Develop Reference

Foreign key Entity Framework - code first migrations

I have a problem with my entities. I'm using EF code-first migrations and the migrations are failing with this error:
Introducing FOREIGN KEY constraint 'FK_OrdersChildsProducts_Orders_OrderId' on table 'OrdersChildsProducts' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Here's my PersonJceProfile entity :
[Table("PersonJceProfiles")]
public class PersonJceProfile : BaseEntity
{
[ForeignKey("Ces")]
public int? CeId { get; set; }
public ICollection<Child> Children { get; set; }
public Order Order { get; set; }
public PersonJceProfile()
{
Children = new List<Child>();
}
}
Here's my Order entity :
[Table("Orders")]
public class Order : BaseEntity
{
[Key]
public int Id { get; set; }
//ForeignKey
[Required]
[ForeignKey("PersonJceProfiles")]
public int PersonJceProfileId { get; set; }
[Required]
public int OrderStatus { get; set; }
[Required]
public bool IsSecurePayment { get; set; }
public int LeftToPayPersonOrder { get; set; }
public string Delivery { get; set; }
public ICollection<OrderChildProduct> OrderChildProduct { get; set; }
public Order()
{
OrderChildProduct = new Collection<OrderChildProduct>();
}
}
Here's my Child entity :
[Table("Childrens")]
public class Child :BaseEntity
{
[Key]
public int Id { get; set; }
[Required]
public string FirstName { get; set; }
[Required]
public string LastName { get; set; }
[Required]
public DateTime? BirthDate { get; set; }
[Required]
public string Gender { get; set; }
public bool? IsActif { get; set; }
public decimal AmountParticipationCe { get; set; }
public bool? IsRegrouper { get; set; }
[Required]
[ForeignKey("PersonJceProfiles")]
public int PersonJceProfileId { get; set; }
}
Here's my Product Entity
public class Product : Good
{
public string File { get; set; }
public bool? IsDisplayedOnJCE { get; set; }
public bool? IsBasicProduct { get; set; }
public int? PintelSheetId { get; set; }
public int OriginId { get; set; }
[Required]
[ForeignKey("Suppliers")]
public int SupplierId { get; set; }
}
Here's my OrderChildProduct entity :
[Table("OrdersChildsProducts")]
public class OrderChildProduct
{
public int OrderId { get; set; }
public int ChildId { get; set; }
public int ProductId { get; set; }
public int LeftToPayChildOrder { get; set; }
public Order Order { get; set; }
public Child Child { get; set; }
public Product Product { get; set; }
}
Here's my context :
modelBuilder.Entity<OrderChildProduct>().HasKey(ccp => new { ccp.OrderId, ccp.ChildId, ccp.ProductId });
I suppose i do destro a relationship like this :
modelBuilder.Entity<Entity>()
.HasRequired(c => c.ForeignKey)
.WithMany()
.WillCascadeOnDelete(false);
but I can't see between which. Because
When I delete PersonJceProfiles : Order must be deleted - OrderChildProduct must be deleted - Child must be deleted
When I delete Order : OrderChildProduct must be deleted
When I delete Order childProduct : nothing must be deleted expect himself
What am I doing wrong? Thanks

The error is self described. You must configure the relationships in the OrderChildProduct table like:
entity.HasOne(p => p.Order)
.WithMany(p => p.OrderChildProduct)
.HasForeignKey(p => p.OrderId)
.OnDelete(Microsoft.EntityFrameworkCore.Metadata.DeleteBehavior.Restrict);
You can use either Restrict or Cascade depending on your requirements.
Also the other 2 relationships must be defined as well.
This is not an error. This is more like a warning... the way EF tells you that it doesn't fully understand the relationships and you must configure them manually.

EF Core self referencing many to many

I have User table and I'd like to add connection called UserFriend between 2 users. I've searched a lot and basicly tried many different solutions and none of them worked. Everytime I get same error:
Introducing FOREIGN KEY constraint 'FK_UserFriends_Users_Friend2Id' on table 'UserFriends' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Here are my models:
public class User
{
[Key]
public Guid Id { get; set; }
public string Username { get; set; }
public string EmailAddress { get; set; }
public string Firstname { get; set; }
public string Lastname { get; set; }
public virtual ICollection<UserFriend> Friends { get; set; }
public virtual ICollection<UserFriend> FriendOf { get; set; }
}
public class UserFriend
{
public User Friend1 { get; set; }
public Guid Friend1Id { get; set; }
public User Friend2 { get; set; }
public Guid Friend2Id { get; set; }
public bool Confirmed { get; set; }
public DateTime Added { get; set; }
}
And here's code in DataContext:
modelBuilder.Entity<UserFriend>().HasKey(sc => new { sc.Friend1Id, sc.Friend2Id });
modelBuilder.Entity<UserFriend>()
.HasOne(c => c.Friend1)
.WithMany(c => c.FriendOf)
.HasForeignKey(f => f.Friend1Id);
modelBuilder.Entity<UserFriend>()
.HasOne(c => c.Friend2)
.WithMany(c => c.Friends)
.HasForeignKey(f => f.Friend2Id)
.OnDelete(DeleteBehavior.Restrict);

