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What's the correct way to reference tables using Code First with EF.Core for searching efficiently

Fairly new to EF.Core and I'm having some issues as my tables start getting more complex. Here's an example of what I have defined for my classes. Note ... there are many more columns and tables than what I have defined below. I've paired them down for brevity.
public class User
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public bool Active { get; set; }
}
Followed by
public class JournalEntry
{
public int Id { get; set; }
public int UserId { get; set; }
public string Details { get; set; }
public DateTime DateEntered { get; set; }
public virtual User User { get; set; }
}
I want to be able to issue the following query and INCLUDE the User Table so that I can then populate a ViewModel with columns from the User Table without having to do another lookup and also to sort the data while retrieving it:
public IQueryable<JournalEntry> GetByUser(int userId)
{
return _DbContext.JournalEntries.Where(j => j.UserId == userId)
.Include(u => u.User)
.OrderBy(u=> u.User.FirstName)
.ThenBy(j => j.DateEntered);
}
My controller would then have something similar to the following:
public IActionResult List(int userId)
{
var journalEntries = new _dbRepository.GetByUser(userId);
var myViewModel = new MyViewModel();
myViewModel.UserName = ($"{journalEntries.User.FirstName} {journalEntries.User.LastName}");
myViewModel.Entries = journalEntries;
etc ....
return View(myViewModel);
}
I'm loading the user's first and last name in the View Model and whatever other attributes from the various tables that are referenced. The problem that I'm having is that I'm getting errors on the Migration creation "Foreign key constraint may cause cycle or multiple cascade paths." And of course, if I remove the line reading public virtual User User { get; set; } from the JournalEntry class then the problem goes away (as one would expect).
I believe that the way I'm doing the models is incorrect. What would be the recommended way that I should code these models? I've heard of "lazy loading". Is that what I should be moving towards?
Thanks a bunch.
--- Val

Your query returns an IQueryable<JournalEntry> not a JournalEntry.
Change the code to get the user details from the first object:
var myViewModel.UserName = ($"{journalEntries.First().User.FirstName} {journalEntries.First().User.LastName}");
In the line above I'm calling First() on your journal entries collection and that would have a User. Then I can access FirstName and LastName.
Also, don't bother with LazyLoading since you are learning. It could cause select n+1 issues if used incorrectly

Conditional Include in asp.net core and Entity Framework

I just started my first project using asp.net core and for the first time I'm gonna use the code repository for my project in C# and VS 2019.
I create a new Model and it called Comment. This Table can save all of the comments on the project, That mean is user comments in POSTS, SOCIALMEDIA, and etc Areas saved in this table
[Key]
public int CommentId { get; set; }
public eTable Table { get; set; }
public int ContentId { get; set; }
[StringLength(1500)]
public string Notes { get; set; }
public virtual AnalysedMarket AnalysedMarket { get; set; }
ContentID is my foreign key, And my eTable enum type is like bellow:
public enum eTable
{
AnalysedMarket,
Blog,
News,
Migration,
}
I created a new class for AnalysedMarket as well to save Users data from our social media area.
[Key]
public int AnalysedMarketId { get; set; }
[StringLength(255)]
public string Images { get; set; }
public int Hits { get; set; }
public string Notes { get; set; }``
Now I created a method in my code repository for extract data using EF and LINQ to get list of AnalysedMarket data but I can't Include my result with Comment table and result of my code repository in the comment section is null always.
public async Task<IEnumerable<AnalysedMarket>> List(int? page, int? perPage, eStatus? status, string userId)
{
var query = _db.AnalysedMarkets.Select(a => a);
if (status.HasValue)
query = query.Where(m => m.Status.Equals(status));
if (!string.IsNullOrEmpty(userId))
query.Where(m => m.CreatedBy.Equals(userId));
query.Include(a => a.Comments.Where(c => c.Table.Equals(eTable.AnalysedMarket) && c.ContentId == a.AnalysedMarketId));
if (page.HasValue && perPage.HasValue)
return await query.OrderBy(a => a.AnalysedMarketId).ToPagedListAsync(page.Value, perPage.Value);
else
return await query.OrderBy(a => a.AnalysedMarketId).ToListAsync();
}
Actually my question is how can I get list of AnalysedMarket data included by Comment data.
And it has a condition and it says include comment if ContentId is equal to AnalysedMarketId and eTable is Table.AnalysedMarket.
I read the articles about conditional Include but I didn't get any thing of them.
Example 1
Example 2

