can we have optional one to many relationship in entity framework
Look at the following classes Department and Person
public class Person
{
public int Id{ get; set; }
public Department Department { get; set; }
public int DepartmentId
}
public class Department
{
public int Id{ get; set; }
public List<Person> Members { get; set; }
}
Person to Department
.HasOptional(m => m.Department)
.WithOptional( d => d.Members)
.HasForeignKey( m=> m.DepartmentId);
and the Result should be like this.
Id Name DepartmentId
1 John x
2 Ahmad y
3 Persony NULL
4 Personz x
as you can see from the above example some person has department and some dont
and the department have a list of persons.
Now this gives me an error. Like this
Multiplicity conflicts with the referential constraint in Role
Because all of the properties in the Dependent Role are non-nullable, multiplicity of the Principal Role must be '1'.
The problem is that your model and configuration does not match. In the fluent API you're configuring the foreign key of the dependent to be optional but in your model the foreign key is required:
In your Person class change:
public int DepartmentId
to
public int? DepartmentId
This way you ensure that the foreign key can actually have the value 'NULL' in the database.
Related
Say I have this existing schema:
and have this domain mapping as follows:
public class SchoolContext : DbContext
{
public DbSet<Person> People { get; set; }
public DbSet<Subject> Subjects { get; set; }
}
protected override OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Person>().ToTable("People");
modelBuilder.Entity<Student>().ToTable("Students");
}
public abstract class Person
{
public int PersonId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
public class Student : Person
{
public int StudentId { get; set; }
public string Course { get; set; }
public ICollection<Subject> Subjects { get; set; }
}
public class Subject
{
public int SubjectId { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public int StudentId { get; set; }
}
And I was given a scenario that I need to query on the subject via PersonId, EF will throw me an exception saying "Invalid column name 'Student_PersonId'".
I understand EF can't see the FK well and I opted to make the Person class as a Base class since there's a chance that I'll have a Teachers table in which it is a Person as well.
Note that Student table need to have its own Primary Key and let's just say the schema was design with a relationship of:
Person -> Student (One-to-Zero or One relationship)
Student -> Subject (One-to-Many relationship)
Is there a way to fix this? Also note that if it's made using Code-First, EF will ommit StudentId on Students table and I do have an existing DB anyway
You should start off by reading this article about TPT in entity framework. Now you don't have a 'Student is a person' kind of relationship, and you'll have to change some things to your database for it to work.
Student's primary key should at the same time be the foreign key to your people table. Since student is a person, it has that database as its baseclass and the Student table should only contain specific properties for student. The properties by Person are inherited.
Person is your abstract base class. Every student, teacher... is a person which is why you can't have a DbSet of Student/teacher... They are persons, so DbSet<Person> is all you need.
You can't map Person to a table. If you really want TPT every person is also a teacher, student... A person alone shouldn't exist, so you shouldn't map it to a table. There's a reason the class is abstract, you can't have just a person. For example Person p = context.Students.FirstOrDefault(); is perfectly valid code for TPT.
That being said, if you think Person can have instances of his own (so certain persons don't have a derived class) you shouldn't opt for TPT and just work with the foreign key to the person table like you do now. If you do want to use TPT you'll have to make above adjustments.
I have two entities which I would like to configure an optional 1-1 relationship (i.e. 0..1 to 0..1). I would like to do this using a key only on one entity, while having navigation properties in both directions.
Consider the following simplified example to illustrate:
public class Person
{
public int PersonId { get; set; }
public int? TicketId { get; set; }
public virtual Ticket Ticket { get; set; }
}
public class Ticket
{
public int TicketId { get; set; }
public virtual Person Person { get; set; }
}
There are a number of People, and a number of Tickets. A person can possess at most one ticket. There are people with no ticket, and unclaimed tickets.
I thought the following might work:
modelBuilder.Entity<Person>()
.HasOptional(p => p.Ticket)
.WithOptionalPrincipal(t => t.Person);
But this creates an additional ID on the Ticket table.
I know this is possible using two optional relationships, but this is not an ideal solution as it requires two calls to SaveChanges, and does not guarantee referential integrity (e.g. Person1 could own Ticket1, but Ticket1 could point to Person2).
Similar questions have usually focussed on a 1-0..1 relationship where the principal entity's primary key can be used on the dependent - this is not suitable either.
I am using EF6 Code-First.
I'm having problems trying to create relationships of 0..1 to 0..1
using code first between AspNetUsers table extending the applicationuser class and MovieModel.
