I am new to entity framework and am having a hard time trying to figure out how to query with a join when my models look like this (drastically simplified)
class Customer
{
public int Id {get; set;}
public Vehicles Vehicles {get; set;}
}
class Vehicles
{
public List<Vehicle> Items {get; set;}
}
class Vehicle
{
public int Id {get; set;}
public int CustomerId {get; set;}
}
If I put the List<Vehicle> on the customer class directly. I am able to do fluent mapping like this
builder.Entity<Customer>()
.HasMany(x => x.Items)
.WithOne()
.HasForeignKey(x => x.CustomerId);
Which then I can do this and I get back a customer object with vehicles
db.Customers.Include(x => x.Items).FirstOrDefault(x => x.Id == 1);
What I am not understanding is how to do this with my original set of models. I would like to keep them the way they are if possible. I have tried doing various versions of this in my onModelCreating method with no luck.
builder.Entity<Customer>(t =>
{
t.OwnsOne(x => x.Vehicles, v =>
{
v.HasMany(x => x.Items).WithOne().HasForeignKey(x => x.CustomerId);
});
});
It's possible to map the original classes, but in quite counterintuitive way.
Since the Vehicles class is just a container, mapping it as owned entity as you have tried seems the most natural way. However currently EF Core does not allow owned entity to be at the principal side of the relationship, and in your case this is needed.
So instead you need to map the Vehicles class as regular "entity" sharing the same table with the Customer - the so called table splitting. You have to do explcitly all that EF Core does implicitly for owned entities - define a shadow property and map is a both PK and FK for the one-to-one relationship with the Customer. You'd need also the explicitly map the Vehicle.CustomerId as a FK because from EF point of view the Vehicle is related to Vehicles rather than to Custome, hence the conventional FK property / column name assumed will be VehiclesId. Note that with this model you'll never be able to define an inverse navigation property Customer of the Vehicle.
With that being said, here is the fluent configuration needed:
modelBuilder.Entity<Vehicles>(builder =>
{
// Table
builder.ToTable(modelBuilder.Entity<Customer>().Metadata.Relational().TableName);
// PK
builder.Property<int>("Id");
builder.HasKey("Id");
// One-to-one relationship with Customer
builder.HasOne<Customer>()
.WithOne(e => e.Vehicles)
.HasForeignKey<Vehicles>("Id");
// One-to-many relationship with Vehicle
builder.HasMany(e => e.Items)
.WithOne()
.HasForeignKey(e => e.CustomerId);
});
and usage:
db.Customers
.Include(x => x.Vehicles.Items) // <--
// ...
Use .Join
See this question for some examples:
Entity Framework Join 3 Tables
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 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);
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 have a simple 1:many aggregate relationship, lets say:
public class Parent
{
public string Name {get; set;}
public Child SelectedChild {get; set;}
public Child PublishedChild {get; set;}
public virtual ICollection<Child> AllChildren {get; set;}
}
public class Child
{
public string Name {get; set;}
[Required]
public Parent Father {get; set;}
}
When creating the schema from this model I get the error:
Introducing FOREIGN KEY constraint 'Parent_SelectedChild' on table 'Parent' may cause cycles or multiple cascade paths.
Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints
So I add the following to OnModelCreating:
modelBuilder.Entity<Child>()
.HasRequired(v => v.Parent)
.WithOptional(c => c.SelectedChild)
.WillCascadeOnDelete(false);
modelBuilder.Entity<Child>()
.HasRequired(v => v.Parent)
.WithOptional(c => c.PublishedChild)
.WillCascadeOnDelete(false);
This gets round the original error but I now get:
Unable to determine the principal end of the 'xxx.Parent_SelectedChild' relationship.
Multiple added entities may have the same primary key.
Can anyone help?
All I essentially want to do is refer to particular child records on a 1:many aggregate relationship from the parent. I assume EF will create INT child id columns on the parent called e.g. SelectedChild_Id & PublishedChild_Id (or similar).
Thanks in advance
-macon
Edit: In response to #Slauma:
I can get a schema generated using:
modelBuilder.Entity<Parent>()
.HasOptional(p => p.SelectedChild)
.WithOptionalPrincipal()
.WillCascadeOnDelete(false);
modelBuilder.Entity<Parent>()
.HasOptional(p => p.PublishedChild)
.WithOptionalPrincipal()
.WillCascadeOnDelete(false);
modelBuilder.Entity<Parent>()
.HasMany(p => p.AllChildren)
.WithRequired(c => c.Father)
.WillCascadeOnDelete(false);
But this generates multiple FK on the Child record e.g. Parent_Id, Parent_Id1. I just want a reference from the Parent to one of the child rows e.g. Parent_SelectedChildId. Do I have to do this manually with an int column on parent?
