20. Many-to-Many Relationships in Entity Framework Core

[@odamuser]

Man, you saved my life! Clean, easy, perfect! You're awesome, man!! Thank u!

[@DotNetHow]

You are welcome. Thanks for watching! 🙏

[@ExpatTraderFX]

Bravo "shume bukur" explanation

[@DotNetHow]

Thanks

[@erikipsen1682]

Nice, simple and strait to the case! Thanks for uploading this video 🙂

[@renatocarvalho6059]

Amazingly useful, clean and clear! Thank you very much!

[@DotNetHow]

Thank you as well

[@RohitSharma-vq2gn]

This is extremely lucid explanation of both Fluent Api usage and EF Core. Great work, Ervis :)

[@DotNetHow]

Thank you so much for your feedback, Rohit! ☺

[@Engineer2261]

Thanks Ervis for the very clear explanation.
How do you add a primary Author constraint to a book? Let's say one book has only one primary author, all the others are considered secondary. Do we need different models for that or can we simply apply it to the joint table?

[@DotNetHow]

In the joining table you can add a column, isPrimaryAuthor: boolean

[@yoannhenry6361]

Thanks a lot : It helps me in minutes !! Great Job!!

[@motoviagensmg4400]

Excellent explanation, very concise.

[@DotNetHow]

Thank you

[@JustasNomeika]

Thanks for the video.
Should I create instances of all - Book, Author and Author_Book objects? and then add them to the database?

[@TheSamuelssmelo]

You are an amazing teacher. Great content!!

[@DotNetHow]

Thank you soooo much Samuel

[@LafsGaming]

You made me understand this concept... Thanks for that ✌️

[@sherlockholmes1121]

Very Very useful thanks

[@DotNetHow]

Thanks for watching

[@arohawrami8132]

Thanks a lot Ervis. It is a very useful tutorial.

[@DotNetHow]

Thanks for watching. I am glad you found them useful.

[@pritomsarkar2963]

Awesome Sir. But Please try to Create a dynamically multitenant simple web application.

[@DotNetHow]

I am building this app about book management. So, you can probably learn the concepts and build that app as your personal project. That would be great

[@eliumoraes]

Hello Ervis! Thanks for sharing! I would like to know how can I add more columns in the Books_Authors table like the date to know when the association between this author and book were created.

[@DotNetHow]

Add a mew property -> Add-Migration -> Update-Database

[@pourianayeb1063]

I have 2 questions:
01. How to create composition key for book_authors table, could it be happening by Key attribute or fluent api or maybe both?
02. I'm totally sure I never use fluent api for many-to-many and it works like a charm, why do we need this additional config?

[@DotNetHow]

Hello Pouria!
Regarding your questions:
1. Yes, you can use a composition key for the books_authors table. In our case it would be:
modelBuilder.Entity()
.HasKey(t => new { t.AuthorId, t.BookId });
2. You do not need additional FluentAPI code if you want to keep the default columns that the entity framework will generate, but if you want to customize them, then you need to use fluent API. I prefer to use fluent API to set the join table names with underscore "_ ".
In our case, EF Core would generate a table named AuthorBook with two columns, AuthorsId, BooksId

[@DotNetHow]

I used the default conventions in One-to-Many, but wanted to show that you can customize relations (table names, columns) using Fluent API

[@pourianayeb1063]

@@DotNetHow just got it, thanks 😊

[@DotNetHow]

@@pourianayeb1063 you are welcome

[@imermamani2205]

this is very very easy to learn

[@DotNetHow]

Thank you

[@fieryscorpion]

This is amazing. Thank you!
If you add authentication and some clean architecture (eg: Domain Driven Design) to your Udemy course, I'll buy and study it ASAP!

[@EnGamology]

This one is the best

[@DotNetHow]

Thanks

[@Spirittism]

wished you did some interaction with the db using linq

[@SharpCoder]

How it use on practice. Related entities does not updates

[@robxlift]

Introducing FOREIGN KEY constraint 'FK_dbo.VendorDetails_dbo.States_StateID' on table 'VendorDetails' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Could not create constraint. See previous errors.

[@DotNetHow]

Can you provide additional info, like what are your models, what did you write inside OnModelCreating?

[@robxlift]

@@DotNetHow Introducing FOREIGN KEY constraint 'FK_StudentCourses_Students_StudentId' on table 'StudentCourses' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Could not create constraint or index. See previous errors.
protected override void OnModelCreating(ModelBuilder modelBuilder)
{

modelBuilder.Entity()
.HasKey(t => new { t.StudentId, t.CourseId});
}

public DbSet Courses { get; set; }
public DbSet Departments { get; set; }
public DbSet Students { get; set; }
public DbSet StudentCourses { get; set; }

[@robxlift]

Models
in course
public Department Department { get; set; }
public List StudentCourses { get; set; }
in department
public List Students { get; set; }
public List Courses { get; set; }
in student
public Department Department { get; set; }
public List StudentCourses { get; set; }
in studentCourse
public Student Student { get; set; }
public Course Course { get; set; }

[@DotNetHow]

@@robxlift I do not see the State anywhere in your models (FK_dbo.VendorDetails_dbo.States_StateID). You need to share the full models, otherwise, it is impossible to offer any help.

[@robxlift]

@@DotNetHow i delete old project and make new one , but same error but with new models

[@LeartBajrami-co1gn]

valid

[@DotNetHow]

thanks

[@Elyeslahmar]

Je tenais à vous remercier pour la vidéo excellente. J'ai cependant remarqué un point à corriger concernant la table Book_Author. Il n'est pas nécessaire d'ajouter une clé primaire distincte. En fait, la clé primaire peut être composée des clés étrangères AuthorId et BookId.
Voici la syntaxe correcte à ajouter dans la méthode OnModelCreating de votre classe de contexte DbContext
/*****modelBuilder.Entity().HasKey(r => new{ r.PermissionId,r.RoleId });***/

[@asfandalikhan6269]

Thanks bro

[@DotNetHow]

You are welcome!

[@sobrelaroca2701]

Where is the create? update?

[@semajxocliw]

ef core should be able to handle many-to-many automatically as of 5.0

[@DotNetHow]

That is right. I just wanted to show that it is customisable

[@qwertz3813]

But you can customize the key of a pivot if you do it this way.
Example:
modelBuilder.Entity
.HasKey(ma => new { ma.MovieId, ma.ActorId, ma.RoleName });
where RoleName is something new to both of the tables