I have an issue with many-to-many relations.
I have 3 model classes:
Article - >>> Item
Keyword - >>> Keyword
TableForRelation between Articles And Keywords - >>> ItemKeywords
With Entity Framework Core, I write these 3 classes and they work fine
public class Item
{
public int Id { get; set; }
public string Content { get; set; }
public virtual ICollection<ItemKeyWords> ItemKeyWords { get; set; }
}
public class KeyWord
{
public int Id { get; set }
public string Text { get; set; }
public virtual ICollection<ItemKeyWords> ItemKeyWords { get; set; }
}
public class ItemKeyWords
{
public int Id { get; set; }
public int ItemId { get; set; }
public virtual Item Item { get; set; }
public int KeyWordId { get; set; }
public virtual KeyWord KeyWord { get; set; }
}
Question is: how can I tell Entity Framework if Keyword exists do not put that in keyword table and just create a relation to that in ItemKeywords table.
database uml
before to add a KeyWord to Item.ItemKeyWords you have to try to load it from context.Set<KeyWord>().
If the load results on a null, then do as actually.
If the load != null then add the loaded value.
Related
I'm quite new to .net and entity framework (this is my first project) and I'm getting the following error when trying to update the database:
*Introducing FOREIGN KEY constraint 'FK_Rating_User_UserId' on table 'Rating' 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.*
I tried doing what it says (at least I think so) by adding the following to my dbContext class:
protected override void OnModelCreating(ModelBuilder modelbuilder)
{
modelbuilder.Entity<Rating>().HasOne(u => u.User).WithMany().OnDelete(DeleteBehavior.Restrict);
modelbuilder.Entity<Rating>().HasOne(g => g.Game).WithMany().OnDelete(DeleteBehavior.Restrict);
}
Not sure have I formulated that method correctly but it did not help (I tried with different DeleteBehavior like SetNull and NoAction)
The thing that really got me confused is that the issue appears even after removing all fields related to other tables from Rating class or even all references between all classes.
My Rating class:
public class Rating
{
public long RatingId { get; set; }
//[Rating]
public virtual Game Game { get; set; } // issue appears even after removing this and User line
//[Rating]
public int Score { get; set; }
public string CommentTitle { get; set; }
public string CommentDescription { get; set; }
//[Rating]
public virtual User User { get; set; }// issue appears even after removing this and Game line
}
User class:
public class User
{
public long UserId { get; set; }
//[Required]
public bool IsModerator { get; set; }
//[Required]
public string Username { get; set; }
//[Required]
public string Email { get; set; }
public string Name { get; set; }
public string Surname { get; set; }
//[Required]
public string Password { get; set; }
//[Required]
public string Salt { get; set; }
public string Description { get; set; }
}
Game class:
public class Game
{
public long GameId { get; set; }
//[Required]
public virtual User User { get; set; }
//[Required]
public string Title { get; set; }
public string Description { get; set; }
//[Required]
public string PricingType { get; set; }
public float MinDonation { get; set; }
public float MaxDonation { get; set; }
//[Required]
public string FileLocation { get; set; }
public float AverageRaiting { get; set; }
public int DownloadCount { get; set; }
}
GameImage class (probably unrelated to the issue just wanted to give a full context)
public class GameImage
{
public long GameImageId { get; set; }
//[Required]
public virtual Game Game { get; set; }
//[Required]
public string Location { get; set; }
//[Required]
public bool IsThumbnail { get; set; }
}
dbContext class:
public class dbContext : DbContext
{
public dbContext(DbContextOptions<dbContext> options) : base(options)
{
}
public DbSet<User> User { get; set; }
public DbSet<Rating> Rating { get; set; }
public DbSet<GameImage> GameImage { get; set; }
public DbSet<Game> Game { get; set; }
}
The issue only appeared after I tried to update the database. The first few migrations and updates were ok, however, then I tried adding [Required] annotation (you can see them commented in the above code) as I noticed that most of the fields were created as nullable in my database - after that the issue starting to occur even after removing the annotations.
In case that matters, I'm using Visual Studio 2019 and SQL Server Express
Does anyone have any idea what may be the cause of this?
Edit:
Image of of my database schema diagram from SSMS
As you can see in the database schema it's visible that there are indeed cycles in the database, however, I cannot get rid of them as Entity Framework's command "Update-Database" does not update the DB and just throws the error mentioned above.
Based on my test, you can try the following steps to solve the problem.
First, please change your dbcontext class into the following code.
public class dbContext : DbContext
{
public dbContext() : base("name=MyContext") { }
public DbSet<User> User { get; set; }
public DbSet<Rating> Rating { get; set; }
public DbSet<GameImage> GameImage { get; set; }
public DbSet<Game> Game { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
}
}
Second, please delete all the tables the database.
Third, please try the following command in your package console.
PM> Update-Database -Force
Finally, you can see the new tables in the databse.
i'm trying create DB using codefirst. i want to create two ForeingKey from same table. But when i set up two navigation properties of the same type, get error like :
The foreign key name 'FollowedUser' was not found on the dependent type Models.UserUserWatchListItem'. The Name value should be a comma separated list of foreign key property names.
public class UserUserWatchListItem
{
public int Id { get; set; }
[Key,ForeignKey("FollowedUser")]
public virtual User FollowedUser { get; set; }
public int FollowedUserId { get; set; }
[Key,ForeignKey("FolloweeUser")]
public int FolloweeUserId { get; set; }
public virtual User FolloweeUser { get; set; }
}
Use this :
public class UserUserWatchListItem
{
public int Id { get; set; }
public int FollowedUserId { get; set; }
public int FolloweeUserId { get; set; }
[ForeignKey("FollowedUser")]
[InverseProperty("FollowedUsers")]
public virtual User FollowedUser { get; set; }
[ForeignKey("FolloweeUser")]
[InverseProperty("FolloweeUsers")]
public virtual User FolloweeUser { get; set; }
}
public class User
{
...
