I am working on a project which involves EF Core.
I would like to use the foreign keys from Category with one single navigation property.
Therefore, Item stores the foreign keys of Category, and the names of the Category can be shown.
This is how the relationship looks like:
Classes:
[Table("Item" , Schema = "public")]
public class Item
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ItemID {get; set;}
public string Name {get; set;}
public int CategoryID {get; set;}
//Single Navigation Property
public Category Category {get; set;}
}
[Table("Category" , Schema = "public")]
public class Category
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int CategoryID {get; set;}
public string Name {get; set;}
}
DbContext:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Item>().ToTable("Item");
modelBuilder.Entity<Category>().ToTable("Category");
modelBuilder.Entity<Item>()
.HasOne(i=>i.Category)
.WithOne()
.HasForeignKey<Item>(i=>i.CategoryID);
}
It shows an error
Duplicate key value violates unique constraint "IX_ItemDB_CategoryID"
Apparently, it means CategoryID cannot be duplicate in Item.
What am I doing wrong here? Thanks!
actually your answer in this article. What you need to do is change the location of the navigation property. So Item should not have an Category property, Category should have a collection of Item for single navigation. the article describes other ways.
In case I understand properly You need one to many relation and I can offer you that structure and if you use Migration your tables will be properly build in the database. No to do anything in the FluentApi to, Your FK, PK(identity) and Indexes will be automatically created
[Table("Item" , Schema = "public")]
public class Item
{
public int Id {get; set;}
public string Name {get; set;}
public int CategoryId {get; set;}
public Category Category {get; set;}
}
[Table("Category" , Schema = "public")]
public class Category
{
public Category()
{
this.Items = new HashSet<Item>();
}
public int Id {get; set;}
public string Name {get; set;}
public virtual ICollection<Item> Items {get; set;}
}
Ivan Stoev is correct. The model of my question is fine and fluent configurations are not required. EFCore will handle the rest.
Related
I am trying to work out how to add a reference an object from within EF.
I little hard to explain so I thought I would share a dotnetfiddle example
https://dotnetfiddle.net/4n5Flk
public class ReportConfig
{
[Key]
public int ReportConfigKey {get; set;}
public int ConfigTypeKey {get; set;}
public int ConfigValue {get; set;}
[ForeignKey("ConfigTypeKey")]
public virtual <ConfigType> ConfigType {get; set;}
}
public class ConfigType
{
[Key]
public int ConfigTypeKey {get; set;}
//This can be
//Address
//Car etc etc.
public string ConfigName {get; set;}
}
public class Car
{
[Key]
public int CarId {get; set;}
//other items
}
public class Address
{
[Key]
public AddressId {get; set;}
}
In a nutshell I am trying to create a navigation property to either a car or an address based on the ConfigValue and the ConfigTypeKey
I was thinking to create 2 navigation properties "Car" and "Address" and for both add 2 foreign key's 1 to the object and 1 as a hardcoded reference to ConfigName as Car or Address
is this possible atall
Sorry for the poor explanation.
I'm using C# and .NET Core with MySql and Entity Framework.
I have an object with a collection of properties. Like this:
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public IEnumerable<Property> Properties { get; set; }
}
public class Property
{
public int Id { get; set; }
public string Name { get; set; }
public object Value { get; set; }
}
In this case in the database, I should have tables Products, Properties (where property is described, like name and some additional info), and link table ProductProperties, storing product Id, property Id and Value.
But I can't figure out how to do this with a code-first approach.
How could I implement it with code first?
Is it a good way to create one more entity PropertyValue and store it under Product?
Something like this should give you a 1-to-many relationship, although you need to give Value a type, like string to store it in the database, often for dynamic solutions like this you would then maybe add a type to specify the type to deserialize into, but since you then deserialize anyway you could also just add things as json or something else in the db.
public class Product
{
public int Id {get; set;}
public string Name{get; set;}
public ICollection<Property> Properties{get; set;}
}
public class Property
{
public int Id {get; set;}
public string Name {get; set;}
public string Value {get; set;}
public int ProductId {get; set;}
}
Unless you are making a very dynamic system, it doesn't seem right to have the properties as a table, depends a lot of what you are making, and maybe key-value db might be a better tool for the job if thats what your main problem is, as with most complicated things, it depends.
This example is a convention based approach, which is why properties like ProductId have to be called exactly that. You can look at EntityTypeConfigurations if you want more control of names and relationships and such, or use data annotations to achieve the same job.
