I have a table in the database that has 4 foreign keys referencing to it. When I add the table to the edmx, the table and navigational properties are there. However, the foreign key ids from this table is missing and only the virtual objects are there.
This is the following table that is generated in the .tt file:
public partial class Device
{
public int SolutionId { get; set; }
public string SiteId { get; set; }
public string Name { get; set; }
public int SysId { get; set; }
public Nullable<int> SysType { get; set; }
public string SerialNumber { get; set; }
public Nullable<int> ParentId { get; set; }
public virtual DeviceModel DeviceModel { get; set; }
public virtual DeviceType DeviceType { get; set; }
public virtual SolutionApplication SolutionApplication { get; set; }
public virtual SolutionType SolutionType { get; set; }
}
There are a few members missing:
DeviceModelId, DeviceTypeId, SolutionApplicationId, and SolutionTypeId
Why is it missing? Is there any way to get those keys actually be part of the partial class?
using EntityFrameworks v6.0.2. Lazy Loading
In short, Entity Framework 'abstracts that away'.
Its clever enough to recognise that your FKs represent relationships and so allows you to work with the objects themselves. So instead of having you worry about checking the FK constraint, etc. for, say, SolutionTypeId - you just need to add a SolutionType object to your Device object and let Entity Framework sort it out. (Of course, this causes problems if you try to add a new SolutionType that violates the SolutionType PK so maybe you need to first find an existing object from the SolutionTypes table).
So, instead of thinking of it as a Device table linked to a SolutionType table via a FK - just think of it as a Device object with a SolutionType object as a property. EF sorts out the db for you when you save changes (assuming your model is accurate!)
Related
I've got 2 entities with a 1-0..1 relationship between them, but restrictions on what the generated DB schema can look like.
So 1 Vehicle to 0 or 1 RecVehicle entity
I need to be able to have a navigation property from Vehicle to RecVehicle, but without the DB Schema for the Vehicles table having a FK to RecVehicle. The PK of the RecVehicle table should be the Id of the Vehicle entity it relates to.
We are using EF code first
public class Vehicle
{
[Key]
public int Id { get; set; }
public virtual RecVehicle RecVehicle { get; set; } // Need to be able to use as navigation
}
public class RecVehicle
{
[Key]
public int VehicleId { get; set; }
[ForeignKey("VehicleId")]
public Vehicle Vehicle { get; set; }
}
The generated schema needs to be something like this:
Vehicles
[ Id(int, pk, not null), ...] <-- no FK column to RecVehicles
RecVehicles
[ VehicleId(int, pk, fk, not null), ...]
Originally what I had tried something like this:
public class Vehicle
{
[Key]
public int Id { get; set; }
[InverseProperty("Vehicle")]
public virtual RecVehicle RecVehicle { get; set; } // Need to be able to use as navigation
}
but this causes this exception:
Unable to determine the principal end of an association between the types 'Contract.Entities.Vehicle' and 'Contract.Entities.RecVehicle'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.
I'm not sure what fluent API relationships to setup to make this work, nor the correct set of data annotations to make this work, or if it's even possible.
Reasoning
The reason there is strict limitations on the DB schema is our Data team has a migration/data import process that we can not alter
We have an existing code base that uses the navigation property in many places (2 teams, desync in schema) so changing to use a lookup in code requires many changes in the code base that we are trying to avoid.
The RecVehicle can be connected to multiple Vehicles
Can you try the following navigation property?
public virtual ICollection<RecVehicle> RecVehicle { get; set; }
instead of
public virtual RecVehicle RecVehicle { get; set; }
Due to the RecVehicle primary key this list only maximum contains one element
Ended up being able to get this relationship to work like this:
public class Vehicle
{
[Key]
public int Id { get; set; }
public virtual RecVehicle RecVehicle { get; set; }
}
public class RecVehicle
{
[Key]
public int VehicleId { get; set; }
[ForeignKey("VehicleId"), Required] //<--- Required attr fixed the principal/dependent confusion EF was having
public virtual Vehicle Vehicle { get; set; }
}
As you know that developers mostly mock the relationship between tables instead of using physical relationships between table (yeah, the line drawn from one table to another if you put a foreign key constraint on the column).
But I believe that Entity Framework doesn't work properly if physical relationships aren't there for navigational properties.
So, is there any way around?
My classes:
public class Phones
{
public int ID { get; set; }
public string Model { get; set; }
public string Manufacturer { get; set; }
public List<Users> Users { get; set; }
}
public class Sims
{
public int ID { get; set; }
public string Code { get; set; }
}
This creates a 1-M relationship from User -> Sims.
But what if I drop the foreign key constraint and leave it as it is, how will the navigational properties work then?
At this case better to remove references from both classes and handle relations manually outside of these classes:
public class Sims
{
public int ID { get; set; }
public string Code { get; set; }
//public User User { get; set; }
public int UserID { get; set; }
}
I'm in a situation where one table has two One-None/One Relationships. How do I implement this using Entity Framework Code-First?
I've seen the following links
https://www.safaribooksonline.com/library/view/programming-entity-framework/9781449317867/ch04s07.html
https://cpratt.co/0-1-to-1-relationships-in-entity-framework/
https://www.tektutorialshub.com/one-to-one-relationship-entity-framework/
Where essentially it's said that the dependent end needs to have a primary key that is the same as that of the principal end. But I'm weary of implementing this with more than one One-None/One Relationship without confirmation and proper knowledge of what's going on. Furthermore I am not sure how to construct statements as it does not have a conventional Foreign Key.
I've also seen Configuring multiple 1 to 0..1 relationships between tables entity framework which confused me beyond recognition.
See below for the relevant part of my DB Diagram:
So Essentially, a Player shouldn't be saved without a DKImage, similarly a Product shouldn't be saved without a DKImage.
Below is the code for Models: Players, Products, DKImages (I know it's not correct, I only implemented it this way so I can generate the database and show the diagram)
Player
public enum Positions { PG, SG, SF, PF, C }
public class Player
{
[Key]
[ForeignKey("Images")]
public int PlayerID { get; set; }
[Required]
public string PlayerName { get; set; }
[Required]
public string PlayerLastName { get; set; }
[Required]
public int PlayerAge { get; set; }
[Required]
public Positions Position { get; set; }
[Required]
public bool Starter { get; set; }
[Required]
[Display(Name = "Active / Not Active")]
public bool Status { get; set; }
//Foreign Keys
public int PlayerStatsID { get; set; }
//Navigation Properties
[ForeignKey("PlayerStatsID")]
public virtual IQueryable<PlayerStats> PlayerStats { get; set; }
public virtual DKImages Images { get; set; }
}
DKImages
public class DKImages
{
[Key]
public int ImageID { get; set; }
[Required]
public string ImageURL { get; set; }
[Required]
public DateTime DateUploaded { get; set; }
//Foreign Keys
[Required]
public int CategoryID { get; set; }
//Navigation Properties
public virtual Products Products { get; set; }
public virtual Category Category { get; set; }
public virtual Player Player { get; set; }
}
Products
public class Products
{
[ForeignKey("Images")]
[Key]
public int ProductID { get; set; }
[Required]
public string ProductName { get; set; }
[Required]
public DateTime DateAdded { get; set; }
//Foreign Keys
[Required]
public int ProductTypeID { get; set; }
//Navigation Properties
[ForeignKey("ProductTypeID")]
public virtual ProductType ProductType { get; set; }
public virtual DKImages Images { get; set; }
}
Edit
I have been told that the code above is correct. If so then how do I create CRUD LINQ Statements (Or any method of constructing CRUD statements for that matter) with the above code.
What you want here is referred to as polymorphic associations: several entities having child entities of one type. They're typically used for comments, remarks, files etc. and usually applied to 1:n associations. In your case there are polymorphic 1:1 associations. Basically these associations look like this (using a bit more generic names):
How to implement them?
Entity Framework 6
In EF6 that's problem. EF6 implements 1:1 associations as shared primary keys: the child's primary key is also a foreign key to its parent's primary key. That would mean that there should be two FKs on Image.ID , one pointing to Person.ID and another one pointing to Product.ID. Technically that's not a problem, semantically it is. Two parent entities now own the same image or, stated differently, an image should always belong to two different parents. In real life, that's nonsense.
The solution could be to reverse the references:
But now there's another problem. The entity that's referred to is named the principal, the other entity is dependent. In the second diagram, Image is the principal, so in order to create a Person, its image must be inserted first and then the person copies its primary key. That's counter-intuitive and most likely also impractical. It's impossible if images are optional.
Nevertheless, since in your case you want images to be required let me show how this association is mapped in EF6.
Let's take this simple model:
public class Person
{
public int ID { get; set; }
public string Name { get; set; }
public virtual Image Image { get; set; }
}
public class Product
{
public int ID { get; set; }
public string Name { get; set; }
public virtual Image Image { get; set; }
}
public class Image
{
public int ImgID { get; set; } // Named for distinction
public string Url { get; set; }
}
The required mapping is:
modelBuilder.Entity<Image>().HasKey(pd => pd.ImgID);
modelBuilder.Entity<Person>().HasRequired(p => p.Image).WithRequiredDependent();
modelBuilder.Entity<Product>().HasRequired(p => p.Image).WithRequiredDependent();
As you see, Image has two required dependents. Perhaps that's better than two required parents, but it's still weird. Fortunately, in reality it's not a problem, because EF doesn't validate these associations. You can even insert an image without a "required" dependent. I don't know why EF doesn't validate this, but here it comes in handy. The part WithRequiredDependent might as well have been WithOptional, it doesn't make a difference for the generated data model, but at least this mapping conveys your intentions.
An alternative approach could be inheritance. If Person and Product inherit from one base class this base class could be the principal in a 1:1 association with Image. However, I think this is abusing a design pattern. People and products have nothing in common. From a design perspective there's no reason for them to be part of one inheritance tree.
Therefore, in EF6 I think the most feasible solution is to use the third alternative: separate image tables per entity.
Entity Framework Core
In EF-core 1:1 associations can be implemented the EF6 way, but it's also possible to use a separate foreign key field in the dependent entity. Doing so, the polymorphic case looks like this:
The Image class is different:
public class Image
{
public Image()
{ }
public int ImgID { get; set; }
public int? PersonID { get; set; }
public int? ProductID { get; set; }
public string Url { get; set; }
}
And the mapping:
modelBuilder.Entity<Person>().Property(p => p.ID).UseSqlServerIdentityColumn();
modelBuilder.Entity<Person>()
.HasOne(p => p.Image)
.WithOne()
.HasForeignKey<Image>(p => p.PersonID);
modelBuilder.Entity<Product>().Property(p => p.ID).UseSqlServerIdentityColumn();
modelBuilder.Entity<Product>()
.HasOne(p => p.Image)
.WithOne()
.HasForeignKey<Image>(p => p.ProductID);
modelBuilder.Entity<Image>().HasKey(p => p.ImgID);
Watch the nullable foreign keys. They're necessary because an image belongs to either a Person or a Product. That's one drawback of this design. Another is that you need a new foreign key field for each new entity you want to own images. Normally you want to avoid such sparse columns. There's also an advantage as compared to the EF6 implementation: this model allows bidirectional navigation. Image may be extended with Person and Product navigation properties.
EF does a pretty good job translating this into a database design. Each foreign key has a filtered unique index, for example for Person:
CREATE UNIQUE NONCLUSTERED INDEX [IX_Image_PersonID] ON [dbo].[Image]
(
[PersonID] ASC
)
WHERE ([PersonID] IS NOT NULL)
This turns the association into a genuine 1:1 association on the database side. Without the unique index it would be a 1:n association from the database's perspective.
An exemple in your Player table would be this :
public class Player
{
// All the rest you already coded
[Required]
public int ImageID
[ForeignKey("ImageID")]
public virtual DKImage DKImage {get;set;}
}
This would force a player to have a DKImage, but as said in the comments, this create a one to many relationship.
Another way out would be to put all Player fields into the DKImage table, those fields would be null if there is no player associated to this DKImage.
Edit for 1 to 1..0
Ivan Stoev's link got some pretty interesting insight on how to accomplish this :
https://weblogs.asp.net/manavi/associations-in-ef-4-1-code-first-part-3-shared-primary-key-associations
It seems like you will have to put a bit more code in your class :
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<DKImage>().HasOptional(t => t.Player).WithRequired();
}
If the tutorial is correct, this would read as :
"DKImage entity has an optional association with one Player object but this association is required for Player entity".
I have not tested it yet.
Suppose that I need to have two tables named Wagons and WagonTypes. Obviously enough, each row in the Wagons table should reference to the correspoding WagonTypes record via foreign key.
Am I doing this right?
public class Wagons
{
public Guid Id { get; set; }
[Required]
public WagonTypes Type { get; set; }
}
public class WagonTypes
{
public Guid Id { get; set; }
[Required]
public string Name { get; set; }
}
Yeah, it works and all that but I don't unserstand why there's an additional field in the docs then:
public int BlogId { get; set; }
public Blog Blog { get; set; }
What's the point of having a BlogId field? Should I define it too?
You don't have to add the foreign key, but it's recommended because it makes your life easier.
Imagine you want to edit some row in table Wagons (for example property Name). You have to get the object, edit Name, then load property Type and then call SaveChanges. If you didn't load Type, EF would think you want to edit that Type too.
If you had public int TypeId{ get; set; } in your Wagons class, you could just get that object, directly edit Name and call SaveChanges without any further loading.
I'm working on generating code (models) from my database. I'm not sure how to, if possible, setup my database to create a relationship including cardinality. Is this something that can be done, or am I stuck with simply generating models that match a table without relationships or cardinality because I did a data-first design?
Oh, and in case I'm using the incorrect term, cardinality is the type of relationship (one-to-one, one-to-many, many-to-many). That way my models will generate with a reference to another model, or to an ICollection<T> of models.
For example:
public class OrderInformation
{
public virtual int OrderId { get; set; }
public virtual DateTime OrderDate { get; set; }
public virtual BillingInformation BillingInfo { get; set; }
public virtual Address DeliveryAddress { get; set; }
public virtual ICollection<ItemInformation> ShoppingCart { get; set; }
}