If I have a navigation property (ie: virtual), for example:
public virtual User Author { get; set; }
And I want to have also the id of that User, ie:
public int AuthorId { get; set; }
How can I tell EF that this "AuthorId" must be related to the Author property?
I don't like the idea of this being automatic (EF magically deducing this).
Because one could have multiple references to the same table:
public virtual User Author { get; set; }
public int AuthorId { get; set; }
public virtual User Receiver { get; set; }
public int ReceiverId { get; set; }
Entity framework will assume that the AuthorID is the FK of the Author class. See this blog post for the details.
You could also explicitly tell EF, by using data annotations:
[ForeignKey("Author")]
public int AuthorId {get;set;}
or by using fluent mappings:
modelBuilder.Entity<YourClass>().HasRequired(p => p.Author)
.WithMany()
.HasForeignKey(p => p.AuthorId);
Related
I am having problems figuring out the data annotations to map more than one 1:1 relationships so that EF Core 3.11.7 understands it and can build a migration.
I have a Person table and a Notes table.
There is a 0:M Notes relationship in Person. A person record can have 0 or more notes.
In the notes table is a CreatedBy field which is a Person. It also has a LastEditedBy field which is also a person. EF keeps bombing on how to construct the relationship for Note.CreatedBy. If this were non EF, both fields would be ints with the PersonID of the proper person record. How do it, preferabbly with Data Annotations, explain this to EF Core?
When I try to create a migration it fails and says:
System.InvalidOperationException: Unable to determine the relationship represented by navigation property 'Note.CreatedBy' of type 'Person'. Either manually configure the relationship, or ignore this property using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;
using System.Threading.Tasks;
namespace VetReg.Domain.Model
{
public class Family
{
public int FamilyID { get; set; } = -1;
public string FamilyName { get; set; }
public List<Pet> Pets { get; set; } = new List<Pet>();
public List<PersonFamily> People { get; set; }
public int AddressID { get; set; } = -1;
public List<Note> Notes { get; set; }
}
public class Person
{
public int PersonID { get; set; }
public string LastName { get; set; }
public string FirstName { get; set; }
public DateTime? Birthdate { get; set; }
public string Password { get; set; }
public List<PersonFamily> Families { get; set; }
public List<Note> Notes { get; set; }
} // class People
public class Note
{
public int NoteID { get; set; }
public int CreatedByID { get; set; }
[ForeignKey("CreatedByID")]
public Person CreatedBy { get; set; }
public DateTime DateCreated { get; set; }
public int LastEditByID { get; set; }
[ForeignKey("LastEditByID")]
public Person LastEditBy { get; set; }
public DateTime? LastEditDate { get; set; }
public string NoteText { get; set; }
}
public class PersonFamily
{
public int PersonID { get; set; }
public int FamilyID { get; set; }
public Person Person { get; set; }
public Family Family { get; set; }
}
}
The question is (and this is what makes impossible to EF to automatically determine the relationships) what is the relation between Person.Notes and Note.CreatedBy / Note.LastEditBy - none probably? You've said there is 0:M relationship between Person and Note, but note that there are potentially 3 one-to-many relationships there - notes associated with person, notes created by person and notes edited by person, which potentially leads to 3 FKs to Person in Note.
Also note that none of the navigation properties is required, but when present they must be paired.
Assuming you want 3 relationships, i.e. there is no relation between Note.CreatedBy / Note.LastEditBy and Person.Notes, you need to tell EF that Note.CreatedBy and Note.LastEditBy do not have corresponding (a.k.a. inverse) navigation property in Person. This is not possible with data annotations. The only available data annotation for that purpose [InverseProperty(...)] does not accept empty/null string name, hence cannot be used for what is needed here.
Also there is another problem here which you will encounter after resolving the current, which also cannot be resolved with data annotations. Since you have multiple required (thus cascade delete by default) relationships from Person to Note, it creates the famous "cycles or multiple cascade paths" problem with SqlServer, and requires turning off at least one of the cascade delete.
With that being said, the model in question needs the following minimal fluent configuration:
modelBuilder.Entity<Note>()
.HasOne(e => e.CreatedBy)
.WithMany()
.OnDelete(DeleteBehavior.Restrict);
modelBuilder.Entity<Note>()
.HasOne(e => e.LastEditBy)
.WithMany()
.OnDelete(DeleteBehavior.Restrict);
The essential for the original issue are the HasOne / WithMany pairs. Once you do that, EF Core will automatically map the unmapped Person.Notes collection to a third optional relationship with no inverse navigation property and shadow FP property (and column) called "PersonId", i.e. the equivalent of
modelBuilder.Entity<Person>()
.HasMany(e => e.Notes)
.WithOne()
.HasForeignKey("PersonId");
Regarding the second issue with multiple cascade paths, instead of Restrict you can use any non cascading option or the newer ClientCascade. And it could be for just one of the relationships, as soon as it breaks the "cascade path" (apparently you can't break the cycle because it is demanded by the model).