Ok so create a table like this:
public class ProductProprties
{
public int ProductId {get; set;}
public Product Product {get;set;}
public int PropertyId {get; set;}
public Property Property {get;set;}
//other props
}
If you are using EntityFramework Core, then you have to add this to your databse context as well:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<ProdcutProprties>().HasKey(x => new { x.ProductId , x.PropertyId });
}
I have the following construct; a person with an address (ownsone, sub-entity) and an address with a country (hasone, one-to-one)
public class Person
{
public Guid Id {get; set;}
public string Name {get; set;}
public Address Address {get; set;}
}
public class Address
{
public Guid Id {get; set;}
public Guid CountryId {get; set;}
public Country Country {get; set;}
}
public class Country
{
public Guid Id {get; set;}
public string CountryCode {get; set;}
}
public class EntityConfiguration<Person> where Person : class
{
public void Configure(EntityBuilder<Person> builder)
{
builder.OwnsOne(p => p.Address, addressBuilder =>
addressBuilder.HasOne(address => address.Country).WithOne();
}
}
When I run Add-Migration I get a block of code for each entity which owns one address. With auto-generated keys and so on. But I want to specify the relation explicitly with HasForeignKey. How to do this?
EF Core provides 2 fluent APIs for one-to-one relationships - HasForeignKey and HasPrincipalKey.
The main difference with one-to-many APIs is that you need to explicitly provide the generic type argument, because the principal and dependent end of the relationship cannot be determined by the HasOne / WithOne calls (for one-to-many the one is always the principal and many is the dependent). The navigation properties in this case doesn't matter:
addressBuilder.HasOne(address => address.Country)
.WithOne()
.HasForeignKey<Address>(address => address.CountryId)
Reference: Relationships
I have the following models:
public class Order
{
public int Id {get; set;}
public int CustomerId {get; set;}
public virtual Category Category {get; set;}
//Many more properties...
}
public class OrderLine
{
public int Id {get; set;}
public int OrderId {get; set;}
public virtual Order Order {get; set;}
public virtual Product Product {get; set;}
//Other properties...
}
I need to get the orders of a particular customer. In order not to retrieve too many information, I created a class:
public class CustomerOrder
{
public int CustomerId {get; set;}
public int OrderId {get; set;}
public string ProductName {get; set;}
public virtual ICollection<OrderLine> {get; set;}
}
I have mapping configuration for the Order and OrderLine classes but none for CustomerOrder as I was thinking that I can project data into this class.
I can:
Use EF to retrieve the data by specifying includes. After the data is retrieved I can project it into the CustomerOrder class. However, will this force EF to retrieve all columns for the main and included tables?
Use a custom SQL query to retrieve the required details from the Order table (maybe directly from a view). The use Linq to join this resultset with OrderLine to have the complete projection. However, will I need to have mapping configuration for the view?
To avoid too many columns and join in the SQL select statement, what is the best way to project the data into CustomerOrder?
You can do it as shown below.You have to do some changes on your models as well.I have done that.Please see that too.
public class Order
{
public int Id {get; set;}
public int CustomerId {get; set;}
public virtual Category Category {get; set;}
public virtual ICollection <OrderLine> OrderLines {get; set;}
//Many more properties...
}
public class OrderLine
{
public int Id {get; set;}
public int OrderId {get; set;}
public virtual Order Order {get; set;}
public virtual Product Product {get; set;}
//Other properties...
}
public class CustomerOrder
{
public int CustomerId {get; set;}
public int OrderId {get; set;}
public string ProductName {get; set;}
public virtual ICollection<OrderLine> OrderLines {get; set;}
}
Final Query :
var orderList = (from order in _context.Orders
from orderLine in order.OrderLines)
select new CustomerOrder
{
CustomerId = order.CustomerId,
OrderId = orderLine.OrderId,
ProductName= orderLine.Product.ProductName,
OrderLines = order.OrderLines
}).AsNoTracking().ToList();
A 1 : No.Only the projected columns will be fetched from the db.
Best Approach : Always use the custom projection (like CustomerOrder).That is the best when we consider the Performance of the EF query.You can use that to send data to the View too (it's like a DTO (Data Transfer Object)).
How can i add a foreign key to a Model (code first)
i have a model Product which has an ID (primary key) which i want to add to my model order like.
public class Order
{
public int ID {get; set;}
[Required]
public int Total {get; set;}
[Required]
public int ProductId{get; set;}
}
but how can i make the ProductId refer to the id of my Product model like a foreign key?
On Stackoverflow there are alot simmilar questions but all with different answers, but they arent working for me. I really hope someone has a solution or can points me in the right direction with an explanation.
You need to add a navigation property:
public virtual Product Product { get; set; }
So the Order class will look like this:
public class Order
{
public int ID {get; set;}
[Required]
public int Total {get; set;}
[Required]
public int ProductId{get; set;}
[Required]
public virtual Product Product { get; set; }
}
Also, strictly speaking the ProductId property isn't needed once you have the virtual Product property.
You could do something like this:
public class Order
{
public int ID {get; set;}
[Required]
public int Total {get; set;}
[Required]
public int ProductId{get; set;}
[ForeignKey("ProductId")]
public virtual Product Product {get; set;}
}