In a scenario where a product can have many categories I'm trying to create this using code-first, I have a Product model which has a collection of Category like so:
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Category> Categories { get; set; }
}
My Category looks like:
public class Category
{
public Category(CategoryEnum #enum)
{
Id = (int)#enum;
Name = #enum.ToString();
}
public Category() { }
[Key, DatabaseGenerated(DatabaseGeneratedOption.None)]
public int Id { get; set; }
public string Name { get; set; }
public static implicit operator Category(CategoryEnum #enum) => new Category(#enum);
public static implicit operator CategoryEnum(Category category) => (CategoryEnum)category.Id;
}
Creating a migration then updating the database doesn't create a new table for this to join the 2 (Product and Category) together. I'd expect a new table with a ProductId and CategoryId but this isn't the case. Instead, it just creates a ProductId in the Category table?
How do I make EF create a table which joins the 2 together without having to create a new DbSet<T>
That is how it's supposed to be.
Example:
Product 1 Chicken
Categorie 1 Meat idProduct = 1
Categorie 2 Healthy idProduct = 1
etc...
You don't need another table for a relation one to many. The table is only usefull for many to many
Related
Update: At this moment I can assign only one product to Recipe. What I want to do is add access to all products from db in recipe (controller create) - here Im using public int ProductId but it allow to save only one product. I want to choose a few products from this list and save foreign keys in database. photo
I also tried add public List < int > in ProductId but I got error from entity framework.
I will be grateful for any help.
public class Recipe
{
[Key]
public int Id { get; set; }
[Required]
public string Name { get; set; }
[Required]
public int ProductId { get; set; }
public List<Product> Products { get; set; }
public Recipe()
{
this.Products = new List<Product>();
}
}
public class Product
{
[Key]
public int Id { get; set; }
[Required]
public string Name { get; set; }
[Required]
public Recipe? Recipes { get; set; }
}
If you want to create a one-to-many relationship you are almost in the correct direction, but you should remove the public int ProductId { get; set; } and re-arrange as like as below example.
Say you have the following classes:
public class Recipe
{
[Key]
public int Id { get; set; }
[Required]
public string Name { get; set; }
public List<Product> Products { get; set; } = new();
}
public class Product
{
[Key]
public int Id { get; set; }
[Required]
public string Name { get; set; }
[Required]
public Recipe Recipe { get; set; }
}
You can instantiate and use as per below:
public static void Main()
{
var recipe = new Recipe
{
Name = "My Recipe",
Products = new List<Product>
{
new Product { Name = "Product 1" },
new Product { Name = "Product 2" },
new Product { Name = "Product 3" }
}
};
recipe.Products.ForEach(product =>
{
Console.WriteLine(product.Name);
});
}
It sounds like you are looking for a many-to-many relationship rather than a one-to-many.
If you are using Code-First and EF6 or EF Core 5+ then you can use:
public class Recipe
{
[Key]
public int Id { get; set; }
[Required]
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; } = new List<Product>();
}
public class Product
{
[Key]
public int Id { get; set; }
[Required]
public string Name { get; set; }
public virtual ICollection<Recipe> Recipes { get; set; } = new List<Recipe>();
}
To understand what is happening behind the scenes, EF should create a joining table called ProductRecipe or RecipeProduct which contains two FKs. ProductId and RecipeId. These will also form a composite PK for this table. Using this table, EF can associate one product to several recipes while also associating one recipe to the various products. In the object model you get the collection of products for each recipe, and the collection of recipes for each product.
With earlier versions of EF Core you were limited to having to declare this linking entity so you would have something more like:
public class Recipe
{
// ...
public virtual ICollection<ProductRecipe> ProductRecipes { get; set; } = new List<ProductRecipe>();
}
public class Product
{
// ...
public virtual ICollection<ProductRecipe> ProductRecipes { get; set; } = new List<ProductRecipe>();
}
public class ProductRecipe
{
[Key, Column(Order = 0)]
public int ProductId { get; set; }
[Key, Column(Order = 1)]
public int RecipeId { get; set; }
public virtual Product Product { get; set; }
public virtual Recipe Recipe { get; set; }
}
This approach is still an option in the other versions of EF, and is required if you want to support adding any additional fields to the joining table. For instance if you want to track things like CreatedDate/ModifiedDate etc. to record when a product was associated to a recipe etc. To expose that information to an application through EF, EF needs to know about the ProductRecipe as an entity. The trade off is that this approach is "messier" when usually you care about the Products for a Recipe etc. To get a list of products for a recipe you would need:
var products = context.Products
.Where(p => p.ProductRecipes.Any(pr => pr.RecipeId == recipeId)
.ToList();
or
var products = context.Recipies
.Where(r => r.RecipeId == recipeId)
.SelectMany(r => r.ProductRecipies.Select(pr => pr.Product).ToList())
.ToList();
vs. the implied joining table in the first approach:
var produts = context.Recipes
.Where(r => r.RecipeId == recipeId)
.SelectMany(r => r.Products)
.ToList();
... which is arguably easier to read.
