I have two tables: Place, and MenuSection, that currently have a one-to-many relationship defined like so:
public class Place
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
[Key]
public int PlaceID { get; set; }
public virtual ICollection<MenuSection> MenuSections { get; set; }
}
public class MenuSection
{
[Key]
public int MenuSectionID { get; set; }
public int PlaceID { get; set; }
}
However, I now need a many-to-many relationship. If I was just starting out then this would be achieved by changing the MenuSection class to look like this:
public class MenuSection
{
[Key]
public int MenuSectionID { get; set; }
public virtual ICollection<Place> Places { get; set; }
}
The problem is I already have vast amounts of data and business logic associated with the current relationship. So I figure I'll have to leave the PlaceID property in for now and add the places collection.
My question then is: how do I then tell EF the relationship is now many-to-many and to populate the auto-generated joining table with the existing relationships so that I can then remove the PlaceID property from the MenuSection class?
Alternatively I suppose I could manually create a joining table and rewrite all the business logic, manually move the existing relationships over and rewrite all the business logic like so:
public class Place
{
[Key]
[ForeignKey("Place")]
public int PlaceID { get; set; }
[Key]
[ForeignKey("MenuSection")]
public int MenuSectionID { get; set; }
public virtual Place Place { get; set; }
public virtual MenuSection MenuSection { get; set; }
}
I'm surprised this question hasn't been asked before so I just wanted to check I haven't missed a trick?
Related
When I have two models with one to many relationship, they look like the models below:
public class Student
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int StudentID { get; set; }
public string Name { get; set; }
public int ClassID { get; set; }
[ForeignKey("ClassID")]
public virtual Class Class { get; set; }
}
public class Class
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int ClassID { get; set; }
public string Name { get; set; }
public virtual ICollection<Student> Students { get; set; }
}
This means that I can use the include method to get the related data. Now I work on a project with more than 600 tables. For these tables there are no relationships and I can not create relationships between the tables. Is there a way to link the models somehow so that I will be able to get the related data?
Yes, you can join tables without Relationships in Model Classes.
For example assume you have TeacherId in both of your tables Student and Class
You can join two tables based on TeacherId as follows
DbContext.Students
.Join(DbContext.Classes,student=>student.TeacherId,class=>class.TeacherId, (std,tchr)=> new {std,tchr});
I have some entities that can be associated with each other. A simple pair of classes to do this would ideally look like:
public class linkableEntity
{
public int Id { get; set;}
public virtual ICollection<Link> Links { get; set; }
}
public class Link
{
public int Id { get; set; }
public int SomeProperty { get; set; }
public int entity1Id { get; set; }
public virtual LinkableEntity entity1 { get; set;}
public int entity2Id { get; set; }
public virtual LinkableEntity entity2 { get; set;}
}
With tables something like:
Table linkableEntity
Column Id
Table link
Column entityId1 - foreign key to linkableEntity.Id
Column entityId2 - foreign key to linkableEntity.Id
Column someProperty
Having tried this out, and looking at this question: Entity Framework Code First - two Foreign Keys from same table I don't think that what I want to do was possible in EF4, has anything changed in EF6 that would make this possible? (I haven't found any more recent questions addressing this subject)
If not, is there a better way of representing this than changing linkableEntity to something like:
public class linkableEntity
{
public int Id { get; set;}
public virtual ICollection<Link> LinksWhereFirst { get; set; }
public virtual ICollection<Link> LinksWhereSecond { get; set; }
}
and then dealing with the mess?
I've the following situation I try to solve : I've 2 tables, a Course table with some fields and a CourseDescription table which is optional (so Course may have a CourseDescription but CourseDescription must have a Course). I'm trying to set this up. So far, here's what I have :
public class Course
{
[Key, Column("Key_Course")]
public int ID { get; set; }
public string Name { get; set; }
public virtual CourseDescription CourseDescription { get; set; }
}
public class CourseDescription
{
[Key, ForeignKey("Course")]
public int ID { get; set; }
public string Description { get; set; }
public string PreRequis { get; set; }
public int CoursesID { get; set; }
[ForeignKey("CoursesID")]
public Course Course { get; set; }
}
This "works" meaning that EF doesn't complains about my model but the relation is not properly done because EF associate the PK of CourseDescription with the PK of Course. In my database, this is not the case (ex : CourseDescription.ID=1 is associated with CourseDescription.CoursesID=3, not 1).
Is there a way to fix that with data annotation ? I know I can use the fluent API but I don't want to override the model building just for that (unless there's no other way).
Thanks
Well, I think you have two choices:
Configure an one to many relationship
If you want to map the FK of the relationship between Course and CourseDescription, and you don't want to declare that FK property as Key of the CourseDescription entity, then, you don't have other choice that configure an one-to-many relationship. In that case your model would be like this:
public class Course
{
[Key, Column("Key_Course")]
public int ID { get; set; }
public string Name { get; set; }
public virtual ICollection<CourseDescription> CourseDescriptions { get; set;}
}
public class CourseDescription
{
[Key]
public int ID { get; set; }
public string Description { get; set; }
public string PreRequis { get; set; }
[ForeignKey("Course")]
public int CourseID { get; set; }
public Course Course { get; set; }
}
Configure an one-to-one relationship but not map the FK of the
relationship
The only way that EF lets you map the FK in an one-to-one relationship is when the FK is declared as a PK too, so if you want to have diferent Ids in both entities and you want to stablish an one-to-one relationship, then you could do something like this:
public class Course
{
[Key, Column("Key_Course")]
public int ID { get; set; }
public string Name { get; set; }
public CourseDescription CourseDescription { get; set;}
}
public class CourseDescription
{
[Key]
public int ID { get; set; }
public string Description { get; set; }
public string PreRequis { get; set; }
[Required]
public Course Course { get; set; }
}
And work with the navigations properties.
