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Setting up Models for related data MVC 5/EF6

I have been trying to work this out for a while now and can't find an answer that makes sense to me. The concept is very common, so I must be totally misunderstanding a basic concept.
If I have a recipe class that can be found in many recipe categories then I have;
public class Recipe
{
public int ID { get; set; }
public string Title { get; set; }
public int CategoryID { get; set; }
public virtual ICollection<Category> Categories { get; set; }
}
public class Category
{
public int ID { get; set; }
public string Description { get; set; }
public int RecipeID {get; set;
public virtual void Recipe Recipe {get; set;}
But I also need a join table that relates a recipe to a Category. I want to display this;
Recipe Title | Category
Mac-N-Cheese | Pasta
| Easy
Pot Roast | Beef
| Slow cooker
The Category is a table of available categories. So the join table has
RecipeID | CategoryID
I tried setting up the models using the Entity Framework format of foreign keys and navigation properties.
So I set up the join table like this;
public class RecipeCategories
{
public int ID { get; set; }
public int RecipeID { get; set; }
public int CategoryID { get; set; }
public virtual ICollection<Recipe> Recipes { get; set; }
public virtual ICollection<Category> Categories { get; set; }
}
So a recipe can have many categories. The join table can have many recipes and many categories. The category table is just a simple list of categories. What am I missing? When I try to run the view there is no list of categories for the given recipe. The best I have achieved is the CategoryID.
Sorry for the long post, but you need all the details.

The problem is your Category model. The way you've currently defined it you have a one-to-many relationship between Category and Recipe (a Recipe can have many Categories but a Category one has a single Recipe). What you want is a many-to-many relationship so put a collection of Recipes on the Category and EF should automatically generate the join table.
public class Recipe
{
public int ID { get; set; }
public string Title { get; set; }
public int CategoryID { get; set; }
public virtual ICollection<Category> Categories { get; set; }
}
public class Category
{
public int ID { get; set; }
public string Description { get; set; }
public virtual ICollection<Recipe> Recipes { get; set; }
}

I am no getting actual scenario as you trying to achieve.
as you mention your model and then what you expected both contradict. as per you mention you have recipe and category (one to many) but later you change your model and mention you want (many to many) so you need join table. as a relation model you can handle 2 ways in EF. 1st without creating separate table and keep collection map to each model and 2nd way creating separate table and explicitly map that in your model. you need to explicitly specify while model building.
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
modelBuilder.Entity<Recipe>()
.HasMany(c => c.Categories).WithMany(i => i.Recipes)
.Map(t => t.MapLeftKey("RecipeID")
.MapRightKey("CategoryID")
.ToTable("ReceipeCategory")
);
you can define your class model (and third table will generate but don't required specific model )
class Recipe {.... public virtual ICollection<Category> Categories { get; set; }
class Category {... public virtual ICollection<Recipe> Recipes { get; set; } }

Entity Framework DbContext Delete child object

I am trying to delete the child objects in foreach loop but that doesn't seem to be working.. Here is what I have.
I have a meeting and meeting_category entities which has 1-to-many relationship..
foreach (meeting_category meetingCategory in currentMeeting.meeting_category)
{
dbContext.meeting_category.Remove(meetingCategory);
dbContext.Entry(meetingCategory).State = EntityState.Deleted;
dbContext.SaveChanges();
}
I am then returning to the same view with updated results.. This seems to be very inconsistent. Sometimes it deletes entities and sometimes it doesn't. Even when it deletes it, my meeting object still have meeting_category objects I deleted.
When it doesn't delete from DB, it updates the meeting object and removed meeting_category objects from the meeting..
Is there any kind of reset or refresh that I will have to do in order for meeting object to remove the meeting_category objects..
How can I make sure that it consistently deletes the meeting_category objects both from DB and from the meeting object and when I return to the view, I have an updated meeting object?
Here is my meeting entity
public partial class meeting
{
public meeting()
{
this.meeting_questions = new HashSet<meeting_questions>();
this.meeting_abstract = new HashSet<meeting_abstract>();
this.meeting_category = new HashSet<meeting_category>();
this.meeting_image = new HashSet<meeting_image>();
}
public int meeting_id { get; set; }
public int language_id { get; set; }
public string meeting_code { get; set; }
public string meeting_name { get; set; }
public string meeting_description { get; set; }
public System.DateTime meeting_start_date { get; set; }
public System.DateTime meeting_end_date { get; set; }
public System.DateTime abstract_cutoff_date { get; set; }
public string meeting_guidelines { get; set; }
public string created_by { get; set; }
public Nullable<System.DateTime> created_datetime { get; set; }
public Nullable<bool> meeting_published { get; set; }
public Nullable<bool> meeting_deleted { get; set; }
public Nullable<bool> meeting_fully_created { get; set; }
public virtual language language { get; set; }
public virtual ICollection<meeting_questions> meeting_questions { get; set; }
public virtual ICollection<meeting_abstract> meeting_abstract { get; set; }
public virtual ICollection<meeting_category> meeting_category { get; set; }
public virtual ICollection<meeting_image> meeting_image { get; set; }
}
And here is my meeting_category entity
public partial class meeting_category
{
public meeting_category()
{
this.abstract_category = new HashSet<abstract_category>();
}
public int meeting_category_id { get; set; }
public int meeting_id { get; set; }
public int category_type_id { get; set; }
public int category_id { get; set; }
public string category_name { get; set; }
public string category_name_en { get; set; }
public virtual ICollection<abstract_category> abstract_category { get; set; }
public virtual category category { get; set; }
public virtual category_type category_type { get; set; }
public virtual meeting meeting { get; set; }
}

