I created an entity called Student
public class Student
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public string Name { get; set; }
}
When Required attribute is added to Id property, I have to input a value for Id. I want to generate Id property automatically and identity via EF Core.
static void Main(string[] args)
{
var db = new AppDbContext();
db.Add(new Student { Name = "Peter" });
db.SaveChanges();
}
If I add DatabaseGenerated attribute, Does Id become the primary key?
How can I define a primary key that automatically generated and I do not have to set the key value for it?
You can specify the primary key using the [Key] attribute. It can be defined with your identity as:
public class Student
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public string Name { get; set; }
}
Related
I have a problem with Entity Framework.
If I add a Datatable from my DB over my Entity Data Model and this model has 2 Foreign Keys to the same table, the names of this Foreign Keys becomes confusing. Can I make any configurations to set this Foreign Key names beforehand?
I dont want to make any changes after the model is generated.
Here a example from my model
public partial class PERSON
{
public System.Guid ID { get; set; }
public string NAME { get; set; }
public System.Guid TABLE_REGION_FK { get; set; }
public virtual TABLE_REGION TABLE_REGION { get; set; } // -> property name should be TABLE_REGION_PARENT
public virtual TABLE_REGION TABLE_REGION1 { get; set; } // -> property name should be TABLE_REGION_CHIELD
}
Is there an easy way to have a setup like this in EF Core?
ProjectEntity
Id
Name
List<Notes>
CustomerEntity
Id
Name
List<Notes>
NotesEntity
Id
Date
Note
Every parent entity would have a one-to-many relation to same child entity. So I can not use normal behavior as
NotesEntity
Id
ParentId
Date
Note
I have some idea to have like above but also add one field that said what the parent entity is, is that the right way to do it or is there a better way? If I use this way I can't use EF Core normal behavior with one-to-many relationship? I need to make more manual work for search / add and so on?
Edit :
Entity Framework multiple parent tables I found this solution, but there I need to make a connection from my child to every parent I use, it could be alot of them.
Did also find a solution like :
BaseEntity
List<Notes>
ProjectEntity:BaseEntity
NotesEntity
Id
BaseEntityId
...
This last solution maybe is the best way to do it if I have alot of parent entities?
[EDIT 220922]
Could [Owned] type has collection of other Items? Or this feature won't work on owned entitys? I guess this behavior isn't supported?
[Owned]
public class Note
{
public int Id { get; set; }
public string Text { get; set; }
public int UserId { get; set; }
public User User { get; set; }
public ICollection<string> Tags { get; set; }
}
I got an error on ICollection-row when I try to add-migration.
Unabel to determine the relationshop represented by navigation ... of
typ 'ICollection' Either manually configure the relationship, or
ignore this property using the '[NotMapped]' attribute.....
Maybe I could have one middleentity like :
public class NoteTagsEntity
{
public int Id { get; set; }
public ICollection<string> Tags { get; set; }
}
And then :
[Owned]
public class Note
{
public int Id { get; set; }
public string Text { get; set; }
public int UserId { get; set; }
public User User { get; set; }
public int NoteTagsId { get; set; }
public NoteTagsId NoteTagsId { get; set; }
}
Edit
I solved the Note functionality with having more FK's, one that point to Id of parent and one FK Id that point to what module that use that particular note. Here I don't have parent - child relation in my entities, I need to do this connection by myself but in this way it's easy to apply more modules that use note's later.
