I thought it might be helpful to get a definitive answer on when to use WithOptionalDependent and when to use WithOptionalPrincipal. The help for the two functions is a little unclear, and I find myself digging through multiple Stack Overflow answers and answers on other sites combining answers in order to feel confident I've got the relationship going the correct direction.
Here's what MSDN says about WithOptionalDependent:
Configures the relationship to be optional:optional without a
navigation property on the other side of the relationship. The entity
type being configured will be the dependent and contain a foreign key
to the principal. The entity type that the relationship targets will
be the principal in the relationship.
and here is what it says about WithOptionalPrincipal:
Configures the relationship to be optional:optional without a
navigation property on the other side of the relationship. The entity
type being configured will be the principal in the relationship. The
entity type that the relationship targets will be the dependent and
contain a foreign key to the principal.
The line "The entity type being configured" is the part that always confuses me (and I assume others).
In this example:
class MyEntityA
{
[Key]
public int Id { get; set; }
public int BId { get; set; }
[ForeignKey("BId")]
public MyEntityB B { get; set; }
}
class MyEntityB
{
[Key]
public int Id { get; set; }
}
modelBuilder.Entity<MyEntityA>().HasOptional(a => a.B).WithOptionalDependent();
is "The entity type being configured" referring to MyEntityA or MyEntityB? I assume it is the former.
If that's correct, what's an example of when you'd use WithOptionalPrincipal?
I actually think in my code example it should really be WithMany and neither of the WithOptional options. Clearly I'm still confused!
There are overloads for both of these functions that take the navigation property going the other direction. I assume those overloads don't change those answers, but please correct me if I'm wrong.
I hope this will be helpful to the larger community as well.
For example, lets modify your EntityB by navigation property and make BId nullable (as we are talking about optional relationship).
class MyEntityA
{
[Key]
public int Id { get; set; }
public int? BId { get; set; }
[ForeignKey("BId")]
public virtual MyEntityB B { get; set; }
}
class MyEntityB
{
[Key]
public int Id { get; set; }
public virtual MyEntityA A { get; set; }
}
then we can use:
modelBuilder.Entity<MyEntityB>().HasOptional(a => a.A).WithOptionalPrincipal();
MyEntityA has FK to MyEntityB, so in your example you configure MyEntityA and use WithOptionalDependent. But you can start configuration from MyEntityB-side, then you need WithOptionalPrincipal.
The answer to your question is: "The entity type being configured" is MyEntityA
This can be seen definitively by looking at the documentation for
OptionalNavigationPropertyConfiguration<TEntityType, TTargetEntityType>
which is the type returned by HasOptional and which says:
TTargetEntityType
The entity type that the relationship targets.
which provides more context for the phrases:
The entity type being configured
The entity type that the relationship targets
So, in your case you get back from HasOptional an
OptionalNavigationPropertyConfiguration<MyEntityA, MyEntityB>
Thus, WithOptionalDependent means that MyEntityB will be the Principal with an optional Navigation Property pointing back to MyEntityA (specified via the overload's lambda parameter) and MyEntityA will be the Dependent and contain a Foreign Key and Navigation Property (as specified in the lambda parameter of HasOptional). This is the scenario in your model.
Conversely, WithOptionalPrincipal means that MyEntityA will be the Principal and MyEntityB the Dependent with Foreign Key and Navigation Property.
Related
Using EF6 and .NET 4.6.1. I know this somewhat is a duplicate (I've looked at this stack overflow post) but hear me out. My case is different and I have tried to get it to work using their solutions with mine but it didn't work. So no this isn't actually a duplicate. It's another issue altogether and I haven't found a post that really helps me on this topic.
I am trying to map relationships between 3 models; Employee, Position and Employment. I want a one-to-many between Employment and Position (employments map to one position) and a one-to-one between Employment and Employee.
public class Employment
{
public int EmploymentID { get; set;}
...
public Position Position { get; set; }
public Employee Employee { get; set; }
}
public class Position
{
public int PositionID { get; set;}
...
[InverseProperty("Position")]
public ICollection<Employment> Employments { get; set; }
}
public class Employee
{
public int EmployeeID { get; set;}
...
[InverseProperty("Employee")]
public Employment Employment { get; set; }
}
However, when I try to run this with DbContext automapping, it fails and says it can't find the relationships. I've tried multiple combinations of data annotations like setting inverseproperties and foreignkey("____ID") on some of them but haven't been able to get it to work.
I did also try adding virtual keywords in for some of the but that didn't do anything either.
I'd rather not use FluentAPI as I want to let the auto mapper do as much as possible with this. It's not complicated a problem enough to warrant manually mapping it with FluentAPI (At least in my opinion it isn't. Maybe I'm wrong).
What data annotations do I need? I've looked at this stack overflow post and various articles on entityframeworktutorial.net trying to apply their solutions to my case. But haven't gotten anything to work.
The failing line is here:
using (EmploymentContext ctx = new EmploymentContext())
{
Position pos = new Position()
{
PositionID=1,
Name="General Manager"
};
ctx.Positions.Add(pos); // Failing here
ctx.SaveChanges();
}
and the error message is:
'Unable to determine the principal end of an association between the types 'Ianmann.Hr.DataAccess.Employment.Employee and Ianmann.Hr.DataAccess.Employment.Employment. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.'
