Dynamic Proxy Entities (POCO Proxy)
Tags: webdev, programming, productivity, opensource
Published: 2023-05-31 09:19:50

Dynamic Proxy Entities, also known as POCO Proxies (Plain Old CLR Objects), are a concept used in the .NET framework to provide transparent lazy loading and change tracking capabilities to entity objects.

When working with an Object-Relational Mapping (ORM) framework like Entity Framework, POCO entities represent the objects that are mapped to database tables. Dynamic Proxy Entities are a specific type of POCO entity that is dynamically generated at runtime to enable additional features like lazy loading and change tracking.

Lazy loading is a technique where related data is loaded from the database only when it is accessed for the first time. This helps to improve performance by reducing the amount of data retrieved from the database upfront. With dynamic proxy entities, the ORM framework can intercept property access and load the related data on demand.

Change tracking allows the ORM framework to keep track of changes made to the entity objects. When you modify a property of a dynamic proxy entity, the framework detects the change and marks the entity as "dirty." This information is then used to generate appropriate SQL statements when saving changes back to the database.

Dynamic proxy entities are created by the ORM framework by subclassing the original POCO entity class. The proxy class overrides the properties of the original class to provide the additional functionality. The proxy class is generated at runtime using reflection or by using libraries like Castle DynamicProxy or LinFu.

To work with dynamic proxy entities, you typically interact with them as if they were regular POCO objects, without being aware of the transparent lazy loading and change tracking happening behind the scenes. However, it's important to be aware that using dynamic proxies can introduce some considerations and limitations, such as potential performance overhead, serialization challenges, and compatibility with certain code patterns or frameworks.

Dynamic proxy entities offer a convenient way to enhance POCO entities with additional features like lazy loading and change tracking in the context of an ORM framework like Entity Framework.

Sure! Here's a simple example to illustrate the concept of dynamic proxy entities using Entity Framework.

Let's say we have two entities, `Customer` and `Order`, with a one-to-many relationship (one customer can have multiple orders). We'll focus on the `Customer` entity for this example.

```csharp
public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Order> Orders { get; set; }
}
```

In Entity Framework, you would typically use this POCO entity class to map to a database table. However, if you want to enable lazy loading and change tracking, you can use dynamic proxy entities.

To enable dynamic proxy entities, you'll need to make a few modifications. First, you need to mark the `virtual` keyword on the navigation property `Orders`. This tells Entity Framework to create a proxy for the `Customer` class.

```csharp
public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Order> Orders { get; set; }
}
```

Next, when you configure your Entity Framework context, you need to enable proxy creation. This is typically done in the constructor of your context class.

```csharp
public class MyDbContext : DbContext
{
    public MyDbContext() : base("YourConnectionString")
    {
        this.Configuration.ProxyCreationEnabled = true;
    }

    public DbSet<Customer> Customers { get; set; }
    public DbSet<Order> Orders { get; set; }
}
```

With these modifications, Entity Framework will create dynamic proxy entities for the `Customer` class. When you fetch a customer from the database, you'll receive an instance of the proxy class.

```csharp
using (var context = new MyDbContext())
{
    var customer = context.Customers.Find(1);
    
    // The 'customer' object is a dynamic proxy entity
    // You can access its properties as usual
    Console.WriteLine(customer.Name);
    
    // Accessing the 'Orders' property will trigger lazy loading
    // The related orders will be fetched from the database on-demand
    foreach (var order in customer.Orders)
    {
        Console.WriteLine(order.OrderNumber);
    }
}
```

In this example, when you access the `Orders` property of the `customer` object, Entity Framework will load the related orders from the database if they haven't been loaded already. This lazy loading is transparent to you as a developer.

Additionally, if you make changes to the `customer` object, Entity Framework will track those changes and generate appropriate SQL statements when you save the changes back to the database.

Note that the specific implementation of dynamic proxies may vary depending on the version of Entity Framework or the underlying library used for proxy generation. The example provided here is based on the general principles and practices associated with dynamic proxy entities in Entity Framework.