Configure the EF Core Provider

Create a POCO

Create a Plain old CLR/Class object, or POCO, to use as a model for your entity. A POCO is a simple class object that doesn't inherit features from any framework-specific base classes or interfaces.

The following code example shows how to create a POCO that represents a customer:

public class Customer
{
    public ObjectId Id { get; set; }
    public string Name { get; set; } = null!;
    public string Order { get; set; } = null!;
}

Create a DB Context Class

To begin using Entity Framework Core, create a context class that derives from DBContext. The DbContext derived class instance represents a database session and is used to query and save instances of your entities.

The DBContext class exposes DBSet properties that specify the entities you can interact with while using that context.

The following example creates an instance of a DBContext derived class and specifies the Customer object as a DBSet property:

public class MyDbContext : DbContext
{
    public DbSet<Customer> Customers { get; init; } = null!;
    public MyDbContext(DbContextOptions options)
        : base(options)
    {
    }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<Customer>().ToCollection("customers");
    }
}

The previous code example overrides the OnModelCreating() method. Overriding the OnModelCreating() method allows you to specify configuration details for your model and its properties. This example uses the ToCollection() method to specify that the Customer entities in your application map to the customers collection in MongoDB.

Use MongoDB

Once you've created a DBContext class, construct a DbContextOptionsBuilder object and call its UseMongoDB() method. This method takes two parameters: a MongoClient instance and the name of the database that stores the collections you are working with.

The UseMongoDB() method returns a DbContextOptions object. Pass the Options property of this object to the constructor for your DBContext class.

The following example shows how to construct a DBContext object in this way:

var mongoClient = new MongoClient("<connection string>");
var dbContextOptions =
    new DbContextOptionsBuilder<MyDbContext>().UseMongoDB(mongoClient, "<database name>");
var db = new MyDbContext(dbContextOptions.Options);

MongoClient and DbContext Lifetimes

The lifetime and configuration of your MongoClient and DbContext objects directly affect memory usage and connection pool efficiency.

Register MongoClient as a singleton and share a single instance across all DbContext registrations. Because each MongoClient object manages its own internal connection pool, creating a separate instance for each DbContext scope wastes connections and increases latency. To learn more, see Manage MongoClient Disposables in the .NET/C# Driver documentation.

Register DbContext as a scoped service so that each request uses a new change tracker. A singleton DbContext accumulates tracked entity state across all requests, which causes stale data, memory growth, and increasingly slow change-detection as the tracker grows larger. To learn more, see DbContext in Dependency Injection for ASP.NET Core in the Microsoft Entity Framework Core documentation.

Example

The following code example shows how to register services by using dependency injection, configure the EF Core Provider, and insert a document into the database:

var serviceCollection = new ServiceCollection();
serviceCollection.AddSingleton<IMongoClient>(
    new MongoClient("<connection string>"));
serviceCollection.AddDbContext<MyDbContext>((serviceProvider, options) =>
{
    var mongoClient = serviceProvider.GetRequiredService<IMongoClient>();
    options.UseMongoDB(mongoClient, "<database name>");
});
var app = serviceCollection.BuildServiceProvider();
using (var scope = app.CreateScope())
{
    var db = scope.ServiceProvider.GetRequiredService<MyDbContext>();
    // Add a new customer and save it to the database
    db.Customers.Add(new Customer() { Name = "John Doe", Order = "1 Green Tea" });
    db.SaveChanges();
}