To define a foreign key as I know, I have only reference the field like explained in this text :
public class Book
{
public int Id { get; set; }
[Required]
public string Title { get; set; }
public int Year { get; set; }
public decimal Price { get; set; }
public string Genre { get; set; }
// Foreign Key
public int AuthorId { get; set; }
// Navigation property
public Author Author { get; set; }
}
But for me this approach is not working and I need use a code like this :
[ForeignKey("MyFkName")]
public virtual ForeignKeyTable ForeignKeyProperty { get; set; }
public int? MyFkName{ get; set; }
What I'm doing wrong please ?
The error is that you forgot to declare your Author property virtual;
// a Book belongs to exactly one Author using Foreign Key:
public int AuthorId {get; set;}
public virtual Author Author {get; set;}
Furthermore your Author should have a reference to the Books it has:
// Every Author has zero or more Books:
public ICollection<Book> Books {get; set;}
This is all that is needed to inform entity framework that you are modelling a one-to-many relationship
That your Author property should be declared virtual makes sense. After all, your Book doesn't have the Author data readily available as data.
When addressing one of the properties in Book.Author, entity framework has to create a join query instead of returning data.
Hence the Author in the Author property isn't a real Author, but an object derived from Author that knows how to get the Author data of the Book from the database.
public class Team
{
public Team()
{
TeamSchemes = new HashSet<Scheme>();
TeamUsers = new HashSet<PLUser>();
}
public int ID { get; set; }
public string Name { get; set; }
[ForeignKey("Office")]
public int OfficeID { get; set;}
public virtual Office Office { get; set; }
[ForeignKey("TeamLeader")]
public int TeamLeaderID { get; set; }
public virtual PLUser TeamLeader { get; set; }
public virtual ICollection<Scheme> TeamSchemes { get; set; }
public virtual ICollection<PLUser> TeamUsers {get;set;}
}
I have a team object and a user object.
The relationships i want are:
A Team has a TeamLeader (User)
A Team has many Users which can be in that team
here is what i have in my User object for these relationships
[ForeignKey("Team")]
public int? TeamID { get; set; }
public virtual Team Team { get; set; }
public virtual ICollection<Team> TeamsLeading { get; set; }
however when running codeFirst migrations i was getting an extra column called Team_ID from somewhere
i explicitly stated my relationships in modelbuilder like so:
modelBuilder.Entity<Team>().HasRequired(x => x.TeamLeader).WithMany(u=>u.TeamsLeading).HasForeignKey(t=>t.TeamLeaderID);
modelBuilder.Entity<PLUser>().HasOptional(x => x.Team).WithMany(t=>t.TeamUsers).HasForeignKey(x => x.TeamID);
modelBuilder.Entity<PLUser>().HasMany(u => u.TeamsLeading).WithRequired(t => t.TeamLeader);
The migration code ran succesfully and seem to show the intended outcome. However when i run the application i get the following error and the app won't run:
System.Data.SqlClient.SqlException: Invalid column name 'TeamID'.
Any help on the model relationship / fixing issue
You are correct in your comment that EF can't determine the relationships. One way to do it with annotations is with InverseProperty. Try:
[InverseProperty("Team")]
public virtual ICollection<PLUser> TeamUsers {get;set;}
and
[InverseProperty("TeamLeader")]
public virtual ICollection<Team> TeamsLeading { get; set; }
EDIT: You may have to play with it (been a while since I did it), but you may want to go something like this:
[InverseProperty("TeamsLeading")]
public virtual PLUser TeamLeader { get; set; }
public virtual ICollection<Scheme> TeamSchemes { get; set; }
[InverseProperty("Team")]
public virtual ICollection<PLUser> TeamUsers {get;set;}
The persistent attribute ForeignKey usage is wrong here. You are applying it to the primitive value itself.
The correct usage is to apply it to navigation properties, to indicate what primitive property stores its FK value.
In your case it is not required because EF will resolve it by convention:
public class PLUser{
public int? TeamID { get; set; }
public virtual Team Team { get; set; }
}
When EF finds Team navigation property, it will try to find within PLUser a primitive property named TeamID or TeamId, with the same type as the Team class PK, to use it as ForeignKey.
