I am new to EF, and trying to get many-to-many unidirectional relationship with code first approach. For example, if I have following two classes (not my real model) with be a N * N relationship between them, but no navigation property from "Customer" side.
public class User {
public int UserId { get; set; }
public string Email { get; set; }
public ICollection TaggedCustomers { get; set; }
}
public class Customer {
public int CustomerId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
The mapping code looks like ...
modelBuilder.Entity()
.HasMany(r => r.TaggedCustomers)
.WithMany(c => c.ANavgiationPropertyWhichIDontWant)
.Map(m =>
{
m.MapLeftKey("UserId");
m.MapRightKey("CustomerId");
m.ToTable("BridgeTableForCustomerAndUser");
});
This syntax force me to have "WithMany" for "Customer" entity.
The following url, says "By convention, Code First always interprets a unidirectional relationship as one-to-many."
Is it possible to override it, or should I use any other approach?
Use this:
public class User {
public int UserId { get; set; }
public string Email { get; set; }
// You must use generic collection
public virtual ICollection<Customer> TaggedCustomers { get; set; }
}
public class Customer {
public int CustomerId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
And map it with:
modelBuilder.Entity<User>()
.HasMany(r => r.TaggedCustomers)
.WithMany() // No navigation property here
.Map(m =>
{
m.MapLeftKey("UserId");
m.MapRightKey("CustomerId");
m.ToTable("BridgeTableForCustomerAndUser");
});
Related
I am using the Sakila Sample Database from MySql on a MySql server. The Diagram looks as follows.
The important tables are the store, inventory and film tables. The is a many-to-many relationship between the tables and the linker table is the inventory table.
I scaffolded this Database in a new dotnetcore project using EFCore 2.
I am trying to get a list of stores and their list of films.
The Entities are defined as follows:
Store
public class Store
{
public Store()
{
Customer = new HashSet<Customer>();
Inventory = new HashSet<Inventory>();
Staff = new HashSet<Staff>();
}
public byte StoreId { get; set; }
public byte ManagerStaffId { get; set; }
public short AddressId { get; set; }
public DateTimeOffset LastUpdate { get; set; }
public Address Address { get; set; }
public Staff ManagerStaff { get; set; }
public ICollection<Customer> Customer { get; set; }
public ICollection<Inventory> Inventory { get; set; }
public ICollection<Staff> Staff { get; set; }
}
Inventory
public partial class Inventory
{
public Inventory()
{
Rental = new HashSet<Rental>();
}
public int InventoryId { get; set; }
public short FilmId { get; set; }
public byte StoreId { get; set; }
public DateTimeOffset LastUpdate { get; set; }
public Film Film { get; set; }
public Store Store { get; set; }
public ICollection<Rental> Rental { get; set; }
}
Film
public partial class Film
{
public Film()
{
FilmActor = new HashSet<FilmActor>();
FilmCategory = new HashSet<FilmCategory>();
Inventory = new HashSet<Inventory>();
}
public short FilmId { get; set; }
public string Title { get; set; }
public string Description { get; set; }
public short? ReleaseYear { get; set; }
public byte LanguageId { get; set; }
public byte? OriginalLanguageId { get; set; }
public byte RentalDuration { get; set; }
public decimal RentalRate { get; set; }
public short? Length { get; set; }
public decimal ReplacementCost { get; set; }
public string Rating { get; set; }
public string SpecialFeatures { get; set; }
public DateTimeOffset LastUpdate { get; set; }
public Language Language { get; set;
public Language OriginalLanguage { get; set; }
public ICollection<FilmActor> FilmActor { get; set; }
public ICollection<FilmCategory> FilmCategory { get; set; }
public ICollection<Inventory> Inventory { get; set; }
}
My context looks as follows:
modelBuilder.Entity<Inventory>(entity =>
{
entity.ToTable("inventory", "sakila");
entity.HasIndex(e => e.FilmId)
.HasName("idx_fk_film_id");
entity.HasIndex(e => new { e.StoreId, e.FilmId })
.HasName("idx_store_id_film_id");
And lastly the repo looks as follows:
public IEnumerable<Store> GetStores()
{
return _context.Store.
Include(a => a.Inventory).
ToList();
}
Problem:
When I call this method from a Controller to get the list of stores I don´t get any json response on Postman. Yet if I debug into the list that is returned from the Controller I find the list of stores.
