NPGSQL relation "Blog" does not exist

Question

I'm trying to set up entity framework core for a project and i'm working through the entity framework core guide on the NPGSQL site: https://www.npgsql.org/efcore/index.html

and i'm getting the following error:

Microsoft.EntityFrameworkCore.DbUpdateException
  HResult=0x80131500
  Message=An error occurred while saving the entity changes. See the inner exception for details.
  Source=Microsoft.EntityFrameworkCore.Relational
  StackTrace:
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.Execute(IRelationalConnection connection)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.Execute(IEnumerable`1 commandBatches, IRelationalConnection connection)
   at Microsoft.EntityFrameworkCore.Storage.RelationalDatabase.SaveChanges(IList`1 entries)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(IList`1 entriesToSave)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(StateManager stateManager, Boolean acceptAllChangesOnSuccess)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.<>c.<SaveChanges>b__104_0(DbContext _, ValueTuple`2 t)
   at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlExecutionStrategy.Execute[TState,TResult](TState state, Func`3 operation, Func`3 verifySucceeded)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(Boolean acceptAllChangesOnSuccess)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChanges(Boolean acceptAllChangesOnSuccess)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChanges()
   at Program.Main(String[] args) in C:\Users\brandp3.DTINET\source\repos\EF-ModelFirst\EF-ModelFirst\Program.cs:line 15

  This exception was originally thrown at this call stack:
    [External Code]

Inner Exception 1:
PostgresException: 42P01: relation "Blog" does not exist

POSITION: 13

here's the code:

static void Main(string[] args)
    {
        using (var db = new BloggingContext())
        {
            // Create and save a new Blog
            Console.Write("Enter a name for a new Blog: ");
            var name = Console.ReadLine();

            var blog = new Blog { Name = name };
            db.Blogs.Add(blog); // error thrown here
            db.SaveChanges();

            // Display all Blogs from the database
            var query = from b in db.Blogs
                        orderby b.Name
                        select b;

            Console.WriteLine("All blogs in the database:");
            foreach (var item in query)
            {
                Console.WriteLine(item.Name);
            }

            Console.WriteLine("Press any key to exit...");
            Console.ReadKey();
        }
    }

The model:

    public class Blog
    {
        public int ID { get; set; }
        public string Name { get; set; }    

        public virtual List<Post> Posts { get; set; }
    }

    public class Post
    {
        public int ID { get; set; } 
        public string Title { get; set; }
        public string Content { get; set; }  
        
        public int BlogId { get; set; }
        public virtual Blog Blog { get; set; }  
    }

and the dbcontext setup

public class BloggingContext : DbContext
    {
        public DbSet<Blog> Blogs { get; set; }
        public DbSet<Post> Posts { get; set; }  

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseNpgsql("Host=localhost;Database=postgres;Username=postgres;Password=mysecretpassword");
        }
    }

From what I understand the tables and relations should be created when I first run the program. At least the guide doesn't indicate that I need to push the schema to the database

Answer 1

From what I understand the tables and relations should be created when I first run the program.

EF Core doesn't automatically create the database schema for you - if you read this somewhere, can you please point to where that is? You'll have to either use Migrations or EnsureCreated (though that's discouraged).

See also the EF getting started guide, where minimal migration creation is shown.