70 Modify DBContext for the entity (Author). Primary Key and One To Many relations. (Wpf, Xamarin) - chempkovsky/CS2WPF-and-CS2XAMARIN GitHub Wiki

The DBContext Wizard is a tool that creates or modifies an existing DBContext file. There are a lot of such tools. And the question is, "why was it created."

• The answer is as follows:
  • Other wizards (ModelViews, WebApiServices) parse the DBContext file and Entities files for their own needs. But the task of creating full-feature parser is a time consuming. On the other hand, only a few fluent api constructs are used by ModelViews, WebApiServices wizards. So, instead of creating a fully functional parser, I created a small code generator for a very short list of constructs. According to (https://www.entityframeworktutorial.net/efcore/configure-one-to-many-relationship-using-fluent-api-in-ef-core.aspx) some fluent api designs can be done in more than one way. To make sure that the ModelViews and WebApiServices wizards parse the fluent api structures correctly, a DBContext Wizard was developed. So, using DBContext Wizard is absolutely necessary. It generates fluent api constructs in a way that ModelViews and WebApiServices wizards parse correctly.

• Step #1:
  • Right Click “Literature” of the “Dm02Context”-project and Select “DBContext Wizard” menu item to open the Wizard dialog

- Note:
    - On the first page of the dialog the destination folder is shown. The destination folder is the folder in which the generated file will be created.
    - Click “Next”-button

• Step #2:
  • The developer is on the second page. Now select the "Dm02Context" project and the "LitDbContext" context that has already been created.

- Click “Next” 

• Step #3:
  • On the third page select “Dm01Entity”-project and “LitAuthor”-entity.

- Click “Add required property to DbContext”
    - `DbSet<LitPublisher>`
- property will be added to the context

• Step #4:
  • On the same third page, the “Modify”-button became available.
  • The developer must explicitly define the primary key.

- Click “Modify”

• Step #5:
  • Add ”AuthorId” to the primary key list. The order is important!
  • Select “HasKey.Net.cs.t4” template
  • Click “Create(Modify)” button. It will add Fluent Api definition of the primary key for “LitAuthor”.

    modelBuilder.Entity<LitAuthor>().HasKey(p => p.AuthorId);

Click "Next"-button. You are on the third page again

to define one-to-many (optional-to-many) relation click "Next"-button

• Step #6:
  • On the "Foreign Key"-page select "Country" and click "Next"-button

• Step #7:
  • On the "Create (Modify) Foreign Key"-page
    • select "Iso3CntrRef" and "Iso2CntrRef" fields
    • One-to-many
    • select "OneToCollection.Net.cs.t4"
    • click "Create(Modify)"-button

It will add Fluent Api definition of the foreign key.

            modelBuilder.Entity<LitAuthor>().HasRequired(d => d.Country)
                .WithMany(m => m.Authors)
                .HasForeignKey(d => new { d.Iso3CntrRef, d.Iso2CntrRef });

• Step #8 (Optional):
  • Open “LitDbContext.cs” file
  • Find the constructor and change as follows:

      public LitDbContext()
        : base("name=LitConnection")
      {
      }