EF lookup items being added when they already exist - asp.net-mvc

I'm pretty sure this isn't a duplicate question (or I don't know how to ask it properly) so here goes. I have an ASP.NET MVC project using EF 6.1. In it I have an entity called Member. The Member has a property called Races that can contain one or more Race entities. The Races property on Member:
public virtual ICollection<Race> Races { get; set; }
The Race entity:
public class Race : ILookupListItem {
public int Id { get; set; }
public string Description { get; set; }
public bool Active { get; set; }
[JsonIgnore]
public virtual ICollection<Member> Members { get; set; }
}
The Race entity is what I have always called a lookup.
My issue arises when I try to save the entity after updates have occurred on the client. My SaveMember controller method is below along with my business logic method for actually saving the entities. (To avoid any confusion, InjectFrom is the ValueInjecter method and the JSONResponseError and JSONResponseSuccess classes are our custom wrappers around a JsonResult.)
public JsonResult SaveMemberInfo(MemberInfoModel model) {
try {
// retrieve member
var member = new Member();
member.InjectFrom(model);
var races = new List<Race>();
races.InjectFromList(model.Races);
member.Races = races;
// save member
var savedMember = _members.UpdateMember(member, out errId);
var savedModel = GetMemberChartViewModel(savedMember);
// notify user of success
return new JsonResponseSuccess(savedModel);
}
catch (Exception ex) {
return new JsonResponseError(message);
}
}
The _members.UpdateMember method is below.
public Member UpdateMember(Member contract, out int? errId) {
try {
using (_db = new ApplicationContext(_currentUserID)) {
// updates entity state in the context using the entity's State field from Julie Lerman's example on MSDN.
_db.FixState();
_db.SaveChanges();
errId = null;
return contract;
}
}
catch (Exception ex)
{
// log error to db and return id
errId = LogError(ex, "MemberLogic.UpdateMember");
return null;
}
}
When I get the data contract back from the UpdateMember method, the Races property has all the races saved to the memeber before the update, plus any that I just saved (so it's adding but not doing a diff to determine which items were already there and which were removed). In addition the Races table will now have duplicate entries for the "new" races. My assumption is that this isn't EF's default behavior but I've never worked with a dropdown list that populated a list of items, usually it's just a single property (like Gender or Country). Is there something obvious I'm missing?
Thanks!
EDIT: It just occurred to me that the EntityConfiguration for the Member and Race intersection table would be useful, added below. Obviously, this is only the part I thought to be relevant to the question.
HasMany(t => t.Races).WithMany(t => t.Members).Map(m =>
{
m.ToTable("MemberRaces", "dbo");
m.MapLeftKey("MemberId");
m.MapRightKey("RaceId");
});