Use Owned Entity Types, and each entity will get its own notes table.
eg
public abstract class Entity
{
public int Id { get; set; }
}
public abstract class EntityWithNotes: Entity
{
public virtual ICollection<Note> Notes { get; set; }
}
[Owned]
public class Note
{
public int Id { get; set; }
public string Text { get; set; }
}
public class Project : EntityWithNotes
{
public string Name { get; set; }
}
public class Customer : EntityWithNotes
{
public string Name { get; set; }
}
creates
CREATE TABLE [Customer_Notes] (
[Id] int NOT NULL IDENTITY,
[CustomerId] int NOT NULL,
[Text] nvarchar(max) NOT NULL,
CONSTRAINT [PK_Customer_Notes] PRIMARY KEY ([CustomerId], [Id]),
CONSTRAINT [FK_Customer_Notes_Customer_CustomerId] FOREIGN KEY ([CustomerId]) REFERENCES [Customer] ([Id]) ON DELETE CASCADE
);
CREATE TABLE [Project_Notes] (
[Id] int NOT NULL IDENTITY,
[ProjectId] int NOT NULL,
[Text] nvarchar(max) NOT NULL,
CONSTRAINT [PK_Project_Notes] PRIMARY KEY ([ProjectId], [Id]),
CONSTRAINT [FK_Project_Notes_Project_ProjectId] FOREIGN KEY ([ProjectId]) REFERENCES [Project] ([Id]) ON DELETE CASCADE
);
I created a linked table between Users and Tenants called UserTenants.
Now I want to drop the foreign key column: UserId. The problem is that I can't find the model for UserClaim which I can edit. I've tried to create a new one like this:
public class UserClaim : CreationAuditedEntity<long>{
[Key]
public int Id { get; set; }
public const int MaxClaimTypeLength = 256;
public virtual int? TenantId { get; set; }
public virtual long UserId { get; set; }
public virtual User User { get; set; }
[StringLength(256)]
public virtual string ClaimType { get; set; }
public virtual string ClaimValue { get; set; }
public UserClaim() {
}
public UserClaim(AbpUserBase user, Claim claim)
{
TenantId = user.TenantId;
UserId = user.Id;
ClaimType = claim.Type;
ClaimValue = claim.Value;
}
}
But the Error I'm getting is:
System.InvalidOperationException: Cannot use table 'UserClaims' for entity type 'UserClaim' since it is being used for entity type 'UserClaim' and potentially other entity types, but there is no linking relationship. Add a foreign key to 'UserClaim' on the primary key properties and pointing to the primary key on another entity type mapped to 'UserClaims'.
I have a problem with the Entity Framework.
public class User : Receiver
{
public User()
{
if (Groups == null)
Groups = new List<Group>();
if (Buddies == null)
Buddies = new List<User>();
}
[Required]
public string PhoneNumber { get; set; }
[ForeignKey("Guid"), JsonIgnore]
public IList<User> Buddies { get; set; }
[ForeignKey("Guid"), JsonIgnore]
public IList<Group> Groups { get; set; }
}
public class Receiver
{
public Receiver()
{
Guid = Guid.NewGuid();
Created = DateTime.Now;
}
[Key]
public Guid Guid { get; set; }
[Required]
public DateTime Created { get; set; }
}
When i try to add a user...
User user = new User
{
Guid = new Guid("8cd094c9-e4df-494e-b991-5cf5cc03d6e3"),
PhoneNumber = "+4991276460"
};
cmc.Receivers.Add(user);
... it ends in follogwing error.
The object of the Type "System.Collections.Generic.List`1[Project.Models.User]" can't be converted to "Project.Models.User".
When i comment out following two lines:
[ForeignKey("Guid"), JsonIgnore]
public IList<User> Buddies { get; set; }
...the programm runs fine.
I hope someone can help me to fix this problem.
Otherwise it runs into an error at this line : cmc.Receivers.Add(user);
In your mapping...
[ForeignKey("Guid"), JsonIgnore]
public IList<User> Buddies { get; set; }
...you specify that User.Buddies is part of a one-to-many relationship and that User.Guid (=Receiver.Guid) is the foreign key in this relationship. But User.Guid is also the primary key, hence it must be unique. As a result a User cannot have a list of Buddies but only a single reference.
The mapping makes no sense but the exception is not very helpful and difficult to understand. (Somehow EF seems to recognize internally that the Buddies cannot be a list with that mapping and wants to cast the list to a single reference. It should detect in my opinion that the mapping is invalid in the first place.)
