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Root Question Message
Populus2/12/2023
✅ ForeignKey Entity Framework and Identity
I've got the following classes: "Account", "Post", "Tag" and "Image".
The "Post" class contains the following:
I can't seem to quite understand how this type of mapping works. Why can't the Lists simply reference the correct AccountId? I see no reason there could not be different fields referencing the same "Id" for different purposes.
What am I doing wrong?
I've got the following classes: "Account", "Post", "Tag" and "Image".
The "Post" class contains the following:
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid? PostId { get; set; }
public List<Tag> Tags { get; set; }
public List<Image> AttachedImages { get; set; }
[ForeignKey("Account")]
public Guid? OriginalPosterId { get; set; }
public Account? OriginalPoster { get; set; }
[ForeignKey("Account")]
public List<Guid> PostParticipantsIds { get; set; }
public virtual ICollection<Account> PostParticipants { get; set; }
[ForeignKey("Account")]
public List<Guid> UsersAttendingIds { get; set; }
public virtual ICollection<Account> UsersAttending { get; set; }I can't seem to quite understand how this type of mapping works. Why can't the Lists simply reference the correct AccountId? I see no reason there could not be different fields referencing the same "Id" for different purposes.
What am I doing wrong?
Populus2/12/2023
Here's the latest error message among many.
System.InvalidOperationException: 'There are multiple navigations in entity type 'Post' which are pointing to same set of properties 'Account' using a [ForeignKey] attribute: 'PostParticipantsIds', 'UsersAttendingIds'.'
Angius2/12/2023
Well, this won't work, unless you have a table of GUIDs
[ForeignKey("Account")]
public List<Guid> PostParticipantsIds { get; set; }Angius2/12/2023
In general, lists of IDs won't work
Angius2/12/2023
It's because that's how many-to-one relationships in databases work
Angius2/12/2023
Databases, in general, have no concept of a list
Angius2/12/2023
So if you want a relationship where one post can have one category, and one category can have many posts, it is the post that needs a foreign key to the category
Angius2/12/2023
The category cannot have a list of foreign keys to posts
Populus2/12/2023
I was hoping I could declare a List<Guid> and have the DB populate it with every associated AccountId one-by-one as they become relevant.
"it is the POST that needs a FK..." - My attempt at this was to create these List<Guid>.
What is your recommended course of action?
"it is the POST that needs a FK..." - My attempt at this was to create these List<Guid>.
What is your recommended course of action?
Angius2/12/2023
To set it up properly
Angius2/12/2023
Also, get rid of those
virtuals while you're at itAngius2/12/2023
Lazy loading is the devil
Populus2/12/2023
Maybe I can create a "Participator" class and a "Attending" class. Both with "List<Account>" fields.
Angius2/12/2023
class Account
{
public required Guid Id { get; set; }
public List<Post> Participates { get; set; } = new();
public List<Post> AttendingPosts{ get; set; } = new();
}
class Post
{
public required Guid Id { get; set; }
public List<Tag> Tags { get; set; } = new();
public List<Image> Images { get; set; } = new();
public required Account OriginalPoster { get; set; }
public Guid OriginalPosterId { get; set; }
public List<Account> Participants { get; set; } = new();
public List<Account> AttendingUsers { get; set; } = new();
}
class Tag
{
public required Guid Id { get; set; }
public List<Post> Posts { get; set; } = new();
}
class Image
{
public required Guid Id { get; set; }
public required Post Post { get; set; }
}Angius2/12/2023
Something like this
Angius2/12/2023
Those coloured pairs will create many-to-many relationships and necessary pivot tables
Angius2/12/2023
Since there are two many-to-many relationships between accounts and posts, you'll need to configure them a bit
Angius2/12/2023
builder.Entity<Post>(cfg => {
cfg.HasMany(p => p.Participants)
.WithMany(a => a.Participates);
cfg.HasMany(p => p.AttendingUsers)
.WithMany(a => a.AttendingPosts);
});Angius2/12/2023
Configuring the post with this should just about do the trick
Populus2/12/2023
This utilizes "Fluent API"? Searching in NuGet and wondering whether it's "Henk Mollema" or "Jeremy Skinner" who made it?
Angius2/12/2023
Yes, it is fluent config
Angius2/12/2023
No clue who made it
Populus2/13/2023
Thanks ZZ