I'm trying to create a One-to-One relationship between two tables using a primary key and a unique key of the two tables (rather the primary keys).
The following is what I'd like to work.
// The principal end
public class A
{
// The primary Key
public int AId { get; set; }
// The navigation property
public virtual B B { get; set; }
}
// The dependent end
public class B
{
// The primary Key
public int BId { get; set; }
// The unique key
[Index(IsUnique = true)]
public int AId { get; set; }
// The navigation property
public virtual A A { get; set; }
}
But then I see this error:
Unable to determine the principal end of an association between the types 'A' and 'B'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.
I'm quite sure a primarykey-uniquekey relationship is allowed in SQL Server. Looks like EF6 doesn't support it. EF Core 1.0 seems to, but it's not feasible to port to EF Core right now.
Why we need a need a relationship of this kind:
We have two tables A and B in production, but the one-to-one relationship, which should have been there is missing. The relationship is something we need so we can navigate from an A object to a B object with EF. Since both tables have values, we can't really make the primary key, the foreign key - we'll end up with incorrect data.
My approach to fixing this was to:
add a column
fill it with the correct A ids
make it unique
establish the 1-1 relationship
An alternate approach to fixing this is more than welcome.
This is possible with EF Core using Fluent API's .HasPrincipalKey() method. Unfortunately not supported in EF6 which is a shame as relationships over unique keys can essentially be treated the same as foreign key constrains so I'd imagine it would have been an easy addition.
Now that MS has forgot about EF6 and is focusing on EF Core, this will never happen. I really liked using the visual entity designers as it saved so much time. Looking at the thousand+ lines of code the EF Core DbContext scaffold generator spits out for me is discouraging to say the least. Sure, it's pretty when you're dealing with a demo project consisting of two cute tables but we all know this is never the case in the real world. The whole point of using an ORM is to save time but I'm not sure if having to manage thousands of lines of configuration code is any better. Just by two cents.
Related
The EF Core documentation about One-To-One relations says: "When configuring the relationship with the Fluent API, you use the HasOne and WithOne methods." A closer look shows that this configures One-To-ZeroOrOne or ZeroOrOne-To-ZeroOrOne relations depending on whether IsRequired is used or not. Example:
public class ParentEntity
{
public Int64 Id { get; set; }
public ChildEntity Child { get; set; }
}
public class ChildEntity
{
public Int64 Id { get; set; }
public ParentEntity Parent { get; set; }
}
The derived context class contains:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<ParentEntity>().HasOne(p => p.Child).WithOne(d => d.Parent)
.HasForeignKey<ChildEntity>("ParentFk").IsRequired();
}
With this configuration, context.SaveChanges fails after context.Add(new ChildEntity()) as expected (with SqlException: Cannot insert the value NULL into column 'ParentFk' ... because of IsRequired) but succeeds after context.Add(new ParentEntity()) and context.Add(new ChildEntity() { Parent = new ParentEntity() }), i.e., the ParentEntity-ChildEntity relation is One-To-ZeroOrOne. In other words: the parent of a child is required, the child of a parent is optional.
Is there a way to configure a "real" One-To-One relation where both ends are required?
Maybe this cannot be enforced within the database. But can it be enforced by EF Core? (BTW: It can be enforced by EF6.)
Is there a way to configure a "real" One-To-One relation where both ends are required?
At the time of writing (EF Core 2.1.2), the answer is (unfortunately) negative.
The Required and Optional Relationships section of the documentation says:
You can use the Fluent API to configure whether the relationship is required or optional. Ultimately this controls whether the foreign key property is required or optional.
There is also a closed issue EF Core 2: One to One Required Not Being Enforced (also Navigation no longer needed?) #9152 asking the same question, and part of the response is:
when a relationship is made "Required" it means that a dependent entity cannot exist without an associated principal entity. This is done my making the FK non-nullable--i.e. the FK value must reference some principal entity.
However, it says nothing about the principal entity existing without the dependent. This is always possible because there isn't really any way to restrict it when working with partially loaded graphs. (This was the same with the old stack, although there were some situations where the state manager would, almost arbitrarily, stop certain things happening.) With stronger semantics applied to aggregates that limit partially loading of graphs it may be possible to enforce such a restriction in the future, but that isn't done yet.
I have a class as
public class fooClass
{
[Key]
public virtual fooRefClass staff { get; set; }
public Int64 fooProp1{ get; set; }
public DateTime fooProp2{ get; set; }
}
when i do the migration it give me error as "no key defined" but i had added the key attonation already .My intention is to make the referenced entity "fooRefClass " as primary key as well as foreign key, i know there is a way by mentioning the attribute id of the referenced entity and writing the foreign-key annotate over there, but i want to deal with entity directly ,rather than id only, how can i attain this functionality ,please help me with the issue.
