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Entity Framework Code First in Serverside Blazor: Problem with two relations between the same tables

I'm working on a serverside blazor project (.net 6) using Entity Framework with code first. I have two tables, let's say (in order to protect private data), we have the Tables Band and Bandsman. Originally, every band could have exactly one bandsman, a bandsman could be connected to more then one band though. It's an example, so please don't question this assumptive circumstances.
I created two classes:
[Table("Band")]
public partial class Band
{
[Key]
public int Id { get; set; }
public string BandName { get; set; }
public int? BandsmanId { get; set; }
public virtual Bandsman Bandsman { get; set; }
}
[Table("Bandsman")]
public partial class Bandsman
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
public virtual List<Band> Band { get; set; }
}
So far everything works fine. Entity Framework set the correct foreign key. But now I have to insert a second bandsman. Let's say, the first bandsman is a keyboarder, now I need a drummer as well. So I altered the existing classes:
[Table("Band")]
public partial class Band
{
[Key]
public int Id { get; set; }
public string BandName { get; set; }
public int? BandsmanId { get; set; }
public int? DrummerId { get; set; }
public virtual Bandsman Bandsman { get; set; }
public virtual Bandsman Drummer { get; set; }
}
[Table("Bandsman")]
public partial class Bandsman
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
public virtual List<Band> Band { get; set; }
public virtual List<Band> Drummer { get; set; }
}
I know I have to tell Entity Framework now how to map the tables. So I added mapping instructions to the OnModelCreating-Method in DbContext:
builder.Entity<Band>().HasOne(a => a.Bandsman).WithMany().HasForeignKey(b => b.BandsmanId);
builder.Entity<Band>().HasOne(a => a.Drummer).WithMany().HasForeignKey(b => b.DrummerId);
This doesn't work. When I create the migrations I see that Entity Frameworks tries to create new Columns BandsmanId1 and BandsmanId2 to the Band-Table instead of using the Columns I defined.
So I tried to add the instructions the other way around, too, in addition to the previous ones:
builder.Entity<Bandsman>().HasMany<Band>(a => a.Band).WithOne().HasForeignKey(b => b.BandsmanId);
builder.Entity<Bandsman>().HasMany<Band>(a => a.Drummer).WithOne().HasForeignKey(b => b.DrummerId);
It's still the same, Entity Framework tries to add new columns and map the foreign keys to them.
I also tried to rename Band.BandsmanId to Band.KeyboarderId or rather add and map a new column with the new name (so existing data won't get lost), rename Band.Bandsman to Band.Keyboarder and Bandsman.Band to Bandsman.Keyboarder. With no effect, Entity Framework still seems incapable to use the colums I want it to use. I guess the instructions I added to OnModelCreating in DbContext are incorrect, but I'm not able to find out how to put it right. I found some examples here on stackoverflow and elsewhere, but I can't manage to convert one of this examples to my code.
So I hope someone can help me to put the classes and instructions right.

After posting my question, I found the solution in a post that was shown as possibly related:
Entity Framework Code First - two Foreign Keys from same table
I was close, my only mistake was not to name the virtual List-Property of the Bandsman-Class in the .HasMany()-Part of the instructions. So Entity Framework didn't now these properties were related to the foreign key columns in the band-table and tried to create the assumed-to-be-missing columns on its own. This way it works:
builder.Entity<Band>().HasOne(a => a.Bandsman).WithMany(b => b.Band).HasForeignKey(a => a.BandsmanId);
builder.Entity<Band>().HasOne(a => a.Drummer).WithMany(b => b.Drummer).HasForeignKey(a => a.DrummerId);

Is there any way to embed a class Element into a class Element in Entity Framework?

This is my code:
namespace MyProject.Models.Database
{
public class Recipe
{
public Guid Id { get; set; } = Guid.NewGuid();
public string Name { get; set; }
public string? Description { get; set; }
public string? Picture { get; set; }
public int Worktime { get; set; }
public int? Cooktime { get; set; }
public int Difficulty { get; set; }
public int Portions { get; set; }
public List<Ingredient> Ingredients { get; set; }
}
public class Ingredient
{
public Guid Id { get; set; } = Guid.NewGuid();
public Guid IngredientId { get; set; }
public int Qty { get; set; }
public string QtyUnit { get; set; }
}
}
I want the class "Recipe" to include many elements of type "Ingredient". Ive read stuff about One-to-One and Many-To-Many but i just dont get it...
any Ideas?
thx

