Tag Archives: EFCore

Links to My Recent DDD+EFCore Content

Time to aggregate the various articles and videos I’ve created filled with lessons on how EF Core support for direct mapping of domain models to your relational databases has been improving:


Announcing: Deep Dive into EF Core 2-Day Workshop

Join me in London June 17-18 for a 2-day deep dive into Entity Framework Core.

This is a new addition to Skills Matter course catalog. Because it is a new course, we are looking to get feedback on the proposed list of topics to be covered. If you are interested in attending, your input will be helpful.

Is the list of topics too long for 2 days? Does it touch on what you would want to learn in an advanced class? You can provide feedback on the course description page.

Day 1: Leverage Advanced Features

  • High level review of EF Core differences from EF6
  • Implementing logging to capture EF Core’s database and in-memory activity. Learn about different types of logging data to be captured
  • Learn various approaches to seeding such as via database scripts, code or using the migration-based seeding introduced in EF Core 2.1. You’ll also learn when each approach may be appropriate
  • Using migrations during development,within source control and during deployments
  • Integration testing your EF Core code

Day 2: EF Core in Your Software Architecture

  • The Great Repository Debate: Pros and Cons of the Repository Pattern/Generic Repositories for exposing EF Core
  • Designing Data Layers/APIs
  • Understanding complicated mapping conventions and supplementing those with custom mappings using the Fluent API
  • Designing for performance
  • *Bonus topic* If all modules have been covered, you will also look at EF Core in Azure Functions and EF Core with Azure Cosmos DB (given adequate time)

Logging in EF Core 2.2 Has a Simpler Syntax–More like ASP.NET Core

Logging EF Core’s memory operations and SQL operations has evolved a few times since EF Core arrived. It takes advantage of the same underlying features that ASP.NET Core uses. If you are using ASP.NET Core, logging is baked in and it is really simple to turn it on for EF Core and add filtering. See Shawn Wildermuth’s blog post about EF Core logging in ASP.NET Core.

But if you aren’t using ASP.NET Core, it’s a little more complicated. Not terribly, but still there’s some extra work to do. It involves setting up an ILoggerFactory in your DbContext and defining any filters at the same time.

I wrote an article about this (with the focus being on taking advantage of the various available filters for EF Core logging) in MSDN Magazine earlier this …oh wait, it’s Jan 1, so I can say “last  year”.  Data Points – Logging SQL and Change-Tracking Events in EF Core. I also used it heavily in my EF Core 2 Getting Started course, EF Core 2:Mappings and EF Core 2.1: What’s New courses on Pluralsight. (Note that I’ve updated the sample code for the Getting Started course to EF Core 2.2 and put it on GitHub at github.com/julielerman/PluralsightEFCore2GettingStarted)

My article and courses were using Console apps to demonstrate EF Core behavior and therefore the ConsoleLoggerProvider to tie the logger to the console. Note that the Data Points article contains a lot of good details about the various types of filtering. So you can use the new syntax (below) to specify that there should be a filter, but be sure to read the article to learn about the flavors of filtering and what type of details you’ll be able to see based on the choices you make.

But the logging API has continued to evolve and is providing some of the same shortcuts that ASP.NET had created. And the ConsoleLoggerProvider has been deprecated. The API is not part of EF Core. It’s part of .NET Core. Both EF Core and ASP.NET Core use it.

If you are using EF Core 2.2, the syntax has changed (simplified) and it’s going to get even more streamlined in 3.0.

In fact, if you use the earlier syntax with 2.2, you’ll get a warning about the ConsoleLoggerProvider:

Obsolete(“This method is obsolete and will be removed in a future version. The recommended alternative is using LoggerFactory to configure filtering and ConsoleLoggerOptions to configure logging options.”)

For a point of comparison, here is an example of using theold syntax to turn on logging, only show logs related to database commands and only show messages that are tagged as “Information”.

EF Core 2.0 & 2.1 Logic

public static readonly LoggerFactory MyConsoleLoggerFactory
            = new LoggerFactory(new[] {
              new ConsoleLoggerProvider((category, level)
                => category == DbLoggerCategory.Database.Command.Name
               && level == LogLevel.Information, true) });

Once your logger factory field is defined in the context class you tell the DbContext to use it when configuring.

protected override void OnConfiguring
  (DbContextOptionsBuilder optionsBuilder)
{
  var connectionString = 
    ConfigurationManager.ConnectionStrings["WPFDatabase"].ToString();
  optionsBuilder
    .UseLoggerFactory(MyConsoleLoggerFactory)
    .EnableSensitiveDataLogging(true)
    .UseSqlServer(connectionString);
}

So it’s the creation of the logger factory whose syntax is a little convoluded. The newer API follows how ASP.NET Core lets you filter with an AddFilter method that takes the filters as parameters. No lambdas needed. Also configuring the filter is a separate bit of logic that tellig the logger that it should be tied to the console.

