I want to create a referencing / parent-child relationship one-to-zero or one in Entity Framework Core. I mean that my entity could have a parent:
public class MyEntity
{
public Guid Id { get; set; }
public Guid? ParentEntityId { get; set; }
public MyEntity ParentEntity { get; set; }
public MyEntity ChildEntity { get; set; }
}
I am trying to configure it via fluent api:
entity.HasOne(x => x.ParentEntity)
.WithOne(x => x.ChildEntity)
.HasForeignKey( .... )
I do not understand what I do have to write in the last line. I am not either sure my entity is correct.
Can anyone help me please?
EDIT: This question does not resolve my problem: Self referencing / parent-child relationship in Entity Framework
My problem is about create the foreign key. This line does not work:
.HasForeignKey(x => x.ParentEntityId)
HasForeignKey expects a string in input.
In a one-to-one relationship you always have to specify the dependent entity type in the HasForeignKey call, i.e. the entity that will contain the foreign key. For a one-to-one relationship between two different classes that makes sense, see the standard EF example. For a self-reference it looks obvious that EF should figure out there's no option. Still, you have to specify the type:
modelBuilder.Entity<MyEntity>()
.HasOne(x => x.ParentEntity)
.WithOne(x => x.ChildEntity)
.HasForeignKey<MyEntity>(c => c.ParentEntityId);
Related
This question already has an answer here:
What is the correct way to do many to many entity relation insert?
(1 answer)
Closed 11 months ago.
I have a many-to-many relationship established code-first that works, with thousands of fake records generated for an API. Now I'm trying to save a new record on one side of that relationship given only the ids of the other side, as the client is passing in an array of int ids.
I've found plenty of questions with problems and answers about saving many-to-many in general, but none specifically about doing so with just a list of foreign keys. Perhaps I'm simply using the wrong terminology?
I could grab all the records for those ids up front, but it seems very heavy to wait for a database query, assign those entities to the new entity, and then go to the database again to save, when all I really need is to establish a relationship with ids I already have.
For single relationships I would just add the foreign key as a separate property and set that instead of the foreign entity itself:
public int? CarId { get; set; }
[ForeignKey("CarId")]
public CarModel? Car { get; set; }
Is there perhaps a similar paradigm for many-to-many?
Entity setup:
public class ClownModel {
public int Id { get; set; }
public List<CarModel> Cars { get; set; }
}
public class CarModel {
public int Id { get; set; }
public List<ClownModel> Clowns { get; set; }
}
DB Context OnModelCreating:
builder.Entity<ClownModel>()
.HasMany(x => x.Cars)
.WithMan(x => x.Clows);
You can use a "stub entity" to add an existing Car to a new or existing Clown without fetching the Car. Eg
var newClown = new Clown();
var car = new Car() { Id = carId };
db.Entry(car).State = EntityState.Unchanged;
newClown.Cars.Add(car);
db.Set<Clown>().Add(newClown);
db.SaveChanges();
Or include the linking entity in your model, which you can do without adding a DbSet property or changing the Many-to-Many navigation properties.
eg
builder.Entity<Clown>()
.HasMany(x => x.Cars)
.WithMany(x => x.Clowns)
.UsingEntity<ClownCar>(
c => c.HasOne(x => x.Car)
.WithMany()
.HasForeignKey(x => x.CarId),
c => c.HasOne(c => c.Clown)
.WithMany()
.HasForeignKey(c => c.ClownId)
);
then
var newClown = new Clown();
var clownCar = new ClownCar();
clownCar.CarId = carId;
clownCar.Clown = newClown;
db.Set<ClownCar>().Add(clownCar);
db.SaveChanges();
I've always defined my many-to-many relationships like this:
modelBuilder.Entity<PriceList>()
.HasMany(i => i.Brands)
.WithMany(p => p.PriceLists)
.Map(m =>
{
m.ToTable("PriceListsBrands");
m.MapLeftKey("PriceListId");
m.MapRightKey("BrandId");
});
And it has always worked well.
But now that I'm using "Entity Framework Extensions Bulk Insert" (https://entityframework-extensions.net/bulk-insert) I want to bulk insert into PriceListsBrands table.