One recipe can consist of many ingredients, one ingredient can also be in many recipes. This is a many-to-many relationship.
What you need to do is create a new class that contains Id, RecipeId, IngredientId.Name that class something like RecipeIngredient. When you are creating a DbSet<RecipeIngredient> in your db context, name your table RecipesIngredients.
What should be the data types of the properties in RecipeIngredient?
The Id property will be the primary key, you can decide the data type.
RecipeId will be a foreign key for the Recipe, so it needs the same data type as the primary key of the Recipe (in your case Guid).
IngredientId will be the foreign key for the Ingredient, so the data type will again be Guid in your case.
Note that instead of putting Id in your RecipeIngredient, you can create a composite key instead.
When should you do that? -> here
I suggest you learn about the different relationships and how to apply them using C# and Entity Framework Core -> here
Good luck on your learning journey! When you don't feel you understand a topic, don't worry and don't get discouraged, you just need more experience. Keep up the good work :)

Map column to child object in EF Core 3

Giving the sample below, is there any way to have Address in the same table as User without making use of table splitting or owned types (eg like EF6 complex types)? The generated SQL prevents me from using it and complex types does not seem to be supported in EF Core 3:
public class User
{
public int Id { get; set; }
public Address Address { get; set; }
public string UserName { get; set; }
}
public class Address
{
public string StreetAddress { get; set; }
public string City { get; set; }
public string State { get; set; }
public string ZipCode { get; set; }
}
The only other options I see would be to map Address to its own table.

I will use a 1 to 0..1 relationship or include the properties in User directly.
Nevertheless, using Owned Types as a replacement for ComplexTypes like in EF 6 is horrible , if not completely useless from a SQL perspective, and I cannot see any reason for the joins. Maybe someone can clarify a proper justification for completness

How do I use EF to automatically create a database and repository in ASP.NET MVC?

I have started to learn ASP.NET MVC, and at this time of studying I wanna create simple blog site. I have decided to use ASP.NET MVC and ORM Entity Framework. Probably you have some useful links about this theme?
I tried to start from creating Model code first.
i have 3 classes Post, User(User can be admin), Comments.
Please I need help to make the relations between the database models. I have code like this right now:
public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public List<Comment> Comments { get; set; }
public DateTime PublishDate { get; set; }
}
public class User
{
public readonly bool IsAdmin { get; set; }
public string FirstName { get; set; }
public string SecondName { get; set; }
public string Email { get; set; }
public string Password { get; set; }
public DateTime DateOfBirthday { get; set; }
public string Country { get; set; }
public string City { get; set; }
public List<Post> Posts { get; set; }
public List<Comment> Comments { get; set; }
}
public class Comment
{
public int CommentId { get; set; }
public string UserName { get; set; }
public string Content { get; set; }
public DateTime PublishDate { get; set; }
}
These are my classes to create database tables, but I'm not sure how make relations like many-to-one.
Is it correct to make List of Comments for Post or just write int CommentID?? I have never use database very deep, just saw a few lessons. Can somebody to advise how make repository or correct my Model code?
Thank you very much!

There are plenty of good tutorials out there about how to do this. This one, for example:
http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/creating-an-entity-framework-data-model-for-an-asp-net-mvc-application
To answer some of your questions, yes, the name CommentId is correct; every EF class that you want stored in the database must have either a field called Id or a field called MyClassId (where "MyClass" is the name of your class). I've found that the latter makes your life easier, especially when doing joins.
Unless you have some relationships that EF can't figure out automatically, you don't have to specify the relationships yourself: EF will automatically detect the correct relationship for you. I don't see anything in your code that EF can't handle automatically.
One thing you will have to do is make the List<Post> and List<Comment> fields virtual; that way EF can supply database-backed relationships.
Good luck.

I enjoyed the Building an MVC 3 App with Code First and Entity Framework 4.1
tutorial. Includes a video that I found very easy to follow.

Many to Many self Join with Entity Framework Code First

Consider this Poco:
public class User
{
public int Id { get; set; }
public string Username { get; set; }
public string Fullname { get; set; }
}
Now i want to implement a follow technique where a user may follow other users so basically its self Many to Many relationship
problem is i don't know how exactly i can achieve this in Entity Framework Code-First ?
I thought of a linker Table :
public class UserFollow
{
public int Id { get; set; }
public int Follower { get; set; }
public int Following { get; set; }
public DateTime FollowDate { get; set; }
}
i want to be able to get All Followers and Following from every User Object?

This is quite simple using EF code-first as you only need the User POCO:
public class User
{
public int Id { get; set; }
public string Username { get; set; }
public string Fullname { get; set; }
public ICollection<User> FollowedUsers { get; set; }
}
The collection means that a User is related to other users.
PS: I noted you added a timestamp in your solution example. To achieve that you should still add the collection changing the generic type to whatever suits your needs.
Hope it helps.