EF Core 2.2 Logic

With EF Core 2.2, you can set up the logger factory in the constructor or another method as long as it’s available when you are configuring the option builder. I’m creating it in a method then using that method as a parameter of UseLoggerFactory. I’m still filtering on showing only database commands and log details flagged as Information.

private ILoggerFactory GetLoggerFactory()
{
  IServiceCollection serviceCollection = new ServiceCollection();
  serviceCollection.AddLogging(builder =>
         builder.AddConsole()
                .AddFilter(DbLoggerCategory.Database.Command.Name, 
                           LogLevel.Information)); 
  return serviceCollection.BuildServiceProvider()
          .GetService<ILoggerFactory>();
}

and then I’m calling GetLoggerFactory() in the UseLogging method on the optionsbuilder:

optionsBuilder.UseLoggerFactory(GetLoggerFactory())

Packages and References

In order to use the AddConsole() method, you still have to use the Microsoft.Extensions.Logging.Console package that the earlier ConsoleLoggerProvider was in. However, you do not need a using statement for the namespace (as you did for the ConsoleLoggerProvider).

EF Core’s IsConfigured and Logging

I got a little confused about some behavior today and finally realized my mistake so thought I would share it. This mostly happens in demo apps that I’m building that are not using  ASP.NET Core.

In these cases, I typically stick the DbContext provider configuration in the OnModelConfiguring method. For example, if I’m using SQLite, then I would specify that in the method as such:

protected override void OnConfiguring
 (DbContextOptionsBuilder optionsBuilder)
{
   optionsBuilder.UseSqlite (@"Filename=Data/PubsTracker.db");
}

I also have been using the logging factory a lot. After defining it, I also configure it. I hadn’t thought much about where I was placig it so added it in randomly.

protected override void OnConfiguring 
  (DbContextOptionsBuilder optionsBuilder)
{
  optionsBuilder.UseLoggerFactory (MyConsoleLoggerFactory);
  optionsBuilder.UseSqlite (@"Filename=Data/PubsTracker.db");
}

Then I added in some tests to had to avoid the SQLite provider if the InMemory provider was already configured, so I wrapped the UseSqlite method with a check to see if the options builder was already configured.

protected override void OnConfiguring
  (DbContextOptionsBuilder optionsBuilder)
{
  optionsBuilder.UseLoggerFactory (MyConsoleLoggerFactory);
  if(!optionsBuilder.IsConfigured)
  {
    optionsBuilder.UseSqlite (@"Filename=Data/PubsTracker.db");
  }
}

But my logic wasn’t working. I was running some migrations but they were suddenly not recognizing the UseSqlite method. I’ve used this pattern so many times. It took me a while to realize what was going on. The UseLoggerFactory is a configuration!

I just had to move the UseLoggerFactory logic after the IsConfigured check and all was well.

This is one of those dumb things that seems so silly you wouldn’t imagine someone else would make such a mistake. But since it bit me, I thought it was worth sharing mostly for the sake of the next coder who is trying to solve the same problem.

New Pluralsight Course! EF Core 2: Getting Started

I’ve recently published my 19th course on Pluralsight.com: Entity Framework Core 2: Getting Started.

It’s 2hrs 40 minutes long and focuses on the basics.

This is using EF Core 2.0.1 in Visual Studio 2017.

Future plans: I’ve begun working on an intermediate level course to follow up and have others in the pipeline…such as a course to cover features of EF Core 2.1 when it gets released (I will wait until it has RTMd for stability) and other advanced topics. I am also planning to do a cross-platform version using VS Code on macOS because that’s my fave these days.

If you are not a Pluralsight subscriber, send me a note and I can give you a 30-day trial so you can watch the course. Be warned: the trial is akin to a gateway drug to becoming a subscriber.

