Monthly Archives: October 2016

EF Core Lets Us Finally Define NoTracking DbContexts

Data Access, , , ,

Way back in 2012, I added a feature request to EF6 to allow us to define a context that will never track entities that it retrieves from the database.

(Support Read-Only Context or DbSet)

This is instead of having to add AsNoTracking to all of your queries if you have a DbContext you are using for read-only data. Or more importantly, if your DbContext is being used for data that’s going to be disconnected and therefore never tracked post-query. That means a Web API or service or a controller. Tracking can be expensive if you are retrieving a lot of data and have no plans to update it. And having to remember to add AsNoTracking to every query is a PIA.

I just discovered that this is possible with EF Core and I think it was even in the EF Core 1.0 release!

There is a ChangeTracker property called QueryTrackingBehavior that takes a QueryTrackingBehavior enum whose options are NoTracking and TrackAll.

There are plenty of places to use it, but the one I’m excited about is to place it directly in the constructor of a DbContext to make that context default to never track any entities.

public class BookContext : DbContext
{
  public BooksReadOnlyContext() { 
    ChangeTracker.QueryTrackingBehavior = 
       QueryTrackingBehavior.NoTracking;
  }
 public DbSet<Book> Books {get;set;}
 etc ...

A quick test where I retrieved some books and the inspected the ChangeTracker.Entries returned 0, to show that this was doing what I’ve been dreaming of for over 5 years! Thanks EF team!

 Console.WriteLine(
   $"Tracked Entities: {context.ChangeTracker.Entries().Count()}");

Another point to be aware of is that just as you have always been able to use the DbSet’s AsNoTracking method to turn off tracking for a particular query, you can now use AsTracking to turn on tracking for a particular query.

Visual Studio Code Snippets to Make Coding EF Core a Little Simpler

Tools, ,

I’ve been using the user snippet feature of Visual Studio Code to make it easier to get some of the code I commonly use for EF Core into my files. For example I have C# snippets for DbContext to create a constructor overload that takes in a DbContextOptions parameter, OnConfiguring or OnModeling . I have json snippets to add in the EFCore Commands dependency and the Tools section with EF Core tools.

github.com/julielerman/EFCoreSnippetsForVSCode

I finally created a github repository to share them. Since you’ll need to add the csharp snippets into your existing csharp snippets and the same with the json, i have put them into separate csharp.json and json.json files from which you can copy and past my snippets into your own.

Although the instructions are on the user defined snippets page I just linked to, the TL;DR is:

From menu, choose Code, Preferences then User Snippets

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That will open a list of snippet files. Choose C# for the C# snippets and Json for the Json snippets. Paste in my snippets!

2016-10-30_11-57-25

Completely New EF in the Enterprise Course on Pluralsight

Data Access, DDD, , ,

My baby is here! A brand new Entity Framework in the Enterprise.

[See also:  New EF Core Course on Pluralsight!]

In 2012, I published a course on Pluralsight called Entity Framework in the Enterprise. Since then I have learned so much, most importantly, I’ve become very active with Domain-Driven Design, even publishing the DDD Fundamentals course that I co-created with Steve Smith. This has had a big impact on how I think about designing and architecting software and in turn,how I approach incorporating EF in to large, complex applications.

I’ve been wanting to re-do that old course to share my new views. I finally began in January of this year, but had a 3 month conference travel hiatus. So while it feels like a baby that I spent 9 months on, it was really only 6 months. Still quite a long time!

The course is now live! Entity Framework in the Enterprise

In the course, I use VS2015 and EF6. Why EF6? Because EF Core is too new. Most of the patterns I discuss and demonstrate are totally applicable to EF Core. There is one thing that is not yet in EF Core: Value Objects, but that is coming. Also the module on testing focuses on mocking and does not take EF Core’s new In Memory provider into account. Other than that, you can use what you learn here with EF Core as well.

I put a lot of thought into this course and I think this comment on the discussion forum for the course expresses it so well:

I just watched Julie Lerman’s prior Entity Framework in the Enterprise three weeks ago, before this new course was released, and boy am I glad she’s updated the course. I had thought the previous version was a bit dated (2016 vs 2012 & EF6 vs EF4) and a bit basic with what Julie refers to as Demo Ware. This updated course goes into more details about architecting projects, improved Moq testing with EF6, and a better explanation of DDD with Bounded Contexts using Schema to segregate areas. I already had a good understanding of EF, DDD, Repositories, UoW, and CQRS before watching and while I wouldn’t set up things 100% this way in my own applications they did jump start some refactorings and rethinking on how I maintain my solution, which is the purpose of these courses, to give fresh ideas as technology evolves, just as Entity Framework has. Thanks for updating the course and for those who have watched the previous version, definitely give this new one a watch.

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New EF Core Course on Pluralsight

Data Access

Pluralsight has recently published a Play by Play that I did with Geoffrey Grosenbach called EF Core 1.0 First Look.

[See also Completely New EF in the Enterprise Course!! Published Sept 23 2016]

This is a video of me showing EF Core to Geoffrey on my Mac. I spent 1.5 hours talking to him about EF Core, how it aligns with .NET Core’s which is cross platform, EF teams goals and some of the fun new things.

There are no slides. The video is 100% screen capture of my laptop while I’m creating a new ASP.NET Core Web API and adding EF Core into the APIs, connecting to a new PostgreSQL database, seeding the database, interacting with the data, testing with the new InMemory provider and even deploying to Docker.

The goal of this video is to get you, as it’s titled, a first look at EF Core. It also allowed me to get EF Core in front of you quickly while I now work on a “normal” course which is Getting Started with EF Core. This course will mostly be on Windows and Visual Studio but I will also flip over to Mac for a few demos at the end. The Getting Started course I’m working on will be a real step by step walkthrough, introductory course.

So in the meantime, take a look at this new Play by Play!

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