I am trying to create a zero to one relationship with code first entity framework. With the sample code below, I am getting error message:
Unable to determine the principal end of an association between the types 'CompanyView' and 'MemberView'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.
With this error, I have tried added in a configuration to fix this.
modelBuilder.Entity<CompanyView>().HasOptional(x => x.MemberView).WithOptionalPrincipal(x => x.CompanyView);
Which ended up with another error message.
CompanyView_MemberView_Target: : Multiplicity is not valid in Role 'CompanyView_MemberView_Target' in relationship 'CompanyView_MemberView'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.
Anyone have any idea on what is going one here?
Thanks.
public class CompanyView
{
[Key]
public Guid Id { get; private set; }
public Guid? MemberId { get; private set; }
[ForeignKey("MemberId")]
public MemberView MemberView { get; private set; }
}
public class MemberView
{
[Key]
public Guid Id { get; private set; }
public Guid? CompanyId { get; private set; }
[ForeignKey("CompanyId")]
public CompanyView CompanyView { get; private set; }
}
The end result I would expected is as below:
A MemberView can have 0 or 1 CompanyView, each CompanyView can have 0 to 1 MemberView.
Relationship as you specified is unusual (one or zero at both directions). You try to create foreign keys at both tables, as the result you have insoluble loop. You can easily create relation one or zero in case when one entity is principal and one is dependent. You can try to simulate desired relation via many to many relationship. Also you can to not annotate fields with foreign key attributes, as the result you will not have some benefits, but you will be able to flexible manipulate relationships manually on your own. At the end, I demonstrate relation where, for example, MemberView is dependent table:
public class CompanyView
{
[Key]
public Guid Id { get; private set; }
public MemberView MemberView { get; private set; }
}
public class MemberView
{
[Key, ForeignKey("CompanyView")]
public Guid CompanyId { get; private set; }
public CompanyView CompanyView { get; private set; }
}
Related
I am creating a web api that needs to return details about vehicles. The first part works fine, just returning data from my vehicles table. Now I have another table which may or may not contain additional data about vehicles in the first table. So when I get vehicle data, I want all of the vehicle data, and any additional data from the second table if it exists, like a left join in SQL.
Here are my classes (very much abridged for readability):
public class Vehicle
{
[Key]
[Required]
public string registrationNo { get; set; }
public string capacity{ get; set; }
public string maxGross{ get; set; }
}
public class VehicleDvlaDetail
{
[ForeignKey("Vehicle")]
public string? registrationNumber { get; set; }
public int? co2Emissions { get; set; }
}
And in my context class OnModelCreating I have (again, very abridged):
modelBuilder.Entity<Vehicle>(entity =>
{
entity.HasOne(dvlaRec => dvlaRec.dvlaDetail).WithMany().HasForeignKey(dvla => dvla.registrationNo);
});
This works fine when there is an associated record in the DVLA table, but that isn't always the case. I need to keep them as separate entities as my API will be required to return details from the DVLA table separately as well. Is there any way to create an optional foreign key, as clearly, what I am doing is wrong.
Friendly advice:
Primary key as a string is not a good practice because of performance issues when data table has lots of data in it.
It would be better if you create your model like this:
public class Vehicle
{
public long Id { get; set; }
public string RegistrationNo { get; set; }
public string Capacity { get; set; }
public string MaxGross { get; set; }
public List<VehicleDvlaDetail> VehicleDvlaDetails { get; set; }
}
public class VehicleDvlaDetail
{
public long? VehicleId { get; set; }
public int? Co2Emissions { get; set; }
public Vehicle Vehicle { get; set; }
}
Vehicle and VehicleDvlaDetail are now connected without additional code in OnModelCreating method and it is possible to fetch vehicles with details like this (this is assuming you have named properties in dbcontext Vehicles and VehicleDvlaDetails):
_dbContext.Vehicles.Include(x => x.VehicleDvlaDetails).ToList();
Also as foreign key VehicleId is nullable - this allows for vehicles not to have any dvla details.
Wow. I spent about 3 hours looking for the answer, just posted the question and came across this:
Create an optional foreign key using the fluid-API for Entity Framework 7
So simple...
