I have two tables
public class ConcreteParameter
{
public int ParameterId { get; set; }
public Parameter Parameter { get; set; }
public string AnotherId {get; set}
public string Value { get; set; }
}
public class Parameter
{
public int Id{ get; set; }
public string DefaultValue { get; set; }
}
ParameterId from ConcreteParameter is foreign key to Parameter table.
{ParameterId, AnotherId} primary key
In Parameter table lets say I have {Id: 1, DefaultValue = "White"}
In Concrete table 3 lines
ParameterId Value AnotherId
1 Blue 100
1 Red 200
1 Green 300
If I want to include the Parameter navigation property
Entities.Include(p => p.Parameter),
One Entity will have Parameter null and the other 2 will have it loaded, I don't know why.
If I have 10 entities, 9 will load the Parameter navigation property but one will have it null.
If I have 1 record, the navigation property is loaded.
The problem is when the foreign key ParameterId is duplicated.
My configuration:
public void Configure(EntityTypeBuilder<ConcreteParameter > builder)
{
builder.HasKey(p => new { p.AnotherId, p.ParameterId });
builder.HasOne(g => g.Parameter).WithOne().HasForeignKey<Parameter>(g => g.ParameterId);
builder.HasIndex(ug => new { ug.ParameterId }).IsUnique(false);
}
Related
I have a legacy database which has broken all the rules of Codd. Here are the entities
class Item {
[Key]
public int ItemId {get;set;}
public string ItemNo {get;set; }
[ForeignKey("ItemId")]
public virtual NumericItem {get;set;} //navigation
}
class NumericItem { //This is a subset of the Item entity
[ForeignKey("ItemId")]
public Item Item {get; set;}
[Key]
public int ItemNo { get; set; } //this is a primary key, different type
public int ItemId { get; set; } //this is also a primary key and a foreign key
}
How do I tell EF Code first using Fluent API that NumericItem always has a Item and Item may or may not have a NumericItem. The cardinality is always zero/one
This is the case of the foreign unique key.
Normally, when you have a principal entity (like Item) and an optional dependent (NumericItem) in a relationship of 0 or 1, the dependent primary key is also the foreign key for the principal. In your case, since database is already like that, you could do like this:
public class Item
{
public int ItemId { get; set; }
public string ItemNo { get; set; }
public virtual NumericItem NumericItem {get;set;} //navigation
}
public class NumericItem
{ //This is a subset of the Item entity
public Item Item { get; set; }
public int ItemNo { get; set; } //this is a primary key, different type
}
public class NumericItemConfiguration : EntityTypeConfiguration<NumericItem>
{
public NumericItemConfiguration()
{
HasKey(n => n.ItemNo);
HasRequired(n => n.Item).WithOptional(i => i.NumericItem).Map(m => m.MapKey("ItemId"));
}
}
public class MyContextContext : DbContext
{
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
// do your stuff, and add your configuration here...
modelBuilder.Configurations.Add(new NumericItemConfiguration());
}
}
or you can do it without this NumericItemConfiguration class, doing the config directly in your OnModelCreating method:
public class MyContextContext : DbContext
{
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
// do your stuff, and add your configuration here...
modelBuilder.Entity<NumericItem>().HasKey(n => n.ItemNo);
modelBuilder.Entity<NumericItem>().HasRequired(n => n.Item).WithOptional(i => i.NumericItem);
}
}
Take note I had to remove your ItemId property from NumericItem class, otherwise EF would complain like this:
ItemId: Name: Each property name in a type must be unique. Property
name 'ItemId' is already defined.
I am trying to create one-to-many and reverse one-to-one relationship using code first. Here is what I ma trying to do
1) One-to-Many between two classes and it works as expected.
public class X
{
[Key]
public int XId { get; set; }
public ICollection<Y> Y { get; set; }
}
public class Y
{
[Key]
public int YId { get; set; }
public int XId { get; set; }
public X X { get; set; }
}
public class DataContext : DbContext
{
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Y>()
.HasRequired(y => y.X)
.WithMany(x => x.Y)
.HasForeignKey(y => y.XId);
}
}
Now what I want to do is to create Reverse One-to-One optional relationship between Y and X, such that the X will contain a foreign key of Y...How is it possible? Here is what I am trying to do and it throws some Multiplicity Error
public class X
{
[Key]
public int XId { get; set; }
public ICollection<Y> Y { get; set; }
public int YId {get; set; }
[ForiegnKey("YId")]
public Y YOptional { get; set; }
}
public class Y
{
[Key]
public int YId { get; set; }
public int XId { get; set; }
public X X { get; set; }
public X XOptional {get; set; }
}
public class DataContext : DbContext
{
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Y>()
.HasRequired(y => y.X)
.WithMany(x => x.Y)
.HasForeignKey(y => y.XId);
modelBuilder.Entity<X>()
.HasOptional(x => x.YOptional)
.WithOptionalDependent(y=> y.XOptional);
}
}
You can't have a relationship between two entities that is defined differently from either end. So you can't do 1:* from one direction and 1:1 from another.