I have the current table, named Reviews: (I confirmed this directly in sql)
Id Name Summary Rating
1 Reviewer one Review one. 2.5
1 Reviewer two Review two. 1.5
1 Reviewer three Review three. 3.9
I'm trying to get all 3 reviews using id == 1 which is a foreign key but what happens is I get the first review 3 times:
Id Name Summary Rating
1 Reviewer one Review one. 2.5
1 Reviewer one Review one. 2.5
1 Reviewer one Review one. 2.5
Is there anything wrong with my code?
public List<Review> GetReviewModels(int restaurantId) //restaurantId is 1
{
List<Review> reviews = new List<Review>();
using (var db = new ReviewEntities())
{
reviews = db.Reviews.Where(e => e.id.Equals(restaurantId)).ToList();
}
return reviews;
}
And here's the review entity model:
public partial class Review
{
public int id { get; set; }
public string Username { get; set; }
public string Summary { get; set; }
public double Rating { get; set; }
public virtual Restaurant Restaurant { get; set; }
}
Your problem is in your Table/Model Your Model Should look Like:
public partial class Review
{
public int id { get; set; }
public string Username { get; set; }
public string Summary { get; set; }
public double Rating { get; set; }
public int RestaurantId {get;set;}
public virtual Restaurant Restaurant { get; set; }
}
And you will need to add this to your Sql:
ALTER TABLE Reviews
DROP CONSTRAINT /*Name of Id fied constraint here*/
-- on a side note, you may have to Drop foreign key depending on the way it is in the database
ALTER TABLE Reviews
ALTER COLUMN Id INT NOT NULL PRIMARY KEY IDENTITY(1,1)
ALTER TABLE Reviews
ADD COLUMN RestrauntId INT NOT NULL /*you can make this null if you need*/ FOREIGN KEY FK_Reviews_TO_Restraunt REFERENCES Restraunt(Id)
Changing
reviews = db.Reviews.Where(e => e.id.Equals(restaurantId)).ToList();
to
reviews = db.Reviews.AsNoTracking().Where(e => e.id.Equals(restaurantId)).ToList();
fixed the problem
You can try this in other way. As Reviews table references Restaurant table id so Restaurant entity model will be having List Reviews so in order to fetch all reviews for restaurant id 1 the goes is:
This is the Review Model class.
public partial class Review
{
public int id { get; set; }
public string Username { get; set; }
public string Summary { get; set; }
public double Rating { get; set; }
public virtual Restaurant Restaurant { get; set; }
}
This is the Restaurant Model class
public partial class Restaurant
{
public int Id{get;set;}
//Rest all other fields.
//Foreign key relationship/ Navigation property
public List<Reviews> Reviews {get;set;}
}
And the function code is as follows:
public List<Review> GetReviewModels(int restaurantId) //restaurantId is 1
{
List<Review> reviews = new List<Review>();
using (var db = new RestaurantEntity())
{
reviews = db.Restaurant.Where(e => e.id==restaurantId).Select(x=>
x.Reviews).FirstOrDefault();
}
return reviews;
}
I have a Products table:
ProductId
ProductDescription
CategoryId
And a Categories table:
CategoryId
CategoryDescription
***For every product, I would like to display a line like so:
Product Id | Product Description | Category Description
I have not been successful in forming the necessary mapping that is required for the above task.
Products Mapping I am using:
public ProductsMap()
{
Table("Products");
Id(x => x.ProductId);
Map(x => x.ProductDescription);
Map(x => x.CategoryId);
References(x => x.Categories)
.Column("CategoryId")
.Not.Nullable();
// Need Join() statement here?
...
My Products class:
public class Products
{
public virtual int ProductId { get; set; }
public virtual string ProductDescription { get; set; }
public virtual int CategoryId { get; set; }
public virtual Category Category { get; set; }
public virtual int? CategoryDescription { get; set; } // Not in the db table.
}
My goal is to have the CategoryDescription field in the above class to be populated automatically by Fluent-NHibernate through the mapping specified.
I used the join statement suggested by this answer but I got various exceptions for the following statement:
List<Products> products = session.Query<Products>().ToList();
Note: I can pull in all products from the database without the corresponding column in the Categories table, so I know that my database connectivity is good, and that the basic functionality of the application is sound.
I am new to Fluent-NHibernate, have invested quite a bit of time on this, but feel I am not getting anywhere. I would appreciate some directed guidance.
