Add OnModelCreatingExt partial method to generated DbContext (fixes #29)

README.md

@@ -67,7 +67,7 @@ Scaffold EF Core models using Handlebars templates.
     specific interfaces.
     - When you run the _dotnet-ef-dbcontext-scaffold_ command again, you will see your updated reflected in the generated classes.
 
-## Handlebars Helpers
+## 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.
@@ -110,3 +110,30 @@ public class ScaffoldingDesignTimeServices : IDesignTimeServices
 }
 ```
 - To use Handlebars helper defined above, add the following to any of the .hbs files within the CodeTemplates folder: `{{my-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 `OnModelCreatingExt` 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 `OnModelCreatingExt` method with the same signature as the partial method defined in the generated `DbContext` class.
+
+```csharp
+// Place in separate class file (NorthwindSlimContextExt.cs)
+public partial class NorthwindSlimContext
+{
+    partial void OnModelCreatingExt(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));
+    }
+}
+```

sample/ScaffoldingSample/CodeTemplates/CSharpDbContext/DbContext.hbs

@@ -12,7 +12,6 @@ namespace {{namespace}}
 
 {{/if}}
 
-{{{on-configuring}}}
 {{{on-model-creating}}}
     }
 }

sample/ScaffoldingSample/Contexts/NorthwindSlimContext.cs

@@ -25,15 +25,6 @@ public partial class NorthwindSlimContext : DbContext
         // My Handlebars Helper
         public virtual DbSet<Territory> Territory { get; set; }
 
-        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
-        {
-            if (!optionsBuilder.IsConfigured)
-            {
-#warning To protect potentially sensitive information in your connection string, you should move it out of source code. See http://go.microsoft.com/fwlink/?LinkId=723263 for guidance on storing connection strings.
-                optionsBuilder.UseSqlServer("Data Source=(localdb)\\MSSQLLocalDB; Initial Catalog=NorthwindSlim; Integrated Security=True");
-            }
-        }
-
         protected override void OnModelCreating(ModelBuilder modelBuilder)
         {
             modelBuilder.HasAnnotation("ProductVersion", "2.2.0-rtm-35687");
@@ -184,6 +175,10 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
                     .IsRequired()
                     .HasMaxLength(50);
             });
+
+            OnModelCreatingExt(modelBuilder);
         }
+
+        partial void OnModelCreatingExt(ModelBuilder modelBuilder);
     }
 }

sample/ScaffoldingSample/Contexts/NorthwindSlimContextExt.cs

@@ -0,0 +1,23 @@
+using System;
+using Microsoft.EntityFrameworkCore;
+
+namespace ScaffoldingSample.Models
+{
+    public partial class NorthwindSlimContext
+    {
+        partial void OnModelCreatingExt(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));
+        }
+    }
+}

sample/ScaffoldingSample/Models/Country.cs

@@ -0,0 +1,8 @@
+namespace ScaffoldingSample.Models
+{
+    public enum Country
+    {
+        UK = 1,
+        USA = 2
+    }
+}

sample/ScaffoldingSample/Models/Customer.cs

@@ -14,7 +14,7 @@ public Customer()
         public string CompanyName { get; set; }
         public string ContactName { get; set; }
         public string City { get; set; }
-        public string Country { get; set; }
+        public Country Country { get; set; }
 
         public CustomerSetting CustomerSetting { get; set; }
         public ICollection<Order> Order { get; set; }

sample/ScaffoldingSample/Models/Employee.cs

@@ -16,7 +16,7 @@ public Employee()
         public DateTime? BirthDate { get; set; }
         public DateTime? HireDate { get; set; }
         public string City { get; set; }
-        public string Country { get; set; }
+        public Country Country { get; set; }
 
         public ICollection<EmployeeTerritories> EmployeeTerritories { get; set; }
     }

sample/ScaffoldingSample/Sample.ReadMe.md

@@ -37,13 +37,20 @@ public class ScaffoldingDesignTimeServices : IDesignTimeServices
         // Add optional Handlebars helpers
         services.AddHandlebarsHelpers(myHelper);
 
-        // Add optional Handlebars transformers
+        // Add Handlebars transformer for Country property
         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"));
+            propertyTransformer: e =>
+                e.PropertyName == "Country"
+                    ? new EntityPropertyInfo("Country", e.PropertyName)
+                    : new EntityPropertyInfo(e.PropertyType, e.PropertyName));
+
+        // 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
@@ -55,6 +62,39 @@ public class ScaffoldingDesignTimeServices : IDesignTimeServices
 ```
 - To use Handlebars helper defined above, add the following to any of the .hbs files within the CodeTemplates folder: `{{my-helper}}`
 