I don't know why you insist on using data annotations. Everything you can do with data annotation can be done with the Fluent API, but the opposite is not true. Also, and especially with relationships, the data annotations are not intuitive and error prone.
In the concrete case the problem is with the one-to-one relationship (btw, the error message should contain that information). It's because EF cannot determine the principal and the dependent of the relationship when the ends of the relationship are both optional (as in your case) or both required. So one way to resolve it is to mark the principal by making the navigation property required:
public class Employment
{
public int EmploymentID { get; set; }
...
public Position Position { get; set; }
[Required] // <--
public Employee Employee { get; set; }
}
The InverseProperty is redundant (not needed) in this case.
The same can be achieved more intuitively with fluent API:
modelBuilder.Entity<Employment>()
.HasRequired(e => e.Employee)
.WithOptional(e => e.Employment);
But please note that while either way will resolve the issue in question, the resulting design will be the so called Shared Primary Key association, where EmploymentID is both PK and also FK to Employee. In case you want a separate FK property / column, then fluent API is a must as it cannot be done via data annotations:
modelBuilder.Entity<Employment>()
.HasRequired(e => e.Employee)
.WithOptional(e => e.Employment)
.Map(m => m.MapKey("EmployeeID"));
I have a problem with the Entity Framework that I can't figure out.
I have a Module class that links to another Module (a one-to-one relationship) in two ways.
Code:
public class Module {
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid Id {get;set;} /* primary key */
public Guid? OtherModule1 {get;set;}
[ForeignKey("OtherModule1")]
public Module OtherModule {get;set;}
public Guid? OtherModule2 {get;set;}
[ForeignKey("OtherModule2")]
public Module OtherModule2 {get;set;}
}
This gives the error that the principal end of the association cannot be determined.
Unable to determine the principal end of an association between the types 'Module' and 'Module'
I understand what the error means, but here's the thing. The relationship with OtherModule1 has always existed without a problem. This code works:
public class Module {
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid Id {get;set;} /* primary key */
public Guid? OtherModule1 {get;set;}
[ForeignKey("OtherModule1")]
public Module OtherModule {get;set;}
}
There is no Fluent configuration present on this table
Now, if I add a new column, OtherModule2 and link it in the exact same way, this error pops up.
Does anyone have an idea of how to handle this?
TL/DR: one table has two foreign keys to the same table. One foreign key is handled correctly while the other is not.
The working model by convention defines one-to-many unidirectional (with only navigation property at the many side) relationship. It's equivalent of the following fluent configuration:
modelBuilder.Entity<Module>()
.HasOptional(e => e.OtherModule)
.WithMany()
.HasForeignKey(e => e.OtherModule1);
When you add a second FK / navigation property pair (I've renamed the FK property because you can't have 2 properties with the same name in the class):
public class Module
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid Id { get; set; } /* primary key */
public Guid? OtherModule1 { get; set; }
[ForeignKey("OtherModule1")]
public Module OtherModule { get; set; }
[Column("OtherModule2")]
public Guid? OtherModule2_Id { get; set; }
[ForeignKey("OtherModule2_Id")]
public Module OtherModule2 { get; set; }
}
EF cannot automatically determine the relationships - it could be 2 unidirectional one-to-many or 1 bidirectional one-to-one, hence the error.
There is no way to specify that with data annotations in this case, so you need to use fluent configuration to either fully configure the relationships, or when combined with data annotations, to simply specify the cardinality and the navigation properties involved.
The following fluent configuration is sufficient to resolve the issue for the above data annotated model:
modelBuilder.Entity<Module>()
.HasOptional(e => e.OtherModule)
.WithMany();
modelBuilder.Entity<Module>()
.HasOptional(e => e.OtherModule2)
.WithMany();
I've read as many posts as I can on this topic but none of the solutions I have tried seem to work. I have an existing database and created a new Code First From Existing Database project.
I have a base table called Thing. Every object has a record in this table using Id as the Unique Primary Key. Each other object inherits from this but they use the same Id in the child tables without using a new Identity column in the sub tables. Effectively giving each 'Thing' a unique Id:
public class Thing
{
public int Id { get; set; }
public string Name { get; set; }
}
public class Car
{
public int Id { get; set; }
//other properties
}
public class Person
{
public int Id { get; set; }
//other properties
}
public class Color
{
public int Id { get; set; }
//other properties
}
Every new record first creates an item in 'Thing' and then using that Id value creates a new record in its respective table, creating multiple 1 to 0..1 relationships where the Id field on the derived tables is also the FK to Thing.
Thing 1 to 0..1 Car
Thing 1 to 0..1 Person
Thing 1 to 0..1 Color
and so on
I have tried many different Data Annotation and Fluent API combinations but it always comes back to the same error:
'Unable to retrieve metadata for Model.Car'. Unable to determine the principal end of association between the types 'Model.Thing' and 'Model.Car'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.'