Change your code to below and remove the other lines you have posted.
public class User
{
[Key]
public Guid Id { get; set; }
public string Username { get; set; }
public string EmailAddress { get; set; }
public string Firstname { get; set; }
public string Lastname { get; set; }
public virtual ICollection<UserFriend> Friends { get; set; }
public virtual ICollection<UserFriend> FriendOf { get; set; }
}
public class UserFriend
{
public User Friend1 { get; set; }
[ForeignKey("Friend1")]
public Guid? Friend1Id { get; set; }
public User Friend2 { get; set; }
[ForeignKey("Friend2")]
public Guid? Friend2Id { get; set; }
public bool Confirmed { get; set; }
public DateTime Added { get; set; }
}
modelBuilder.Entity<User>();
modelBuilder.Entity<UserFriend>();

How to create a third table for Many to Many relationship in Entity Framework Core?

I have two classes:
One is User
public class User
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Email { get; set; }
public List<Subscription> Subscriptions { get; set; }
}
Other is Subscription:
public class Subscription
{
public int Id { get; set; }
public string Name { get; set; }
public decimal Price { get; set; }
}
As you can see that User has a list of Subscriptions.
Now when using the entity framework code first approach I am getting a table for User which doesn't contain Subscriptions but a new column for User Id is being added to Subscription table. I was expecting to have a third table which contains two columns one with User ID and the other with subscription ID.
How can I achieve this?

From documentation:
Many-to-many relationships without an entity class to represent the join table are not yet supported. However, you can represent a many-to-many relationship by including an entity class for the join table and mapping two separate one-to-many relationships.
So this answer is correct.
I just corrected code a little bit:
class MyContext : DbContext
{
public DbSet<Use> Users { get; set; }
public DbSet<Subscription> Subscriptions { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<UserSubscription>()
.HasKey(t => new { t.UserId, t.SubscriptionId });
modelBuilder.Entity<UserSubscription>()
.HasOne(pt => pt.User)
.WithMany(p => p.UserSubscription)
.HasForeignKey(pt => pt.UserId);
modelBuilder.Entity<UserSubscription>()
.HasOne(pt => pt.Subscription)
.WithMany(t => t.UserSubscription)
.HasForeignKey(pt => pt.SubscriptionId);
}
}
public class User
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Email { get; set; }
public List<UserSubscription> UserSubscriptions{ get; set; }
}
public class Subscription
{
public int Id { get; set; }
public string Name { get; set; }
public decimal Price { get; set; }
public List<UserSubscription> UserSubscriptions{ get; set; }
}
public class UserSubscription
{
public int UserId { get; set; }
public User User { get; set; }
public int SubscriptionId { get; set; }
public Subscription Subscription { get; set; }
}
PS. You don't need use virtual in navigation property, because lazy loading still not available in EF Core.

Create a third middle table named: UserSubscriptions for example.
public class User
{
public int ID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Email { get; set; }
public virtual ICollection<UserSubscription> Subscriptions { get; set; }
}
public class Subscription
{
public int ID { get; set; }
public string Name { get; set; }
public decimal Price { get; set; }
}
public class UserSubscription
{
public int ID { get; set; }
public int SubscriptionID { get; set; }
public decimal Price { get; set; }
public int UserID { get; set; }
public virtual User { get; set; }
public DateTime BeginDate { get; set; }
public DateTime EndDate { get; set; }
}
Second Solution:
Add reference for Subscription to User and name it CurrentSubscription for example.
public class User
{
public int ID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Email { get; set; }
public int CurrentSubscriptionID { get; set; }
public virtual Subscription Subscription { get; set; }
}
public class Subscription
{
public int ID { get; set; }
public string Name { get; set; }
public decimal Price { get; set; }
}

Linq Include not loading List

I've been for a while trying to find out why the Include clause is not loading the related collection: I have two classes with a one-to-many relationship:
public class AgencyNote : IAutId
{
[Key]
public int aut_id { get; set; }
public string Comment { get; set; }
[DisplayName("Note Created Date")]
public DateTime NoteDate { get; set; }
[DisplayName("Contact Date")]
public DateTime ContactDate { get; set; }
[ForeignKey("tbl_agency")]
public int AgencyId { get; set; }
[DisplayName("User")]
public string RipsUser { get; set; }
public virtual ICollection<AgencyNoteAttachment> AgencyNoteAttachments { get; set; }
public virtual tbl_agency tbl_agency { get; set; }
}
and
public class AgencyNoteAttachment
{
[Key]
public int aut_id { get; set; }
public string Url { get; set; }
public string FileName { get; set; }
public int AgencyNoteId { get; set; }
[NotMapped]
[ForeignKey("AgencyNoteId")]
public virtual AgencyNote AgencyNote { get; set; }
}
Context class:
public DbSet<AgencyNote> AgencyNotes { get; set; }
public DbSet<AgencyNoteAttachment> AgencyNoteAttachments { get; set; }
This is the action where I'm using the Include clause:
private IQueryable<AgencyNote> GetNotes(int agencyId)
{
return _ctx.AgencyNotes
.Include(a => a.tbl_agency)
.Include(a => a.AgencyNoteAttachments)
.OrderByDescending(f => f.NoteDate)
.Where(x => x.AgencyId == agencyId);
}
I'm getting AgencyNotesAttachments always null from this action even if I know it's not null, what's going on? Any question let me know...

