Entity Framework Core: Getting Started on Pluralsight

I’m happy to share a new course on Pluralsight with you – Entity Framework Core: Getting Started.

Here’s how I described it in the trailer:

Most software – whether for business or entertainment – is driven by data that users need to interact with. In Entity Framework Core: Getting Started, you will learn how to use Microsoft’s modern data access platform, Entity Framework Core. You will learn how to build data models, use EF Core to bridge your software with  your data store and how to incorporate all of this into desktop, mobile and web applications. When you’re finished with this course, you will have a foundational knowledge of Entity Framework Core that will help you as you move forward to build software in .NET, whether you are targeting Windows, OS X or Linux. Software required: Visual Studio 2015 or Visual Studio 2017.

pluralsight course

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Here is the list of modules in the course. You can see the titles of various clips in each module on Pluralsight.

To see the full list of my courses on Pluralsight, go to pluralsight.com/authors/julie-lerman

EF Core CLI Commands with VS2017 RC3

Visual Studio 2017 RC3 was released yesterday but unfortunately an install issue has take it back off the shelf for a brief period. Watch this space for the return of RC3!

But I did manage to get it installed and wanted to show you that the EF Core CLI commands are now working. If you’ve been playing with VS2017 RC and EF Core you may have run into the problem that the EF Core tooling package was not in sync yet with the MSBuild tooling for .NET Core. That’s fixed now and not only does it work but there’s a change that I’m really happy to see.

As always, I have my dbcontext in its own project. Here are the csproj contents for that project:

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Notice that the DotNetCliToolReference is pointing to Microsoft.EntityFrameworkCore.Tools.DotNet . The dotnet and PowerShell commands are exposed in separate packages. With “.DotNet” is the package that has the CLI commands. Without “.DotNet” is the package that contains the PowerShell commands.

More importantly, the package version went from “1.1.0-preview4” to “1.0.0-msbuild3-final”. I can’t explain why we went from 1.1.0 down to 1.0.0 but this is the newer and correct package.

With that in place,  I then open up a command prompt. I can use a regular one but I’m using a PowerShell command for a single benefit…that I can shorten the prompt. Here’s the command I did to trim most but not all of the path:

Quora: How do I get just the current folder name in my Windows Powershell prompt function?

Remember that I’m pointed to the path of a class library. DotNet EF requires you to point to a path containing an executable in order to run the commands. However with the latest bits, you can get HELP without having to point to the executable. Thank you Brice Lambson. It was a little meta to have to figure that out because rather than just getting help from the command, you had to googlebing for help on how to get help. So here are a simple dotnet ef command to get top level dotnet ef help, followed by dotnet ef dbcontext to get help on the dbcontext sub-commands.

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To run commands that depend on the APIs, you still have to point to a startup-project if you are running the commands from a class library. Here I’ve run the command to list the migrations in my project. I’ve only got one, sqlite-init.

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Some Insights into Features (Besides EDMX) Being Dropped in the Move From EF6 to EF Core

I had written these details for my Pluralsight EF Core course (hopefully published at end of Jan 2017) but decided not to spend the time on this explanation in the course. Instead, I’ll put it here and the course will have a link to this blog post! Clever, huh?

You’ve probably heard a lot about EF Core not bringing forward  the designer based EDMX from EF Core. This is a feature cut that I’ve heard the most feedback about. But there are other EF features that are also getting cut. These are not as worrisome to developers — based on my own experience and paying attention to response in social media — but it’s important to be aware of the biggest of these cut features.

ObjectContext API

The first is the ObjectContext API. This was the original mechanism for EF’s change tracking and database interaction. Since EF4.1 was released with the DbContext in early 2011, Microsoft has recommended that all new projects use DbContext. The DbContext sits on top of the ObjectContext and does the more cumbersome work of interacting with the ObjectContext on your behalf. But the ObjectContext has remained a public API for backwards compatibility with EF4 and EF3.5 projects. Also, we could access the ObjectContext to do low level tasks as needed.

There will not be an ObjectContext API in EF Core. Rather than relying on the ObjectContext for metadata work, change tracking and database interaction, this low-level activity is being  restructured and we’ll get at it directly from the DbContext. If you have old software that is still using the ObjectContext and you haven’t updated it by now, hopefully, you won’t want to update it to EFCore anyway. I wrote a 2 part article for MSDN magazine in 2014 that included guidance for moving ObjectContext code to DbContext if you think you may want to explore that.