I have complex type for Audit fields
My complex type:
[ComplexType]
public class AuditData {
[Column("CreatorUserId")]
public int? CreatorUserId { get; set; }
public DateTime? CreationTime { get; set; }
[Column("ModifierUserId")]
public int? ModifierUserId { get; set; }
public DateTime? ModificationTime { get; set; }
}
My base Entity (all other inherti this one) has AuditData property:
public abstract class Entity : IEntity, IAuditedEntity, INotifiedDbContextBeforeSave
{
// Summary:
// Unique identifier for this entity.
public int Id { get; set; }
public bool IsActive { get; set; }
public int Old_Id { get; set; }
public string Old_TableName { get; set; }
[Timestamp]
public byte[] RowVersion { get; set; }
public AuditData AuditData { get; set; }
// can this 2 lines below work as navigation property with foreign key in complex type
public virtual User CreatorUser { get; set; }
public virtual User ModifierUser { get; set; }
//... other fields
}
I have 2 navigation properties CreatorUser and ModifierUser.
I know you cant have navigation property in ComplexType but can my navigation property on entity be mapped with foreign key in complexType
something like:
[ForeignKey("CreatorUserId")] // --> should point to AuditData.CreatorUserId
public virtual User CreatorUser { get; set; }
becouse CreatorUserId will be property in every entity but EF is not aware of it.
Mybe there is solution in fluent API ?
The official documentation says:
Complex types are non-scalar properties of entity types that enable scalar properties to be organized within entities. Like entities, complex types consist of scalar properties or other complex type properties. Because complex types do not have keys, complex type objects cannot be managed by the Entity Framework apart from the parent object.
It follows that that complex types can not participate in any relations among entities, so they can't contain foreign keys
I have a SalesOrder table which inherits from a SalesDocument table using Table Per Type Inheritance
The ( simplified) table classes are;
[Table("SalesDocumentHeaders")]
public abstract class SalesDocumentHeader
{
[ForeignKey("CreatedByUserId")]
public virtual User CreatedBy { get; set; }
[Required]
public int CreatedByUserId { get; set; }
[Required]
public virtual DateTime? DocumentDate { get; set; }
[Required]
public String ReferenceNumber { get; set; }
}
[Table("SalesOrders")]
public class SalesOrder : SalesDocumentHeader
{
[Required]
public String CustomerOrderNumber { get; set; }
public DateTime? DeliverBy { get; set; }
public virtual SortableBindingList<SalesOrderLine> Lines { get; set; }
}
The context contains
public DbSet<SalesOrder> SalesOrders { get; set; }
public DbSet<SalesDocumentHeader> SalesDocumentHeaders { get; set; }
It doesn't strictly need the SalesOrders DBSet, since SalesOrder inherits from SalesDocumentHeader however I find it convenient.
It seems to work OK, but I am worried that there are 2 ways of reaching the same record , am I doing something wrong?
Usually you only need to keep the DBSet for the base table. This helps when you have multiple derived tables (call them A and B) and you need to decide the actual type dynamically.
For example if you have another entity which references type A or B (like a user can have different types of contact information), you can reference the base table and EF will resolve the correct concrete type at runtime. Though of course this adds some extra casting code.
I am unable to get the one to one relationship with EF to work properly. I've scored blogs, SO, and msdn docs, but nothing I do seems to work.
I have two models, a Class and an Exam that look like the following:
[Table("classes")]
public class Class
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
[StringLength(255), Required]
public string Title { get; set; }
public virtual Exam Exam { get; set; }
}
[Table("exams")]
public class Exam
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
[DisplayFormat(DataFormatString = "{0:h:mm tt}")]
public DateTime? Time { get; set; }
public int ClassId { get; set; }
public virtual Class Class { get; set; }
}
I want to be able to access the exam from the Class and the Class from the Exam, but no matter what I do, I find some error.
Trying to create/run migrations I get the following.
The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.