Here is the table of contents for the course:

Introducing a New, Lighter Weight Version of EF   32m 40s
Introduction and Overview
What Is Entity Framework Core?
Where You Can Build and Run Apps with EF Core
How EF Core Works
The Path From EF6 to EF Core to EF Core
EF Core 2 New Features
Looking Ahead to EF Core 2.1 and Beyond
Review and Resources

Creating a Data Model and Database with EF Core    42m 36s
Introduction and Overview
Setting up the Solution
Adding EF Core with the NuGet Package Manager
Creating the Data Model with EF Core
Specifying the Data Provider and Connection String
Understanding EF Core Migrations
Adding Your First Migration
Inspecting Your First Migration
Using Migrations to Script or Directly Create the Database
Recreating the Model in .NET Core
Adding Many-to-many and One-to-one Relationships
Reverse Engineering an Existing Database
Review and Resources

Interacting with Your EF Core Data Model 34m 11s
Introduction and Overview
Getting EF Core to Output SQL Logs
Inserting Simple Objects
Batching Commands When Saving
Querying Simple Objects
Filtering Data in Queries
Updating Simple Objects
Disconnected Updates
Deleting Objects with EF Core
Review and Resources

Querying and Saving Related Data   20m 49s
Introduction and Overview
Inserting Related Data
Eager Loading Related Data
Projecting Related Data in Queries
Using Related Data to Filter Objects
Modifying Related Data
Review and Resources

Using EF Core in Your Applications    30m 52s
Introduction and Overview
EF Core on the Desktop or Device
The Desktop Application: Windows Presentation Foundation (WPF)
Creating the WPF Application
Walking Through the WPF Data Access
EF Core in ASP.NET Core MVC
Adding Related Data into the MVC App
Coding the MVC App’s Relationships
Review and Resources

The Secret to Running EF Core 2.0 Migrations from a NET Core or NET Standard Class Library

I have had two people that watched my Pluralsight EF Core Getting Started course (which will soon be joined by an EF Core 2: Getting Started course) ask the same question, which mystified me at first.

The were running migrations commands which caused the project to compile, but the commands did not do anything. For example, add-migration didn’t add a migration file. get-dbcontext did not return any information. The most curious part was there was no error message! I was able to duplicate the problem.

With EF6 it was possible to use migrations from a class library with no exe project in sight. EF Core migrations can run from a .NET Framework or .NET Core project but not .NET Standard. It needs a runtime. A common workaround is that even if you haven’t gotten to the UI part of your app yet, to just add a .NET Core console app project to the solution, add the EF Core Design Nuget package to it and set it as the startup project. But it’s still possible to do this without adding in a dummy project.

We already knew about the multi-targetting fix which solved an error when you try to run migrations from a .NET Standard library. But even with that fix in place, we were getting the mysterious nothingness.

The answer to the question was buried in a GitHub issue and in comments for the Migrations document in the EF Core docs. This same solution solved a problem I was having when trying to use migrations in a UWP app (again, not .NET Core or .NET Framework) that used a separate class library to host its DbContext.

I’m writing this blog post to surface the solution until it is resolved.

The solution that we used with EF Core 1.0 in order to run migrations from a .NET Standard library was to multi-target for .Net Standard (so you can use the library in a few places) and .NET Core (so you can run migrations).

That means replacing

<PropertyGroup>       
  <TargetFramework>netstandard20</TargetFramework>
</PropertyGroup>

with

<PropertyGroup> 
  <TargetFrameworks>netcoreapp2.0;netstandard2.0</TargetFrameworks>
</PropertyGroup>

Notice that the attribute name is now plural and there is a semi-colon between the two SDKs.

But there’s one more secret which is not in the documentation.

For .NET Standard 2.0 (and EF Core 2.0), you also need to add the following to csproj.

<PropertyGroup>
 <GenerateRuntimeConfigurationFiles>true</GenerateRuntimeConfigurationFiles></PropertyGroup>

Now with the DbContext project set as the startup and ensuring that the package manager console (or command line) are pointing to the same project, your migration commands will work.

Thanks to Christopher Moffat who found the solution in the GitHub issues and shared it in the comments on the EF Core Package Manager Console Tools document.


Screenshot for Tony ..see my comment in reply to your comment below.

Domain-Driven Design Europe 2018 in Amsterdam

I’m excited to be attending and speaking at DDD Europe 2018 in Amsterdam on Feb 1-2 2018. It’s an honor to be on the speaker roster with so many DDD gurus and other people with amazing DDD experiences stories to share.

The lowest early-bird ticket prices can still be bought through Nov 30 at €599 (+21% VAT =  €724 (app. ~$860US +). The ticket will go to €699 (+VAT) from Dec 1-Dec31 and then to €749 (+VAT) until the conference.