Data Points : Tips for Updating and Refactoring Your Entity Framework Code Part 1

Data Points : Tips for Updating and Refactoring Your Entity Framework Code Part 2

Entity SQL

Entity SQL was the original string-based querying SQL like language written for EF. By the time EF was first released, it had already embraced the also-new LINQ. ESQL is only usable with the ObjectContext API. I think I  used to be one of the few people in the world who really knew how to use ESQL because I wrote about it extensively in my first EF book, giving it equal visibility as LINQ to Entities. In the 2nd edition, I had split the ESQL details out into their own chapter because by then it was clear that it was barely being used. I haven’t had any reason to use ESQL in many years. I’ve not heard of anyone using it either. So it is going to fade away along with the ObjectContext API and won’t be part of EFCore.

Edge-Case Mappings & the Original Metadata APIs

Entity Framework has allowed a lot of variations on mappings between your classes/properties and your database tables/fields. It has even let you combine many of these crazy mappings in one model. The EF team blog post highlights and example: “an inheritance hierarchy that combined TPH, TPT, and TPC mappings as well as Entity Splitting all in the same hierarchy.” This was possible because of the Metadata Workspace API. But building in this flexibility also meant that using that API was very complex. Internal query compilation was difficult to design. And for developers, discovering information about a model’s metadata has been very cumbersome.

So, EFCore has a simpler metadata model which means some of the truly edge case mappings won’t be achievable. This doesn’t mean things like inheritance will go away (although currently, EF Core only supports TPH), just the funky, rare mapping combinations.

MEST (Multiple Entities for a Single Type)

One single mapping technique that will go away is MEST. In all of my years of working with EF, I’ve never come across anyone who was taking advantage of it. It was only supported with EDMX and ObjectContext and the team decided not to bring it forward to the code-based model and DbContext for EFCore.

Automatic Migrations

Migrations are a critical technique for evolving a database schema from a code-based model. We’ve had two ways to use EF migrations – the default way which is to explicitly add migrations through the package manager console and then to apply those migrations using a variety of techniques. Another option has been to use automatic migrations that are worked out and executed on the fly at run time. Supporting automatic migrations caused a number of major headaches for migrations support overall. It forced migrations to store model snapshots directly in the database. This caused problems for developers using regular migrations – especially with source control. I’ve been in loops where I can’t add a migration because it thinks I need to execute one, but when I try to execute a migration it tells me I have to add one. I’m  not the only one who has gotten all tangled up in some circular problems when trying to manage migrations. These problems will go away because EFCore will not attempt to automate migrations at all. You can read more about this in Brice Lambson’s blog post about EFCore Migrations at design time. Brice is an engineer on the EF team and has a lot of other interesting blog posts worth checking out.

These are the most notable EF features that the team is not planning to implement at all in EFCore. Personally, I have not been using any of them ever or in a long time and I have guided my clients away from them as well. So if you are on that same path, you are well-positioned to use EF Core without having to worry about them.

EF Core, Postgres and the Camel-Cased Identity Tables

PostgreSQL doesn’t really like camel-case too much. I’m no expert but I know that at least.

I was doing yet another exploration of  EF Core in Visual Studio Code on my MacBook. Usually I use JetBrain’s DataGrip (database IDE) to check out the actual data. But this time I wanted to play with  the Visual Studio Code extension called “vscode-database” which lets you interact with MySQL and PostgreSQL right in the IDE.

There are a bunch of database extensions in fact:

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I’ve already been using the mssql extension to muck about with SQL Server data inside of VS Code:

As I was using a default web app from the template, ASP.NET Identity was involved and the context to manage identity inherits from Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityDbContext

And IdentityDbContext has fluent API code to explicitly map table names which are not the same as the entity’s they are mapping. And it makes those names all camel-cased.

DataGrip did not mind the camel cased identity table names but vscode-database didn’t comprehend the table names when it was reading the database to build Intellisense for the tooling. It’s anticipating lowercase and throwing exceptions when it hits the camelcased names. Shay Rojansky, who maintains the npgsql PostgreSQL providers for EF & EF Core, explained to me that if the tool simply placed quotes around the names, it would be okay.

Update: The vscode-database maintainers have fixed the problem and you can now easily use the identity tables …just remember to put quotes around the camel-cased database objects when typing SQL. Although right now the installer hasn’t been updated with the new bits yet. I just fixed up the extension files manually for the time being.

If you prefer not to have to do that and do want the identity tables etc to be all lower case, then you may still find my hack to be useful.

For a temporary workaround,  I wanted to just change them to lower case so I could reap the benefits of vscode-database extension.

Since the IdentityDbContext class creates the table names in its OnModelCreating override, I needed to change those names to lower case after the fact.

It’s easy enough to do if you know the right path through the APIs.

Here’s my DbContext class that handles Identity in my ASP.NET Core app. I’ve added the foreach clause to lower case the name after the base class (IdentityDbContext) has already changed the names.