So I had to create the relationship object per sé...(which I usually don't need because I already have the navigation properties Brands and PriceLists)
public class PriceListBrand
{
public long PriceListId { get; set; }
public virtual PriceList PriceList { get; set; }
public long BrandId { get; set; }
public virtual Brand Brand { get; set; }
public PriceListBrand()
{
}
}
To finally call BulkInsert:
var priceListsBrands = new List<PriceListBrand>();
// Populate
// ...
dbContext.BulkInsert(priceListsBrands);
But then I'm getting this exception:
EntityType 'PriceListBrand' has no key defined. Define the key for this EntityType.
I tried adding the following FluentAPI definition above my previous FluentAPI code:
modelBuilder.Entity<CustomerPriceListBrand>()
.HasKey(e => new { e.PriceListId, e.BrandId })
.ToTable("PriceListsBrands");
But then I'm getting this exception:
The EntitySet 'PriceListBrand1' with schema 'dbo' and table
'PriceListsBrands' was already defined.
(Notice the "1": it is trying to define twice the relationship)
So the question is: how can I both define a "many to many" relationship and a relationship object too?
I'm trying to create a tree structure in the db where items can reference each other. I was considering that to be a simple task, however, EF Core decided to strike. I can't get it to generate the correct foreign keys, it keeps throwing an exception:
Unable to determine the relationship represented by navigation 'Item.Parent' of type 'Item'. Either manually configure the relationship, or ignore this property using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.
My class looks like this (simplified):
public class Item
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid Id { get; set; }
[ForeignKey("Parent")]
public Guid? ParentId { get; set; }
public virtual Item Parent { get; set; }
[InverseProperty("Parent")]
public virtual IEnumerable<Item> Children { get; set; }
}
I have even tried to remove the Children property, but with the same result.
Another thing I have tried was Fluent API:
entity
.HasOne(e => e.Parent)
.WithMany(e => e.Children)
.HasForeignKey(e => e.ParentId);
//or
entity
.HasOne<Item>(e => e.Parent)
.WithMany()
.HasForeignKey(e => e.ParentId);
//or
entity
.HasMany(e => e.Children)
.WithOne(e => e.Parent)
.HasForeignKey(e => e.ParentId);
//or
entity
.HasMany(e => e.Children)
.WithOne(e => e.Parent);
They all keep generating the same error, I'm kind of lost on what am I doing wrong.
I was looking at some other answers too and they look pretty much like what I'm trying to do, however, my EF will not generate the migration.
Disregard this question, I've figured out my own mistake. I will leave it here in case someone faces the same problem as the error message is very misleading.
What has happened was a copy&paste issue where I have created another configuration for an unrelated entity, but forgot to update the type:
{
public void Configure(EntityTypeBuilder<Item> entity)
{
entity
.HasNoKey();
}
}
Notice the Item type in the generics definition. This lead the EF Core to wipe out the key that was originally set on the entity and made EF Core confused about the relationship (as now I'm targeting foreign key to a property that's neither key nor index).
I have two entities:
public class EntityA
{
public int? Id { get; set; }
public string Name { get; set; }
public EntityB { get; set; }
}
public class EntityB
{
public int? Id { get; set; }
public string Version { get; set; }
}
I have existing records for EntityB already in the database. I want to add a new EntityA with reference to one of the EntityB records.
var entityB = _dbContext.EntityB.FirstOrDefault(e => e.Id == 1);
var entityA = new EntityA { Name = "Test", EntityB = entityB };
_dbContext.Add(entityA);
_dbContext.SaveChanges();
When the above code runs I get the following error:
System.InvalidOperationException: The property 'Id' on entity type 'EntityB' is part of a key and so cannot be modified or marked as modified. To change the principal of an existing entity with an identifying foreign key first delete the dependent and invoke 'SaveChanges' then associate the dependent with the new principal.
