Using EF 4.0 with the 4.1 upgrade for POCO / code-first.
OK so I have a domain model where type Car has, in a collection, multiple objects of type Part. So a one:many relation.
HasMany(v => v.Parts)
.WithRequired()
.HasForeignKey(v => v.CarId)
.WillCascadeOnDelete();
The problem with this is that it requires me to add a CarId property to my Part type. This is leaking ORM detail into my domain model - which is bad. Marking everything virtual is annoying enough.
Looking at the XML doc comment for the HasForeignKey() method says this:
Configures the relationship to use
foreign key property(s) that are
exposed in the object model. If the
foreign key property(s) are not
exposed in the object model then use
the Map method.
That's great and all. But it introduces a catch-22 situation because if I refactor my Part type by removing the CarId property that I don't want and update my EF model builder to not bother with mapping that property. Then as you can imagine it means I cannot then call HasKey() for defining the composite key, ala:
HasKey(v => new { v.CarId, v.PartId });
HasKey() doesn't appear to support defining the keys based upon non-Property lambdas.
What is the solution here?
If you absolutely don't like to have foreign key properties in your model you could remove the convention to detect FK properties to avoid that EF marks properties automatically as FK properties ...
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions
.Remove<NavigationPropertyNameForeignKeyDiscoveryConvention>();
}
... and then simply don't specify the FK property in your mapping:
HasMany(v => v.Parts)
.WithRequired()
.WillCascadeOnDelete();
You still need CarId in your model because it is part of the primary key, but this way it doesn't act anymore as foreign key property.
Just an idea, I am not sure if it works.
Well, what about adding a new key field to CarParts table like CarPartId, so you would not need the composite key. (Composite Key support is not that great when working with ORMs.)
Related
Consider two tables, table BaseService with PK ID, and table SubService with PK BaseServiceID, which is a foreign key to ID in the BaseService table. I wish to map these to classes in EF6 where SubService inherits from BaseService. I'm not sure how to describe in the mapping that the foreign key is from SubService.BaseServiceID to BaseService.ID. At the moment I have something like this:
modelBuilder.Entity<SubService>(e => {
e.ToTable("SubService");
});
and
modelBuilder.Entity<BaseService>(e => {
e.ToTable("BaseService");
e.HasKey(x => x.ID);
});
When I query though, the resulting query tries to join using BaseService.ID to SubService.ID. I've tried a few variations on my mapping, but I'm getting nowhere - can anyone suggest how this should be done?
From my testing, EF doesn't currently support having different column names for the keys in the tables in a TPT mapping. If you configure one entity to map its "Id" property to a column called "FooId", then all entities in the hierarchy will map their keys to "FooId".
You can create an EF Core Issue to provide feedback on this scenario.
modelBuilder.Entity<SubService>()
.ToTable("SubService")
.HasRequired(s => s.BaseService)
.WithMany(b => b.SubServices)
.HasForeignKey(s => s.BaseServiceID);
In this example, a HasRequired method is used to specify that the entity requires a and the method is used to specify the ability to navigate on the side of the relationship. Finally, `BaseService' property class'SubService' 'BaseService' 'WithMany' 'BaseService' 'HasForeign' 'KeyBase' 'ServiceID' 'SubService'
In EF Core, many APIs have changed, so I'm confused how to properly configure my relationships.
Suppose one Book has many Pages, and one Page must be part of one Book (it cannot exist on its own).
builder.Entity<Book>()
.HasMany(e => e.Pages)
.WithOne(e => e.Book)
//.IsRequired() // is this, erm, required?
.OnDelete(DeleteBehavior.Cascade);
I've gone through the official docs, but I'm still confused about the .IsRequired() call for my case as I don't have/need a foreign key in the Page entity.
Is .IsRequired() required?
I assume:
it refers to the "child"/dependant end of the relationship, i.e. Page
if included then Book:Pages = 1:0..n
if not then Book:Pages = 0..1:0..n
If you don't include a foreign key property in the Page class, EF will create a nullable shadow foreign key property, with a cascade action of NO ACTION. You will have to use the Required method to override that if you want the resulting BookId column to be configured as not null, and you also need to specify the Cascade action as you have done to ensure that dependants are deleted when the book is deleted.
So the answer to your questions is yes, it is required in your scenario.
I have existing DB with the following structure:
I'm using EF fluent API to configure relationships between tables:
public GroupEntityConfiguration()
{
HasMany(x => x.Employees).WithRequired().HasForeignKey(x => x.GroupId).WillCascadeOnDelete(true);
}
public EmployeeEntityConfiguration()
{
HasOptional(x => x.InnerGroupMember).WithRequired();
}
With this configuration applied I can add new Employee, new InnerGroupMember or fetch data. The problem appears when I try to remove Employee. Then I get an exception:
The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a relationship, the related foreign-key property is set to a null value. If the foreign-key does not support null values, a new relationship must be defined, the foreign-key property must be assigned another non-null value, or the unrelated object must be deleted.