The nature of the relationship is that a user can rent one movie or not and
a movie can be rented to one renter or not. Each entity can stand by itself
and when there is no movie rented or renter the foreign fields are just nulls
My models:
public class MovieModel
{
[Key]
public int MovieId { get; set; }
[Required]
[StringLength(50)]
[Column(TypeName="varchar")]
[Display(Name = "Movie Name")]
public string MovieName { get; set; }
[Display(Name = "Release Year")]
public string RenterId { get; set; }
[ForeignKey("RenterId")]
public virtual ApplicationUser Renter { get; set; }
ApplicationUser Class
public class ApplicationUser : IdentityUser
{
public int? MovieId { get; set; }
[ForeignKey("MovieId")]
public virtual MovieModel Movie{ get; set; }
public async Task<ClaimsIdentity> GenerateUserIdentityAsync(UserManager<ApplicationUser> manager)
{
// Note the authenticationType must match the one defined in CookieAuthenticationOptions.AuthenticationType
var userIdentity = await manager.CreateIdentityAsync(this, DefaultAuthenticationTypes.ApplicationCookie);
// Add custom user claims here
return userIdentity;
}
}
Logically it should work. Got two foreign keys. One foreign key in ApplicationUser class (AspNetUser table) and one foreign key in MovieModel
Somehow I get this error on adding migration:Unable to determine the principal end of an association between the types 'VideoLibrary.Models.ApplicationUser' and 'VideoLibrary.Models.MovieModel'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotation
Why do I get this kind of error? I don't need a principal entity in the relationship. They both can stand alone.
Thanks in advance
EF Code First supports 1:1 and 1:0..1 relationships. Maybe you should try "one to zero-or-one".
I removed the data annotation and created it by the model builder.
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<AllesVersUser>()
.HasOptional<MovieModel>(l => l.Movie)
.WithOptionalDependent(c => c.Renter)
.Map(p => p.MapKey("MovieId"));
base.OnModelCreating(modelBuilder);
}
Tried this in my solution, and I can have movies without a renter, and users without a movie.
I am receiving this error in my migrations:
Person_EventModerator_Target: : Multiplicity is not valid in Role 'Person_EventModerator_Target' in relationship 'Person_EventModerator'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.
Here are my models (note: base entity holds the primary key for all models):
public class EventModerator : BaseEntity
{
......
// foreign keys
public int PersonId { get; set; }
// associations
[ForeignKey("PersonId")]
public Person Person { get; set; }
}
public class Person : BaseEntity
{
public Person()
{
....
// association
public virtual EventModerator EventModerator { get; set; }
}
My Mappings:
modelBuilder.Entity<Person>()
.HasOptional(e => e.EventModerator)
.WithRequired(e => e.Person);
This is a 1 to 0.1 relationship.
Can anyone point out my error please?
OK, this worked, but frankly I do not understand the need for ".WithMany()"
internal static void Map(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<EventModerator>()
.HasRequired(e => e.Person)
.WithMany()
.HasForeignKey(e => e.PersonId)
.WillCascadeOnDelete(false);
}
Your answer will not produce 1 to 0.1 relationship. There is another key generated on Person table in the database, that is nullable EventModerator_Id.
To have 1 to 0.1, the dependent EventModerator primary key must also be the foreign key.
You can either add [Key] attribute on PersonId.
[Key]
public int PersonId { get; set; }
Or since you have BaseEntity which might have derived Id property (which by default convention is a primary key), then you just need to remove the PersonId property and link foreign key to Id property.
//public int PersonId { get; set; }
// associations
[ForeignKey("Id")]
public Person Person { get; set; }
I have two classes
public class Product
{
public Guid Id { get; set; }
public string ProductDetails { get; set; }
}
public class SpecialProductDetails
{
public Guid Product_Id { get; set; } // PK and FK to Product class
public string SpecialName { get; set; }
public string SpecialDescription { get; set; }
public virtual Product Product { get; set; }
}
SpecialProductDetails is mapped 1-1 with Product class and is optional. It shares the same PrimaryKey and ForeignKey.
In Fluent API i am mapping this relationship like this (inside SpecialProductDetails)
public SpecialProductDetails()
{
HasKey(p => p.Product_Id);
HasRequired(p => p.Product).WithMany().HasForeignKey(p => p.Product_Id).WillCascadeDelete(true);
}
This gives me this error when trying to generate the Database
\tSystem.Data.Entity.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'SpecialProductDetails_Product_Source' in relationship 'SpecialProductDetails_Product_Source'. Because the Dependent Role refers to the key properties, the upper bound of the multiplicity of the Dependent Role must be '1'.
How can i have a column set as PK and FK on EF Code First?
I'm quite sure you have already solved that, but I hit the same problem and the solution I found was:
public SpecialProductDetails()
{
HasKey(p => p.Product_Id);
HasRequired(p => p.Product).WithOptional();
}
"it worth noting that when we are mapping a one-to-one association with fluent API, we don't need to specify the foreign key as we would do when mapping a one-to-many association with HasForeignKey method. Since EF only supports one-to-one associations on primary keys, it will automatically create the relationship in the database on the primary keys."
after http://weblogs.asp.net/manavi/associations-in-ef-4-1-code-first-part-3-shared-primary-key-associations