Entity Framework Core Scaffolding with Handlebars

Scaffold EF Core models using Handlebars templates.

• Uses Handlebars.NET to compile Handlebars templates when generating models with the Entity Framework Core scaffolding tools.

Contributing

Before creating a pull request, please refer to the Contributing Guidelines.

Prerequisites

• Visual Studio 2019 16.4 or greater.
• .NET Core 3.1 SDK.
• EF Core CLI.
  • Install global dotnet-ef tool.

    dotnet tool install --global dotnet-ef
    

  • Update global dotnet-ef tool.

    dotnet tool update --global dotnet-ef
    

Database Setup

1. Use SQL Server Management Studio to connect to SQL Server
   • The easiest is to use LocalDb, which is installed with Visual Studio.
     Connect to: (localdb)\MsSqlLocalDb.
   • Create a new database named NorthwindSlim.
   • Download the data file from http://bit.ly/northwind-slim.
   • Unzip NorthwindSlim.sql and run the script to create tables and populate them with data.

Usage

1. Create a new .NET Core class library.

   • If necessary, edit the csproj file to update the TargetFramework to 3.1.

   Note: Using the EF Core toolchain with a .NET Standard class library is currently not supported. Instead, you can add a .NET Standard class library to the same solution as the .NET Core library, then add existing items and select Add As Link to include entity classes.

2. Add EF Core SQL Server and Tools NuGet packages.

   • Microsoft.EntityFrameworkCore.SqlServer
   • Microsoft.EntityFrameworkCore.Design

3. Add the EntityFrameworkCore.Scaffolding.Handlebars NuGet package:

   • EntityFrameworkCore.Scaffolding.Handlebars

4. Remove Class1.cs and add a ScaffoldingDesignTimeServices class.

   • Implement IDesignTimeServices by adding a ConfigureDesignTimeServices method that calls services.AddHandlebarsScaffolding.
   • You can optionally pass a ReverseEngineerOptions enum to indicate if you wish to generate only entity types, only a DbContext class, or both (which is the default).

   public class ScaffoldingDesignTimeServices : IDesignTimeServices
   {
       public void ConfigureDesignTimeServices(IServiceCollection services)
       {
           services.AddHandlebarsScaffolding(options =>
               options.ReverseEngineerOptions = ReverseEngineerOptions.DbContextAndEntities);
       }
   }

5. Open a command prompt at the project level and use the dotnet ef tool to reverse engineer a context and models from an existing database.

   • Get help on dotnet-ef-dbcontext-scaffold at the command line: dotnet ef dbcontext scaffold -h
   • Execute the following command to reverse engineer classes from the NorthwindSlim database:

   dotnet ef dbcontext scaffold "Data Source=(localdb)\MSSQLLocalDB; Initial Catalog=NorthwindSlim; Integrated Security=True" Microsoft.EntityFrameworkCore.SqlServer -o Models -c NorthwindSlimContext -f --context-dir Contexts
   

   • You should see context and/or entity classes appear in the Models folder of the project.
   • You will also see a CodeTemplates folder appear containing Handlebars templates for customizing generation of context and entity type classes.
   • Add -d to the command to use data annotations. You will need to add the System.ComponentModel.Annotations package to a .NET Standard library containing linked entity classes.

6. You may edit any of the template files which appear under the CodeTemplates folder.

   • For now you can just add some comments, but you may wish to customize the templates in other ways, for example, by inheriting entities from a base class or implementing specific interfaces.
   • When you run the dotnet-ef-dbcontext-scaffold command again, you will see your updated reflected in the generated classes.

Nullable Reference Types

Take advantage of C# nullable reference types by enabling them in your .csproj file.

<PropertyGroup>
  <TargetFramework>netcoreapp3.1</TargetFramework>
  <LangVersion>8.0</LangVersion>
  <Nullable>enable</Nullable>
</PropertyGroup>

Then enable nullable reference types for Handlebars scaffolding.

services.AddHandlebarsScaffolding(options =>
{
    options.EnableNullableReferenceTypes = true;
});

Non-nullable properties will include the null forgiving operator.

public partial class Product
{
    public string ProductName { get; set; } = default!;
    public decimal? UnitPrice { get; set; }
}

Excluded Tables

You can optionally exclude certain tables from code generation. These may also be qualified by schema name.

services.AddHandlebarsScaffolding(options =>
{
    // Exclude some tables
    options.ExcludedTables = new List<string> { "Territory", "dbo.EmployeeTerritories" };
});

Custom Template Data

You may find it useful to add your own custom template data for use in your Handlebars templates. For example, the model namespace is not included by default in the DbContext class import statements. To compensate you may wish to add a models-namespace template to the DbImports.hbs template file.

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata; // Comment
using {{models-namespace}};

Likewise you may wish to specify the name of a model base class in the same way.

public partial class {{class}} : {{base-class}}
{
    {{{> constructor}}}
    {{> properties}}
}

You can then set the value of these templates in the TemplateData property of HandlebarsScaffoldingOptions.

services.AddHandlebarsScaffolding(options =>
{
    // Add custom template data
    options.TemplateData = new Dictionary<string, object>
    {
        { "models-namespace", "ScaffoldingSample.Models" },
        { "base-class", "EntityBase" }
    };
});

Schema Folders

You can generate models in different folders by database schema.

services.AddHandlebarsScaffolding(options =>
{
    // Put Models into folders by DB Schema
    options.EnableSchemaFolders = true;
});

Embedded Templates

Handlebars templates may be embdedded in a separate .NET Standard project that can be shared among multiple .NET Core scaffolding projects. Simply copy the CodeTemplates folder to the .NET Standard project and edit the .csproj file to embed them as a resource in the assembly.

