I am working with Entity Framework Code First.
I have an Entity Called Notes
I also have other Entities such as
BusinessPartners
Opportunities
WorkOrders
All of these entities may have notes.
What is the best way to model this
1.) in the notes table have optional foreign keys to Business partners, Opportunities, and workorders. Then just set the optional key to which the note is related
2.) have intermediate tables such as BusinessPartnerNotes, with two field BusinessPartnerId and NoteId
It should be mentioned that a note is never going to be related to two entities at the same time.
Any help or suggestions would be appreciated.
Given your description of the cardinalities, and assuming Notes for BusinessPartners have the same format of Notes for Opportunities, I'd go with the simplest approach (option 1. in your list).
class Note
{
public int Id { get; set; }
public string Content { get; set; }
}
class BusinessPartner
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Note> Notes { get; set; }
}
class Opportunity
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Note> Notes { get; set; }
}
Which should generate the following tables:
Notes
Id
Content
BusinessPartner_Id
Opportunity_Id
BusinessPartners
Id
Name
Opportunities
Id
Name
Related
This is my code:
namespace MyProject.Models.Database
{
public class Recipe
{
public Guid Id { get; set; } = Guid.NewGuid();
public string Name { get; set; }
public string? Description { get; set; }
public string? Picture { get; set; }
public int Worktime { get; set; }
public int? Cooktime { get; set; }
public int Difficulty { get; set; }
public int Portions { get; set; }
public List<Ingredient> Ingredients { get; set; }
}
public class Ingredient
{
public Guid Id { get; set; } = Guid.NewGuid();
public Guid IngredientId { get; set; }
public int Qty { get; set; }
public string QtyUnit { get; set; }
}
}
I want the class "Recipe" to include many elements of type "Ingredient". Ive read stuff about One-to-One and Many-To-Many but i just dont get it...
any Ideas?
thx
One recipe can consist of many ingredients, one ingredient can also be in many recipes. This is a many-to-many relationship.
What you need to do is create a new class that contains Id, RecipeId, IngredientId.Name that class something like RecipeIngredient. When you are creating a DbSet<RecipeIngredient> in your db context, name your table RecipesIngredients.
What should be the data types of the properties in RecipeIngredient?
The Id property will be the primary key, you can decide the data type.
RecipeId will be a foreign key for the Recipe, so it needs the same data type as the primary key of the Recipe (in your case Guid).
IngredientId will be the foreign key for the Ingredient, so the data type will again be Guid in your case.
Note that instead of putting Id in your RecipeIngredient, you can create a composite key instead.
When should you do that? -> here
I suggest you learn about the different relationships and how to apply them using C# and Entity Framework Core -> here
Good luck on your learning journey! When you don't feel you understand a topic, don't worry and don't get discouraged, you just need more experience. Keep up the good work :)
I am trying to build an organization hierarchy where each team might contain one or many members and/or one or many sub-teams.
To do so, my model is:
public class Team
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Employee> Members { get; set; }
public virtual ICollection<Team> SubTeams { get; set; }
public Employee Manager { get; set; }
}
When adding a migration and updating database, everything seems logical in the table.
EF has added an extra nullable column "Team_Id" where the Id of the parent Team gets stored.
My question is about getting the Id of the parent Team from my model.
I tried adding:
public int? Team_Id
To my model, but EF considered it as a model change and asked for another migration.
How can I get the value of column Team_Id in my model? getting this info takes too much processing when looping through teams.
I always add foreign key in my model. When it adds to the model, EF won't add Team_Id .
public class Team
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Employee> Members { get; set; }
public virtual ICollection<Team> SubTeams { get; set; }
public Employee Manager { get; set; }
public int? ParentId { get; set; }
[ForeignKey("ParentId")]
public Team ParentTeam { get; set; }
}
I hope this example be helpful.
Here are the business requirements, in short:
All employees need to be stored in a database
Some employees have assistants, some do not
Some employees have more than one assistant
Assistants are employees, as well
There is obviously a bit of a self-referencing situation. But the difference from a typical "Employee-Manager" situation is that here one Employee can have 0 or multiple assistants. So, the combination of Employee and employee's Assistants needs to be stored in a separate table in a one-to-many relationship between Employee and EmployeeAssistant. But I'm getting confused how to model this in Entity Framework 6 Code First.
I started with this:
public class Employee
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
public class EmployeeAssistant
{
[ForeignKey("Employee")]
public int EmployeeId { get; set; }
public virtual Employee Employee { get; set; }
[ForeignKey("Assistant")]
public int AssistantId { get; set; }
public virtual Employee Assistant { get; set; }
}
But I get an error during Update-Database command:
Introducing FOREIGN KEY constraint 'FK_dbo.EmployeeAssistant_dbo.Employee_EmployeeId' on table 'EmployeeAssistant' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
What am I missing? Should I approach this differently?
since each employee may have one or more assistants (and each assistant will have one or more employees) and all are employees, the simplest solution is one class with two collections for assistants and employees, and the relations will be managed by the framework:
public class Employee
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public ICollection<Employee> Assistants { get; set; }
public ICollection<Employee> Employees { get; set; }
}
when you use package manager console to add migration it will automatically create two tables, one for employees, and another for many to many relations.
then all you have to do is to find related assistants and/or employees by using Include extension method.
db.Employees.Where(x=>x.Id==id).Include(x=>x.Assistants).FirstOrDefault()
and/or
db.Employees.Where(x=>x.Id==id).Include(x=>x.Employees).FirstOrDefault()
Based on this link Introducing FOREIGN KEY constraint may cause cycles or multiple cascade paths - why?