I did manage to get past this error by using virtual with the inverse annotation and setting the Id field to be Key and ForeignKey, but then the message jumps to Person. If you then set it up the same as Car the message reverts back to Car.
It seems I could go back and create a normal Foreign Key to each child table, but that is a lot of work and I am sure it is possible to get this working somehow. Preferably using fluent API.
If you are going to use Data Annotations, you need to declare the PK of the dependent entity as FK too:
public class Thing
{
public int Id { get; set; }
public string Name { get; set; }
public virtual Car Car{get;set;}
}
public class Car
{
[Key,ForeignKey("Thing")]
public int ThingId { get; set; }
//other properties
public virtual Thing Thing{get;set;}
}
And if you are going to use Fluent Api (remove the attributes from your model), the configuration would be like this:
modelBuilder.Entity<Car>().HasRequired(c=>c.Thing).WithOptional(t=>t.Thing);
Based on the multiplicity that is specified, it only makes sense for Thing to be the principal and Car to be the dependent, since a Thing can exist without a Car but a Car must have a Thing.
As you can see you don't need to specify that ThingId is the FK of this relationship.This is because of Entity Framework’s requirement that the primary key of the dependent be used as the foreign key. Since there is no choice, Code First will just infer this for you.
Update
Reading again your question I think you are trying to create a hierarchy. In that case you could use the Table per Type (TPT) approach.
I have an entity which is already being used with an underlying database, and it was created with just the navigational property to an optional entity (1:0..1). So by default conventions, EF created a nullable foreign key column in the DB and gave it the "MyProp_Id" name with underscore, according to that convention.
Now, I wish to expose that foreign key as a property on the entity, because it will make certain scenarios easier for me. I don't want to rename/change the underlying foreign key column in the DB (the MyProp_Id one). In fact, there shouldn't be any underlying DB updates, I just want to expose that FK on the entity. A code sample to clarify:
public class MyEntityA
{
public long Id { get; set; }
//public long? MyOptionalEntityB_Id { get; set; } <== this is what I am trying to add
//public long? MyOptionalEntityBId { get; set; } <== this didn't work either
public MyEntityB MyOptionalEntityB { get; set; }
}
I've tried just simply adding the "MyOptionalEntity_Id" property as property on the entity, hoping that EF would "automagically" see that because the names are the same, it would just map and be happy. NO DICE.
Then I tried to name my property "MyOptionalEntityId" (no underscore), but still NO DICE.
Then I tried adding an explicit mapping configuration to say:
this.Property(p => p.MyOptionalEntityId).HasColumnName("MyOptionalEntity_Id");
NO DICE
Is there a way to do this? Is this clear and make sense?
Try adding foreign key attribute.
public long? MyOptionalEntityB_Id { get; set; }
[ForeignKey("MyOptionalEntityB_Id")]
public MyEntityB MyOptionalEntityB { get; set; }
Or using fluent api.
modelBuilder.Entity<MyEntityA >()
.HasOptional(x => x.MyOptionalEntityB)
.WithMany().HasForeignKey(x => x.MyOptionalEntityB_Id);
// ^^^ -> if MyEntityB has collection of MyEntityA, mention it
I would like to know what rules Entity Framework follows in regards to the naming/generation of navigation properties. I have observed several scenarios which don't seem to make sense so I was wondering if anyone knows exactly how these work.
Scenario 1:
public class Post
{
public int Id { get; set; }
public User Author { get; set; }
}
Generates
ie. by default navigation properties generate FKs named [PropertyName]_Id
Scenario 2:
It makes sense that if EF generates properties such of the format [PropertyName]_Id when you manually specify a FK Id it will follow the same rules however:
public class Post
{
public int Id { get; set; }
public int? Author_Id { get; set; }
public User Author { get; set; }
}
Generates
As you can see this doesn't automatically register as a nav property.
Scenario 3:
If it doesn't work for Scenario 2 why does it work for an alternate naming convention?
public class Post
{
public int Id { get; set; }
public int? AuthorId { get; set; }
public User Author { get; set; }
}
Generates
What are the rules around navigation property detection and generation?
That is expected behavior and it is based on two different conventions based by EF
In the first example you are using Independent association where your entity doesn't have FK property. EF will create FK in the database using simple pattern: NameOfNavigationProperty_NameOfRelatedPK This convention follows traditional database naming.
In the second example you defined property with the same name as FK used by EF. EF detected this and added 1 to its generated FK. The reason why your property is not used as FK is the second convention which searches for FK properties. This convention expects that FK property will have this name (conventions follows traditional .NET naming):
NameOfNavigationPropertyNameOfRelatedPK provided by NavigationPropertyNameForeignKeyDiscoveryConvention
NameOfRelatedTypeNameOfItsPK provided by TypeNameForeignKeyDiscoveryConvention
NameOfRelatedPK provided by PrimaryKeyNameForeignKeyDiscoveryConvention
In the last example you correctly defined FK property and EF detected it so it uses Foreign key association.
In addition to #Ladislav Mrnka's answer above, you can find a detailed reference of the entity framework default conventions here:
http://msdn.microsoft.com/en-us/library/system.data.entity.modelconfiguration.conventions(v=vs.103).aspx