You need to add a reference from AnalysedMarket to comment like this in your AnalysedMarket-Class:
ICollection<Comment> Comments { get; set; }
And then include them while querying your AnalysedMarkets like this:
var query = _db.AnalysedMarkets.Include(c => c.Comments);
/Edit:
Regarding your comment - for this you would need kind of an hierarchy/inheritance structure. It seems to be supported by EfCore and something like this should work:
public class CommentableItem {
ICollection<Comment> Comments {get;set;}
}
public class Comment {
CommentableItem CommentableItem {get;set;}
}
public class AnalysedMarket : CommentableItem {
}
Than you should be able to use the include for each item inheriting from CommentableItem. I did not use the inheritance feature yet (as far as I know this is quite new for EF Core), so for further instructions check the documentation

Does anyone know why I'm getting this warning from NHibernate/NH Profiler?

"Disabled lazy properies fetching for fully_qualified_type_name beacuse it does not support lazy at the entity level".
This warning was reported by NH Profiler, and as a result, I'm experiencing the dreaded SELECT N + 1 side affect. So if 2200 Subgroup entities are returned, an additional query is being executed to retrieve each InvoicePreference entity (2201 queries total). Something about that relationship seems to be causing the issue.
Here are the entities in question and their respective mappings.
Entity 1
public class Subgroup : Entity
{
public virtual string GroupNumber { get; set; }
public virtual string RUSNumber { get; set; }
public virtual string REANumber { get; set; }
public virtual string CustomerType { get; set; }
public virtual string Name { get; set; }
public virtual IList<IndividualEmployment> Employees { get; set; }
public virtual IList<BenefitsAdministrator> Administrators { get; set; }
public virtual InvoicePreference InvoicePreference { get; set; }
}
Entity 2
public class InvoicePreference : IEntity
{
public virtual Guid Id { get; set; }
public virtual Guid SubgroupId { get; set; }
public virtual bool PaperlessNotifications { get; set; }
}
Mapping 1
public static AutoPersistenceModel ConfigureSubGroup(this AutoPersistenceModel
autoPersistenceModel)
{
return autoPersistenceModel.Override<Subgroup>(map =>
{
map.Table("SubgroupV");
map.Id(s => s.Id).Column(SubGroupPrimaryKeyColumn);
map.Map(s => s.CustomerType, "BAS_Customer_Type");
map.Map(s => s.RUSNumber, "BAS_RUS_Number");
map.Map(s => s.GroupNumber, "BAS_Group_Number");
map.Map(s => s.REANumber, "BAS_REA_Number");
map.HasMany(s => s.Administrators).KeyColumn(SubGroupPrimaryKeyColumn);
map.HasMany(s => s.Employees).KeyColumn(SubGroupPrimaryKeyColumn);
map.HasOne(s => s.InvoicePreference).PropertyRef(i => i.SubgroupId);
});
}
Mapping 2
public static AutoPersistenceModel ConfigureInvoicePreference(this AutoPersistenceModel autoPersistenceModel)
{
return autoPersistenceModel.Override<InvoicePreference>(map =>
{
map.Table("SubgroupInvoicePreference");
map.Schema(RetirementStatementsSchemaName);
});
}

InvoicePreference is referenced as hasone. Since it is lazyloaded by default NHibernate will create a proxy to populate the property InvoicePreference and to do that it needs the identity from InvoicePreference which is not present in the Subgroup. Therefor it has to query for it using the property in the propertyref.
To remedy that do .Not.LazyLoad() and/or .Fetch.Join()