It seems if you delete an EmployeeAssistant with your code, it causes two cascading delete paths.
I would suggest a structure such as this:
After edit
public class Employee
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public List<EmployeeAssistant> Assistants { get; set; } //if an employee has no assistants this List can easily just be empty
OR
public ICollection<EmployeeAssistant> Assistants { get; set; } // depending on your architecture, choose the one that would suit you better
}
public class EmployeeAssistant
{
[ForeignKey("Employee")]
public int EmployeeId { get; set; } //this is the employee who 'has' this assistant
public virtual Employee Employee { get; set; }
public int Id { get; set; } //this is the assistant's own information - identical to employee's basic info
public string FirstName { get; set; }
public string LastName { get; set; }
}
After a while of brain-boggling, I even came up with a possibility where you just need 1 class, Employee, but it includes a bool IsAssistant denoting if this employee is an assistant, and AssistantEmployeeId which is an employee ID of the employee who 'has' this assistant.
For example:
public class Employee
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public bool IsAssistant { get; set; }
public int EmployeeAssistantID { get; set; }
}
I know this second method is very messy and probably doesn't suit your needs, but personally I always create database tables first then do 'Generate Model from Database' so I'm inexperienced at code-first approach.
I have created these entities Product, Order, OrderedItem in EF using Code First.
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
[NotMapped]
public int IssuedQuantity { get; set; }
[NotMapped]
public int InhandQuantity { get; set; }
public virtual ICollection<OrderedItem> OrderedItems { get; set; }
...
}
public class Order
{
public int Id { get; set; }
public string ReferenceNumber { get; set; }
public virtual ICollection<OrderedItem> OrderedItems { get; set; }
...
}
public class OrderedItem
{
public int OrderId { get; set; }
public string ProductId { get; set; }
[ForeignKey("OrderId")]
public virtual Order Order { get; set; }
[ForeignKey("ProductId")]
public virtual Product Product { get; set; }
...
}
Now I want to get all products by passing current user id to a stored procedure. It will then return all products along with total product quantity currently in user's hand.
The problem is that EF is not mapping SP results back to Product entity for NotMapped properties. i.e. all properties in product entity have values but NotMapped properties are set to NULL even when I return their values from SP.
What I want to ask is that does EF support this kind of functionality? If yes then how?
NOTE I know about Computed Properties but that will create unneccessary columns in tables and I don't want that, since these properties are calculated at run-time.
NOTE I know that I don't need to create OrderedItem entity. But I am storing some other properties in it, which are removed here for brevity.
I'm quite sure that EF does not support dynamic mapping (you could try to change the mapping metadata but is not a clean way or delete the mapping cache but then EF will be very slow). In this case the razionale is that the entity are 2 different entities because they have different data. In your case probably the best thing is to do 2 entities the ProductWithQuantities that inherits from Product.
BTW Thinking about ERPs, the model of orders/wms usually is different. Products does not contain informations about QtyOnHand or sales/buy information. Usually is another object (Inventory?) that contains this informations.
I would create a View Model of the product with all the required properties and pass that to the view instead of the Product model. Then you are not constrained by the mappings of the Product model and you do not have to use the [NotMapped] Attribute on the fields.
[NotMapped]
public class ProductVM
{
public int Id { get; set; }
public string Name { get; set; }
public int IssuedQuantity { get; set; }
public int InhandQuantity { get; set; }
public virtual ICollection<OrderedItem> OrderedItems { get; set; }
...
}
I hope that helps.
Goal. I have a "Gift" entity that describes what someone has to offer (babysitting, dog walking, etc) with a rating. And I want a "GiftCategory" entity that gives general category descriptive information (pets, sports, automotive, etc) for someone to search apon and then get all gift that have those categories. A "Gift" entity can have multiple "GiftCategory" entities associated with it. I want the ability to search for a category and pull out all "Gift" entities that have been created with those categories associated with them. Here is what I have so far but it doesn't seem to work with the entity first approach. Maybe I need another table that connects the two entities because currently the way the two tables are connected doesn't seem correct?
Gift entity:
public class Gift
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<GiftCategory> Categories { get; set; } // is this incorrect???
public int Rating { get; set; }
}
Category entity:
public class GiftCategory
{
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
}
The "GiftCategory" table that gets created creates a gift_id column that links the "GiftCategory" back to a gift (not what I want)!!!!
It seems like I would need to create a entity that connects the two entities? Something like:
public class ConnectGifts
{
public int Id { get; set; }
public string GiftId{ get; set; }
public string GiftCategoryID{ get; set; }
}
This way I can have multiple categories for a Gift, but the thing I don't understand is with entity first I really don't need this entity I just need what would be this table to get/query the "GiftCategory" entities for ids then get the gift ids to get all the gifts. So it seems like creating this entity is overkill? Is there a way to do it without creating a third table/entity ("ConnectGifts") with code first? Or am I not understanding that all entities are tables and all tables are entities? I'm also using linq-to-sql for all querying.
You're looking for a many-to-many relationship and can be defined as:
public class Gift
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<GiftCategory> Categories { get; set; } // is this incorrect???
public int Rating { get; set; }
}
public class GiftCategory
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Gift> Gifts { get; set; }
}
So each has a collection of the other. Gift has many Categories and Category had many Gifts. You could use a bridge table like you've done with ConnectGifts but it's not necessary with EF. Using just Gift and GiftCategory, EF will actually create the bridge table for you.