I have a couple of questions about what it is that you are trying to achieve.
Firstly are you sure that the Meeting -> Category relationship is many-to-one? I would normally expect it to be many-to-many, i.e. each Meeting can have many Categories and each Category can be attached to many Meetings.
Secondly, are you actually trying to delete the Category or are you trying to remove a Category from a Meeting?
If you are simply trying to remove the relationship between a Meeting and a Category then you need to edit the navigation property, i.e. MyMeeting.Categories.Remove(MyCategory).
If you are trying to delete the actual Category then you will need to make sure that that Category is not currently linked to any Meeting otherwise you will get a Foreign Key violation if you try to remove the Category.
On top of all of this you may be encountering chaching or simply object lifetime management issues.
What type of application are you creating? ASP.NET? WinForms? etc.
How are you actually instantiating a concrete version of your DBContext? Are you using DI?
Cheers Mike

I managed to fix the issue by creating the DbContext per controller action and destroying it before loading the view.
The problem was that I was creating the DbContext in another class and was reusing the same context on all controller action. Since Entities are cached in dbcontext, I was always getting the old cached copy of entities and was working very inconsistently.

Designing tables to avoid circular reference

Working in one project (Catering theme ) when I was designing the database I didn't take care about some thing , and now Is very hard to avoid some kine of errors(Circular error).
Suppose I have following scenario :
I have Meal object that should be composed from a list of semi-finished products (we will call it Product ) and list of simple Resources.
One Product is composed from a list of Resoruces and list of products.
So in real example this will look like this:
Meal: Pizza that contains list of Resoruces(cheese,dough) and list of Products : in our case will be just :Sauce.
Sauce will be composed from List of Resources(salt,Some cheese ,tomato Sauce) and a List of Products (in our case will be just one "Chopped tomatoes with salt")
So now I have following classes:
public class Resource
{
public int Id { get; set; }
public string Name { get; set; }
}
public class ProductToProduct
{
public int Id { get; set; }
public Product MainProduct { get; set; }
public Product Component { get; set; }
public double Quantity { get; set; }
}
public class ProductToResource
{
public int Id { get; set; }
public Product Product { get; set; }
public Resource Resource { get; set; }
public double Quantityt { get; set; }
}
public class Meal
{
public int Id { get; set; }
public string Name { get; set; }
public IList<MealToProduct> MealToProducts { get; set; }
public IList<MealToResource> MealToResources { get; set; }
}
public class MealToResource
{
public int Id { get; set; }
public Meal Meal { get; set; }
public Resource Resource { get; set; }
public double Quantity { get; set; }
}
public class MealToProduct
{
public Meal Meal { get; set; }
public Product Product { get; set; }
public double Quantity { get; set; }
}
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public IList<ProductToResource> ProdcutToResources { get; set; }
public IList<ProductToResource> ProductToProducts { get; set; }
}
My problem is in relation between Product to Product.
Suppose I will have Product1, Product2 , Product3 , Product4.
Product 1 will be composed from something and Prodcut2, Product4.
Product2 will be composed from something and Prodcut3.
Prodcut 3 will be composed from something and Prodcut4.
Prodcut 4 will be composed from something and Prodcut1 , in this case when I will try to calcualte Cost for Product1 , or Product 4 I will get an Circular error.
So my problem is in ProductToProduct table.
My question is how I must to design tables to avoid this kind of errors .
I AM VERY SORRY FOR MY EXPLICATION BUT IT IS VERY HARD TO EXPLAIN THIS PROBLEM.
PLEASE ASK ME IF SOMETHING IS UNCLEAR.
THANKS FOR YOUR ATTENTION.
Note:This is not so important for this case but I am working in ASP.Net mvc , orm is Fluent Nhibernate.