I guess that there is some reason why NH disabled lazy loading "on entity level", which I understand as not creating proxies. There may be several reasons for that. Did you get another warning before? I don't really understand why it disabled "lazy properies", which means that some properties are lazy loaded. This is a feature that is used in the mapping explicitly, but I can't see something like this in your mapping definitions.
To overcome the N+1, you may use Fetch.Join. I had bad experience with that, because the queries get really large. In a complex model, you could hit some database server limits (like max. number of columns of a query). It is mostly better to use batch size, which reduces the number of queries notably. Take a look at my answer to "Nhinerbate lazy loading of reference entity".

EF Code First 4.1: "Multiple Inheritence" (Is A) Question

I am trying to model a sort of "multiple inheritence" relationship with EF 4.1 Code First. Here is an example what I am trying to do.
Let's say I am attempting to model the way a user interacts with my application using a "User" object. This, being the base class, is used to describe the current user when they aren't doing anything in particular (such as visiting the homepage). It may look like this:
public class User
{
public Guid ID { get; set; } // Just use the forms authentication user ID
public string FirstName { get; set; }
public string LastName { get; set; }
}
Now, if I want to create a representation of that same user but in a different portion of the site, say, as a shopper, it may look like this:
public class Shopper : User
{
public virtual ICollection<Orders> Orders { get; set; }
}
And so on, and so forth. When I go to insert a Shopper that has a pre-existing User entry, it throws an exception because the PK is already taken in the User table.
Is there any way to model this (IsA) relationship with EF Code First? Or am I going to be stuck with something like this?
public class Shopper
{
public Guid UserID { get; set; }
public virtual User User { get; set; }
public virtual ICollection<Order> Orders { get; set; }
public string FirstName
{
get { return User.FirstName; }
set { User.FirstName = value; }
}
// yada, yada, yada...
}
I would like to stick with Code First and model the relationships right in my DbContext, but I can't figure out quite how to do something like this. Thanks!
EDIT:
So, I am trying to do something like this:
public void SomeMethod ()
{
var UserID = Guid.NewGuid ();
var MyUser = new User () { ID = UserID };
SaveUserToDatabase (MyUser);
var ShopperRepresentation = GetUserAsShopper (UserID);
// Do stuff.
}
Basically like using object-oriented roles, I guess. I want to use the same PK for every represenation of that user, but store all of their basic information in a base class called User. I know this is possible if I write my own SQL, of course, but I want to see if EF Code First can do it, too.

Yes, you can do it the way you describe in your first two code examples.
I think you just need to define a mapping, which you'll want to do in your OnModelCreating function of your DataContext in addition to having your classes set up right. How you do it depends on what mapping scheme you're using. I went for Table-Per-Type (TPT) in my most recent project, so I had something like this:
modelBuilder.Entity<User>().ToTable("Users");
modelBuilder.Entity<Shopper>().ToTable("Shoppers");
modelBuilder.Entity<OtherUser>().ToTable("OtherUsers");
Let me know if that doesn't work for you and I'll see what I can do.
Edit:
Having seen your clarification below, I can't think of a way to do that. You'd have to keep each objects stored separately (having EF treat a Shopper as just a Shopper, not a Shopper and a User), even though they share common data. That could lead to data mismatches (if, say, Shopper got its LastName updated but User didn't). I think you might be better off going with something like:
public class User
{
public virtual Guid ID { get; set; }
public virtual string FirstName { get; set; }
public virtual string LastName { get; set; }
public virtual ShopperInfo { get; set; }
}
public class ShopperInfo
{
public virtual ICollection<Order> Orders { get; set; }
}
and then when you need to treat User as a Shopper, you just access the ShopperInfo (and if its not there, you create it). EF will be able to properly set that up for you no problem.
Though if you're going to have a lot of types of users, that might get cumbersome. Just a suggestion though - I think its a bit cleaner.