Related

Updating many-to-many relationship entity framework

I have problem with updating entites that have many-to many relationship. Below my User and category class:
public class User : IEntity
{
[Key]
public virtual long Id { get; set; }
private ICollection<Category> _availableCategories;
public virtual ICollection<Category> AvailableCategories
{
get { return _availableCategories ?? (_availableCategories = new List<Category>()); }
set { _availableCategories = value; }
}
}
public class Category : IEntity
{
[Key]
public long Id { get; set; }
/// <summary>
/// Full name or description of a category
/// </summary>
[StringLength(255)]
public string FullName { get; set; }
}
This is code snippet from my repository
public override void Edit(User user)
{
var dbUser = _context.Users.Include(x => x.AvailableCategories)
.Single(x => x.Id == user.Id);
var categories = _context.Categories;
dbUser.AvailableCategories.Clear();
foreach (var cat in user.AvailableCategories)
{
dbUser.AvailableCategories.Add(cat);
}
_context.Entry(dbUser).State = EntityState.Modified;
}
However the categories don't get updated. What EF does is insert empty rows into category table and sets relations to this new rows with user.
How can I update User so that I change only categories that already exist in the database?
User that I pass to Edit method has AvailableCategories with only Ids set (rest of properties are empty).
When you're doing something like posting back M2M relationships, you either must post the full object, as in every single property on those objects, or simply post a list of ids and then use those to query the associated objects back from the database. Otherwise, Entity Framework understands your purpose to be to update the properties on the objects as well, in this case with empty values.
Obviously the first option is quite unwieldy, so the second way is the preferred and standard way. Generally, for this, you'd want to use a view model so you could have a property like the following, that you would post into:
public List<long> SelectedCategories { get; set; }
But, if you insist on using the entity directly, you can get much the same result by simply doing:
var selectedCategories = user.AvailableCategories.Select(m => m.Id)
Once you have the ids:
var newAvailableCategories = _context.Categories.Where(m => selectedCategories.Contains(m.Id));
And then finally set that on your user:
dbUser.AvailableCategories = newAvailableCategories;
I notice you are also adding the user.AvailableCategories directly into dbUser.AvailableCategories. I've noticed when binding back complex objects from an MVC view that DB Entities are no longer attached to the DbContext. If you look at the entity, you can verify by checking dbContext.Entry(cat).State is "detached" (or something unexpected) I believe.
You must query those entities back out of the dbContext (possibly by using the returned cat.Id's). Or otherwise manually set the entities as "unchanged". And then add those "non-detached" items into dbUser.AvailableCategories. Please see Chris's answer as it shows with specific code how to get this done.
Also, I might use a linking entity. Possibly something like this:
public class UserCategory
{
public User User {get;set;}
public Category Category {get;set;}
}
And add it to DB context. Also, drop the linking lists in your current User and Category class. This way you can manipulate the UserCategory class (and DbSet) to manage your many-to-many relationship.

Self referencing loop detected when serializing Data models in MVC5 / EF6

I am getting this error "Self referencing loop detected" while serializing using 'Json.NET'
I have a Book model
public class Book
{
public Book()
{
BookPersonMap = new List<BookPersonMap>();
}
public int BookId { get; set; }
public virtual ICollection<BookPersonMap> BookPersonMap { get; private set; }
(And many other virtual Icollections)
}
And this is the BookPerson Mapping class:
public class BookPersonMap
{
public int BookId { get; set; }
public string PersonName { get; set; }
public int PersonTypeId { get; set; }
public virtual Book Book { get; set; } // Foreign keys
public virtual PersonType PersonType { get; set; }
}
When I try to Serialize the Book object it throws:
"Self referencing loop detected for property 'Book' with type 'System.Data.Entity.DynamicProxies.Book_57F0FA206568374DD5A4CFF53C3B41CFDDC52DBBBA18007A896 08A96E7A783F8'. Path 'BookPersonMap[0]'."
I have tried the things suggested in some of the similar posts
Example:
PreserveReferencesHandling = PreserveReferencesHandling.Objects in Serializer settings returned a string with length 3 million!
ReferenceLoopHandling = ReferenceLoopHandling.Ignore in Serializer settings :
"An exception of type 'System.OutOfMemoryException' occurred in Newtonsoft.Json.dll but was not handled in user code"
^ Same luck with "ReferenceLoopHandling.Serialize"
MaxDepth = 1 : Infinite loop again.
Putting [JsonIgnore] on the virtual properties is working but it is a tedious task (because of numerous FK references) and not efficent, since if I miss one property and it will throw exception.
What is missing from above Json settings for them be not working?
services.AddMvc().AddJsonOptions(opt => {
opt.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
});
I have found the best way to solve this type of error is to flatten your model using a view model.
Put a break point on your object before it is serialized and start drilling into the child properties. You will probably find that you can go on indefinitely.
This is what the serializer is choking on.
Create a Constructor for your controller and put on it this line of code :
db.Configuration.ProxyCreationEnabled = false;
//db is the instance of the context.
For asp.net mvc 5 use this
Add the code below to your Application_Start method inside globax.asax file or startup file.
protected void Application_Start()
{
..
GlobalConfiguration.Configuration.Formatters.JsonFormatter
.SerializerSettings
.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
}
Disable lazy loading and
ensure your controller does not return
Json(..obj)
rather it should return
Ok(..obj)

Simple approach to CRUD intersection table in MVC ASP.NET and EF?

