Is it possible to build two optional one-to-one relationship in SQL?
I'd like to have:
public class EventInvoice
{
[Key]
public int ID { get; set; }
[ForeignKey("SZ_Event")]
public Nullable<int> SZ_EventID { get; set; }
public virtual SzopbudkaEvent SZ_Event { get; set; }
[ForeignKey("UP_Event")]
public Nullable<int> UP_EventID { get; set; }
public virtual Event UP_Event { get; set; }
}
public class Event
{
[Key]
public int EventID { get; set; }
public virtual EventInvoice EventInvoice { get; set; }
}
public class SzopbudkaEvent
{
[Key]
public int ID { get; set; }
public virtual EventInvoice EventInvoice { get; set; }
}
My invoice can be combined only with one of those objects (Event or SzopbudkaEvent). Is it possible to use it like this or I have to write something different?
You can do this but there are two things to bear in mond.
If the constraint is only one of the FK's can exist, then in the database the FK columns on the EventInvoice tale must be nullable. You've got this but I thought I'd emphasise it.
If there is also a constraint that there must be one of them (missing both is not allowed) then you have to work out how to validate that constraint. In the DB I'd use a trigger fir insert, update that raises an exception if both are null. I'd match that in code with a pre-save check: this describes implementing interface IValidatableObject with a Validate method which EF will call when the object is affected by SaveChanges.
Related
I have my ApplicationUser model defined like so:
public class ApplicationUser : IdentityUser
{
public virtual UserProfileInfo UserProfileInfo { get; set; }
}
With UserProfileInfo being an auxiliary table containing extra user data, defined as such:
public class UserProfileInfo
{
public int Id { get; set; }
public string SuperiorId { get; set; }
[ForeignKey("SuperiorId")]
public virtual ICollection<ApplicationUser> Superior { get; set; }
}
Each user has one or more people who are superior to them, in a business hierarchy. However, attempting to do a migration results in the following error:
The ForeignKeyAttribute on property 'Superior' on type 'Project.Models.UserProfileInfo' is not valid. The foreign key name 'SuperiorId' was not found on the dependent type 'Project.Models.ApplicationUser'.
How can I make a foreign key reference to ApplicationUser in my situation?
You need to do it the other way around, the ID is the foreignkey of the navigational property:
public class UserProfileInfo
{
public int Id { get; set; }
[ForeignKey("Superior")]
public string SuperiorId { get; set; }
public virtual ICollection<ApplicationUser> Superior { get; set; }
}
I am buys designing the model below:
public class LogModel
{
public class UserActivityLogs
{
[Key]
public int id { get; set; }
//Id of the user
public string userId { get; set; }
//Time of the log
public DateTime time { get; set; }
public LogActions action { get; set; }
}
// Types of actions to log
public class LogActions
{
[Key]
public int id { get; set; }
public string name { get; set; }
public string description { get; set; }
}
}
Now what I would like to know is do I need to add a table in the context for Logactions as well as UserActivityLogs or will EF see that the two tables are linked and create the log action table automatically?
Also have I specified my relationships correctly? What I was aiming for is that I can define multiple types of Logactions and then a userlog will then have a single log action associated to it.
First, don't use nested classes, it's a needless complication. Use namespaces to organize classes.
Second, don't use plural names for classes. One instance of class represents one entity. Also, use CamelCase names for properties.
Third, yes, Entity Framework will be aware of the associations between the two classes and create a database model with two tables and a foreign key.
So this leaves you with:
namespace MyApp.LogModel
{
public class UserActivityLog
{
[Key]
public int Id { get; set; }
public string UserId { get; set; }
public DateTime Time { get; set; }
public LogAction LogAction { get; set; }
}
public class LogAction
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
}
}
I have a relationship set up between 2 tables using code first and Fluent API. This works and the schema is generated with the correct fields and key assignments. However, my problem is I need to be able to say SupplyPoint.SupplyPointPricing in my resultant Model. What I have below only gives me the other way around.
I figure there must be a way to keep the structure I have but just MAP SupplyPoint.
public partial class SupplyPoint
{
[Key]
public int SupplyPointId { get; set; }
public string SupplyPointName { get; set; }
}
public class SupplyPointPricing
{
public int SupplyPointPricingId { get; set; }
public int? SupplyPointId { get; set; }
[ForeignKey("SupplyPointId")]
public virtual SupplyPoint SupplyPoint { get; set; }
}
Then I use Fluent API and this gives me the 1-1 between the tables and the Schema I expect
modelBuilder.Entity<SupplyPointPricing>()
.HasOptional(a => a.SupplyPoint)
.WithMany()
.HasForeignKey(u => u.SupplyPointId);
Last time I had this problem I had to change the design around and have a foreign key in the SupplyPoint table. On that previous occasion that was OK since it was a 1-1 required where there are always a matching record. This time around I need to keep this structure since there is 1-0 between SupplyPoint and SupplyPointPricing.
