I've manay-to-many relationship between two entities: Categories <--> Items
public class CategoryMaster
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
public virtual List<SubCategoryMaster> SubCategories { get; set; }
public List<ItemMaster> Items { get; set; }
}
public class ItemMaster
{
public long Id { get; set; }
public string Name { get; set; }
public List<CategoryMaster> Categories { get; set; }
}
Whenever I try to explicit load related items to all/certain categories, it gives me
all related items
related categories to those items
related items to those categories and so on...nested/circular references
db.CategoryMaster
.Include(x=>x.Items)
.Include(x=>x.SubCategories.Select(y=>y.Items))
.ToList();
Hence results in below error while serializing it to JSON on *.cshtml with Json.Encode();
A circular reference was detected while serializing an object of type 'GoGreen.Data.Entities.SubCategoryMaster'.
Since I've disabled the lazy loading at property level, I'm not expecting it to load all nested entities(circular references) at any point of time. Is there a way to load all related level one records i.e. Categories and related items.
Related question - But Iodon't want to go with any of the two ways suggested.
NOTE : I'm more interested in knowing why EF behaves like this. It seems a bug to me.
First approach: you can add attribute above properties you don't want to exclude it from being serialized using [ScriptIgnore], you can create partial class and add your customization if your entities are auto generated
Second approach: Create a Model with only properties you need in your view and select only this model and set your properties
EFcontext.Tabel.include(x=>x...).Select(x=>new MyModel { ... });
One workaround, and please don't kill me :-) After object loading and before serializing, just set the loaded objects which are causing the circular reference to null. I tried it and worked like a charm.
use meta data redirection. figured I would help anyone who stumbled here.
[MetadataType(typeof(CategoryMasterMetadata))]
public partial class CategoryMaster
{
}
public class CategoryMasterMetadata
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
[JsonIgnore]
public virtual List<SubCategoryMaster> SubCategories { get; set; }
public List<ItemMaster> Items { get; set; }
}
Related
I am currently facing the following problem:
I have a model class LargeDataClass with many fields (200+).
Many of these fields (~50-80) are enum-like (i.e. they can be filled out with certain sets of options in the UI).
Now my approach was to model these as enum classes, like
[Table("tbl_enum_one")]
class EnumOne {
public int ID { get; set; }
public string Name { get; set; }
}
[Table("tbl_large_dataclass")]
class LargeDataClass {
public EnumOne EnumOne { get; set; }
public int EnumOneId { get; set; }
//...
}
This has the major advantage of being easily extendable (to add a dropdown option in the UI, just add a row to the table).
Now I am facing some concerns/problems:
When I fetch my model class LargeDataClass from the DB with all its enum fields included, there will be a lot of joins (as I stated above, there are like 50 to 80 of these fields). I am worried that will have a big impact on query performance. Plus create/update/delete might be quite slow due to the large number of indexes to be updated.
MySQL won't even let me create a table tbl_large_dataclass with that many FKs (too many indexes on a single table).
So now I am considering two (in my view really unfortunate) options:
Using regular enums, so no enum classes with their own tables, storing them as simple int/string fields in the DB. This would cause no performance concerns at all, but unfortunately, the 'live' extendability is quite important, so this option would only be the last resort.
Using the Enum classes, but having just the ID of the enum in the LargeDataClass, so kind of keeping the fact that this is a foreign key secret from the DB. If I wanted to display a LargeDataClass object somewhere, I would have to separately fetch the enum classes. Plus I would have to make extra sure everywhere that I only use Ids that are really present in the enum table.
I am really unsure what would be the best approach here.
Database is not an object store and you have to design it accordingly. I have changed you schema and only two tables are needed for storing dropdown values.
[Table("tbl_enum_type")]
public class EnumType {
public int ID { get; set; } // PK
public string Name { get; set; }
}
// PK (EnumTypeId, Id) - reusing the same index for dropdown generation
[Table("tbl_enum_value")]
public class EnumValue {
public int ID { get; set; }
public string Name { get; set; }
public int Order { get; set; } // for dropdown ordering
public int EnumTypeId { get; set; }
public EnumType EnumType { get; set; }
}
// store only ID's, no FK
[Table("tbl_large_dataclass")]
public class LargeDataClass {
public int EnumOneId { get; set; } // EnumTypeId 1
public int EnumSecondId { get; set; } // EnumTypeId 2
//...
}
For generating dropdowns, you have to cache EnumType and EnumValue tables in memory in useful structure.
Override method SaveChanges/SaveChangesAsync and check saved Id's according to cached data.
It will not help if your database is changed via SQL, but here we have trade-off between performance and consistency. Probably good trigger may help here.
UPDATE:
Consider to restructure LargeDataClass to two tables
[Table("tbl_option_bag")]
public class OptionBag {
public int Id { get; set; }
public ICollection<Option> Options { get; set; }
}
[Table("tbl_options")]
public class Option {
public int Id { get; set; }
public int OptionBagId {get; set; }
public int EnumTypeId { get; set; }
public int EnumId { get; set; }
//...