This seems to me, that the save is trying to also add EntityB, not just a reference to it. I do have the relationship specified in the database as well as in Entity Framework, e.g. when querying for EntityA if I include EntityB in the select, I get the referenced entity as well (so the relationship works).
modelBuilder.Entity<EntityA>(e =>
{
e.HasKey(p => p.Id);
e.HasOne(p => p.EntityB)
.WithOne()
.HasForeignKey<EntityB>(p => p.Id);
}
modelBuilder.Entity<EntityB>(e =>
{
e.HasKey(p => p.Id);
}
How can I save a new EntityA, with only a reference to the selected EntityB, rather than saving both entities?
It looks like you are trying to Extend EntityB with an optional 1:1 reference to a Row n the new table EntityA. You want both records to have the same value for Id.
This 1:1 link is sometimes referred to as Table Splitting.
Logically in your application the record from EntityB and EntityA represent the same business domain object.
If you were simply trying to create a regular 1 : many relationship, then you should remove the HasOne().WithOne() as this creates a 1:1, you would also not try to make the FK back to the Id property.
The following advice only applies to configure 1:1 relationship
you might use Table Splitting for performance reasons (usually middle tier performance) or security reasons. But it also comes up when we need to extend a legacy schema with new metadata and there is code that we cannot control that would have broken if we just added the extra fields to the existing table.
Your setup for this is mostly correct, except that EntityA.Id cannot be nullable, as the primary key it must have a value.
public class EntityA
{
public int Id { get; set; }
public string Name { get; set; }
public EntityB { get; set; }
}
If you want records to exist in EntityA that DO NOT have a corresponding record in EntityB then you need to use another Id column as either the primary key for EntityA or the foreign key to EntityB
You then need to close the gap with the EntityA.Id field by disabling the auto generated behaviour so that it assumes the Id value from EntityB:
modelBuilder.Entity<EntityA>(e =>
{
e.HasKey(p => p.Id).ValueGeneratedNever();
e.HasOne(p => p.EntityB)
.WithOne()
.HasForeignKey<EntityB>(p => p.Id);
}
I would probably go one step further and add the Reciprocating or Inverse navigation property into EntityB this would allow us to use more fluent style assignment, instead of using _dbContext.Add() to add the record to the database:
public class EntityB
{
public int Id { get; set; }
public string Version { get; set; }
public virtual EntityA { get; set; }
}
With config:
modelBuilder.Entity<EntityA>(e =>
{
e.HasKey(p => p.Id).ValueGeneratedNever();
e.HasOne(p => p.EntityB)
.WithOne(p => p.EntityA)
.HasForeignKey<EntityB>(p => p.Id);
}
This allows you to add in a more fluent style:
var entityB = _dbContext.EntityB.FirstOrDefault(e => e.Id == 1);
entityB.EntityA = new EntityA { Name = "Test" };
_dbContext.SaveChanges();
This will trip up because you are using EntityA's PK as the FK to Entity B, which enforces a 1 to 1 direct relation. An example of this would be to have something like an Order and OrderDetails which contains additional details about a specific order. Both would use "OrderId" as their PK and OrderDetails uses it's PK to relate back to its Order.
If instead, EntityB is more like an OrderType reference, you wouldn't use a HasOne / WithOne relationship because that would require Order #1 to only be associated with OrderType #1. If you tried linking OrderType #2 to Order #1, EF would be trying to replace the PK on OrderType, which is illegal.
Typically the relationship between EntityA and EntityB would require an EntityBId column on the EntityA table to serve as the FK. This can be a property in the EntityA entity, or left as a Shadow Property (Recommended where EntityA will have an EntityB navigation property) Using the above example with Order and OrderType, an Order record would have an OrderId (PK) and an OrderTypeId (FK) to the type of order it is associated with.
The mapping for this would be: (Shadow Property)
modelBuilder.Entity<EntityA>(e =>
{
e.HasKey(p => p.Id);
e.HasOne(p => p.EntityB)
.WithMany()
.HasForeignKey("EntityBId");
}
An OrderType can be assigned to many Orders, but we don't have an Orders collection on OrderType. We use the .HasForeignKey("EntityBId") to set up the shadow property of "EntityBId" on our EntityA table. Alternatively, if we declare the EntityBId property on our EntityA:
modelBuilder.Entity<EntityA>(e =>
{
e.HasKey(p => p.Id);
e.HasOne(p => p.EntityB)
.WithMany()
.HasForeignKey(p => p.EntityBId);
}
On a side note, navigation properties should be declared virtual. Even if you don't want to rely on lazy loading (recommended) it helps ensure the EF proxies for change tracking will be fully supported, and lazy loading is generally a better condition to be in at runtime than throwing NullReferenceExceptions.