For a correct one-to-many mapping you need a foreign key that is different from the primary key. You can achieve that by either removing the [ForeignKey] annotation altogether...
[JsonIgnore]
public IList<User> Buddies { get; set; }
...in which case EF will create a default foreign key in the Receivers table (it will be some column with an underscore in its name, but you can rename that with Fluent API if you don't like the default name) or by adding your own foreign key property to the User class:
public Guid? BuddyGuid { get; set; }
[ForeignKey("BuddyGuid"), JsonIgnore]
public IList<User> Buddies { get; set; }
I am using EF 4.1 code first and I am struggling with the association entity and getting the value that was set in the association table. I tried to follow the post on: Create code first, many to many, with additional fields in association table.
My tables are as follows (all are in plural form):
Table: Products
Id int
Name varchar(50)
Table: Specifications
Id int
Name varchar(50)
Table: ProductSpecifications
ProductId int
SpecificationId int
SpecificationValue varchar(50)
My related classes:
public class Product : IEntity
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<ProductSpecification> ProductSpecifications { get; set; }
}
public class Specification : IEntity
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<ProductSpecification> ProductSpecifications { get; set; }
}
public class ProductSpecification
{
public int ProductId { get; set; }
public virtual Product Product { get; set; }
public int SpecificationId { get; set; }
public virtual Specification Specification { get; set; }
public string SpecificationValue { get; set; }
}
My context class:
public class MyContext : DbContext
{
public DbSet<Product> Products { get; set; }
public DbSet<Specification> Specifications { get; set; }
public DbSet<ProductSpecification> ProductSpecifications { get; set; }
protected override void OnModelCreating(DbModelBuilder dbModelBuilder)
{
}
}
My repository method where I do my call (not sure if it is correct):
public class ProductRepository : IProductRepository
{
MyContext db = new MyContext();
public Product GetById(int id)
{
var product = db.Products
.Where(x => x.Id == id)
.Select(p => new
{
Product = p,
Specifications = p.ProductSpecifications.Select(s => s.Specification)
})
.SingleOrDefault();
return null; // It returns null because I don't know how to return a Product object?
}
}
Here is the error that I am getting back:
One or more validation errors were detected during model generation:
System.Data.Edm.EdmEntityType: : EntityType 'ProductSpecification' has no key defined. Define the key for this EntityType.
System.Data.Edm.EdmEntitySet: EntityType: EntitySet �ProductSpecifications� is based on type �ProductSpecification� that has no keys defined.
What does it mean that no keys are defined? Won't the ProductId and SpecificationId map to Id of Product and Id of Specification respectively?
How would I return a single product with the all the specifications for it?
Entity Framework will recognize that ProductId is a foreign key property for the Product navigation property and SpecificationId is a foreign key property for the Specification navigation property. But the exception complains about a missing primary key ("Key" = "Primary Key") on your ProductSpecification entity. Every entity needs a key property defined. This can happen either by conventions - by a specific naming of the key property - or explicity with data annotations or Fluent API.
Your ProductSpecification class doesn't have a property which EF would recognize as a key by convention: No Id property and no ProductSpecificationId (class name + "Id").
So you must define it explicitely. Defining it with data annotations is shown in the post you linked:
public class ProductSpecification
{
[Key, Column(Order = 0)]
public int ProductId { get; set; }
public virtual Product Product { get; set; }
[Key, Column(Order = 1)]
public int SpecificationId { get; set; }
public virtual Specification Specification { get; set; }
public string SpecificationValue { get; set; }
}
And in Fluent API it would be:
modelBuilder.Entity<ProductSpecification>()
.HasKey(ps => new { ps.ProductId, ps.SpecificationId });
Both ways define a composite key and each of the parts is a foreign key to the Product or Specification table at the same time. (You don't need to define the FK properties explicitely because EF recognizes it due to their convention-friendly names.)
You can return a product including all specifications with eager loading for example:
var product = db.Products
.Include(p => p.ProductSpecifications.Select(ps => ps.Specification))
.SingleOrDefault(x => x.Id == id);