How to inject EF Core DbContext in an Azure Function

Time needed: 10 minutes

How to configure injecting a DbContext in an Azure Function?

1. Add a Startup class (WebJobsStartUp -attribute) to your Azure Function

   The steps to achieve this are described in this earlier blog post, so I’m not repeating them here:
   
   How to configure Azure Function’s startup?

2. In the Startup, configure your DbContext like this:

   
   builder.Services.AddDbContext(options1 =>
{
options1.UseLazyLoadingProxies(false);
options1.UseSqlServer(
config["ConnectionStrings:DefaultConnection"],
builder =>
{
builder.EnableRetryOnFailure(5, TimeSpan.FromSeconds(10), null);
builder.CommandTimeout(10);
}
);
});
   
   The configuration options are only shown as an example – not required.

3. Configure the database context to support being instantiated with options

   Now, you need to add a constructor to your database context class, like below:
   public ApplicationDbContext(DbContextOptions options) : base(options) { }
   Don’t worry about it being empty. EF Core figures out all the details, it just needs a method to work with :)
   
   If you skip this step, you might run into an error like the below:
   
   Microsoft.EntityFrameworkCore: AddDbContext was called with configuration, but the context type ‘ApplicationDbContext’ only declares a parameterless constructor. This means that the configuration passed to AddDbContext will never be used.
   
   If the configuration is passed to AddDbContext, then ‘ApplicationDbContext’ should declare a constructor that accepts a DbContextOptions and must pass it to the base constructor for DbContext.
   
   Value cannot be null. (Parameter ‘provider’)

4. Configure the DbContext to be injected into your Azure Functions

   This is pretty nifty – since the database context is injected in your app as a service, you can just configure it to be injected at class initialization, directly in the constructor:
   
   private readonly ApplicationDbContext _applicationDbContext;

public Function1 (ApplicationDbContext applicationDbContext) {
_applicationDbContext = applicationDbContext;
}
   
   You’ll need using -statements somewhat like these:
   
   (“DataLayer” in the example above is the namespace my database context is in!)
5. Use the database context in your function!

   Now it’s safe to use your database context in your code. No need to dispose of it – it’s tied to your Azure Function App’s lifecycle:
   
   if (!string.IsNullOrEmpty(name))
{
_applicationDbContext.Entities.Add(
new DataLayer.Entities.Entity()
{
Name = name,
Description = "Created in the Azure Function"
}
);
}
_applicationDbContext.SaveChanges();