<ItemGroup>
  <EmbeddedResource Include="CodeTemplates\**\*.hbs" />
</ItemGroup>

Then reference the .NET Standard project from the .NET Core projects and specify the templates assembly when adding Handlebars scaffolding in the ScaffoldingDesignTimeServices class.

public class ScaffoldingDesignTimeServices : IDesignTimeServices
{
    public void ConfigureDesignTimeServices(IServiceCollection services)
    {
        // Get templates assembly
        var templatesAssembly = Assembly.Load("TemplatesAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null");

        // Add Handlebars scaffolding using embedded templates templates
        services.AddHandlebarsScaffolding(options => options.EmbeddedTemplatesAssembly = templatesAssembly);
    }
}

Handlebars Helpers and Transformers

You can register Handlebars helpers in the ScaffoldingDesignTimeServices where setup takes place.

• Create a named tuple as shown with myHelper below.
• The context parameter of the helper method provides model data injected by the Handlebars scaffolding extension.
• Pass the tuple to the AddHandlebarsHelpers extension method.
• To use Handlebars helper defined above, add the following to any of the .hbs files within the CodeTemplates folder: {{my-helper}}
• You may register as many helpers as you wish.

You can pass transform functions to AddHandlebarsTransformers in order to customize generation of entity type definitions, including class names, constructors and properties.

public class ScaffoldingDesignTimeServices : IDesignTimeServices
{
    public void ConfigureDesignTimeServices(IServiceCollection services)
    {
        // Add Handlebars scaffolding templates
        services.AddHandlebarsScaffolding(options =>
        {
            // Generate both context and entities
            options.ReverseEngineerOptions = ReverseEngineerOptions.DbContextAndEntities;

            // Enable Nullable reference types
            options.EnableNullableReferenceTypes = true;

            // Put Models into folders by DB Schema
            //options.EnableSchemaFolders = true;

            // Exclude some tables
            options.ExcludedTables = new List<string> { "Territory", "EmployeeTerritories" };

            // Add custom template data
            options.TemplateData = new Dictionary<string, object>
            {
                { "models-namespace", "ScaffoldingSample.Models" },
                { "base-class", "EntityBase" }
            };
        });

        // Register Handlebars helper
        var myHelper = (helperName: "my-helper", helperFunction: (Action<TextWriter, Dictionary<string, object>, object[]>) MyHbsHelper);

        // Add optional Handlebars helpers
        services.AddHandlebarsHelpers(myHelper);

        // Add Handlebars transformer for Country property
        services.AddHandlebarsTransformers(
            propertyTransformer: e =>
                e.PropertyName == "Country"
                    ? new EntityPropertyInfo("Country", e.PropertyName, false)
                    : new EntityPropertyInfo(e.PropertyType, e.PropertyName, e.PropertyIsNullable));

        // Add optional Handlebars transformers
        //services.AddHandlebarsTransformers(
        //    entityNameTransformer: n => n + "Foo",
        //    entityFileNameTransformer: n => n + "Foo",
        //    constructorTransformer: e => new EntityPropertyInfo(e.PropertyType + "Foo", e.PropertyName + "Foo"),
        //    propertyTransformer: e => new EntityPropertyInfo(e.PropertyType, e.PropertyName + "Foo"),
        //    navPropertyTransformer: e => new EntityPropertyInfo(e.PropertyType + "Foo", e.PropertyName + "Foo"));
    }

    // Sample Handlebars helper
    void MyHbsHelper(TextWriter writer, Dictionary<string, object> context, object[] parameters)
    {
        writer.Write("// My Handlebars Helper");
    }
}

Extending the OnModelCreating Method

There are times when you might like to modify generated code, for example, by adding a HasConversion method to an entity property in the OnModelCreating method of the generated class that extends DbContext. However, doing so may prove futile because added code would be overwritten the next time you run the dotnet ef dbcontext scaffold command.

• Rather than modifying generated code, a better idea would be to extend it by using partial classes and methods. To enable this scenario, the generated DbContext class is already defined using the partial keyword, and it contains a partial OnModelCreatingPartial method that is invoked at the end of the OnModelCreating method.
• To implement the partial method, simply add a new class to your project with the same name as the generated DbContext class, and define it as partial. Then add a OnModelCreatingPartial method with the same signature as the partial method defined in the generated DbContext class.

// Place in separate class file (NorthwindSlimContextPartial.cs)
public partial class NorthwindSlimContext
{
    partial void OnModelCreatingPartial(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Employee>()
            .Property(e => e.Country)
            .HasConversion(
                v => v.ToString(),
                v => (Country)Enum.Parse(typeof(Country), v));

        modelBuilder.Entity<Customer>()
            .Property(e => e.Country)
            .HasConversion(
                v => v.ToString(),
                v => (Country)Enum.Parse(typeof(Country), v));
    }
}

Generating TypeScript Entities

To generate TypeScript entities simply pass LanguageOptions.TypeScript to AddHandlebarsScaffolding. Since generating a DbContext class is strictly a server-side concern, you should also pass ReverseEngineerOptions.EntitiesOnly to AddHandlebarsScaffolding.

public class ScaffoldingDesignTimeServices : IDesignTimeServices
{
    public void ConfigureDesignTimeServices(IServiceCollection services)
    {
        // Generate entities only
        var options = ReverseEngineerOptions.EntitiesOnly;

        // Generate TypeScript files
        var language = LanguageOptions.TypeScript;

        // Add Handlebars scaffolding templates
        services.AddHandlebarsScaffolding(options, language);
    }
}