Let me make a guess that you don't really want it to be 1:1 from the dependent end. From that end it will always only point to one thing.
In mappings, unlike in life, unless you have many to many, a child only has one parent.
You can, however, create a 0..1 : * relationaship (zero or one to many). Where the parent can have one or more children (e.g. "many") but the child can exist without a parent, but it can never have more than one parent (e.g. "zero or one").
Here is the simplest method of making your classes result in a [zero or one] to many relationship. Notice that I made the foreign key in the class Y a nullable int. WIth this setup, EF conventions will result in a mapping that lets a child exist without a parent.
public class X
{
[Key]
public int XId { get; set; }
public ICollection<Y> Y { get; set; }
}
public class Y
{
[Key]
public int YId { get; set; }
public int? XId { get; set; }
public X X { get; set; }
}
public class DataContext : DbContext
{
public DbSet<X> XSet { get; set; }
public DbSet<Y> YSet { get; set; }
}
Here is a screenshot of visual model derived from the above classes and context.
I think this achieves the behavior you are seeking if my guess that you may just be perceiving it differently is correct.
Using the actual class names you mentioned in the comments:
Mapping a User that can have many Singles is not a problem. However, when you want to map a 1:1 association between a User and a Single you have to choose which of the two is the "principle" entity. You can't have a foreign key column in both tables because one entity will always be inserted before the other one. The "dependent" entity is inserted next, and it refers to the principal's primary key value.
So if User is the principal entity, you could have a class model similar to this:
public class User
{
public User()
{
this.Singles = new HashSet<Single>();
}
public int UserId { get; set; }
public string Name { get; set; }
public Single Single { get; set; }
public virtual ICollection<Single> Singles { get; set; }
}
public class Single
{
public int SingleId { get; set; }
public string Name { get; set; }
public virtual User User { get; set; }
public int SuperUserId { get; set; }
public User SuperUser { get; set; }
}
And two options for mappings:
Option 1: User as principal
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<User>().HasMany(u => u.Singles)
.WithRequired(s => s.SuperUser).HasForeignKey(s => s.SuperUserId);
modelBuilder.Entity<User>().HasOptional(s => s.Single)
.WithOptionalPrincipal(s => s.User).Map(m => m.MapKey("UserId"));
}
In the data model, Single now has two foreign keys, UserId and SuperUserId. This is how to create a User and a Single in User.Single and User.Singles:
var superUser = new User { Name = "superUser1" };
var single = new Single { Name = "single" };
superUser.Singles.Add(single);
db.Users.Add(superUser);
superUser.Single = single;
db.SaveChanges();
And EF will first insert the User, then the Single having both foreign keys equal to the User's primary key.
Option 2: Single as principle
You can also make Single the principal entity in the 1:1 association:
modelBuilder.Entity<User>().HasOptional(s => s.Single)
.WithOptionalDependent(s => s.User).Map(m => m.MapKey("SingleId"));
Now there's only one foreign key in Single (SuperUserId) and a foreign key in User (SingleId). If you execute the same code, now EF will throw
Unable to determine a valid ordering for dependent operations.
This is because there is a chicken-and-egg problem: the Single must be created before the dependent User can be created, but the User must be created before the Single can be added to its Singles collection. This could be solved by assigning the Single later:
var superUser = new User { Name = "superUser1" };
var single = new Single { Name = "single" };
superUser.Singles.Add(single);
db.Users.Add(superUser);
db.SaveChanges();
superUser.Single = single;
db.SaveChanges();
You'd want to wrap this in a TransactionScope, so I think this option is less viable.
Note
As you see, in a 1:1 mapping the foreign key can't be mapped to a property in the class model. There is no HasForeignKey in the fluent API after WithOptionalDependent or WithOptionalPrincipal. Also, this association can only be mapped by the fluent API. In data annotations there is not attribute to indicate the principal end of an association.
How can I implement a child that has multiple parents in Entity Framework?
The resulting tables must be as follows:
1.Courses:
CourseID int identity
CourseTitle nvarchar
.
.
.
