Add-Migration NullReferenceException

The database context generated by Scaffold-DbContext. After generating the context I moved all entity configurations in OnModelCreating to separate config file implementing IEntityTypeConfiguration<T>. OnModelCreating is like this now.

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
      modelBuilder.ApplyConfigurationsFromAssembly(GetType().Assembly);
}

The same setup is working in EF Core v2.2.6.

Steps to reproduce

Add-Migration IntitialSchema

StackTrace

DesignTimeDbContextFactoryBase.BasePath: D:\Working_Projects
DesignTimeDbContextFactoryBase.Create(string): Connection string: 'Server=DW;Database=DeveDB;Trusted_Connection=True;Application Name=Portal;'.
DbContext Assembly: Portal.Persistence, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.EntityFrameworkCore.Design.Internal.CSharpHelper.Literal(String value)
   at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpMigrationOperationGenerator.Generate(CreateTableOperation operation, IndentedStringBuilder builder)
   at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpMigrationOperationGenerator.Generate(String builderName, IReadOnlyList`1 operations, IndentedStringBuilder builder)
   at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpMigrationsGenerator.GenerateMigration(String migrationNamespace, String migrationName, IReadOnlyList`1 upOperations, IReadOnlyList`1 downOperations)
   at Microsoft.EntityFrameworkCore.Migrations.Design.MigrationsScaffolder.ScaffoldMigration(String migrationName, String rootNamespace, String subNamespace, String language)
   at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration.<>c__DisplayClass0_0.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Object reference not set to an instance of an object.

Further technical details

EF Core version: 3.0.0-rc1.19456.14 Database provider: Microsoft.EntityFrameworkCore.SqlServer (3.0.0-rc1.19456.14) Target framework: .NET Core 3.0 SDK: .NET Core 3.0rc1 Operating system: Windows 10 IDE: Visual Studio 2019 16.2.5

[hannan-m]

Yes, it’s related to #17474.

Steps to reproduce.

Create a database

CREATE DATABASE [Blogging];
GO

USE [Blogging];
GO

CREATE TABLE [Blog] (
    [BlogId] int NOT NULL IDENTITY,
    [Url] nvarchar(max) NOT NULL,
    CONSTRAINT [PK_Blog] PRIMARY KEY ([BlogId])
);
GO

CREATE TABLE [Post] (
    [PostId] int NOT NULL IDENTITY,
    [BlogId] int NOT NULL,
    [Content] nvarchar(max),
    [Title] nvarchar(max),
    CONSTRAINT [PK_Post] PRIMARY KEY ([PostId]),
    CONSTRAINT [FK_Post_Blog_BlogId] FOREIGN KEY ([BlogId]) REFERENCES [Blog] ([BlogId]) ON DELETE CASCADE
);
GO

INSERT INTO [Blog] (Url) VALUES
('http://blogs.msdn.com/dotnet'),
('http://blogs.msdn.com/webdev'),
('http://blogs.msdn.com/visualstudio')
GO

Scaffold DbContext

Scaffold-DbContext "Server=(localdb)\mssqllocaldb;Database=Blogging;Trusted_Connection=True;" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models

Create the following models

public class Author
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

    public class AuthorPost
    {
        public int AuthorId { get; set; }
        public ICollection<Post> Posts { get; set; }

        public virtual Author Author { get; set; }
    }

DbContext and entity configurations

public partial class BloggingContext : DbContext
    {
        public BloggingContext()
        {
        }

        public BloggingContext(DbContextOptions<BloggingContext> options)
            : base(options)
        {
        }

        public virtual DbSet<Blog> Blog { get; set; }
        public virtual DbSet<Post> Post { get; set; }
        public virtual DbSet<Author> Authors { get; set; }
        public virtual DbSet<AuthorPost> AuthorPosts { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
                optionsBuilder.UseSqlServer("Server=DW;Database=Blogging;Trusted_Connection=True;");
            }
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.ApplyConfigurationsFromAssembly(GetType().Assembly);
        }
    }

    public class BlogConfiguration : IEntityTypeConfiguration<Blog>
    {
        public void Configure(EntityTypeBuilder<Blog> builder)
        {
            builder.Property(e => e.Url).IsRequired();
        }
    }

    public class AuthorConfiguration : IEntityTypeConfiguration<Author>
    {
        public void Configure(EntityTypeBuilder<Author> builder)
        {
            // remove .HasComment("Author fullname") and then run Add-Migration. It will work.
            builder.Property(e => e.Name).IsRequired().HasComment("Author fullname");
        }
    }

    public class AuthorPostConfiguration : IEntityTypeConfiguration<AuthorPost>
    {
        public void Configure(EntityTypeBuilder<AuthorPost> builder)
        {
            builder.HasNoKey();
        }
    }

    public class PostConfiguration : IEntityTypeConfiguration<Post>
    {
        public void Configure(EntityTypeBuilder<Post> builder)
        {
            builder.HasOne(d => d.Blog)
                .WithMany(p => p.Post)
                .HasForeignKey(d => d.BlogId);
        }
    }

Now run

Add-Migration CreateAuthorAndPostRelation

Stacktrace

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.EntityFrameworkCore.Design.Internal.CSharpHelper.Literal(String value)
   at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpMigrationOperationGenerator.Generate(CreateTableOperation operation, IndentedStringBuilder builder)
   at System.Dynamic.UpdateDelegates.UpdateAndExecuteVoid3[T0,T1,T2](CallSite site, T0 arg0, T1 arg1, T2 arg2)
   at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpMigrationOperationGenerator.Generate(String builderName, IReadOnlyList`1 operations, IndentedStringBuilder builder)
   at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpMigrationsGenerator.GenerateMigration(String migrationNamespace, String migrationName, IReadOnlyList`1 upOperations, IReadOnlyList`1 downOperations)
   at Microsoft.EntityFrameworkCore.Migrations.Design.MigrationsScaffolder.ScaffoldMigration(String migrationName, String rootNamespace, String subNamespace, String language)
   at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration.<>c__DisplayClass0_0.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Object reference not set to an instance of an object.

If we remove .HasComment("Author fullname") migration will add successfully.

[ajcvickers]

@404Prachi You need to update to ASP.NET Core 3.1 and EF Core 3.1.