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There are 2 ways of writing OWIN middleware in ASP.NET Core.

• Pure OWIN - usefull if you want to integrate with OWIN compatible module but not written in C#
• ASP.NET Core OWIN middleware

ASP.NET Core Middleware:

This type of middleware can be:

• delegate of Func<HttpContext, Func<Task>, Task>
• class with IMiddleware imlementation

app.Use(async (context, next) =>
{
    // Do work that can write to the Response.
    await next.Invoke();
    // Do logging or other work that doesn't write to the Response.
});

Pure OWIN Middleware:

This rather would be used to integrate with OWIN middlewares written in different language, so that ASP.NET Core implementation directly is not possible.

• OWIN - Open Web Interface for .NET
• allows web apps to be decoupled from web servers
• defines standard way for middleware to be used in a pipeline to handle requests and provide responses
• ASP.NET Core applications can interoperate with OWIN-based applications, servers and middleware

Microsoft.AspNetCore.Owin package provides two adapter implementations:

• ASP.NET Core to OWIN
• OWIN to ASP.NET Core

This allows ASP.NET Core to be hosted on top of an OWIN compatible server/host or for other OWIN compatible components to be run on top of ASP.NET Core.

• ’tree like’ data structure
• each node is expression (method call, equality comparison, binary operation etc.) representing a piece of code
• you can compile expression tree and run code it represent
• enables dynamic code generation at runtime
• LINQ queries on DBs are implemented with Expression Trees
• used in the dynamic language runtime (DLR)
• anonymous lambda expression can be converted to ExpressionTree via compiler (i.e. x => x*2 can be represented as tree instead of delegate or anonymous lambda function)

Further read:

• lazy loading:

  • delaying load of data until we specifically request for it
  • i.e. accessing customer.Address loads Address of a customer in the background via separate SQL query
  • property needs to be public, virtual
  • context.Configuration.ProxyCreationEnabled should be true
  • context.Configuration.LazyLoadingEnabled should be true
  • to disable lazy loading completely Context.Configuration.LazyLoadingEnabled = false;

• eager loading

  • opposite of lazy loading
  • loads related entities as part of the query
  • done via .Include() query

Further read: