ASP.NET MVC - DbContext good practices

Question

I'm starting a new .NET MVC project with Entity Framework and I am struggling with some problems.

1. In my model I have about 150 entities (generated from the database). Is it a good idea to have only one DbContext? If not, how should I divide my entities?

2. If I have one DbContext and I create a class variable that instantiates a database context object (in Controller), what happens then with this DbContext? Does it create in memory separate space for each of my entities? In my case, when I have 150 entities it would not be very effective. Am I wrong?

3. I will be using my DbContext in many Controllers. Is it a good idea to create a MainController (where I create new DbContext), which will be inherited by the rest of the Controllers? Because this allows others to have access to the same Context.

4. What is the best practise for disposing my DbContext? I've read that it is good practice to use dependency injection. But in this way I will have to inject context to every of my controllers. Which dependency injection way is the most popular and used now?

Really need your advice. It will give me more insight to this piece of development.

Answer 1

1. It is fine to have one DbContext. If you have many you just need to ensure all the entities you need exist in the that context. For example, if you retrieve a Person from the database and their related Address, then both the Person and Address have to exist in the same DbContext.

   I've not tried using multiple DbContext instances, but one thing to look out for is if you include the same table in multiple contexts you could end up with classes with similar names or maybe conflicts. For example, if you include Person in two contexts, then each context will attempt to create a class named Person.

2. When you create a DbContext it will only create objects for the data you retrieve from the database. So if you request one row from a Person table, then only one Person object will be created. If you request 100 rows, then 100 instances will be created.

3. There are really two options. One, create a new instance in each action, do your work, then save it. Or, create a DbContext in your constructor and reuse that throughout the class.

4. This depends one what you choose in point #3. If you pass it into the constructor, then implement IDisposable and release it in there. If you create a new one in each action, then ensure it gets disposed using the using statement.

For dependency injection there are a number of options, tutorials, etc, on how to do this in ASP.NET MVC. I personally use Autofac, and related MVC extensions, and pass a new instance of the DbContext into each controller.

Answer 2

150 Entities is not a huge DbContext, but it is above the size where EF starts to exhibit performance issues in the initialization of the first DbContext. If you can logically separate your entities into areas of responsibility (called a bounded context) then you might consider using more than one DbContext. Also, does your app need to use all those entities? If not, you may be able to simplify things. Also note, you need at least EF6 to make this work effectively, previous versions of Entity Framework had issues with multiple contexts.

You also have to be careful when using multiple contexts. Many people get into trouble because they get an entity from one context, but then call save changes on a different one, and then don't understand why their changes are not saved. Or, they try to add an entity retrieved from one to another, which you can't do. Multiple contexts make things more complicated, so make sure you want to take on that complexity before you split it up.

Don't worry about the amount of memory your DbContext uses, so long as you are properly disposing of it. The amount of memory will be minimal unless you actually load objects from all of those tables.

I consider a common base controller to be a code smell. It's usually completely unnecessary, and it usually ends up becoming a dumping ground for every piece of code you think you want to share, which violates the Single Responsibility Principal. On top of that, you shouldn't be doing data access in your controllers anyways. You should have a service layer of some sort or business layer that call into a data access layer. Properly segregating your concerns is a key part of designing a good MVC application.

Yes, Dependency Injection is a good practice. I'm not sure what you mean by "have to inject into all my controllers". The whole point of dependency injection is to inject your dependencies, so the concept of "having to" makes it seem like you're trying to avoid the very thing you're trying to do.

Dependency Injection is a principle. There are many ways to achieve this principle, and which way you use depends entirely on your own preferences and requirements. We can't tell you what's "best" other than to make sure you're following the principle, and not a specific technology.