I have a less than ideal data model that is something like this (a country can have no or exactly one central bank):
Table COUNTRY:
COUNTRY_ID: Guid
Table CENTRAL_BANK:
CENTRAL_BANK_ID: Guid
COUNTRY_ID: Guid
Of course it would be better if we head a CENTRAL_BANK_ID in the COUNTRY table, then it would probably work as intended.
But now we get something like:
class Country
{
public Guid CountryId { get; set; }
public virtual ICollection<CentralBank> CentralBanks { get; set; }
}
But what we want is of course:
class Country
{
public Guid CountryId { get; set; }
public virtual CentralBank? CentralBank { get; set; }
}
Is there some way to tell the EF Core Power Tools that the relationship is really 1:0..1 and not 1:N?
Related
In the database I have two tables, one student and another student address. They have a one-to-one relationship (1: 1).
When I use ado.net, with EF Designer From DataBase, visual studio understands relationship as one for many (1: n).
Entity student, code:
public partial class student
{
public student()
{
this.studentadress = new HashSet<studentadress>();
}
public int Id { get; set; }
public string Name { get; set; }
public string Age { get; set; }
public virtual ICollection<studentadress> studentadress { get; set; }
}
How do I make him understand, and maintain the relationship of (1: 1). And without it creating a collection attribute in the entity, but an object attribute.
I am a newbie to POCO.I have two tables like tb1 and tb2.Suppose we have a PK and FK relation between these tables.When it come to POCO CF how can we manage this relations?I have a done a sample by following a article.
public abstract class Person
{
public string Name { get; set; }
public int DepartmentId { get; set; }
public virtual Department Department { get; set; }
}
public class Collaborator : Person
{
public int CollaboratorId { get; set; }
public string ManagerCode { get; set; }
public virtual Manager Manager { get; set; }
}
Why they have used the abstract and virtual keywords? Can any one explain me the how can we manage the relations?
I assume you are using a model-first approach. You will want to use the Fluent API to define the relationships. Here is a good article on how to do this.
Good day guys,
I've got quite a specific data model that I'm trying to create in POCO classes, and I've tried so many different approaches and visited so many websites, but none seem to cover my specific example.
So I'm going to throw this out there and hope someone can help me.
I've got products, and products have ingredients. In our business though, these products can get supplied by different vendors, each with a slightly different set of ingredients.
So I've got my base classes:
public class Product
{
public int ProductID { get; set; }
public string ProductNumber { get; set; }
public string Description { get; set; }
public virtual ICollection<Supplier> Suppliers { get; set; }
}
public class Vendor
{
public int VendorID { get; set; }
public string Name { get; set; }
public virtual ICollection<Supplier> Suppliers { get; set; }
}
public class Ingredient
{
public int IngredientID { get; set; }
public string Name { get; set; }
}
public class Supplier
{
public int SupplierID { get; set; }
public virtual ICollection<Product> Products { get; set; }
public virtual ICollection<Vendor> Vendors { get; set; }
}
So as you can see, I've gotten as far as realising that my model needs a join entity, because my ingredients come from a specific vendor for a product, I need that join entity called supplier (I think).
This is where I am getting stuck... My product can be supplied by one or more vendors. Each vendor, per product, will have a list of ingredients for that product
I can't even get past whether I need the join entity or not.
What would be awesome was if I could navigate the data structure like this (or something similar):
articles[1].Vendors[3].Ingredients;
Yet again, I don't know enough about Entity Framework to know if this is possible.
The way I'm doing it now feels... wrong. What is the correct way to be doing what I want to do? Do I need the join table or can I somehow navigate the ingredients for a vendor for a product, maybe using the modelbuilder to make the product->vendor->ingredient link required?
Any help would be greatly appreciated!
Edit:
I also think I don't understand enough about Entity Framework's relationship ideas.
So one product can have multiple vendors, which is a 1-to-many relationship. But a Vendor can have many products. So is this actually a many-to-many?
I can definitely model what I want to do on a SQL Express server, but I really want to use Entity Framework. I just need a better understanding of my modelling requirements.
It is not problem of EF. It is common entity-relationship task. You must simply improve your model. You can for example divide Product into two entities: ProductDefinition, ProductInstance
public class ProductDefinition
{
public int ProductID { get; set; }
public string ProductNumber { get; set; }
public string Description { get; set; }
public virtual ICollection<ProductInstance> Instances { get; set; }
}
public class ProductInstance
{
public int ProductInstanceID { get; set; }
public virtual Supplier Supplier { get; set; }
public virtual ProductDefinition Definition { get; set; }
public vritual ICollection<Ingredient> Ingredients { get; set; }
}
In your system you will work with ProductDefinition instead of original Product. This definition is like group of same products and it points to all possible manufacturings of products provided by different suppliers with different ingredients.
I don't know your context but it seems strange to count products with different ingredients as "same".
Why do you use the code first, instead of making the design of the database first? Maybe this will be a bit easier. Additionally i cant see the relation between Vendor and Ingredient, or Product and Ingredient
For my understanding:
It's a new product, when a vendor uses other ingredients?
Hello everybody again,
I need some help in this logic for EF 4.1
I have one table with data for a customer. I have also another table with a survey i need to compile when needed.
So initally i could insert a new customer and after some days I'll fill the survey form. Then the relationship MUST be one-to-one and optional (just because this survey could never be compiled for a customer).
I digged in some examples online but i'm really stuck.
Thank you in advance.
Simply define your entities like:
public class Customer
{
public int Id { get; set; }
...
public virtual Survey Survey { get; set; }
}
public class Survey
{
[Key, ForeignKey("Customer")]
public int Id { get; set; }
public virtual Customer Customer { get; set; }
}
If you don't like data annotations remove them and place this into OnModelCreating in your context:
modelBuilder.Entity<Customer>()
.HasOptional(c => c.Survey)
.WithRequired(s => s.Customer);
I am trying to practice the model first approach and I am putting together a domain model. My requirement is pretty simple: UserSession can have multiple ShoppingCartItems.
I should start off by saying that I am going to apply the domain model interfaces to Linq2Sql generated entities (using partial classes). My requirement translates into three database tables (UserSession, Product, ShoppingCartItem where ProductId and UserSessionId are foreign keys in the ShoppingCartItem table). Linq2Sql generates these entities for me. I know I shouldn't even be dealing with the database at this point but I think it is important to mention.
The aggregate root is UserSession as a ShoppingCartItem can not exist without a UserSession but I am unclear on the rest. What about Product? It is defiently an entity but should it be associated to ShoppingCartItem?
Here are a few suggestion (they might all be incorrect implementations):
public interface IUserSession {
public Guid Id { get; set; }
public IList<IShoppingCartItem> ShoppingCartItems{ get; set; }
}
public interface IShoppingCartItem {
public Guid UserSessionId { get; set; }
public int ProductId { get; set; }
}
Another one would be:
public interface IUserSession {
public Guid Id { get; set; }
public IList<IShoppingCartItem> ShoppingCartItems{ get; set; }
}
public interface IShoppingCartItem {
public Guid UserSessionId { get; set; }
public IProduct Product { get; set; }
}
A third one is:
public interface IUserSession {
public Guid Id { get; set; }
public IList<IShoppingCartItemColletion> ShoppingCartItems{ get; set; }
}
public interface IShoppingCartItemColletion {
public IUserSession UserSession { get; set; }
public IProduct Product { get; set; }
}
public interface IProduct {
public int ProductId { get; set; }
}
I have a feeling my mind is too tightly coupled with database models and tables which is making this hard to grasp. Anyone care to decouple?
Looks like you are on the right track. Half of the whole "doing DDD right" is having the right base classes. Have a look at this great DDD applied to C# resource:
http://dddpds.codeplex.com/
The source code is available and is very readable.
So, with regards to having ID in the model. The ID is a database thing and the usual approach is to keep all persistence out of the Model and restrict the model to the business logic. However, one normally makes an exception for the identifier and buries it in the Model base class like so:
public class ModelBase {
protected readonly object m_Key;
public ModelBase(object key) {
m_Key = key;
}
}
This key is used by your persistence layer to talk to the database and is opaque. It's considered quite OK to downcast the key to the required type, because you know what it is.
Also, the Domain Objects are pretty much on the bottom of your architecture stack (just above the Infrastructure layer). This means that you can make them concrete classes. You will not have multiple implementations of the domain models, so the interfaces are unnecessary, which is what Domain Driven Design is about - Domain first.
public Class UserSession : ModelBase {
public UserSession(Guid Id):base(Id) {}
public Guid Id { get{ return m_Key as Guid;} }
public IList<ShoppingCartItem> ShoppingCartItems{ get; set; }
}
public class ShoppingCartItem : ModelBase {
public ShoppingCartItem ():base(null) {}
public UserSession UserSession { get; set; }
public Product Product { get; set; }
}
Typical shopping cart or customer-order examples prefer making UserSession (or Order) the root of aggregate. Individual items should be children of this session/order. It is up you whether individual items in the cart should have a meaningful id. I would prefer no, since 5 widgets in the cart are indistinguishable from another 5 widgets. Hence, I would model cart items as a collection of value objects.
Common problem with shopping cart items is whether they should include price, or not. if you include price, you will have your cart independent from changes of product price. It is very desirable if you want to store you cart for historical reasons since it is valuable to know how much items in the cart cost according to price when they were bought, not according to current.
Product should form definitively an aggregate by itself. Period.
Now, I don't know if all of this is easily implementable in LINQ to SQL, but you can try.