+A transformer function is added to convert the property type of the `Country` property from `string` to a `Country` `enum` that has been added to the project. More countries from the Customer table may be added.
+- The commented code for `AddHandlebarsTransformers` provides an example of using all the available transformers to append `"Foo"` to the class and property names of each entity.
+
+```csharp
+public enum Country
+{
+    UK = 1,
+    USA = 2
+}
+```
+
+A partial `NorthwindSlimContext` class has been added to a **NorthwindSlimContextExt.cs** file with an implementation of the partial `OnModelCreatingExt` method that adds a property value conversion.
+
+```csharp
+public partial class NorthwindSlimContext
+{
+    partial void OnModelCreatingExt(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));
+    }
+}
+```
+
 ## Usage
 
 - Open a command prompt at the project root and execute:

sample/ScaffoldingSample/ScaffoldingDesignTimeServices.cs

@@ -30,6 +30,13 @@ public void ConfigureDesignTimeServices(IServiceCollection services)
             // 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)
+                        : new EntityPropertyInfo(e.PropertyType, e.PropertyName));
+
             // Add optional Handlebars transformers
             //services.AddHandlebarsTransformers(
             //    entityNameTransformer: n => n + "Foo",

sample/ScaffoldingSample/ScaffoldingSample.csproj

@@ -10,11 +10,6 @@
     <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="2.2.0" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Folder Include="Contexts\" />
-    <Folder Include="Models\" />
-  </ItemGroup>
-
   <ItemGroup>
     <ProjectReference Include="..\..\src\EntityFrameworkCore.Scaffolding.Handlebars\EntityFrameworkCore.Scaffolding.Handlebars.csproj" />
   </ItemGroup>

src/EntityFrameworkCore.Scaffolding.Handlebars/HbsCSharpDbContextGenerator.cs

@@ -336,9 +336,14 @@ protected virtual void GenerateOnModelCreating(IModel model, bool useDataAnnotat
                     {
                         GenerateSequence(sequence, sb);
                     }
+
+                    sb.AppendLine();
+                    sb.AppendLine("OnModelCreatingExt(modelBuilder);");
                 }
 
-                sb.Append("}");
+                sb.AppendLine("}");
+                sb.AppendLine();
+                sb.Append("partial void OnModelCreatingExt(ModelBuilder modelBuilder);");
 
                 var onModelCreating = sb.ToString();
                 TemplateData.Add("on-model-creating", onModelCreating);

test/Scaffolding.Handlebars.Tests/ExpectedContexts.cs

@@ -52,7 +52,11 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
                     .WithMany(p => p.Product)
                     .HasForeignKey(d => d.CategoryId);
             });
+
+            OnModelCreatingExt(modelBuilder);
         }
+
+        partial void OnModelCreatingExt(ModelBuilder modelBuilder);
     }
 }
 ";
@@ -91,7 +95,11 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
 
                 entity.Property(e => e.RowVersion).IsRowVersion();
             });
+
+            OnModelCreatingExt(modelBuilder);
         }
+
+        partial void OnModelCreatingExt(ModelBuilder modelBuilder);
     }
 }
 ";