I’m grabbing the ToTable name that was specified by ApplicationDbContext and then re-applying the name as lower case.

using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore;
using WebApplication.Models;

namespace WebApplication.Data {

  public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
  {
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options) {
    }

    protected override void OnModelCreating(ModelBuilder builder) {
      base.OnModelCreating(builder);
      // Customize the ASP.NET Identity model and override the defaults if needed.
      // For example, you can rename the ASP.NET Identity table names and more.
      // Add your customizations after calling base.OnModelCreating(builder);
      //quick and dirty takes care of my entities not all scenarios
      foreach (var entity in builder.Model.GetEntityTypes()) {
        var currentTableName = builder.Entity(entity.Name).Metadata.Relational().TableName;
        builder.Entity(entity.Name).ToTable(currentTableName.ToLower());
      }
    }
  }
}

vscode-database has some cool features with Intellisense. It has some UX issues to work on (or maybe I need some training and I’ll raise an issue just in case) but it’s free and let’s you execute queries and commands on the database for those times you don’t need the bells and whistles of a full IDE .

Updated My EFCore / WebAPI / PostreSQL / XUnit Repo to 1.1

Today was dedicated to updating my long running repository sample that I started when EF Core was EF 7  to the newest version of EF Core: 1.1. Here is the updated repo: https://github.com/julielerman/EFCore-ASPNetCore-WebAPI-RTM.

Phase one of this update continues to use project.json.

In addition to updating the version #s of  the Nuget package references, I also made some changes to the code to reflect a few new features.

Pay attention to the tooling packages. In the tools section, the package name has changed – note DotNet at the end –  and the version is currently 1.0.0-preview3 even though IIS version is preview2.

 "tools": {
   "Microsoft.AspNetCore.Server.IISIntegration.Tools": 
       "1.0.0-preview2-final",
   "Microsoft.EntityFrameworkCore.Tools.DotNet":
       "1.0.0-preview3-final"
 },

Also in the dependencies, the EFCore Design package is 1.1.0 like the rest of EFCore. That’s part of the EF APIs, not tooling.

Code changes ….

You’ll discover the DbSet.Find method and change tracker Load method in use in the repository class. These were both added in to EF Core 1.1.

I modified the WeatherEvent class to fully encapsulate its Reactions collection using the support for mapping to IEnumerable. That resulted in some changes to constructors and the addition of an AddReaction method and a local variable.

Unrelated to EF Core, I also modified the SeedData.cs class. It reads a hard coded seeddata.json file to read in seed data. That data used old dates. I wanted the data to show current dates to help me tell that I really and truly pushed new data into the database. Since the Date property of WeatherEvent is private, they way I went about this was to read the raw JSON and update the date value that way then save the raw JSON back to the original file. Then I deserialize the JSON with a current range of dates into a set of WeatherEvents. This also means that I added Delete/Create database back in so the database gets thrown away and recreated/reseeded every time you start up the application.

The tests are also update to use the latest packages. In addition to changing the versions, I had to add a reference to an older package (InternalServices) as its dependency has not yet been updated in xunit.

Here’s the full project.json for the test project since I had to do a bunch of googling to figure it out.

{
 "version": "3.0.0-*",
 "description": "Tests for simple app using aspnetcore, efcore and   
                  postgresql. developed and run on OSX.",
 "authors": [ "Julie Lerman" ],
 "testRunner": "xunit",
 "dependencies": {
   "Microsoft.EntityFrameworkCore.InMemory": "1.1.0",
   "src": "3.0.0",
   "xunit": "2.2.0-beta4-build3444",
   "dotnet-test-xunit": "2.2.0-preview2-build1029",
   "Microsoft.DotNet.InternalAbstractions":"1.0.0"},
 "frameworks": {
 "netcoreapp1.0": {
   "dependencies": {
     "Microsoft.NETCore.App": {
     "type": "platform",
     "version": "1.1.0"
     }
   },
   "imports": [
     "dnxcore50",
     "portable-net45+win8"
     ]
   }
  }
}

I hope you find this repository useful to see EF Core 1.1 in action.

Oh and as per a tweet by Brad Wilson, I added SDK to my global.json file!

Now I have to go learn about why this is important. Clearly it is!

 

EF6 or EF Core? How Do I Choose?

In late October, I spoke at DevIntersection. One of my sessions was called EF6 or EF Core? How Do I Choose? As I’ve been an authority on EF since it’s earliest days, people have been asking me this question frequently, which inspired the talk.

The session was not recorded but I’m sharing my slides on SlideShare. I go into detail on the topic in my upcoming Pluralsight course, “EF Core: Getting Started” which I am currently building. Watch my Pluralsight author page (as well as twitter.com/julielerman and this blog!) for its release.

In the meantime, here is a link to the slides from the DevIntersection talk.ef6-or-ef-core

EF Core Lets Us Finally Define NoTracking DbContexts

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

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!

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Completely New EF in the Enterprise Course on Pluralsight

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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