OtherColumns as neede
2.CoursePreRequisites:
CourseID (FK to Course.CourseID)
PreRequisiteCourseID (FK to Course.CourseID)
or is there any better way to achieve multiple parent for a child record?
You just need two navigation properties in the child class refering to the same parent class and - optionally - two corresponding foreign key properties:
public class Course
{
public int CourseID { get; set; } // PK property
public string CourseTitle { get; set; }
}
public class CoursePreRequisite
{
public int CoursePreRequisiteID { get; set; } // PK property
public int CourseID { get; set; } // FK property 1
public Course Course { get; set; } // Navigation property 1
public int PreRequisiteCourseID { get; set; } // FK property 2
public Course PreRequisiteCourse { get; set; } // Navigation property 2
}
If one or both of the two relationships are optional, use int? instead of int for the foreign key properties.
If you use the property names as indicated in the example above you don't need to configure anything. EF will recognize the two one-to-many relationships by naming conventions.
You can also use collections as inverse properties in the Course entity if you need or want them:
public class Course
{
public int CourseID { get; set; } // PK property
public string CourseTitle { get; set; }
public ICollection<CoursePreRequisite> PreRequisites1 { get; set; }
public ICollection<CoursePreRequisite> PreRequisites2 { get; set; }
}
However, in that case you must specify which navigation property pairs belong together in a relationship. You can do this with data annotations for example:
[InverseProperty("Course")]
public ICollection<CoursePreRequisite> PreRequisites1 { get; set; }
[InverseProperty("PreRequisiteCourse")]
public ICollection<CoursePreRequisite> PreRequisites2 { get; set; }
Or with Fluent API:
modelBuilder.Entity<Course>()
.HasMany(c => c.PreRequisites1)
.WithRequired(p => p.Course) // Or WithOptional
.HasForeignKey(p => p.CourseID);
modelBuilder.Entity<Course>()
.HasMany(c => c.PreRequisites2)
.WithRequired(p => p.PreRequisiteCourse) // Or WithOptional
.HasForeignKey(p => p.PreRequisiteCourseID);
I have built out my models using POCO. When I go to seed my database I get:
Unable to determine the principal end of the 'CSP.Models.Type_Color' relationship. Multiple added entities may have the same primary key
Here's the models in question:
public class Type
{
[Key]
[ScaffoldColumn(false)]
public int TypeId { get; set; }
[Required(ErrorMessage = "A Type Name is Required")]
[Display(Name="Type")]
public string Name { get; set; }
public int ColorId { get; set; }
public bool Other { get; set; }
//Navigations
[ForeignKey("ColorId")]
public virtual Color Color { get; set; }
public virtual List<Tools> tools { get; set; }
}
public class Color
{
[Key]
[ScaffoldColumn(false)]
public int ColorId { get; set; }
[Required(ErrorMessage = "A name is required")]
public string Name { get; set; }
public string Description { get; set; }
//navigation
public virtual List<Type> Types { get; set; }
}
Most of the markup I did after reading suggestions.
My seed code that is getting the error is here:
var colors = new List<Color>
{
new Color{Name="Red"},
new Color{Name="White"}
};
var types = new List<Type>
{
new Type{ Name="Hammer", Color = colors.Where(ws => ws.Name=="Red").Single()},
new Type{ Name= "Electric", Color = colors.Where(ws => ws.Name=="Red").Single()}
};
new List<Tool>
{
new Wine{ Maker= Maker.Single(v => v.Name=="HammerCo"), Type= types.Single(wt => wt.Name=="hammer")},
}
}.ForEach(a => context.Tools.Add(a));
context.SaveChanges();
I also tried adding each value to the context and then saving. I got this error after it tried saving the type entity:
[System.Data.SqlClient.SqlException] = {"The INSERT statement conflicted with the FOREIGN KEY constraint \"Type_Color\". The conflict occurred in database \"TestTools\", table \"dbo.Colors\", column 'ColorId'.\r\nThe statement has been terminated."}
What am I missing?
What is happening is your objects all have the default int value (0) for their primary key. When you add them to the context, EF detects this and throws an error (two objects of the same type cannot have the same key, in this case, 0. I assume your primary key fields in the database are set as IDENTITY columns and will auto increment +1 on insert. This may sound odd, but you need to give your objects placeholder IDs which will be replaced on insert with the IDENTITY values.
new Color{ColorId = 1, Name="Red"},
new Color{ColorId = 2, Name="White"}
new Type{TypeId = 1, Name="Hammer", ...}
new Type(TypeId = 2, Name="Electric", ...}
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);