This is how I have always done 1-to-1 relationships with my models, without using Fluent mapping:
public partial class SupplyPoint
{
[Key]
public int SupplyPointId { get; set; }
public virtual SupplyPointPricing SupplyPointPricing { get; set; }
}
public class SupplyPointPricing
{
[Key, ForeignKey("SupplyPoint")]
public int SupplyPointId { get; set; }
public virtual SupplyPoint SupplyPoint { get; set; }
}
As you can see, the SupplyPointPricing does not have an Id of its own, but only the Id of the SupplyPoint, which acts as a key in the 1-to-1 relatioship.
The only thing I'm not sure of is if the SupplyPointId can be a nullable int.
This will not create a foreign key on the SupplyPoint, so if you don't have a Pricing, the SupplyPoint.SupplyPointPricing property will be null.
public class Slider_Locale
{
[Key]
public int Slider_LocaleID { get; set; }
[ForeignKey("Culture")]
public int CultureID { get; set; }
public string Slogan { get; set; }
public virtual Culture Culture { get; set; }
}
public class Culture
{
[Key]
public int CultureID { get; set; }
public string CultureName { get; set; }
public string DisplayName { get; set; }
public virtual Slider_Locale slider_Locale { get; set; }
}
It gives error as follows:
One or more validation errors were detected during model generation:
System.Data.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role
'Slider_Locale_Culture_Source' in relationship
'Slider_Locale_Culture'. Because the Dependent Role properties are not
the key properties, the upper bound of the multiplicity of the
Dependent Role must be �*�.
How could I design the relationship?. Please help me as I am newbie in mvc and entity.
This is one of those things that's a little tricky to wrap your brain around at first. The issue is that you're trying to set up a 1:1 (or 1:0) mapping, but there's nothing in your model to enforce that kind of mapping. For example, what if you have more than one Slider_Locale object with the same CultureID value? How would your application know which one to pick?
Now, you might know that this will never happen, but the Entity Framework doesn't, and it has to err on the side of caution, so it won't let you set up a relationship that it can't prove is consistent with the table structure. Ideally, it would let you specify unique constraints other than a primary key to work around this, and maybe someday it will, but for now the simplest way around this is to change it to a one-to-many mapping. For example, you could do:
public class Slider_Locale
{
[Key]
public int Slider_LocaleID { get; set; }
[ForeignKey("Culture")]
public int CultureID { get; set; }
public string Slogan { get; set; }
public virtual Culture Culture { get; set; }
}
public class Culture
{
[Key]
public int CultureID { get; set; }
public string CultureName { get; set; }
public string DisplayName { get; set; }
// Note that this got changed to ICollection<>
public virtual ICollection<Slider_Locale> slider_Locales { get; set; }
}
Another thing you could do is change the classes so that they share the same primary key values, but in order to do that you'll have to make at least one of the relationships optional. I could give an example of this if you let me know whether Slider_Locale.Culture can be null, or Culture.slider_Locale, or both.
I feel like this should have a simple answer, but I can't find it.
I have 2 POCOs:
public class Category
{
public int Id { get; set; }
public string Name { get; set; }
}
public class Product
{
public int Id { get; set; }
public int CategoryId { get; set; }
}
Notice that there are no object references on either POCO. With Code-First, how do I make EF4 CTP5 define a relationship between the two database tables?
(I know this is an unusual scenario, but I am exploring what's possible and what's not with Code-First)
No, this is not possible. As you can see below, all of the fluent API methods for setting up associations require specifying the Navigation Property as their parameter.
HasMany<TTargetEntity>(Expression<Func<TEntityType, ICollection<TTargetEntity>>> navigationPropertyExpression)
HasOptional<TTargetEntity>(Expression<Func<TEntityType, TTargetEntity>> navigationPropertyExpression)
HasRequired<TTargetEntity>(Expression<Func<TEntityType, TTargetEntity>> navigationPropertyExpression)
Is there any particular reason you don't want to use object references? It looks very elegant to use them:
public class Category
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
public int Id { get; set; }
public Category Category { get; set; }
}
And you can still access the Category Id via your product as product.Category.Id.