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POEF Code First: Migrations removing needed columns and adding unwanted ones
 

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  1. POEF Code First: Migrations removing needed columns and adding unwanted ones
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    <p>Note: there is a "better" iteration of this question here:</p> <p><a href="https://stackoverflow.com/questions/16274653/ef-code-first-migrations-table-per-hierarchy-bug">EF Code First migrations: Table Per Hierarchy Bug</a></p> <hr> <p>I am trying to figure out the exact steps need to take an existing database and overlay entity framework code first with a Table Per Hierarchy structure. However no matter what I do, the end result migration is "wrong".</p> <p>Here is the sample database, exact steps and output.</p> <p>Existing database structure</p> <pre><code>CREATE TABLE [dbo].[Categories]( [Id] [int] IDENTITY(1,1) NOT NULL Primary Key, [Name] [nvarchar](100) NOT NULL, ) GO CREATE TABLE [dbo].[A]( [Id] [int] IDENTITY(1,1) NOT NULL Primary Key, [Discriminator] [nvarchar](20) NOT NULL, [Description] [nvarchar](100) NOT NULL, [CategoryId] [int] NULL )GO ALTER TABLE [dbo].[A] WITH CHECK ADD CONSTRAINT [FK_dbo.A_dbo.Categories_CategoryId] FOREIGN KEY([CategoryId]) REFERENCES [dbo].[Categories] ([Id]) GO ALTER TABLE [dbo].[A] CHECK CONSTRAINT [FK_dbo.A_dbo.Categories_CategoryId] GO </code></pre> <p>"Reverse Engineer Code First" generates the following:</p> <pre><code> public partial class EntityContext : DbContext { static EntityContext() { Database.SetInitializer&lt;EntityContext&gt;(null); } public EntityContext() : base("Name=Test47Context") { } public DbSet&lt;A&gt; A { get; set; } public DbSet&lt;Category&gt; Categories { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Configurations.Add(new AMap()); modelBuilder.Configurations.Add(new CategoryMap()); } } public partial class A { public int Id { get; set; } public string Discriminator { get; set; } public string Description { get; set; } public Nullable&lt;int&gt; CategoryId { get; set; } public virtual Category Category { get; set; } } public partial class Category { public Category() { this.A = new List&lt;A&gt;(); } public int Id { get; set; } public string Name { get; set; } public virtual ICollection&lt;A&gt; A { get; set; } } public class AMap : EntityTypeConfiguration&lt;A&gt; { public AMap() { // Primary Key this.HasKey(t =&gt; t.Id); // Properties this.Property(t =&gt; t.Discriminator) .IsRequired() .HasMaxLength(20); this.Property(t =&gt; t.Description) .IsRequired() .HasMaxLength(100); // Table &amp; Column Mappings this.ToTable("A"); this.Property(t =&gt; t.Id).HasColumnName("Id"); this.Property(t =&gt; t.Discriminator).HasColumnName("Discriminator"); this.Property(t =&gt; t.Description).HasColumnName("Description"); this.Property(t =&gt; t.CategoryId).HasColumnName("CategoryId"); // Relationships this.HasOptional(t =&gt; t.Category) .WithMany(t =&gt; t.A) .HasForeignKey(d =&gt; d.CategoryId); } } public class CategoryMap : EntityTypeConfiguration&lt;Category&gt; { public CategoryMap() { // Primary Key this.HasKey(t =&gt; t.Id); // Properties this.Property(t =&gt; t.Name) .IsRequired() .HasMaxLength(100); // Table &amp; Column Mappings this.ToTable("Categories"); this.Property(t =&gt; t.Id).HasColumnName("Id"); this.Property(t =&gt; t.Name).HasColumnName("Name"); } } </code></pre> <p>Implement TPH, by </p> <ul> <li>Adding <code>Derived.cs</code> inherits from <code>A.cs</code></li> <li>Moving <code>Category</code> and <code>CategoryId</code> properties from <code>A.cs</code> to <code>Derived.cs</code></li> <li>Remove <code>Discriminator</code> property from <code>A.cs</code></li> <li>In <code>AMap.cs</code> remove <code>Discriminator</code>, <code>CategoryId</code> and <code>Category</code> Foreign Key mapping.