Here's an example of a function you could use to detect whether a parent-child relationship exists. I have assumed that the product relationships are described in a table called ProductLink, which has two foreign keys to Product: ParentProductId and ChildProductId.
This function uses a recursive query to determine the complete list of products which are children of the product denoted by the argument #ParentProductId, then does a simple test to see whether #ChildProductId appears in that list.
create function dbo.ProductRelationshipExists
(
#ParentProductId int,
#ChildProductId int
)
returns bit
as
begin
declare #ChildExists bit = 0;
with ProductChildCTE as
(
-- Base case: Get the parent's direct children.
select ChildProductId from ProductLink where ParentProductId = #ParentProductId
-- Recursive case: Get the children's children.
union all
select
ProductLink.ChildProductId
from
ProductChildCTE
inner join ProductLink on ProductChildCTE.ChildProductId = ProductLink.ParentProductId
)
select #ChildExists = 1 from ProductChildCTE where ChildProductId = #ChildProductId;
return #ChildExists;
end
When someone tries to insert a record into ProductLink, you could use a test like this to determine whether the proposed parent and child are already in the table as child and parent, respectively, and disallow the insertion if so.
This was just a quick write-up to illustrate one possible approach; I should mention that I don't know how well the performance of this thing will scale as the table gets larger. Hopefully it will suffice for your case. If not, let me know how to improve it.

Entity Framework one-to-many relation

I have two simple classes:
class Student
{
public int StudentId { get; set; }
public int IndeksNo { get; set; }
public string Name { get; set; }
public string LastName { get; set; }
public virtual Group Group { get; set; }
}
And
class Group
{
public int GroupId { get; set; }
public string Name { get; set; }
public virtual List <Student > Students { get; set; }
}
Database is created correctly (using Code First). I have added couple items to both tables, but all the time Students list and Group property in Student are null. I have no idea why. I have searched solution for about an hour and i came up with something like this:
modelBuilder.Entity<Student>()
.HasRequired(st => st.Group)
.WithMany(gr => gr.Students)
.WillCascadeOnDelete(false);
But it doesn't help. I have no idea what may went wrong or why Group.Students and Student.Group are always null. List of groups and list of students are selected from db successfully - i mean all params except those connections.

In order to use the Lazy Loading feature of EntityFramework. Your navigation property must be virtual. In your Student class in the the case. The problem is with your Group class. The navigational property is a virtual List<Student> it must be a virtual ICollection<Student>
You can simply change your Group to
class Group
{
public int GroupId { get; set; }
public string Name { get; set; }
public virtual ICollection<Student > Students { get; set; }
}

Retrieve a list of items where an item exists in one of the items lists

Please excuse the slightly confusing title. I have a model (Project) which contains a list of items (Users).
I would like to retrieve all of the projects, where the current user is a member of the user list for that project.
I've tried:
List<Project> _MemberProjects =
_Db.Projects.Where(p =>
p.Users.Contains(_User)
).ToList();
This results in the following error:
Unable to create a constant value of type 'Nimble.Models.UserAccount'. Only primitive types or enumeration types are supported in this context.
User Model:
public class UserAccount
{
public int UserID { get; set; }
public string Username { get; set; }
public string Password { get; set; }
public string Name { get; set; }
public string Surname { get; set; }
public string Email { get; set; }
public ICollection<Project> Projects{....}
}
Project Model
public class Project
{
public int ProjectID { get; set; }
public DateTime CreatedDate { get; set; }
public string ProjectName { get; set; }
public string Owner { get; set; }
public ICollection<UserAccount> Users{...}
public ICollection<ProjectGroup> Groups{...}
}

Haven't tried this, but it might work:
List<Project> _MemberProjects =
_Db.Projects.Where(p =>
p.Users.Any(u => u.UserID == _User.UserID )
).ToList();

The problem is that you are mixing together Linq (the WHERE clause) and a non-Linq Collection operation (Contains). Try using pure Linq. #JamesBond's answer might work.
Are you querying a database? Then a JOIN might be another solution, but the exact syntax depends on how you are storing the relationship between the two tables.