When was lifetime created

Using a singleton, I can easily manage this because every request is using the same instance. Consider the following two classes. If we ran this, what could we expect? It actually blows up on the second Assert.

But why? What gives?! The reason lies in the wording of how DI works. Transient creates a new instance of the service each time the service is requested. This is also true of other types of lifetimes like scoped inside singletons. Where does this really bite you? In my worst experience with Singletons, someone had decided the smart thing to do in their application was make the entire service layer singletons.

But what that meant was that all the database repository code, entity framework contexts, and many other classes that should really be transient in nature then became a single instance being passed around between requests.

Again, use Singleton if you have a real use for it. Admittedly in most cases, you can think of scoped objects being per web request. So common things you might see is a DBContext being created once per web request, or NHibernate contexts being created once so that you can have the entire request wrapped in a transaction.

Another extremely common use for scoped lifetime objects is when you want to create a per request cache. It just so happens that within. For example :. Typically in a simple. In early versions of. However, if the DbContext subtype is itself intended to be inherited from, then it should expose a protected constructor taking a non-generic DbContextOptions. Notice that this is exactly the same pattern as when inheriting from DbContext directly.

A DbContext subclass intended to be both instantiated and inherited from should expose both forms of constructor. EF Core design-time tools such as those for EF Core migrations need to be able to discover and create a working instance of a DbContext type in order to gather details about the application's entity types and how they map to a database schema.

This process can be automatic as long as the tool can easily create the DbContext in such a way that it will be configured similarly to how it would be configured at run-time. While any pattern that provides the necessary configuration information to the DbContext can work at run-time, tools that require using a DbContext at design-time can only work with a limited number of patterns. These are covered in more detail in Design-Time Context Creation. Entity Framework Core does not support multiple parallel operations being run on the same DbContext instance.

This includes both parallel execution of async queries and any explicit concurrent use from multiple threads. Therefore, always await async calls immediately, or use separate DbContext instances for operations that execute in parallel. A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of DbContext, however instance members are not guaranteed to be thread safe.

When concurrent access goes undetected, it can result in undefined behavior, application crashes and data corruption. There are common mistakes that can inadvertently cause concurrent access on the same DbContext instance:. Asynchronous methods enable EF Core to initiate operations that access the database in a non-blocking way. But if a caller does not await the completion of one of these methods, and proceeds to perform other operations on the DbContext , the state of the DbContext can be, and very likely will be corrupted.

This is safe from concurrent access issues in most ASP. NET Core applications because there is only one thread executing each client request at a given time, and because each request gets a separate dependency injection scope and therefore a separate DbContext instance. For Blazor Server hosting model, one logical request is used for maintaining the Blazor user circuit, and thus only one scoped DbContext instance is available per user circuit if the default injection scope is used.

Any code that explicitly executes multiple threads in parallel should ensure that DbContext instances aren't ever accessed concurrently. Using dependency injection, this can be achieved by either registering the context as scoped, and creating scopes using IServiceScopeFactory for each thread, or by registering the DbContext as transient using the overload of AddDbContext which takes a ServiceLifetime parameter.

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Contents Exit focus mode. Tip To quote Martin Fowler from the link above, "A Unit of Work keeps track of everything you do during a business transaction that can affect the database.

Important It is very important to dispose the DbContext after use. This ensures both that any unmanaged resources are freed, and that any events or other hooks are unregistered so as to prevent memory leaks in case the instance remains referenced. DbContext is not thread-safe. Do not share contexts between threads. Make sure to await all async calls before continuing to use the context instance. Such exceptions indicate a program error and are not designed to be recovered from. Until the resolution of RU , a non-static member of a const-qualified type or a reference type prevents its containing object from being transparently replaceable, which makes std::vector and std::deque hard to implement:.

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