</li> <li><p>Adding TPH mapping to <code>OnModelCreating</code></p> <pre><code>public partial class EntityContext : DbContext { static EntityContext() { Database.SetInitializer&lt;EntityContext&gt;(null); } public EntityContext() : base("Name=Test47Context") { } public DbSet&lt;A&gt; A { get; set; } public DbSet&lt;Category&gt; Categories { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Configurations.Add(new AMap()); modelBuilder.Configurations.Add(new CategoryMap()); modelBuilder.Entity&lt;A&gt;() .Map&lt;Derived&gt;(x =&gt; x.Requires("Discriminator").HasValue("Derived")); } } public partial class A { public int Id { get; set; } public string Description { get; set; } } public class Derived : A { public Nullable&lt;int&gt; CategoryId { get; set; } public virtual Category Category { get; set; } } public partial class Category { public Category() { this.A = new List&lt;A&gt;(); } public int Id { get; set; } public string Name { get; set; } public virtual ICollection&lt;A&gt; A { get; set; } } public class AMap : EntityTypeConfiguration&lt;A&gt; { public AMap() { // Primary Key this.HasKey(t =&gt; t.Id); this.Property(t =&gt; t.Description) .IsRequired() .HasMaxLength(100); // Table &amp; Column Mappings this.ToTable("A"); this.Property(t =&gt; t.Id).HasColumnName("Id"); this.Property(t =&gt; t.Description).HasColumnName("Description"); } } public class CategoryMap : EntityTypeConfiguration&lt;Category&gt; { public CategoryMap() { // Primary Key this.HasKey(t =&gt; t.Id); // Properties this.Property(t =&gt; t.Name) .IsRequired() .HasMaxLength(100); // Table &amp; Column Mappings this.ToTable("Categories"); this.Property(t =&gt; t.Id).HasColumnName("Id"); this.Property(t =&gt; t.Name).HasColumnName("Name"); } } </code></pre></li> </ul> <p>"Add-migration TPH" generates the following</p> <pre><code>public partial class TPH : DbMigration { public override void Up() { AddColumn("dbo.A", "Category_Id", c =&gt; c.Int()); AddForeignKey("dbo.A", "Category_Id", "dbo.Categories", "Id"); CreateIndex("dbo.A", "Category_Id"); DropColumn("dbo.A", "Discriminator"); } public override void Down() { AddColumn("dbo.A", "Discriminator", c =&gt; c.String(nullable: false, maxLength: 20)); DropIndex("dbo.A", new[] { "Category_Id" }); DropForeignKey("dbo.A", "Category_Id", "dbo.Categories"); DropColumn("dbo.A", "Category_Id"); } } </code></pre> <ul> <li>Why does it drop the <code>Discriminator</code> column instead of just altering it to <code>nvarchar(128)</code>?</li> <li>Why doesn't just use the existing <code>CategoryId</code> column instead of adding <code>Category_Id</code>?</li> </ul>
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    1. CONo matter what dev team says, Migration API is impractical in real life and results in loss of data, and we do not live in EF friendly world where only predefined migration strategies work. Database first is only practical way to use EF because we do have other or older system which can not be changed to be EF friendly.
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    2. COI fear that EF Code First may not be mature enough for this project. However I will put a few more days into it before I surrender and go back to LINQ to SQL. Thank you for taking the time to share your experience.
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    3. CObut why dont you simply use Database first model, and let EDMX generate model from DB, that is easier and we are using it on live projects.
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      1. POEF Code First: Migrations removing needed columns and adding unwanted ones
      1. USAkash Kava
 

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