispose();
}
}
While this code explicitly disposes the dependency, it could raise some eyebrows to readers, because resources should normally only be disposed by the owner of the resource. Apparently, the Client became the owner of the resource, when it was injected.
Because of this, I favor the use of a factory. Look for instance at this example:
public sealed class Client
{
private readonly IDependencyFactory factory;
public Client(IDependencyFactory factory)
{
this.factory = factory;
}
public void Do()
{
using (var dependency = this.factory.CreateNew())
{
dependency.DoSomething();
}
}
}
This example has the exact same behavior as the previous example, but see how the Client class doesn't have to implement IDisposable anymore, because it creates and disposes the resource within the Do method.
Injecting a factory is the most explicit way (the path of least surprise) to do this. That's why I prefer this style. Downside of this is that you often need to define more classes (for your factories), but I personally don't mind.
RPM1984 asked for a more concrete example.
I would not have the repository implement IDisposable, but have a Unit of Work that implements IDisposable, controls/contains repositories and have a factory that knows how to create new unit of works. With that in mind, the above code would look like this:
public sealed class Client
{
private readonly INorthwindUnitOfWorkFactory factory;
public Client(INorthwindUnitOfWorkFactory factory)
{
this.factory = factory;
}
public void Do()
{
using (NorthwindUnitOfWork db =
this.factory.CreateNew())
{
// 'Customers' is a repository.
var customer = db.Customers.GetById(1);
customer.Name = ".NET Junkie";
db.SubmitChanges();
}
}
}
In the design I use, and have described here, I use a concrete NorthwindUnitOfWork class that wraps an IDataMapper that is the gateway to the underlying LINQ provider (such as LINQ to SQL or Entity Framework). In sumary, the design is as follows:
An INorthwindUnitOfWorkFactory is injected in a client.
The particular implementation of that factory creates a concrete NorthwindUnitOfWork class and injects a O/RM specific IDataMapper class into it.
The NorthwindUnitOfWork is in fact a type-safe wrapper around the IDataMapper and the NorthwindUnitOfWork requests the IDataMapper for repositories and forwards requests to submit changes and dispose to the mapper.
The IDataMapper returns Repository<T> classes and a repository implements IQueryable<T> to allow the client to use LINQ over the repository.
The specific implementation of the IDataMapper holds a reference to the O/RM specific unit of work (for instance EF's ObjectContext). For that reason the IDataMapper must implement IDisposable.
This results in the following design:
public interface INorthwindUnitOfWorkFactory
{
NorthwindUnitOfWork CreateNew();
}
public interface IDataMapper : IDisposable
{
Repository<T> GetRepository<T>() where T : class;
void Save();
}
public abstract class Repository<T> : IQueryable<T>
where T : class
{
private readonly IQueryable<T> query;
protected Repository(IQueryable<T> query)
{
this.query = query;
}
public abstract void InsertOnSubmit(T entity);
public abstract void DeleteOnSubmit(T entity);
// IQueryable<T> members omitted.
}
The NorthwindUnitOfWork is a concrete class that contains properties to specific repositories, such as Customers, Orders, etc:
public sealed class NorthwindUnitOfWork : IDisposable
{
private readonly IDataMapper mapper;
public NorthwindUnitOfWork(IDataMapper mapper)
{
this.mapper = mapper;
}
// Repository properties here:
public Repository<Customer> Customers
{
get { return this.mapper.GetRepository<Customer>(); }
}
public void Dispose()
{
this.mapper.Dispose();
}
}
What's left is an concrete implementation of the INorthwindUnitOfWorkFactory and a concrete implementation of the IDataMapper. Here's one for Entity Framework:
public class EntityFrameworkNorthwindUnitOfWorkFactory
: INorthwindUnitOfWorkFactory
{
public NorthwindUnitOfWork CreateNew()
{
var db = new ObjectContext("name=NorthwindEntities");
db.DefaultContainerName = "NorthwindEntities";
var mapper = new EntityFrameworkDataMapper(db);
return new NorthwindUnitOfWork(mapper);
}
}
And the EntityFrameworkDataMapper:
public sealed class EntityFrameworkDataMapper : IDataMapper
{
private readonly ObjectContext context;
public EntityFrameworkDataMapper(ObjectContext context)
{
this.context = context;
}
public void Save()
{
this.context.SaveChanges();
}
public void Dispose()
{
this.context.Dispose();
}
public Repository<T> GetRepository<T>() where T : class
{
string setName = this.GetEntitySetName<T>();
var query = this.context.CreateQuery<T>(setName);
return new EntityRepository<T>(query, setName);
}
private string GetEntitySetName<T>()
{
EntityContainer container =
this.context.MetadataWorkspace.GetEntityContainer(
this.context.DefaultContainerName, DataSpace.CSpace);
return (
from item in container.BaseEntitySets
where item.ElementType.Name == typeof(T).Name
select item.Name).First();
}
private sealed class EntityRepository<T>
: Repository<T> where T : class
{
private readonly ObjectQuery<T> query;
private readonly string entitySetName;
public EntityRepository(ObjectQuery<T> query,
string entitySetName) : base(query)
{
this.query = query;
this.entitySetName = entitySetName;
}
public override void InsertOnSubmit(T entity)
{
this.query.Context.AddObject(entitySetName, entity);
}
public override void DeleteOnSubmit(T entity)
{
this.query.Context.DeleteObject(entity);
}
}
}
You can find more information about this model here.
UPDATE December 2012
This an an update written two years after my original answer. The last two years much has changed in the way I try to design the systems I'm working on. Although it has suited me in the past, I don't like to use the factory approach anymore when dealing with the Unit of Work pattern. Instead I simply inject a Unit of Work instance into consumers directly. Whether this design is feasibly for you however, depends a lot on the way your system is designed. If you want to read more about this, please take a look at this newer Stackoverflow answer of mine: One DbContext per web request…why?
If you want to get it right, i'd advise on a couple of changes:
1 - Don't have private instances of the data context in the repository. If your working with multiple repositories then you'll end up with multiple contexts.
2 - To solve the above - wrap the context in a Unit of Work. Pass the unit of work to the Repositories via the ctor: public MyRepository(IUnitOfWork uow)
3 - Make the Unit of Work implement IDisposable. The Unit of Work should be "newed up" when a request begins, and therefore should be disposed when the request finishes. The Repository should not implement IDisposable, as it is not directly working with resources - it is simply mitigating them. The DataContext / Unit of Work should implement IDispoable.
4 - Assuming you are using a web application, you do not need to explicitly call dispose - i repeat, you do not need to explicitly call your dispose method. StructureMap has a method called HttpContextBuildPolicy.DisposeAndClearAll();. What this does is invoke the "Dispose" method on any HTTP-scoped objects that implement IDisposable. Stick this call in Application_EndRequest (Global.asax). Also - i believe there is an updated method, called ReleaseAllHttpScopedObjects or something - can't remember the name.
Instead of adding Dispose to IMyRepository, you could declare IMyRepository like this:
public interface IMyRepository: IDisposable
{
SomeClass GetById(int id);
}
This way, you ensure all repository will call Dispose sometimes, and you can use the C# "using" pattern on a Repository object:
using (IMyRepository rep = GetMyRepository(...))
{
... do some work with rep
}