Since there seems to be confusion, I decided to write an answer as well.
With the class you defined, EF would expect a table like
fooClass(bigint fooRefClass_Id, bigint fooProp1, datetime fooProp2);
... which is not valid, because this has no key column (the key annotation on your navigation property does nothing, because you see, it won't appear in the table... it will just tell EF there is a relationship to this table, and because you didn't provide a FK, it creates one to create this relationship). You also can't create this relationship yourself in your current model, because you don't even have a FK... how would you access a property you know nothing about, just that it will be created at some point (usually upon model creating with first accessing the database).
You have to tell EF you want the property, that will be created, to also be a key, not only a foreign key. You can do this by simply creating the property yourself and telling EF you want to use this, for example (I'm not too familiar with Data Annotations, I usually use Fluent API, so please excuse maybe occuring errors)
[Key, Foreign Key(fooRefClass)]
public Int64 StaffId {get; set;}
I have a class Question
CompareItems store CurrentQuestion-to-OtherQuestion compare information.
public class Question
{
public virtual ICollection<QuestionMark> CompareItems { get; set; }
}
public class QuestionMark
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public int Question { get; set; } //Store ID of OtherQuestion
public decimal Mark { get; set; }
}
When I delete some question A I need that all QuestionMark where QuestionMark.Question == A.Id also deleted, because it's no need to have compare information if question not exist. How it possible to do that without making QuestionMark.Question an entity? Maybe EF have some rule in Fluent-API to set that QuestionMark.Question is foreign key on Question entity?
I don't wont to make QuestionMark.Question as entity because it will need to change current solution lot - is a first. Also, question is a quite heavy entity, and to load it multiple time to assign value or delete or something else will be press on performance
I think it's possible to change app to use Entities instead of id, because EF use lazy loading by default and it will not caused performance problems. And I think that using just id instead of entity possible with some fluent API settings or attribute.
If you do not want to make a navigational property Question in QuestionMark class then you need to manually create a foreign key with "cascade delete". Then when every a question is deleted the database will delete the related QuestionMark records.
However this approach has a problem with EF. Because EF does not know there is a "cascade delete" relationship among these entities. So there can be inconsistencies within the locally tracked entities in EF.
You have not given a reason as to why you do not want to map the relationship in EF but I highly advice you against it.
I have a method for inserting in database.
I have 1:n relationship between the tables Point (n) and Line (1). Point has foreign key idLine.
However, the class Point in Entity Framework doesn't have the idLine property.
Now, in my method I have object of type Point, as parameter and here I have a problem because I don't know to what to assign the idSection of the new Point object which is inserted in the table.
How to add the idLine property in the Point class?
I'll assume you're using EF4.0, since this is not possible in previous version (EF1.0 does not include foreigh key properties in model).
In your generation wizard you need to make sure that "Include foreign key columns in the model" checkbox is checked when you're generating data model. Otherwise foreign key columns will be omitted when generating data.
If I'm remembering correctly you cannot simply add forign keys to classes that are already generated. You would need to manually edit all the mappings (not impossible, might be little bit troublesome if you are new to EF). Or you can simply remove this class from design area and add it again (making sure appropriate checkbox is checked this time). This might be simpler if you haven't customized generated classes.
add a foreign key in your model like following :-
public int? LineId { get; set; }
public virtual LineId LineId {get; set; } // this for one to one
I have the following
[DataContractAttribute]
public class Animal
{
[Key]
[XmlElement(ElementName = "Id")]
[DataMember()]
public Guid Id
{
get;
set;
}
[XmlElement(ElementName = "AnimalType")]
[DataMember()]
public List<AnimalType> AnimalType
{
get;
set;
}
}
And i map it through the code first approach with EF to tables
modelBuilder.Entity<Animal>().ToTable("Animal");
As you see I have not performed some complex mapping, but the List of AnimalType enumerations did not get mapped automatically to any columns/tables in the DB. Do i need to add some extra code to the model builder to control the mapping of an enumeration list ?
As of EF CTP5, enums are not supported yet. The team announced that they are going to fully support enums in their next RTM version which is targeted to be released on the first quarter of 2011.
I know for the longest time, enums weren't supported by EF, though I don't know if that is still the case or not.
Either way, I think there is a general problem with having EF handle a list of a type other than another entity. What is the primary key? What is the value? Should it try to store the data in one column or create a separate table and create a foreign key constraint? These are questions that will likely need to be answered before your model can be converted into a database schema.