[InverseProperty("FollowedUser")]
public virtual ICollection<UserUserWatchListItem> FollowedUsers { get; set; }
[InverseProperty("FolloweeUser")]
public virtual ICollection<UserUserWatchListItem> FolloweeUsers { get; set; }
}
I have 2 classes which have a many to many relation.
public class Document
{
public int Id { get; set; }
public string Name { get; set; }
public bool AvailableOffline { get; set; }
public string URL { get; set; }
public virtual ICollection<Profile> Profiles { get; set; }
}
public class Profile
{
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public virtual ICollection<Document> Documents { get; set; }
}
On each profile I wish to have a SortOrder field for each document. So I made the joined table explicit in another class
public class ProfileDocuments
{
[Key, Column(Order = 0)]
public int DocumentId { get; set; }
[Key, Column(Order = 1)]
public int ProfileId { get; set; }
public int SortOrder { get; set; }
[ForeignKey("DocumentId")]
public virtual Document Document { get; set; }
[ForeignKey("ProfileId")]
public virtual Profile Profile { get; set; }
}
But when I update the database the table for this last class will not have a column for SortOrder. It only holds the 2 foreign keys. How can I tell EF to generate this table with my column?
When a junction table in a many-to-many association should contain more information than just the two foreign keys, it's no longer possible to map the association as a 'pure' many-to-many (with hidden junction class).
You need an explicit class in the class model to address the extra information (as you already found out), but this also changes the association into 1-n-1:
class Document
{
...
public virtual ICollection<ProfileDocument> ProfileDocuments { get; set; }
}
class Profile
{
...
public virtual ICollection<ProfileDocument> ProfileDocuments { get; set; }
}
I want to have a list of stands (at a trade show) and a list of exhibitors.
The list of stands is separate to the list of exhibitors - however, once registered, I want the exhibitor to be able to book a stand.
When they select/book a stand - I would like to then be able to have a list the stands in my view, and also show the associated exhibitor who has booked it.
Likewise, I would like to list in another view, the exhibitors, and also which stand they have booked.
So I'm trying to setup a one to one relationship (using EF CodeFirst).
However, when trying to add a controller for either the Stand or the Exhibitor, I get the following error:
My models are:
public class Stand
{
public int StandID { get; set; }
public string Description { get; set; }
public bool Booked { get; set; }
public int ExhibitorID { get; set; }
public virtual Exhibitor Exhibitor { get; set; }
}
public class Exhibitor
{
public int ExhibitorID { get; set; }
public string Company { get; set; }
public int StandID { get; set; }
public virtual Stand Stand { get; set; }
}
I'm certain it's something to do with the "Virtual" part of the models.
Can anyone please help point out what should be updated, to allow the connection?
Thank you,
Mark
EF doesn't know which entity is the principal (parent) and which is the dependent (child). You need to declare a foreign key on the item that entity that should come first. You can do this with an annotation or a fluent mapping.
Annotation
Add the following namespace:
using System.ComponentModel.DataAnnotations.Schema;
Annotate your Stand class with the following annotation:
public class Stand
{
[ForeignKey("Exhibitor")]
public int StandID { get; set; }
public string Description { get; set; }
public bool Booked { get; set; }
public int ExhibitorID { get; set; }
public virtual Exhibitor Exhibitor { get; set; }
}
Fluent Mapping
Override your OnModelCreating method in your DbContext class to include:
modelBuilder.Entity<Stand>()
.HasOptional(s => s.Exhibitor)
.WithRequired(e => e.Stand);
The model you have created is not possible to work with relational databases. The Stand needs an ExibitorId while Exibitor need a StandId. The cyclic relationship does not allow you to insert any rows to either tables.
Assuming an Exibitor may have more than one Stand and converting the relationship to one-to-many is one option.
public class Stand
{
public int StandID { get; set; }
public string Description { get; set; }
public bool Booked { get; set; }
public int? ExhibitorID { get; set; }
public virtual Exhibitor Exhibitor { get; set; }
}
public class Exhibitor
{
public int ExhibitorID { get; set; }
public string Company { get; set; }
public virtual ICollection<Stand> Stands { get; set; }
}
Or you can use shared primary key mapping to make the relationship one-to-one. Where Stand is the principal entity. The Exibitor will use the StandID as its PK.
public class Stand
{
public int StandID { get; set; }
public string Description { get; set; }
public bool Booked { get; set; }
public virtual Exhibitor Exhibitor { get; set; }
}
public class Exhibitor
{
public int ExhibitorID { get; set; }
public string Company { get; set; }
public virtual Stand Stand { get; set; }
}
Using the Fluent API to configure the relationship.
modelBuilder.Entity<Exibitor>().HasRequired(e => e.Stand)
.WithOptional(s => s.Exibitor);
I have a model:
public class QuestionRevision
{
[Key]
public int Id { get; set; }
public int IdEditor { get; set; }
public List<Tag> Tags { get; set; }
}
public class Tag
{
[Key]
public int Id { get; set; }
[Required]
public string Name { get; set; }
}
The problem is, I have additional column in Tags table, called QuestionRevision_Id.
Of course one tag could be assigned to many questions, so it's not what I need.
What annotation I need to add to get the desired result?
I've added at Tag class:
public virtual List<QuestionRevision> QuestionRevisions { get; set; }
and at QuestionRevision:
public virtual List<Tag> Tags { get; set; }
and now I have table TagQuestionRevisions, so now it's work how I want.