}
Here you can use FK and DTO can be generated on selecting Options navigation property.
I am trying to develop a catalog project in ASP.NET MVC 3 and using EF Code first with an existing Database. There is a Categories table in my database that points to itself. For that, I have written the following model class. --"Correct me if the model is wrong"--
public class Category
{
public int CategoryID { get; set; }
public string CategoryName { get; set; }
public int? ParentCategoryID { get; set; }
public string CategoryDesc { get; set; }
[ForeignKey("ParentCategoryID")]
public virtual Category ParentCategory { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
Question : I am unable to understand as to how can i work with this class. While using and passing the following code to the view
var cat = dbStore.Categories.Include("ParentCategory").ToList().
I got this error : Object reference not set to an instance of an object. This is happening because the root category has null ParentCategoryID. Please tell me how will you work with this code or any resource that can help me understand working in such scenarios. Just any sort of code will be helpful that uses the above the model, like displaying a list or a menu or anything, just anything.
Usually what you do is travel from top level categories to bottom level categories. Inorder to do that first you need to define SubCategories collection in your class
public class Category
{
public int CategoryID { get; set; }
public string CategoryName { get; set; }
public int? ParentCategoryID { get; set; }
public string CategoryDesc { get; set; }
[ForeignKey("ParentCategoryID")]
public virtual Category ParentCategory { get; set; }
[InverseProperty("ParentCategory")]
public virtual ICollection<Category> SubCategories{ get; set; }
public virtual ICollection<Product> Products { get; set; }
}
Then you retrieve the top level categories
var topCategories = dbStore.Categories
.Where(category => category.ParentCategoryID == null)
.Include(category => category.SubCategories).ToList();
After that you can traverse the hierachey
foreach(var topCategory in topCategories)
{
//use top category
foreach(var subCategory in topCategory.SubCategories)
{
}
}
If you do not have very many categories you can solve this by loading the whole collection of categories. I think EF will handle the fixup for you so all relations are properly populated.
As far as I know there are no SQL'ish databases/ORM's that can handle this scenario well. An approach I often use is to load the whole collection as I said above and then manually fix the relations. But I do think EF will do that for you.
Basically you should do:
var topCategories = dbStore.Categories.ToList().Where(category => category.ParentCategoryID == null);
public class Car {
public string SomeProperty { get; set; }
public Manufacturer Manufacturer { get; set; }
public IList<Color> Colors { get; set; }
}
public class Manufacturer {
public int Id { get; set; }
public string Name { get; set; }
}
public class Color {
public int Id { get; set; }
public string Name { get; set; }
}
I already have tables full of Colors and Manufacturers. When I create a new car I want to be able to assign it a Color and Manufacturer bound from .net MVC.
When I save my new car with
context.Cars.Add(car);
A new Car is created (great) but a new Color and Manufacturer are also created even though these objects already had an Id and Name set that matched the content in the database.
The two solutions I see are to either write a custom save method for car, and tell the context that the Manufacturer and Color are Unchanged.
context.Cars.Add(car);
context.Entry(car.Manufacturer).State = EntityState.Unchanged;
foreach (Color color in car.Colors)
context.Entry(car.Color).State = EntityState.Unchanged;
Alternatively, to load the Manufacturer and Color from EF and then link them to the Car, instead of using the MVC bound objects.
car.Manufacturer = carRepository.GetManufacturer(car.Manufacturer.Id);
car.Colors = carRepository.GetColorsById(car.Colors);
I am not thrilled by either solution as this example is very trivial, but my real cases are far more complicated. I don't really want to have to fiddle around with EF in detail for each object I save. I have lots of complex object graphs to save and this seems very error prone.
Is there a way of making EF behave more like NHibernate, whereby you can give it something with an ID already assigned and it will assume without your intervention that it already exists?
Edit - question clarified to show collection of existing entities as well as many-to-one relationships.
Unfortunately, EF does not have anything like session.Load in NHibernate that allows you to get a proxy from an id.
The usual way to deal with this in EF is create a separate FK field containing the scalar value that corresponds to the reference. For example:
public virtual Manufacturer Manufacturer { get; set; }
public int ManufacturerId { get; set; }
Then you only have to set ManufacturerId and it will be saved correctly.
(So much for "POCO" and "code first". Pffffff)
You can define scalar properties in your entities and bind the values to them instead. Eg add
ManufacturerId and ColorId
public class Car {
public string SomeProperty { get; set; }
public int? ManufacturerId { get; set; }
public virtual Manufacturer Manufacturer { get; set; }
public int? ColorId { get; set; }
public virtual Color Color { get; set; }
}
Then set those scalar properties when you assign (eg through a DropDownList)
This way you can avoid loading many related entities to populate the entity.
I have a class Mailout with a Status that looks like this:
public class Mailout
{
public int Id {get; set; }
public string Name {get; set; }
public MailoutStatus Status { get; set; }
}
public class MailoutStatus
{
public int Id { get; set; }
public string Name { get; set;}
}
When I insert Mailouts and set the Status property, they are inserted correctly. When I fetch them, Status is always null. Since I don't have (and don't want) the status ID on my Mailout class, I have no way to retrieve it after-the-fact. How do I tell EF to populate this field eagerly, rather than lazily?