CTP5 EF Code First Question

You can find the source code demonstrating this issue # http://code.google.com/p/contactsctp5/
I have three model objects. Contact,ContactInfo,ContactInfoType. Where a contact has many contactinfo's and each contactinfo is a contactinfotype. Fairly simple I guess. The problem I'm running into is when I go to edit the contact object. I pulled it from my contact repository. Then I run "UpdateModel(contact);" and it updates the object with all the values from my form. (monitoring with debug) When I save the changes though, I get the following error:
The operation failed: The relationship
could not be changed because one or
more of the foreign-key properties is
non-nullable. When a change is made to
a relationship, the related
foreign-key property is set to a null
value. If the foreign-key does not
support null values, a new
relationship must be defined, the
foreign-key property must be assigned
another non-null value, or the
unrelated object must be deleted.
It seems like after I call update model it nulls out my references and this seems to break everything? Any thoughts on how to remedy would be greatly appreciated. Thanks.
Here are my models:
public partial class Contact {
public Contact() {
this.ContactInformation = new HashSet<ContactInformation>();
}
public int ContactId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public virtual ICollection<ContactInformation> ContactInformation { get; set; }
}
public partial class ContactInformation {
public int ContactInformationId { get; set; }
public int ContactId { get; set; }
public int ContactInfoTypeId { get; set; }
public string Information { get; set; }
public virtual Contact Contact { get; set; }
public virtual ContactInfoType ContactInfoType { get; set; }
}
public partial class ContactInfoType {
public ContactInfoType() {
this.ContactInformation = new HashSet<ContactInformation>();
}
public int ContactInfoTypeId { get; set; }
public string Type { get; set; }
public virtual ICollection<ContactInformation> ContactInformation { get; set; }
}
My Controller Action:
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(Contact person) {
if (this.ModelState.IsValid) {
var contact = this.contactRepository.GetById(person.ContactId);
UpdateModel(contact);
this.contactRepository.Save();
TempData["message"] = "Contact Saved.";
return PartialView("Details", contact);
} else {
return PartialView(person);
}
}
Context Code:
protected override void OnModelCreating(System.Data.Entity.ModelConfiguration.ModelBuilder modelBuilder) {
modelBuilder.Entity<Contact>()
.HasMany(c => c.ContactInformation)
.WithRequired()
.HasForeignKey(c => c.ContactId);
modelBuilder.Entity<ContactInfoType>()
.HasMany(c => c.ContactInformation)
.WithRequired()
.HasForeignKey(c => c.ContactInfoTypeId);
}

There's a few things going on here.
1 If you are set up for lazy loading child objects are only loaded if you tell them to load. This can be done with the following in your query.
..
context.Contacts.Include(c => c.ContactInfos).Include(c => c.ContactInfos.ContactInfoType)
see this article for full details on making sure objects are loaded as you want.
2 If you don't want to save contactinfo and contactinfotype (because they are not loaded or you just don't want to), you will need to tell the context not to save child objects that shouldn't be updated. This can be done using:
..
context.StateManager.ChangeObjectState(entity.ContactInfos.ContactInfoType, EntityState.Unchanged);
I find I need to do that when changing/using a country object to user data. I definitely never want that to be updated by a user.
In the middle of writing a bit of a guide to all this, but could be weeks until it's done on my blog
3 MVC won't store/send back anything you don't put into the form. If you send an object heirarchy to the form and the values aren't represented in hidden inputs, they will come back empty on your model. For this reason, I generally make viewmodels that are editable only versions of the entities with a ToEntity and a ToModel method on them. This also covers me for security as I don't want all sorts of user ids in hidden inputs, just so my entities map straight into MVC (see this article on overposting).
I WOULD have thought that the fact you have your contactinfo properties set to virtual, the UpdateModel wouldn't mind if they didn't exist on the return, but I could well be wrong as I haven't tried it.

I figured this question out thanks to Morteza Manavi on the entity framework website. My issue was caused by my ContactInformation model properties, 'contactid' & 'contacttypeid' not being nullable. Once I fixed this everything with UpdateModel() worked correctly. Thank you very much!