The problem is that the list contains:
store->inventory->film->store->inventory->film->store... Etc. Creating a circular dependency that fills up the allowed Process memory of the request.
Possible Solutions:
I think it has to do with the fact that on the Context both the Foreign Keys are defined as HasIndex instead of HasKey
entity.HasIndex(e => new { e.StoreId, e.FilmId })
.HasName("idx_store_id_film_id");
When I define it as HasKey then I get an Error:
'The relationship from 'Rental.Inventory' to 'Inventory.Rental' with
foreign key properties {'InventoryId' : int} cannot target the primary
key {'StoreId' : byte, 'FilmId' : short} because it is not compatible.
Configure a principal key or a set of compatible foreign key
properties for this relationship.'
To answer #hamzas comment, I did find a solution to this problem. I used EFCore to build the entities and the DBContext through scaffolding (DB First). As a best practice you should be using Models (Dtos) to represent the Data for the client. EFCore is very helpful in giving us the flexibility to access this M to N relationship however we want. This gives us the flexibility to represent this Data to the client however we want.
Whatever your use case might be. You have to convert the M to N relationship into an 1 to N model.
Use Case #1: You want to show all the movies for a specific store.
Solution
Step #1: You create a StoreDto (Model)
public class StoreDto
{
int StoreId { get; set; }
ICollection<FilmDto> Films { get; set; }
= new List<FilmDto> ();
}
Step #2: Create a FilmDto
public class FilmDto
{
int FilmId { get; set; }
int StoreId { get; set; }
string FilmName { get; set; }
}
Step #3: You provide a Mapping with auto mapper
public class MappingProfiles : Profile
{
public MappingProfiles()
{
CreateMap<Store, StoreDto>();
CreateMap<Film, FilmDto>();
}
}
Step #4: Query the data correctly, Unfortunately I don´t have this example anymore to test this code, so here is where you´ll have to experiment a bit
public Store GetFilmsForStore(byte StoreId)
{
return _context.Store.
Include(a => a.Inventory).
ThenInclude(i => i.Film)
ToList();
}
On the "Include" part you want to only get the Inventory entries where StoreId == Inverntory.StoreId and then Include the Films Object from the resulting list.
I hope you get the jist of it. You want to break up your m to n relationships and make them seem like 1 to m for your clients.
I am have some trouble getting Entity Framework to handle a many to many relationship in my data schema. Here is my model:
public class User
{
public int UserId { get; set; }
public int Username { get; set; }
public IEnumerable<Customer> Customers { get; set; }
...
}
public class Customer
{
public int CustomerId { get; set; }
...
}
public class CustomerUser
{
public int CustomerUserId { get; set; }
public int CustomerId { get; set; }
public int UserId { get; set; }
public DateTime CreatedTimestamp { get; set; }
...
}
Here is the mapping:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<User>().HasKey(u => u.UserId).ToTable("Users");
modelBuilder.Entity<Customer>().HasKey(c => c.CustomerId).ToTable("Customer");
modelBuilder.Entity<CustomerUsers>().HasKey(cu => cu.CustomerUserId).ToTable("CustomerUsers");
modelBuilder.Entity<CustomerUsers>()
.HasRequired(cu => cu.User)
.WithRequiredDependent()
.Map(m =>
{
m.ToTable("Users");
m.MapKey("CustomerUsers.UserId");
});
}
My database has a Users, Customers, and CustomerUsers table with columns that match the model.
I am trying to execute the following query:
result = (from u in context.Users
join customerUsers in context.CustomerUsers on u.UserId equals customerUsers.User.UserId
join customers in context.Customers on customerUsers.CustomerId equals customers.CustomerId into ps
select new
{
User = u,
Customers = ps
}).ToList().Select(r => { r.User.Customers = r.Customers.ToList(); return r.User; });
When I run the code, I get the following error:
The Column 'CustomerUserId' specified as part of this MSL does not exist in MetadataWorkspace
Can anyone see what is wrong with my approach?
Thanks!
I should note that I am intentionally trying to not include a reference to the CustomerUsers table from either the Customer or User class. The majority of the time, the payload of the CustomerUsers table is not important, only which customers are associated to which users. There are some reporting scenarios where the additional information in the join table is necessary, but since this is not the typical situation, I would like to avoid cluttering up the models by having this additional indirection.