I am using C#, MVC3, EF5, SQL Server 2008 R2.
I have an intersection table ie
Lecturer -< LecturerCourse >- Course
The list of Lecturers are populated.
When I add a course, it would be neat to have a list of Lecturers that I could select from, that teach the course in question. When I save the new Course record, this multiselect also should save its data back to the "LecturerCourse" table via Model Binding.
I am using EF5.
Can you recommended a simple and standard approach to solving CRUD for a join, ie "LecturerCourse", table? I have looked online, but some of the approaches seem very complicated.
Many thanks.
Alright, it's going to be a long one. To allow this to happen in "one page" (through POST, or you could use Ajax, technically), you need a combination of a Get and Post version of the method and to construct your view model correctly. Below are the classes that I will use for demonstration purposes:
public class NewCourse
{
[Required]
public string Name { get; set; }
// And your other properties
public int[] LecturerIds { get; set; }
}
public class ViewLecturer
{
public int Id { get; set; }
public int Name { get; set; }
}
public class NewCourseViewModel
{
public NewCourse Course { get; set; }
public IEnumerable<ViewLecturer> Lecturers { get; set; }
}
NewCourseViewModel will be the model for the View (see below). ViewLecturer will give you a lighter mapping between your available Lecturer and the information required to Add to them.
As for the Controller:
public class CourseController : Controller, IDisposable
{
private Lazy<YourContext> lazyContext =
new Lazy<YourContext>(() => new YourContext());
private YourContext Context
{
get { return lazyContext.Value; }
}
public ActionResult New()
{
var model = new NewCourseViewModel {
Course = new NewCourse(),
Lecturers = Context.Lecturers
.Select(l => new ViewLecturer { Id = l.Id, Name = l.Name })
};
return View(model);
}
[HttpPost]
public ActionResult New(NewCourse course)
{
if(ModelState.IsValid)
{
var lecturers = course.Lecturers
.Select(l => new Lecturer { Id = l.Id })
.ToList();
foreach(var lecturer in lecturers)
Context.Lecturers.Attach(lecturer);
var newCourse = new Course {
Name = course.Name,
// ... and the rest of the mapping
Lecturer = lecturers
};
context.Courses.Add(newCourse);
context.SaveChanges();
// Could have to handle DbUpdateException if you want
return RedirectToAction(...);
}
return View(new NewCourseViewModel {
Course = course,
Lecturers = Context.Lecturers
.Select(l => new ViewLecturer { Id = l.Id, Name = l.Name })
});
}
public void Dispose()
{
if(lazyContext.IsValueCreated)
lazyContext.Value.Dispose();
}
}
Your first New method will give you the entry point for your Course creation page. The rest of the validation and actual adding will be done through the [HttpPost]overload. As for your View (that should be in the ~/Views/Course/New.cshtml):
#model NewCourseViewModel
// ... Then when you are ready to begin the form
#using(Html.BeginForm("New", "Course", FormMethod.Post))
{
// Your List of Lecturers
#Html.ListBoxFor(m => m.Course.LecturerIds,
new MultiSelectList(
Model.Lecturers,
"Id",
"Name",
m.Course.LecturerIds ?? new int[0]
))
// Your Other Model binding
}
When the submit button will be pressed, the action matched will be the New(NewCourse course). The names are important because of the way the HtmlHelpers generate their Ids. Because we are only included one property of the whole view model, it will match the parameter name course based on the view model's Course property. You will get a list of Ids for the Lecturers which you will be able to use to attach to the DbContext and add directly to the new Course model (Entity Framework will do the rest). In cases where there was a problem, we can get back the list of lecturers and re-use the same NewCourse in the view model.
Now this is example is very basic but it should give you a good starting point as to how you can structure your view model.