I'm a little confused because you seem to mixing singular and plural, but I would create separate domain mappings for the product and category
public class Product
{
public virtual int ProductId { get; set; }
public virtual string ProductDescription { get; set; }
public virtual Category Category { get; set; }
}
public class Category
{
public virtual int CategoryId { get; set; }
public virtual string CategoryDescription { get; set; }
}
map them the way you are mapping in the question, then create a view model
public class ProductViewModel
{
public virtual int ProductId { get; set; }
public virtual string ProductDescription { get; set; }
public virtual string CategoryDescription { get; set; }
}
that gets populated with this query
var products = session.Query<Products>().Select(p => new ProductViewModel()
{
ProductId = p.ProductId,
ProductDescription = p.ProductDescription,
CategoryDescription = p.Category.CategoryDescription
});
This will produce a query that only returns the columns you need. If you return full entities, you are going to return information you don't need.
I currently have a MVC5 site with a TPH relationship with classes as follows:
public abstract class product{
public int productID {get;set;}
}
public class toy : product {
public virtual List<ChildComment> Comments {get;set;}
public virtual List<AdultComment> Comments {get;set;}
}
public class tool : product {
public virtual List<AdultComment> Comments {get;set;}
}
public class ChildComment {
public CommentID {get;set;}
public string commentText {get;set;}
public virtual product Product {get;set;}
}
public class AdultComment {
public CommentID {get;set;}
public string commentText {get;set;}
public virtual product Product {get;set;}
}
My Issue is when:
1) I am creating a new adult comment in the adult comment controller
2) I use db.Products.find(id) to add a product to the product virtual property of the comment
3) I go to the view of the Product I just added the comment to and see that there are 0 comments (lets say I tried to add a comment to a toy, but remember I didn't cast it as a toy when I added it to the virtual property)
4) When I go to the database, there are 3 key columns in the adultcomment table: one for product, one for toys, and one for tools. The correct id was placed in the product column and the others are null
Do I have to cast a product as either a toy or tool before adding it to the adultcomment's virtual property?
Why are there extra columns in the adultcomment table, is it possible to consolidate to one single id column (since after all, i have one products table in my tph), and should I do so if it is possible?
Add the foreignKey attribute to new Comment class
public class Comment
{
[Key]
public int CommentID { get; set; }
public string commentText { get; set; }
public int productID { get; set; }
[ForeignKey("productID")]
public virtual Product Product { get; set; }
}
so AdultComment now looks like this
public class AdultComment : Comment
{
}
you will have to add a unique Identifier when creating a new product despite database auto generating id
using (var context = new YOUR-CONTEXT())
{
var toy = new Toy
{
productID = 1, //Unique identifier
AdultComments = new List<AdultComment>()
{
new AdultComment { commentText = "Some comment" }
}
};
context.Products.Add(toys);
context.SaveChanges();
}
This is the scenario:
I have a products table and a categories table. The relationship is many-to-many: a category can have 1 or more products....and a product can be in 1 or more categories...
The Code-First mapping looks like this....
public class Product
{
//...additional properties...
public virtual ICollection<Category> AssociatedCategories {get; set;}
}
public class Category
{
//...additional properties...
public virtual ICollection<Product> AssociatedProducts {get; set;}
}
Now, under the hood, entity framework will create a join table called ProductCategory with columns ProductID and CategoryID. That's great....
Here's the thing though, I need to introduce a sort order...basically just a cardinal positioning index, but this number exists only at the part in the relationship where product and category meet each other. For example, a product X might have a sort order value of "5" in Category Y, but that some product--X--could have a different sort value--say 10--in Category Z.
Naturally, I could create an entity specifically for this type of thing...but it would require a new table be made...there would be 3 columns for the Category ID, Product ID, and sort order. What I'd really like to be able to do is tap into the table that entity framework already made....it will already keep track of products IDs and category IDs in the join table....is there any way to make use of the table that already exists?
You need to create a specific entity for the join table in order to do this.
public class Product
{
//...additional properties...
public virtual ICollection<ProductCategoryXref> AssociatedCategories {get; set;}
}
public class Category
{
//...additional properties...
public virtual ICollection<ProductCategoryXref> AssociatedProducts {get; set;}
}
public class ProductCategoryXref
{
public int ProductId { get; set; }
public int CategoryId { get; set; }
public int SortOrder { get; set; }
// Additional Columns...
public virtual Product Product { get; set; }
public virtual Category Category { get; set; }
}
If you are using the Fluent API to configure your entities it will look something like this:
public class ProductCategoryXrefMap : EntityTypeConfiguration<ProductCategoryXref>
{
ProductCategoryXrefMap()
{
HasKey(pk => new { pk.ProductId, pk.CategoryId });
HasRequired(p => p.Product).WithMany(p => p.AssociatedCategories).HasForeignKey(fk => fk.ProductId);
HasRequired(p => p.Category).WithMany(p => p.AssociatedProducts).HasForeignKey(fk => fk.CategoryId);
ToTable("ProductCategoryXref");
}
}