I am a newbie in the EF. I read http://msdn.microsoft.com/en-us/data/gg193958.aspx and still confused.
I have an existing database and I'm writing a Code First model. I have Operators table with op_code Char(6) Primary Key. In the Operator class I named it OperatorCode, e.g.
[Key]
[Column("op_code",TypeName = "char")]
[DisplayName("Operator")]
public virtual string OperatorCode { get; set; }
In several of my tables I have EnteredBy and in some ModifiedBy columns that are FK to the op_code.
Say, for the Clients table I have both of these fields.
So, I added to the Operator class at the bottom:
[InverseProperty("EnteredBy")]
public virtual ICollection<Client> ClientsEnteredBy { get; set; }
[InverseProperty("ModifiedBy")]
public virtual ICollection<Client> ClientsUpdatedBy { get; set; }
and I added the following into the Client class:
public virtual Operator EnteredBy { get; set; }
public virtual Operator ModifiedBy { get; set; }
and I am getting a run-time error about EnteredBy_OperatorCode and ModifiedBy_OperatorCode columns.
What should I fix /add to let EF know my column names?
Thanks in advance.
Your foreign column names in the database do not match the default convention for FK names which is NavigationPropertyName_PrimaryKeyNameinTargetClass. Because your navigation properties are called EnteredBy and ModifiedBy and the primary key property is called OperatorCode EF expects - according to the mentioned convention - EnteredBy_OperatorCode and ModifiedBy_OperatorCode as foreign key columns. But those do not exist in the database which is the reason for your exception. Instead your FK columns are EnteredBy and ModifiedBy.
So, to fix the problem you must override the convention.
If you don't have FK properties in your model use Fluent API:
modelBuilder.Entity<Operator>()
.HasMany(o => o.ClientsEnteredBy)
.WithRequired(c => c.EnteredBy) // or HasOptional
.Map(m => m.MapKey("EnteredBy")); // mapping for the FK column name
modelBuilder.Entity<Operator>()
.HasMany(o => o.ClientsUpdatedBy)
.WithRequired(c => c.ModifiedBy) // or HasOptional
.Map(m => m.MapKey("ModifiedBy")); // mapping for the FK column name
(With this mapping you can remove the InverseProperty attribute.)
An alternative approach is to expose the FKs as properties in the model. Rename the navigation properties and use their names for the FK properties. The mapping is then possible with data annotations.
In Client class:
[ForeignKey("EnteredByOperator")]
public string EnteredBy { get; set; }
[InverseProperty("ClientsEnteredBy")]
public virtual Operator EnteredByOperator { get; set; }
[ForeignKey("ModifiedByOperator")]
public string ModifiedBy { get; set; }
[InverseProperty("ClientsUpdatedBy")]
public virtual Operator ModifiedByOperator { get; set; }
And remove the InverseProperty attributes in the Operator class.
Instead of the data annotations you can also use Fluent API:
modelBuilder.Entity<Operator>()
.HasMany(o => o.ClientsEnteredBy)
.WithRequired(c => c.EnteredByOperator) // or HasOptional
.HasForeignKey(c => c.EnteredBy);
modelBuilder.Entity<Operator>()
.HasMany(o => o.ClientsUpdatedBy)
.WithRequired(c => c.ModifiedByOperator) // or HasOptional
.HasForeignKey(c => c.ModifiedBy);
If both relationships are required you will need to disable cascading delete for at least one of the relationships (append .WillCascadeOnDelete(false) at the end of one of the mappings), otherwise SQL Server will throw an error that multiple cascading delete paths between the tables are not allowed.
I would suggest to use the "alternative approach" (expose foreign keys as properties) because it is easier to work with in most cases.