If you add just the navigation properties between the related entities, then EF will create the FK column for you in the AgencyNoteAttachment table. Now, EF by convention can interpret AgencyNoteId is the FK of that relationship, but is good idea do that explicitly as you already have in your model or using ForeignKey attribute on FK property:
public class AgencyNoteAttachment
{
[Key]
public int aut_id { get; set; }
public string Url { get; set; }
public string FileName { get; set; }
[ForeignKey("AgencyNote")]
public int AgencyNoteId { get; set; }
public virtual AgencyNote AgencyNote { get; set; }
}
If you want to learn more about conventions, take a look this link

composite key as foreign key

I am using Entity framework 4.1 in MVC 3 application. I have an entity where I have primary key consists of two columns ( composite key). And this is being used in another entity as foreign key. How to create the relationship ? In normal scnerios we use :
public class Category
{
public string CategoryId { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
public int ProductId { get; set; }
public string Name { get; set; }
public string CategoryId { get; set; }
public virtual Category Category { get; set; }
}
but what if category has two columns key ?

You can use either fluent API:
public class Category
{
public int CategoryId1 { get; set; }
public int CategoryId2 { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
public int ProductId { get; set; }
public string Name { get; set; }
public int CategoryId1 { get; set; }
public int CategoryId2 { get; set; }
public virtual Category Category { get; set; }
}
public class Context : DbContext
{
public DbSet<Category> Categories { get; set; }
public DbSet<Product> Products { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Category>()
.HasKey(c => new {c.CategoryId1, c.CategoryId2});
modelBuilder.Entity<Product>()
.HasRequired(p => p.Category)
.WithMany(c => c.Products)
.HasForeignKey(p => new {p.CategoryId1, p.CategoryId2});
}
}
Or data annotations:
public class Category
{
[Key, Column(Order = 0)]
public int CategoryId2 { get; set; }
[Key, Column(Order = 1)]
public int CategoryId3 { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
[Key]
public int ProductId { get; set; }
public string Name { get; set; }
[ForeignKey("Category"), Column(Order = 0)]
public int CategoryId2 { get; set; }
[ForeignKey("Category"), Column(Order = 1)]
public int CategoryId3 { get; set; }
public virtual Category Category { get; set; }
}

I believe the easiest way is to use Data Annotation on the Navigation property like this:
[ForeignKey("CategoryId1, CategoryId2")]
public class Category
{
[Key, Column(Order = 0)]
public int CategoryId1 { get; set; }
[Key, Column(Order = 1)]
public int CategoryId2 { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
[Key]
public int ProductId { get; set; }
public string Name { get; set; }
public int CategoryId1 { get; set; }
public int CategoryId2 { get; set; }
[ForeignKey("CategoryId1, CategoryId2")]
public virtual Category Category { get; set; }
}

In .NET Core and .NET 5 < the documentation only shows Data annotations (simple key).
https://learn.microsoft.com/en-us/ef/core/modeling/relationships?tabs=fluent-api%2Cfluent-api-composite-key%2Csimple-key#foreign-key
However using the example from #LadislavMrnka you will get a error message like this:
System.InvalidOperationException: There are multiple properties with
the [ForeignKey] attribute pointing to navigation ''. To define a
composite foreign key using data annotations, use the [ForeignKey]
attribute on the navigation.
Using that error message you can write the code like this:
public class Product
{
[Key]
public int ProductId { get; set; }
public string Name { get; set; }
public int CategoryId2 { get; set; }
public int CategoryId3 { get; set; }
[ForeignKey("CategoryId2,CategoryId3")]
public virtual Category Category { get; set; }
}
Fluent API (composite key) example from Microsoft:
internal class MyContext : DbContext
{
public DbSet<Car> Cars { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Car>()
.HasKey(c => new { c.State, c.LicensePlate });
modelBuilder.Entity<RecordOfSale>()
.HasOne(s => s.Car)
.WithMany(c => c.SaleHistory)
.HasForeignKey(s => new { s.CarState, s.CarLicensePlate });
}
}
public class Car
{
public string State { get; set; }
public string LicensePlate { get; set; }
public string Make { get; set; }
public string Model { get; set; }
public List<RecordOfSale> SaleHistory { get; set; }
}
public class RecordOfSale
{
public int RecordOfSaleId { get; set; }
public DateTime DateSold { get; set; }
public decimal Price { get; set; }
public string CarState { get; set; }
public string CarLicensePlate { get; set; }
public Car Car { get; set; }
}