Instead of trying to map this as many to many, map it as two one to many relationships. See the discussion of many to many join tables with payload in Many-to-Many Relationships in this tutorial:
http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/creating-a-more-complex-data-model-for-an-asp-net-mvc-application
For your model you will need probably two one-to-many relationships and the following navigation properties:
public class User
{
public int UserId { get; set; }
public int Username { get; set; }
// ...
public ICollection<CustomerUser> CustomerUsers { get; set; }
}
public class Customer
{
public int CustomerId { get; set; }
//...
public ICollection<CustomerUser> CustomerUsers { get; set; }
}
public class CustomerUser
{
public int CustomerUserId { get; set; }
public int CustomerId { get; set; }
public int UserId { get; set; }
public DateTime CreatedTimestamp { get; set; }
//...
public User User { get; set; }
public Customer Customer { get; set; }
}
And the following mapping:
modelBuilder.Entity<CustomerUser>()
.HasRequired(cu => cu.User)
.WithMany(u => u.CustomerUsers)
.HasForeignKey(cu => cu.UserId);
modelBuilder.Entity<CustomerUser>()
.HasRequired(cu => cu.Customer)
.WithMany(c => c.CustomerUsers)
.HasForeignKey(cu => cu.CustomerId);
I've looked through several of the questions here and am not quite connecting all the (mental) dots on this. I would appreciate some help.
My Models (code first):
public class cgArmorial
{
[Key]
[Display(Name = "Armorial ID")]
public Guid ArmorialID { get; set; }
[Display(Name = "User ID")]
public Guid UserId { get; set; }
public string Name { get; set; }
public string DeviceUrl { get; set; }
public string Blazon { get; set; }
public virtual ICollection<cgArmorialAward> ArmorialAwards { get; set; }
}
public class cgArmorialAward
{
public cgArmorial Armorial { get; set; }
public cgAward Award { get; set; }
public DateTime AwardedOn { get; set; }
}
public class cgAward
{
[Key]
[Display(Name = "Award ID")]
public Guid AwardID { get; set; }
public string Name { get; set; }
public string Group { get; set; }
public string Description { get; set; }
public string ImageUrl { get; set; }
public string Blazon { get; set; }
public virtual ICollection<cgArmorialAward> ArmorialAwards { get; set; }
}
Then in my Context class I have (last 2 entries):
public class Context : DbContext
{
public DbSet<cgUser> Users { get; set; }
public DbSet<cgEvent> Events { get; set; }
public DbSet<cgEventType> EventTypes { get; set; }
public DbSet<cgArmorial> Armorials { get; set; }
public DbSet<cgAward> Awards { get; set; }
public DbSet<cgArmorialAward> ArmorialAwards { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<cgUser>()
.HasMany<cgEvent>(e => e.EventAutocrats)
.WithMany(u => u.EventAutocrats)
.Map(m =>
{
m.ToTable("EventAutocrats");
m.MapLeftKey("UserId");
m.MapRightKey("EventId");
});
modelBuilder.Entity<cgUser>()
.HasMany<cgEvent>(e => e.EventStaff)
.WithMany(u => u.EventStaff)
.Map(m =>
{
m.ToTable("EventStaff");
m.MapLeftKey("UserId");
m.MapRightKey("EventId");
});
modelBuilder.Entity<cgArmorialAward>()
.HasRequired(a => a.Armorial)
.WithMany(b => b.ArmorialAwards);
modelBuilder.Entity<cgArmorialAward>()
.HasRequired(a => a.Award)
.WithMany(); // b => b.ArmorialAwards
}
}
I am getting this error when I try to run:
System.Data.Edm.EdmEntityType: : EntityType 'cgArmorialAward' has no
key defined. Define the key for this EntityType.
System.Data.Edm.EdmEntitySet: EntityType: EntitySet �ArmorialAwards�
is based on type �cgArmorialAward� that has no keys defined.
Well, as the exception says: You don't have a key defined on your entity cgArmorialAward. Every entity must have a key. Change it to the following:
public class cgArmorialAward
{
[Key, Column(Order = 0)]
[ForeignKey("Armorial")]
public Guid ArmorialID { get; set; }
[Key, Column(Order = 1)]
[ForeignKey("Award")]
public Guid AwardID { get; set; }
public cgArmorial Armorial { get; set; }
public cgAward Award { get; set; }
public DateTime AwardedOn { get; set; }
}
The fields in the composite key are foreign keys to the other two tables at the same time, hence the ForeignKey attribute. (I'm not sure if conventions would detect this automatically because you have non-standard names ("cgXXX" for the classes and "XXXId" for the foreign key properties). On the other hand the property names Armorial and Award match the foreign key property names. I'm not sure if EF conventions would consider this. So, perhaps the ForeignKey attribute is not necessary but at least it's not wrong.)