As far as I understand above exception is connected with GroupId foreign key. Trying to fix it I'm adding following line to EmployeeEntityConfiguration:
HasKey(x => new { x.Id, x.GroupId});
But after adding it I get another exception which I believe is connected with InnerGroupMember object:
Invalid column name 'Guest_Id'. Invalid column name 'Guest_GroupId'.
If I comment out InnerGroupMember navigation property and remove it's configuration, Employee can be removed.
Could you please give me a hint what I'm doing wrong and how to configure entities to be able to perform all needed operations? Thanks!
I have an existing Group entity and I want to remove Employee from the Employees Group collection:
var group = groupRepository.Find(groupId);
group.RemoveEmployee(employeeId);
_unitOfWork.Save();
RemoveEmployee function inside Group entity looks like this:
public void RemoveEmployee(int employeeId)
{
var employee = Employees.Single(n => n.Id == employeeId);
Employees.Remove(employee);
}
That's why I get an exeption:
The relationship could not be changed because one or more of the foreign-key properties is non-nullable....
After reading this post I wanted to fix it adding HasKey(x => new { x.Id, x.GroupId}); function inside EmployeeEntityConfiguration what leads to the second exception:
Invalid column name 'Guest_Id'. Invalid column name 'Guest_GroupId'.
Actually I made this step (I mean adding HasKey function) without changing DB structure. To make it work, inside Employees table I have to create composite key - combination of Id and GroupId which is also a foreign key. This modification forces changes inside InnerGroupMembers table. DB structure looks now as following:
Now I'm able to remove Employee in a way I showed at the beginning.
Anyway I'm not going for this solution. They are different ways to achieve what I want. Here are some links:
Removing entity from a Related Collection
Delete Dependent Entities When Removed From EF Collection
The relationship could not be changed because one or more of the
foreign-key properties is non-nullable
For one-to-one relationships cascading delete is not enabled by default, even not for required relationships (as it is the case for required one-to-many relationships, that is: The WillCascadeOnDelete(true) in your one-to-many mapping is redundant). You must define cascading delete for a one-to-one relationship always explicitly:
HasOptional(x => x.InnerGroupMember).WithRequired().WillCascadeOnDelete(true);
When you delete an Employee now, the database will delete the related InnerGroupMember as well and the exception should disappear.
I using manual mapping entity in my Code First on EF5 project and would like to use FKs as composite PK. I have only navigation properties in mapping class (not FK) as mentioned below:
class MyMapping
{
public virtual Mapped1 {get;set;}
public virtual Mapped2 {get;set;}
}
I do not want to add fields like 'int Mapped1FK'/'int Mapped2FK', but I cannot find how to specify composite key in this case.
I assume that it should be something like:
modelBuilder.Entity<MyMapping>()
.HasKey(k => k.Mapped1)
.HasKey(k => k.Mapped2);
or
modelBuilder.Entity<MyMapping>()
.HasKey(k => { k.Mapped1, k.Mapped2} );
but I do not know what exactly right.
It's not possible to use navigation properties as primary key properties (no matter if composite or not). Key properties must have a primitive type - like int or string or Guid, etc.
As Slauma described it is impossible to do what I want without introducing primitive FK properties.
So I decided to work with my mapping entities as with ordinary POCO - inherits base class with
public int Id {get;set;}
declaration and use it as PK.
Also, in other sources, was recommended following, due architecture senses: when you converting simple mapping (2 FKs) to complex mapping (2FKs + custom field(s)) it becomes an ordinary entity as any other in project and should has the same constraints and structure.
I have two tables:
Requirement
ID (int) PK
ClientID (int)
JobNumber (int)
Comment
ID (int) PK
Job_ID (int)
Comment (varchar)
The tables don't have foreign keys and there's no possibility of adding any. I'm trying to map them in EF. I have classes for each and I'm trying to define the relationship in fluent code to map the Comment.Job_ID to the Requirement.JobNumber. A requirement can have many comments. Requirement has a list of Comments and Comment has a Requirement property.
I have this mapping setup:
modelBuilder.Entity<Comment>().HasRequired(c => c.Requirement)
.WithMany(s => s.Comments)
.HasForeignKey(f => f.Job_ID);
I'm stuck trying to get Comment.Job_ID to map to Requirement.JobNumber.
Any help appreciated.
It's not possible. With Entity Framework the entity that the Comment.Requirement navigation property is refering to is generally identified by the (primary) key property in Requirement, i.e. by ID. There is no mapping option to define that the target property is anything else than the key property - like JobNumber or another non-key property.
I could only imagine that you could "fake" the primary key property in the model to be JobNumber instead of ID (given that JobNumber is unique in the Requirement table):
modelBuilder.Entity<Requirement>().HasKey(r => r.JobNumber);
I don't know if that could have other unwished side effects. (For sure it doesn't work if JobNumber is not unique because EF wouldn't allow to have more than one entity with the same key attached to a context and updates/deletes and so on wouldn't find the correct record in the database.) It feels wrong and hacky to me. I honestly wouldn't even try that, live with the fact that you don't have a real foreign key relationship in the database, forget the navigation properties Requirement.Comments and Comment.Requirement and use manual joins in LINQ to relate the table data/entities as I need them in a given situation.