If I add this to my context:
protected override void OnModelCreating(DbModelBuilder builder)
{
builder.Entity<Exam>()
.HasRequired(e => e.Class)
.WithOptional(c => c.Exam);
}
I get the following error:
System.Data.Entity.Infrastructure.DbUpdateException: Entities in 'BenchContext.Exams' participate in the 'Class_Exam' relationship. 0 related 'Class_Exam_Source' were found. 1 'Class_Exam_Source' is expected. ---> System.Data.UpdateException: Entities in 'BenchContext.Exams' participate in the 'Class_Exam' relationship. 0 related 'Class_Exam_Source' were found. 1 'Class_Exam_Source' is expected.
I'm not sure how to tell the fluent api how to correctly foreign key between the two models and nothing I do seems to affect it.
What am I missing?
You are trying to build one-to-one relation through ClassId property in Exam class. That requires ClassId to be unique (= unique constraint) but unique constraint are not supported by EF yet.
The only way EF currently supports real one-to-one relation is by sharing primary key:
[Table("classes")]
public class Class
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
[StringLength(255), Required]
public string Title { get; set; }
public virtual Exam Exam { get; set; }
}
[Table("exams")]
public class Exam
{
[Key, ForeignKey("Class")]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.None)]
public int Id { get; set; }
[DisplayFormat(DataFormatString = "{0:h:mm tt}")]
public DateTime? Time { get; set; }
public virtual Class Class { get; set; }
}
The Id in Exams table is both PK and FK to Classes table. It cannot have autogenerated value. While this is one-to-one relation it still has 1 - 0..1 multiplicity (Class can exist without Exam but Exam must have Class).
I want to display customer information.
Then I created some classes; Customer, Delivery, Order, OrderLine, Product, and rentalDB.
rentalDB class sets 5 DbSet of Product, Customer, Order, OrderLine, and Delivery.
When I make UserController with list view, I cannot display the customer information, and it takes errors:
One or more validation errors were detected during model generation:
System.Data.Edm.EdmEntityType: : EntityType 'OrderLine' has no key defined. Define the key for this EntityType.
System.Data.Edm.EdmEntityType: : EntityType 'Delivery' has no key defined. Define the key for this EntityType.
System.Data.Edm.EdmEntitySet: EntityType: EntitySet �OrderLine� is based on type �OrderLine� that has no keys defined.
System.Data.Edm.EdmEntitySet: EntityType: EntitySet �Delivery� is based on type �Delivery� that has no keys defined.
I don't know why these entities require key?
I have no idea for this error..
Could you help me?
--UserController.cs--
namespace MvcApplication2.Controllers
{
public class UserController : Controller
{
//
// GET: /User/
rentalDB _db = new rentalDB();
public ActionResult Index()
{
var model = _db.Customer;
return View(model);
}
}
}
--Delivery.cs in Models folder--
namespace MvcApplication2.Models
{
public class Delivery
{
public int trackId { get; set; }
public String address { get; set; }
public String postCode { get; set; }
public decimal deliveryPrice { get; set; }
public DateTime deliveryDate { get; set; }
public DateTime returnDate { get; set; }
}
}
--OrderLine.cs in Models folder--
namespace MvcApplication2.Models
{
public class OrderLine
{
public int basketId { get; set; }
public int productId { get; set; }
public int quantity { get; set; }
}
}
In order to use the entity framework, every entity needs a key. This is how EF tracks objects in its cache, posts updates back to the underlying data store, and links related objects together.
Yours objects already have keys, you just need to tell the EF about them:
namespace MvcApplication2.Models
{
public class Delivery
{
[Key] public int trackId { get; set; }
public String address { get; set; }
public String postCode { get; set; }
public decimal deliveryPrice { get; set; }
public DateTime deliveryDate { get; set; }
public DateTime returnDate { get; set; }
}
}
When you use an ORM (object-relational mapper) framework like NHibernate or Entity framework that helps you map a relational database to an object model you need something that will let you make a meaningful relation between your objects in memory and rows of data in your database and that thing is a key (id as NHibernate call it) and usually that's the natural way that RDBMS track records using a Primary key (usually you use DB primary key as the key of your object)
When you check to see if two objects are equal using == operator you are checking that those objects have the same reference (or address in memory). This kind of equality is not very helpful when you are using an ORM .You can load multiple instances of a record in memory with different references so that it's impossible to check the equality of objects by their references .That's when checking equality by value come into play and keys have the main role in this play.