It looks like you should not use ForeignKey attribute for ID property of CourseDescription class as you don't want to have an association between primary keys. Try to remove it.
Edit: It looks like I misunderstood the question previous time.
You can have your CourseDescription this way.
public class CourseDescription
{
[Key, ForeignKey("Course")]
public int ID { get; set; }
public string Description { get; set; }
public string PreRequis { get; set; }
public Course Course { get; set; }
}
In this case you don't need to have CoursesID field. Entities will be connected by primary keys.
I have this class structure:
public class Activity
{
[Key]
public long ActivityId { get; set; }
public string ActivityName { get; set; }
public virtual HashSet<ActivityLogMessage> ActivityLogMessages { get; set; }
public virtual HashSet<FileImportLogMessage> FileImportLogMessages { get; set; }
public virtual HashSet<RowImportLogMessage> RowImportLogMessages { get; set; }
}
public abstract class LogMessage
{
[Required]
public string Message { get; set; }
public DateTimeOffset CreateDate { get; set; }
[Required]
public long ActivityId { get; set; }
public virtual Activity Activity { get; set; }
}
public class ActivityLogMessage : LogMessage
{
public long ActivityLogMessageId { get; set; }
}
public class FileImportLogMessage : ActivityLogMessage
{
public long? StageFileId { get; set; }
}
public class RowImportLogMessage : FileImportLogMessage
{
public long? StageFileRowId { get; set; }
}
Which gives me this, model
Each Message (Activity, File or Row) must have be associated with an Activity. Why does the 2nd and 3rd level not have the same cardinality as ActivityLogMessage ? My attempts at describing the foreign key relationship (fluent via modelbuilder) have also failed.
This is really an academic exercise for me to really understand how EF is mapping to relational, and this confuses me.
Regards,
Richard
EF infers a pair of navigation properties Activity.ActivityLogMessages and ActivityLogMessage.Activity with a foreign key property ActivityLogMessage.ActivityId which is not nullable, hence the relationships is defined as required.
The other two relationships are infered from the collections Activity.FileImportLogMessages and Activity.RowImportLogMessages. They neither have an inverse navigation property on the other side nor a foreign key property which will - by default - lead to optional relationships.
You possibly expect that LogMessage.Activity and LogMessage.ActivityId is used as inverse property for all three collections. But it does not work this way. EF cannot use the same navigation property in multiple relationships. Also your current model means that RowImportLogMessage for example has three relationships to Activity, not only one.
I believe you would be closer to what you want if you remove the collections:
public virtual HashSet<FileImportLogMessage> FileImportLogMessages { get; set; }
public virtual HashSet<RowImportLogMessage> RowImportLogMessages { get; set; }
You can still filter the remaining ActivityLogMessages by the derived types (for example in not mapped properties that have only a getter):
var fileImportLogMessages = ActivityLogMessages.OfType<FileImportLogMessage>();
// fileImportLogMessages will also contain entities of type RowImportLogMessage
var rowImportLogMessage = ActivityLogMessages.OfType<RowImportLogMessage>();
I have got a User entity there are my users are stored in. For some users (admins) I would like to add additional details.
I have written following code.
public partial class UserProfile
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int UserId { get; set; }
[Display(Name = "EMail")]
[Required]
public string UserName { get; set; }
[ForeignKey("AdminDetailID")]
public virtual AdminDetail AdminDetail { get; set; }
public int? AdminDetailID { get; set; }
}
public class AdminDetail
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int AdminDetailID { get; set; }
[ForeignKey("UserId")]
public virtual UserProfile UserProfile { get; set; }
public int UserId { get; set; }
}
I like to navigate from my AdminDetail table back to my User Profile table by writing eg. admin.UserProfile.UserName. However, when I run Database-Update I receive:
The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.
When I delete the UserProfile property everything works great.. How can I create a "back" navigation within my AdminDetail class?
Entity Framework Code-First allows for polymorphic classes to be stored in the same table. Have you considered using a relationship like this instead?
public partial class UserProfile
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int UserId { get; set; }
[Display(Name = "EMail")]
[Required]
public string UserName { get; set; }
}
public class AdminProfile : UserProfile
{
// AdminProfile members.
}
This results in a UserProfile table with an additional column called Discriminator that EF creates and manages for you. This column indicates whether each row in the table is a UserProfile or an AdminProfile. Rows which are of type UserProfile ignore the columns that are specific to AdminProfile when accessed by EF.
Entity framework handles all of the type discrimination for you so you don't need to worry about that directly. Your DbContext will simply have a DbSet which can also store entities of type AdminProfile.
You don't need to have a FK in your UserProfile class. To set up a proper 1:1 only the AdminDetail class would actually need to have the foreign key to the UserProfile class. You can still keep the virtual property to be able to navigate back and forth, and EF will know what it is that you're doing. Similar to this:
public partial class UserProfile
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int UserId { get; set; }
[Display(Name = "EMail")]
[Required]
public string UserName { get; set; }
public virtual AdminDetail AdminDetail { get; set; }
}