I have one to one relationship with foreign keys but the Cascade Delete is not enabled for some reason. The sample code is below.
public class AppRegistration
{
public int AppRegistrationId { get; set; }
[Required]
[StringLength(50)]
[Display(Name = "Username")]
public string UserName { get; set; }
[Required]
[StringLength(100)]
public string Password { get; set; }
[StringLength(20)]
public string StudentOrAgent { get; set; }
// navigation properties
public virtual AppStatus AppStatus { get; set; }
public virtual Agreement Agreement { get; set; }
public virtual AnotherTable AnotherTable { get; set; }
}
The dependent table with a foreign key is below.
public class Agreement
{
[Key]
[ForeignKey("AppRegistration")]
public int AppRegistrationId { get; set; }
public DateTime DateAgreed { get; set; }
public virtual AppRegistration AppRegistration { get; set; }
}
When I try to delete an entry from the generated AppRegistrations table I get a Reference constraint conflict.
I tried putting [Required] on the navigation property in the dependent table but it doesn't do anything - the Update-Database command shows the No pending code-based migrations. message. Any ideas? Thanks.
Update:
I'm getting the following error message:
The DELETE statement conflicted with the REFERENCE constraint "FK_dbo.AppStatus_dbo.AppRegistrations_AppRegistrationId". The conflict occurred in database "MVCapp", table "dbo.AppStatus", column 'AppRegistrationId'.
I decided to work out the cascade delete problem in a separate sample project. I found the following blog & MSDN pages very useful.
http://blog.bennymichielsen.be/2011/06/02/entity-framework-4-1-one-to-one-mapping/
http://msdn.microsoft.com/en-us/library/gg671256%28v=VS.103%29.aspx
http://msdn.microsoft.com/en-us/library/gg671273%28v=VS.103%29.aspx
Using the Code First approach create the following Model.
public class Category
{
public int CategoryId { get; set; }
public string CategoryName { get; set; }
public virtual Book Book { get; set; }
}
public class Book
{
public int CategoryId { get; set; }
public string BookTitle { get; set; }
public string BookAuthor { get; set; }
public string BookISBN { get; set; }
public virtual Category Category { get; set; }
}
(I realize the entity names suggest one-to-many relationship, but I am trying to model 1-to-1 relationship, as in my original question at the top.)
So, in the above model each Category can only have one Book.
In your DbContext-derived class add the following.
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
modelBuilder.Entity<Book>()
.HasKey(t => t.CategoryId);
modelBuilder.Entity<Category>()
.HasRequired(t => t.Book)
.WithRequiredPrincipal(t => t.Category)
.WillCascadeOnDelete(true);
}
(The following namespaces are required for the above code: System.Data.Entity, System.Data.Entity.ModelConfiguration.Conventions.)
This properly creates the 1-to-1 relationship. You'll have a primary key in each table and also a foreign key in Book table with ON DELETE CASCADE enabled.
In the above code, on the Category entity I used WithRequiredPrincipal() with t => t.Category argument, where the argument is the foreign key column in the dependent table.
If you use WithRequiredPrincipal() without an argument you'll get an extra column in the Book table and you'll have two foreign keys in the Book table pointing to CategoryId in Category table.
I hope this info helps.
UPDATE
Later on I found answer directly here:
http://msdn.microsoft.com/en-us/data/jj591620#RequiredToRequired
A reason why you're not getting cascading delete is because your relationship is optional.
If you want the relationship required i.e. an AppRegistration has to have one Agreement you can use (cascading delete configured automatically):
public class Agreement
{
...
[Required]
public AppRegistration AppRegistration{ get; set; }
}
If you want the relationship to be optional with cascading delete you can configure this using Fluent API:
modelBuilder.Entity<AppRegistration>()
.HasOptional(a => a.Agreement)
.WithOptionalDependent()
.WillCascadeOnDelete(true);
I have a User and an Organization class. They look like this
public class User
{
public int UserId { get; set; }
public string UserName { get; set; }
public string Email { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public virtual ICollection<Organization> Organizations { get; set; }
}
public class Organization : EntityBase
{
public string Name { get; set; }
public string Description { get; set; }
public virtual ICollection<User> Users { get; set; }
}
And both inherit from an EntityBase class to get common fields like Id and created/updated tracking.
public abstract class EntityBase
{
public int Id { get; set; }
public DateTime Created { get; set; }
public virtual User CreatedBy { get; set; }
public DateTime Updated { get; set; }
public virtual User UpdatedBy { get; set; }
}
As denoted by the ICollection properties on both, there should be a many-to-many relation. However when my database is autogenerated I get incorrect foreign keys added to my tables
If I change the CreatedBy and UpdatedBy to be strings instead of User properties I get a join table, which is what I was looking for.
Is this a matter of Entity Framework simply being confused and I need to supply many-to-many configuration in the using fluent mappings, or have I done something wrong?
If you have multiple relationships you need to configure them manually by fluent API or using attributes,
Note:If you have multiple relationships between the same types (for
example, suppose you define the Person and Book classes, where the
Person class contains the ReviewedBooks and AuthoredBooks navigation
properties and the Book class contains the Author and Reviewer
navigation properties) you need to manually configure the
relationships by using Data Annotations or the fluent API
Here is the article from Microsoft.