Associated entities not attaching to parent object when saving

I am working on an application that uses EF 4.2 and database-first development, using the standard T4 template to generate a DbContext and POCOs. The T4 templates generate entities something like this:
public class Address
{
public int AddressId { get;set; }
public string Address1 { get;set; }
public string City { get;set; }
}
public class Account
{
public int AccountId { get;set; }
public string Name { get;set; }
public int AddressId { get;set; }
public Address BillingAddress { get;set; }
}
When I create a billing address for an existing account, my code is something like this:
public void Save(Account updated)
{
var existing = DbContext.Find(updated.AccountId);
MyContext.Entry(existing).CurrentValues.SetEntry(updated);
existing.Address = updated.Address;
MyContext.SaveChanges();
}
Watching SQL Server Profiler, I can see the Address entry being inserted into the database, but unfortunately, it is occurring after the Account entry is updated, so the address is detached from its parent account, and when I next load the account, the billing address is empty again.
A workaround is to add the following code after the call to SaveChanges():
if (existing.AddressId == null && existing.Address != null)
{
existing.AddressId = existing.Address.AddressId;
MyContext.SaveChanges();
}
which, while it may work, requires a second SQL UPDATE to the database, and as the entity grows and adds more associations, requires more and more hacks. Is there something obvious that I'm missing?
** UPDATE **
Following Ladislav's answer below, I added a call to the following method in the WriteNavigationProperty to my T4 template:
void WriteKeyAttribute(CodeGenerationTools code, NavigationProperty navigationProperty, MetadataTools ef)
{
var dependentProperties = navigationProperty.GetDependentProperties();
if (dependentProperties.Any())
{
var keys = new List<string>();
foreach (var key in dependentProperties)
{
keys.Add(String.Format("\"{0}\"", key.Name));
}
#>
[ForeignKey(<#= String.Join(", ", keys) #>)]
<#+
}
}
Hope that helps!
It sounds like your BillingAddress is incorrectly mapped because AddressId is not handled as the FK of the relation.
Try to add this attribute to your navigation property:
[ForeignKey("AddressId")]
public Address BillingAddress { get;set; }
If you are using EDMX with database first make sure that the there is correctly configured relation between those classes. EF uses this information in its store mapping and store mapping defines sequence of the operations. If you don't have correctly configured relation entities are processed in alphabetical order of their type names => Account is processed prior to Address.
Btw. are you sure that your Account is not duplicated during your SaveChanges call?

DeleteOnNull Error

I've got a set of DB objects sitting in an EntitySet on my main object definition. This handles additions and updates fine, but I found the removing items from the list didn't result in the database records being deleted, so I had to create a method in the data repository object to delete the records as the data object doesn't have access to the data-context in which it is being used.
I was looking to see if I could bring this delete into the main object and I found the DeleteOnNull attribute to the association, but when I use it, I get an error "DeleteOnNull can only be true for singleton association members mapped to non-nullable foreign key columns". My code is:
private EntitySet<UserSite> _userSites = new EntitySet<UserSite>();
[Association(Name = "User_UserSites", Storage = "_userSites", ThisKey = "UserID", OtherKey = "UserID", DeleteOnNull=true)]
public IList<UserSite> UserSites { get { return _userSites; } set { } }
my usersite object is
[Table(Name="UserSite")]
public class UserSite
{
[Column]//(IsPrimaryKey = true)]
public int UserID { get; set; }
[Column]//(IsPrimaryKey = true)]
public string Site { get; set; }
[Column]
public bool DefaultSite { get; set; }
[Column(IsPrimaryKey = true, AutoSync = AutoSync.OnInsert)]
public int UniqueID { get; set; }
}
Can I use DeleteOnNull to keep all my data update methods within my main user object, or do I have to handle the deletes at the repository level?
DeleteOnNull is only for singleton associations. So you can put it on UserSite.User but not on User.UserSites. It's still not quite as automatic as you'd like it to be, though. There is an example here.
It's hard for LINQ to SQL to infer the behavior you want, because it can't guess if you want composition or aggregation, so it chooses the safe guess (aggregation).

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