I'm developing a prototype platform using MVC in which users can make a profile and use that profile to make text posts, like a social media site. I have the following two tables in my database:
Profiles
public partial class Profile
{
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
public Profile()
{
this.Posts = new HashSet<Post>();
}
public int Id { get; set; }
public string UserId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Country_ { get; set; }
public System.DateTime DoB { get; set; }
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
public virtual ICollection<Post> Posts { get; set; }
}
}
Posts
public partial class Post
{
public int Id { get; set; }
public string Text { get; set; }
public System.DateTime DATE { get; set; }
public int ProfileId { get; set; }
public virtual Profile Profile { get; set; }
}
}
In my ViewModel I have a list of Posts called PostList, which I want to populate with all of the Post records made by the user. So, I need to populate the list with all records where the ProfileId in Posts is equal to the Id of Profile, which is determined by whether or not the UserId in Profile is equal to the current user's Identity.
In short, I need:
Post List = Posts where ProfileId = Profiles.Id Where Profiles.UserId = CurrentUserId.
Any ideas? I've tried the following, but it's totally wrong:
var userId = User.Identity.GetUserId();
ViewModels.ProfileViewModel pVm = new ViewModels.ProfileViewModel();
pVm.PostList = db.Posts.Include(db.Profiles).Where(a => a.UserId == userId).ToList();
pVm.UserName = User.Identity.GetUserName();
return View(pVm);
You just walk the relationship in your query:
pVm.PostList = db.Posts.Where(a => a.Profile.UserId == userId);
It's unnecessary to use Include since Profile will automatically be joined to make the query.
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`m building an application where I try to make a friend system.
Now, I work with 2 tables for that.
1st: Default AspNetUsers where i store user information.
2nd: Friends Table as below:
public class AspNetFriends
{
public int ID { get; set; }
public string friendFrom { get; set; }
public string friendTo { get; set; }
public bool isConfirmed { get; set; }
}
In this table both "friendFrom" and "friendTo" is string type, and receiving the registered users ID.
What i want to achieve is that when i display this table on my view, i want to show the Username of the same UserID thats either in the "friendFrom" or "friendTo" column.
You need to change your class as followed (I didn't test this):
Default application user of asp.net core
using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
namespace project.Models
{
// Add profile data for application users by adding properties to the ApplicationUser class
public class ApplicationUser : IdentityUser
{
}
}
Model
public class AspNetFriends
{
public int ID { get; set; }
public bool isConfirmed { get; set; }
public virtual ApplicationUser friendFrom { get; set; }
public virtual ApplicationUser friendTo { get; set; }
}
Now you can get to the getters and setters of the aspnet user
Controller
public async Task<IActionResult> Details(int id)
{
var query = from m in _dbContext.AspNetFriends
join ff in _dbContext.Users on
new { m.friendFrom.Id } equals new { Id = cu.Id }
join ft in _dbContext.Users on
new { m.friendTo.Id } equals new { Id = cu.Id }
where m.ID == id
select m;
return View(query.Single());
}
View
#model project.AspNetFriends
<p>
#model.friendFrom.UserName
</P>
#item.CreationUser.UserName
I have 2 questions:
Why am I getting that exception? I want to create a row in my User Table (it has 6 columns: Name, Role, Email, Group, Id, SoftwareVersion) and in the Membership table. The primary key is the pair Id-SoftwareVersion. The code:
code
What's wrong?
Is it possible add more row (with CreateUserAndAccount) by changing the id? Right? Example: try to add a row with "Administrator" as UserName when an entry already exists in the DB with the same name (but I remember the primary key is the pair Id-SoftwareVersion).
My User class:
public partial class User
{
public User()
{
this.dfcs = new HashSet<Dfc>();
this.fids = new HashSet<Fid>();
this.histroyDeliverRequests = new HashSet<Histroyrequest>();
this.histroyProposalRequests1 = new HashSet<Histroyrequest>();
}
public string Name { get; set; }
public string Role { get; set; }
public string Email { get; set; }
public string Group { get; set; }
public int Id { get; set; }
public short SoftwareVersion { get; set; }
public virtual ICollection<Dfc> dfcs { get; set; }
public virtual ICollection<Fid> fids { get; set; }
public virtual ICollection<Histroyrequest> histroyDeliverRequests { get; set; }
public virtual ICollection<Histroyrequest> histroyProposalRequests1 { get; set; }
public virtual Software Software { get; set; }
}
I am thinking you should omit the Id, when inserting into the User Table, as I would think that the Id would auto increment, when inserting a new record?
Having som major problem with many to many relation.
public class Team
{
public Team()
{
Users = new HashSet<User>();
}
public int Id { get; set; }
public string Name { get; set; }
public ICollection<User> Users { get; set; }
}
public class User
{
public User()
{
Teams = new HashSet<Team>();
}
public int Id { get; set; }
public string Username { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public string Cell { get; set; }
public ICollection<Team> Teams { get; set; }
}
After Returning a newly added Team like this
var currentUser = _ctx.Users.Where(u => u.Username == HttpContext.Current.User.Identity.Name).SingleOrDefault();
teamToAdd.Users.Add(currentUser);
var teamAdded = _ctx.Teams.Add(teamToAdd);
Save();
return teamAdded;
I get the following error in the response inner exception:
"Self referencing loop detected with type 'MatchMaker.Data.Team'. Path 'Users[0].Teams'."
There is obviously a circular reference going on but i want a Team to be able to have many Users and a User to be able to have many Teams. Is there any way of getting past this withouth creating DTOs?
I am writing a PhoneGap/Web/JS mobile application that uses the WebAPI and Entity Framework in the backend.
I have a class called Thing which references the User table 4 times (ChangedByUserId, CreatedByUserId etc. The User table is really large (30 user-related fields)
I want to pass as little data over each call as possible, but I need the User's Name for each of these UserID foreign keys. (this is the only information from the user record I need).
When I use the object graph in EF it returns the FULL user record for each foreign key, so a single Thing object becomes massively bloated. I don't want to make multiple calls to get the Thing POCO object and then the User's name by UserID.
What I really want to do is a sort of flattened DTO object which is just the Thing class below but with a string for each user name, e.g. CreatedByUserName, ChangedByUserName etc. Then I would return this DTO as my hydrated POCO object and the data would be small.
So my question is: How do I do this using Entity Framework? (limit related record's return data?)
public partial class Thing
{
public int ThingId { get; set; }
public int FromUserId { get; set; }
public int ToUserId { get; set; }
public string ThingText { get; set; }
public int StatusId { get; set; }
public int ChangedByUserId { get; set; }
public int CreatedByUserId { get; set; }
public virtual User FromUser { get; set; }
public virtual User ToUser { get; set; }
public virtual User CreatedByUser { get; set; }
public virtual User ChangedByUser { get; set; }
}
As you said, you need to flatten Thing
public class FlatThing
{
public int ThingId { get; set; }
public int FromUserId { get; set; }
public int ToUserId { get; set; }
public string ThingText { get; set; }
public int StatusId { get; set; }
public int ChangedByUserId { get; set; }
public int CreatedByUserId { get; set; }
public string FromUserName { get; set; }
public string ToUserName{ get; set; }
}
// assume you have your things
var flatThings = new List<FlatThings>;
foreach (Thing t in things)
flatThings.Add(new FlatThing{ ThingId = t.ThingId, FromUserId = t.FromUserId,
FromUserName = t.FromUser.Name .....});
return flatThings;