I think you have three 1-to-many relationships:
modelBuilder.Entity<Parent>()
.HasOptional(p => p.SelectedChild)
.WithMany()
.WillCascadeOnDelete(false);
modelBuilder.Entity<Parent>()
.HasOptional(p => p.PublishedChild)
.WithMany()
.WillCascadeOnDelete(false);
modelBuilder.Entity<Parent>()
.HasMany(p => p.AllChildren)
.WithRequired(c => c.Father)
.WillCascadeOnDelete(false);
Edit
I've tested my mapping above with exactly the Parent and Child class you provided in your question - with the only exception that I have added a primary key property to both classes: public int Id { get; set; }. Otherwise EF would complain about a missing key property. This mapping doesn't throw an exception and creates the following tables in the database:
Parents table:
- Id int not nullable (PK)
- Name nvarchar(MAX) nullable
- SelectedChild_Id int nullable (FK)
- PublishedChild_Id int nullable (FK)
Children table:
- Id int not nullable (PK)
- Name nvarchar(MAX) nullable
- Father_Id int not nullable (FK)
So, there are the three foreign key columns as expected.
Since you get an exception according to your comment, I guess that there is actually some important difference in the code you have tested.
BTW: Mapping the two navigation properties of the Parent class as One-to-One relationships is much more difficult, if not impossible. In EF you need a shared primary key between the two tables to map a One-to-One relationship, so it would not be possible to assign two different entities to the two navigation properties because they cannot both have the same key as the parent.
I have the following model in my model:
Patient
Vendor
Organization
each of these entities needs Addresses.
The Address basically looks like the following
Address
AddressTypeId // with Navigation Property/Association to AddressType
EntityKey // indicates the PK Id of the entity this address is for
AddressType
EntityId // indicates the entity type this address type corresponds to (Patient or Vendor)
// This should be on the AddressType, not the Address, since we need a way of knowing what kind of AddressTypes are available to create for new addresses for Patients, Vendors, and Organizations
//...that is Patients support AddressType X, Vendors support AddressType Y, etc.
I want to create an association for Patient, Vendor, and Organization on the EntityKey property on Address - each with a filter constraint that the Address's AddressType.EntityId is the matching EntityId for that entity (1 for Patient, 2 for Vendor, 3 for Address).
What is the best way of doing this? Most ORM's on the market support this kind of scenario....and it's certainly a very common one.
NOTE: I don't want to create PatientAddress/PatientAddressType, VendorAddress/VendorAddressType, and OrganizationAddress/OrganizationAddress type derived entities. It severely clutters the model and makes it basically incomprehensible.
Right now I'm solving this by doing explicit joins in my LINQ queries:
const int patientTypeEntityId = 1;
var query = from p in repository.Patients
let addresses = repository.Addresses.Where(a =>
a.EntityKey == p.Id & a.AddressType.EntityId == patientTypeEntityId)
select new { Patient = p, Addresses = a }
but I don't want to continue having to do this.
If I understand correctly you want to have an address collection in your Patient, Vendor, etc...
public class Patient
{
public int Id { get; set; }
public ICollection<Address> Addresses { get; set; }
}
public class Vendor
{
public int Id { get; set; }
public ICollection<Address> Addresses { get; set; }
}
public class Address
{
public int Id { get; set; }
//public int EntityKey { get; set; }
public AddressType AddressType { get; set; }
}
... and somehow tell EF that Patient.Addresses only gets populated with addresses of address type "Patient".
I think that is not possible for several reasons:
If you don't expose the foreign key in Address (no EntityKey property there) you have to tell EF the key in the mapping (otherwise it would create/assume two different FK columns):
modelBuilder.Entity<Patient>()
.HasMany(p => p.PVAddresses)
.WithRequired()
.Map(a => a.MapKey("EntityKey"));
modelBuilder.Entity<Vendor>()
.HasMany(p => p.PVAddresses)
.WithRequired()
.Map(a => a.MapKey("EntityKey"));
This throws an exception due to the duplicate "EntityKey" column for two different relationships.
Next thing we could try is to expose the foreign key as property in Address (EntityKey property is there) and then use this mapping:
modelBuilder.Entity<Patient>()
.HasMany(p => p.PVAddresses)
.WithRequired()
.HasForeignKey(a => a.EntityKey);
modelBuilder.Entity<Vendor>()
.HasMany(p => p.PVAddresses)
.WithRequired()
.HasForeignKey(a => a.EntityKey);
This (surprisingly) doesn't throw an exception but creates two FK constraints in the database between Patient-Address and Vendor-Address with the same FK column EntityKey. For your model, I think, this doesn't make sense because it would require that always a Patient and a Vendor with the same PK exists if you have an address with some EntityKey. So, you would have to remove these FK constraints in the DB manually (which feels very hacky to me).
And the last thing is that you cannot specify a filter for lazy and eager loading of navigation properties. The Addresses collection would always get populated with the addresses which have the same EntityKey as the PK of Patient or Vendor respectively. You can apply a filter though with explicite loading:
var patient = context.Patients.Single(p => p.Id == 1);
context.Entry(patient).Collection(p => p.Addresses).Query()
.Where(a => a.Addresstype.EntityId == patientTypeEntityId)
.Load();
But you would have to ensure that you never use lazy or eager loading for the Addresses collection. So, this is not really a solution and we should forget it immediately.
The ugliest point for me is that you cannot have FK constraints on the EntityKey. In other words: The DB allows to have an EntityKey = 1 with no referenced Patient or Vendor with that PK (because somehow the patient 1 and vendor 1 have been deleted, for example).
For this reason alone I would prefer the solution shown by #Akash - aside from the fact that it is probably the only working and clean solution with EF at all.