Prior to the conference,  there are also 10 amazing workshops ranging from 1/2 day to 2 days across January 30 – 31st.

I’ll be doing a 2  hour workshop during the conference proper on using EF Core 2 to map DDD patterns in your domain. It will be a hands-on workshop and my intention is to build some koans for attendees to work with. Although the flavor of hands-on may shift as I continue to percolate ideas.

Watch my Domain-Driven Design Fundamentals course on Pluralsight

Another Use Case for DbContext.Add in EFCore (and a DDD win)

If you are like me and design your classes following Domain-Driven Design principals , you may find yourself with code like this for controlling how objects get added to collections in the root entity.

public class Samurai {

  public Samurai (string name) : this()
  {
     Name = name;
  }

  private Samurai ()
  {
    _quotes=new List<Quote>();
  }

  public int Id { get; private set; }
  public string Name { get; private set; }
  private readonly List _quotes = new List ()
  private IEnumerable Quotes => _quotes.ToList ();
  public void AddQuote (string quoteText) {
      var newQuote=new Quote(quoteText,Id);
      _quotes.Add (newQuote);
  }

I have a fully encapsulated collection of Quotes. The only way to add a new quote is through the AddQuote method. You can’t just call Samura.Quotes.Add(myquote).

Additionally, because I want to control how developers interact with my API, there is no DbSet for Quotes. You have to do all of your queries and updates via context.Samurais.

A big downside to this is that if I have a new quote and I know the ID of the samurai, I have to first query for the samurai and then use the AddQuote. That really bugs me. I just want to create a new quote, push in the Samurai’s ID value and save it. And that requires either raw SQL or a DbSet<Quote>. I don’t like either option. Raw SQL is a hack in this case and DbSet<Quote> will open my API up to potential misuse.

I was thinking about this problem while laying in bed this morning (admit it, that’s the first thing you do when you wake up, too, right?) and had an idea.

In EF Core, we can now add objects directly to the context without going through the DbSet. The context can figure out what DbSet the entity belongs to and apply the right info to the change tracker. I thought this was handy for being able to call

myContext.AddRange(personobjectA, accountobjectB, productObjectC);

Although I haven’t run into a good use case for leveraging that yet.

What occurred to me is that if DbContext.Add is  using  reflection, maybe EF Core can find a private DbSet.

So I added a private DbSet to my DbContext class:

private DbSet<Quote> Quotes { get; set; }
 And tried out this code (notice I’m using context.Add, not context.Quotes.Add):
static void AddQuoteToSamurai () 
{
  using (var context =newSamuraiContext ()) 
  {
    var quote=newQuote("Voila",1);
    context.Add(quote);
    context.SaveChanges();
  }
}
And it worked! But this isn’t complete yet. I’m breaking my rule of ensuring that only my aggregate root can manage quotes. So this is “dangerous” code from my DDD perspective. However, I was happy to know that EF Core would support this capability.
Currently, Samurai.AddQuote does not have any additional logic to be performed on the quote. What if I were to add in a “RemoveBadWords” rule before a quote can get added?
public void AddQuote (string quoteText) 
{
 Utilities.RemoveBadWords(quoteText);
 var newQuote=new Quote(quoteText,Id);
  _quotes.Add (newQuote);
}
 Now I have an important reason to use Samurai to do the deed. I can add a second, static AddQuote method that also takes an int. Because it’s static, it’s a pass through method.
public static Quote AddQuote(string quoteText,int samuraiId)
{
  Utilities.RemoveBadWords(quoteText); 
  var newQuote=newQuote(quoteText,samuraiId);
  return newQuote;
}

This works and now I don’t have to have an instance of Samurai to use it:

staticvoid AddQuoteToSamurai () 
{
  using (var context =newSamuraiContext ()) {
    context.Add(Samurai.AddQuote("static voila",1));
    context.SaveChanges();
}

One thing I was worried about was if I had an instance of Samurai and tried to use this to add a quote to a different samurai. That would break the aggregate root…it’s job is to manage its own quotes only. It shouldn’t know about other Samurais.

But .NET protects me from that. I can’t call the static method from an instance of Samurai.

I still think that there’s a little bit of code smell from a DDD perspective about having this static, pass-through method in an aggregate root so will have to investigate that (or wait for any unhappy DDDers in my comments). But for now I am happy that I can avoid having to query for an instance of Samurai just to do this one task.