I have two entities that have a relationship for which I create a join table
public class Student
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Image> Images { get; set; }
}
public class Image
{
public int Id { get; set; }
public string Filename { get; set; }
public virtual ICollection<Student> Students { get; set; }
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Student>()
.HasMany(i => i.Images)
.WithMany(s => s.Students)
.Map(m => m.ToTable("StudentImages"));
}
I would like to add an additional column to allow chronological ordering of the StudentImages.
Where should I add insert the relevant code?
Do you want to use that new column in your application? In such case you cannot do that with your model. Many-to-many relation works only if junction table doesn't contain anything else than foreign keys to main tables. Once you add additional column exposed to your application, the junction table becomes entity as any other = you need third class. Your model should look like:
public class StudentImage
{
public int StudentId { get; set; }
public int ImageId { get; set; }
public int Order { get; set; }
public virtual Student Student { get; set; }
public virtual Image Image { get; set; }
}
public class Student
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<StudentImage> Images { get; set; }
}
public class Image
{
public int Id { get; set; }
public string Filename { get; set; }
public virtual ICollection<StudentImage> Students { get; set; }
}
And your mapping must change as well:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<StudentImages>().HasKey(si => new { si.StudentId, si.ImageId });
// The rest should not be needed - it should be done by conventions
modelBuilder.Entity<Student>()
.HasMany(s => s.Images)
.WithRequired(si => si.Student)
.HasForeignKey(si => si.StudentId);
modelBuilder.Entity<Image>()
.HasMany(s => s.Students)
.WithRequired(si => si.Image)
.HasForeignKey(si => si.ImageId);
}
I want to created Bi-Directional One-One relationship between two entities using EF Code First. I have trouble with the following code. What do you think I should do?
public class User
{
public string ID { get; set; }
public string LastName { get; set; }
public string Password { get; set; }
public string FirstName { get; set; }
public int ProfileID { get; set; }
public Profile Profile { get; set; }
}
public class Profile
{
public int UserID { get; set; }
public User User { get; set; }
public int ProfileID { get; set; }
public string ProfileName { get; set; }
public DateTime CreateDate { get; set; }
public DateTime LastUpdateDate { get; set; }
}
I want to have both Navigation property and Foreign Key in both the entities.
This gives me error. What can do I in Fluent Mapping API to make this work?
Use this:
public class User
{
public string ID { get; set; }
public string LastName { get; set; }
public string Password { get; set; }
public string FirstName { get; set; }
public Profile Profile { get; set; }
}
public class Profile
{
[Key, ForeignKey("User")]
public int ProfileID { get; set; }
public string ProfileName { get; set; }
public DateTime CreateDate { get; set; }
public DateTime LastUpdateDate { get; set; }
public User User { get; set; }
}
That is the only valid way to build one-to-one relation in EF - PK of the dependent entity must be also FK to principal entity. There is nothing like bidirectional one-to-one relation in EF because it cannot work in EF.
The way how people sometimes overcome this are two one-to-many relations where principal doesn't have navigation collection for dependent entities + manually defined unique keys in the database. That require manual mapping:
public class User
{
public string ID { get; set; }
public string LastName { get; set; }
public string Password { get; set; }
public string FirstName { get; set; }
// one side MUST be nullable otherwise you have bidirectional constraint where each
// entity demands other side to be inserted first = not possible
public int? ProfileId { get; set; }
public Profile Profile { get; set; }
}
public class Profile
{
public int ProfileID { get; set; }
public string ProfileName { get; set; }
public DateTime CreateDate { get; set; }
public DateTime LastUpdateDate { get; set; }
public int UserId { get; set; }
public User User { get; set; }
}
And in mapping you will define:
modelBuilder.Entity<User>
.HasOptional(u => u.Profile)
.WithMany()
.HasForeignKey(u => u.ProfileId);
modelBuilder.Entity<Profile>
.HasRequired(u => u.User)
.WithMany()
.HasForeignKey(u => u.UserId);
Now you must define Unique keys in the database - if you are using code first use custom database initializer. Be aware that still bidirectional one-to-one is wrong concept because both sides demand unique FK where NULL is still included in unique values so once you insert User before Profile there mustn't be any other User without Profile. That probably leads to serializable transaction.