As per Microsoft “A DbContext instance represents a session with the database and can be used to query and save instances of your entities. DbContext is a combination of the Unit Of Work and Repository patterns.” In simplified way we can say that DbContext is the bridge between Entity Framework and Database. Whatever we are doing in Entity Framework (get data, save data, fetch data or any other opration) is done via DbContext. There are some applications where this type of architecture does make sense. If you’re working on such an application, you should however ask yourself why you’re using Entity Framework in the first place.
Needless to say that whatever system you use to manage your DbContext instance must play well with Entity Framework’s async features. For those coming from an NHibernate background, this is the equivalent of having to manage multiple SessionFactory instances. The architecture of a software system and the design patterns it relies on always evolve over time to adapt to new constraints, business requirements and increasing load. When coming up with or evaluating a DbContext lifetime management strategy, it’s important to keep in mind the key scenarios and functionalities that it must support.
Defining a DbContext Derived Class
If you don’t already have a copy, you can download Visual Studio 2022 here. In this article we’ll dive into DbContext in a little more detail, discuss the DbContext lifetime, and offer some best practices for using DbContext in Entity Framework Core. We can track changes when we use for what is entity framework all type of operations or execution. To use DbContext in our application, we need to create a class that derives from DbContext. The first version of the DbContextScope class I wrote was actually called UnitOfWork. This is arguably the most commonly used name for this type of component.
If an error occurs when the changes are applied to the database, they are rolled back and the database is left in an unmodified condition. So, in the next article, I will discuss where to define the Connection String in Entity Framework Core and how to use it to interact with the SQL Server Database. In this article, I explain the need and use of the DbContext Class in Entity Framework Core. To delete an entity using Entity Framework, you use the Remove method on DbSet. Calling Remove on an entity that has been added but not yet saved to the database will cancel the addition of the entity. The entity is removed from the change tracker and is no longer tracked by the DbContext.
Entity Framework Core DbContext class
If you’re a back-end developer working on a EF-based project, you must know the answers to these questions if you want to be able to write correct code. Jon Skeet wrote an interesting article on the topic of explicitness vs ambient but couldn’t come up with a good solution either. It results in code that’s very easy to understand and maintain, even by developers new to the code base. There are several key behaviours of Entity Framework you should always keep in mind however.
More generally, your service layer (if you have one) should be independent of the type of application it’s used from. It will therefore expect any persistent entity returned by your service method to be attached to the ambient DbContext. While it can be fine to re-use a DbContext across multiple business transactions, its lifetime should still be kept short. Its first-level cache will become eventually become stale, which will lead to concurrency issues. If your application uses optimistic concurrency this will result in business transactions failing with a DbUpdateConcurrencyException. Using an instance-per-web-request lifetime for your DbContext in web apps will usually be fine as a web request is short-lived by nature.
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There is no ambiguity at to what a unit of work means at the database level. The answers here aren’t obvious and will require you to pour through your DI container configuration code to find out. And as we’ve seen earlier, getting this configuration right isn’t as trivial as it may seem at first sight and may end up being fairly complex and / or subtle. And when it comes to managing the correctness and consistency of your data – your most precious asset – magic isn’t a word you want to hear too often.
You can then take advantage of constructor injection in your controller to retrieve an instance of DbContext as shown below. You can extend the DbContext class in EF Core to create your own DbContext class as shown below. To create an ASP.NET Core 8 Web API project in Visual Studio 2022, follow the steps outlined below.
Your DbContext management strategy should support multiple DbContext-derived types
LINQ queries against a DbSet will be translated into queries against the database. EF Core API will create the Student and Grade table in the underlying SQL Server database where each property of these classes will be a column in the corresponding table. This would be completely unexpected and will lead to humongous complexity. A DI container like StructureMap for example doesn’t support decommissioning the components it created. As a result, if you rely on StructureMap to create your DbContext instances, they will never be disposed of, regardless of what lifecycle you choose for them.
- We’ll use a PostgreSQL database using Devart for PostgreSQL to store and retrieve data.
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- Your domain model objects should not be aware of the persistence mechanism, i.e., how the data is persisted in the underlying data store.
- LINQ queries against a DbSet will be translated into queries against the database.
- The main class that coordinates Entity Framework Core functionality for a given data model is the database context class, which allows to query and save data.
You can take advantage of the DbContext to query data in your entities or save your entities to the underlying database. Basically Model is a class that represent database table, stored procedure, function and so on. We can create manually this class and configure it in DbContext like below or we can create all models of all or specific objects from Database.
Founded in 1997, Devart is currently one of the leading developers of database management software, ALM solutions and data providers for most popular database servers. Transient `DbContext` instances cater well to short-lived operations, ensuring a fresh context for each operation. This setup suits tasks needing isolated contexts without dependencies on prior states. However, remember to dispose of these instances properly to prevent memory leaks. The DbContext provides methods for performing the following data operations directly. Now, we are done with the initial domain classes for our application.
You can then use constructor injection in your controller to construct DbContext instances as shown below. There are many articles on Entity Framework and very small information on DbContext in a single place. In this article, I am trying to explain all aspects of DbContext and why it is the most important class in Entity Framework. There are many articles on Entity Framework and very small information on DbContext at a single place.
Ambient DbContext
Which is perfectly fine for many applications but it will become a major limitation in certain cases. As with the explicit approach, the creation and disposal of the DbContext instance is in a clear, well-defined and logical place. In .NET 4.5, ADO.NET introduced (at very long last) support for async database queries.