I'm hoping I can set something up in OnModelCreating() since I want this behavior all the time, not as an option that I can use sometimes by manipulating my LINQ-to-Entities queries.
You need to make your navigation properties virtual.
There is no such option in the ModelBuilder to configure an automatic eager loading of navigation properties in each query. You have to specify it query by query. As a workaround you could encapsulate eager loading in some method or property, for instance in the context:
public class MyContext : DbContext
{
public DbSet<Mailout> Mailouts { get; set; }
public IQueryable<Mailout> MailoutsWithStatus
{
get { return Mailouts.Include(m => m.Status); }
}
// ...
}
And then use in your queries:
context.MailoutsWithStatus.Where(...) ... etc.
Only an idea, it's untested.
Taking from Employee Info Starter Kit - upcoming MVC edition, here is a snippet, that works pretty well, to eager load objects when used:
public class Employee
{
...
public int? ReportsTo { get; set; }
[ForeignKey("ReportsTo")]
public virtual Employee Supervisor { get; set; }
/// <summary>
/// Children object collection of foreign key relation
/// </summary>
public virtual List<Employee> Subordinates { get; set; }
}
I am trying to practice the model first approach and I am putting together a domain model. My requirement is pretty simple: UserSession can have multiple ShoppingCartItems.
I should start off by saying that I am going to apply the domain model interfaces to Linq2Sql generated entities (using partial classes). My requirement translates into three database tables (UserSession, Product, ShoppingCartItem where ProductId and UserSessionId are foreign keys in the ShoppingCartItem table). Linq2Sql generates these entities for me. I know I shouldn't even be dealing with the database at this point but I think it is important to mention.
The aggregate root is UserSession as a ShoppingCartItem can not exist without a UserSession but I am unclear on the rest. What about Product? It is defiently an entity but should it be associated to ShoppingCartItem?
Here are a few suggestion (they might all be incorrect implementations):
public interface IUserSession {
public Guid Id { get; set; }
public IList<IShoppingCartItem> ShoppingCartItems{ get; set; }
}
public interface IShoppingCartItem {
public Guid UserSessionId { get; set; }
public int ProductId { get; set; }
}
Another one would be:
public interface IUserSession {
public Guid Id { get; set; }
public IList<IShoppingCartItem> ShoppingCartItems{ get; set; }
}
public interface IShoppingCartItem {
public Guid UserSessionId { get; set; }
public IProduct Product { get; set; }
}
A third one is:
public interface IUserSession {
public Guid Id { get; set; }
public IList<IShoppingCartItemColletion> ShoppingCartItems{ get; set; }
}
public interface IShoppingCartItemColletion {
public IUserSession UserSession { get; set; }
public IProduct Product { get; set; }
}
public interface IProduct {
public int ProductId { get; set; }
}
I have a feeling my mind is too tightly coupled with database models and tables which is making this hard to grasp. Anyone care to decouple?
Looks like you are on the right track. Half of the whole "doing DDD right" is having the right base classes. Have a look at this great DDD applied to C# resource:
http://dddpds.codeplex.com/
The source code is available and is very readable.
So, with regards to having ID in the model. The ID is a database thing and the usual approach is to keep all persistence out of the Model and restrict the model to the business logic. However, one normally makes an exception for the identifier and buries it in the Model base class like so:
public class ModelBase {
protected readonly object m_Key;
public ModelBase(object key) {
m_Key = key;
}
}
This key is used by your persistence layer to talk to the database and is opaque. It's considered quite OK to downcast the key to the required type, because you know what it is.
Also, the Domain Objects are pretty much on the bottom of your architecture stack (just above the Infrastructure layer). This means that you can make them concrete classes. You will not have multiple implementations of the domain models, so the interfaces are unnecessary, which is what Domain Driven Design is about - Domain first.
public Class UserSession : ModelBase {
public UserSession(Guid Id):base(Id) {}
public Guid Id { get{ return m_Key as Guid;} }
public IList<ShoppingCartItem> ShoppingCartItems{ get; set; }
}
public class ShoppingCartItem : ModelBase {
public ShoppingCartItem ():base(null) {}
public UserSession UserSession { get; set; }
public Product Product { get; set; }
}
Typical shopping cart or customer-order examples prefer making UserSession (or Order) the root of aggregate. Individual items should be children of this session/order. It is up you whether individual items in the cart should have a meaningful id. I would prefer no, since 5 widgets in the cart are indistinguishable from another 5 widgets. Hence, I would model cart items as a collection of value objects.
Common problem with shopping cart items is whether they should include price, or not. if you include price, you will have your cart independent from changes of product price. It is very desirable if you want to store you cart for historical reasons since it is valuable to know how much items in the cart cost according to price when they were bought, not according to current.
Product should form definitively an aggregate by itself. Period.
Now, I don't know if all of this is easily implementable in LINQ to SQL, but you can try.