I have two models and a dbcontext:
public class User
{
public int UserId { get; set; }
public String UserName { get; set; }
public virtual ICollection<Conversation> Conversations { get; set; }
}
public class Conversation
{
public int ConversationId { get; set; }
public String Text { get; set; }
public int UserId { get; set; }
public virtual User User { get; set; }
}
public class ChatContext : DbContext
{
public DbSet<User> Users { get; set; }
public DbSet<Conversation> Conversations { get; set; }
}
I am trying to add a conversation entity so I need to retrieve the UserId from User table. So far I have:
var newtext = new Conversation()
{
Text = message, // message is sent from user
UserId = ChatContext.User.Where(u => u.UserName == name).Select(u => u.UserId)
};
I need to query the user table to retrieve the userId associated with that particular name. How should I achieve this? The error is:
ChatContext does not have a definition for user.
Firstly: You must add static to Users like this:
public class ChatContext : DbContext
{
public static DbSet<User> Users { get; set; }
public DbSet<Conversation> Conversations { get; set; }
}
Secondly: You must add FirstOrDefault method to your query, Because it will return an iQueryable like this:
var newtext = new Conversation()
{
Text = message, // message is sent from user
UserId = ChatContext.Users.FirstOrDefault(u => u.UserName == name).UserId
};
This should works.
Related
In an ASP.NET core (dotnet 6) web application, we have a small user management functionality in which a user can be assigned to a specific site (physical location) with certain rights. A user can be assigned to one or more sites and a site can also be assigned to one or more users, thus the many to many relationship. We have the following classes:
public class User
{
public int ID { get; set; }
public string SamAccountName { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public int GroupID { get; set; }
public bool IsEnabled { get; set; }
public ICollection<UserSite> UserSites { get; set; }
}
public class Site
{
public int ID { get; set; }
public string Name { get; set; }
public string Code { get; set; }
public ICollection<UserSite> UserSites { get; set; }
}
The many to many relationship is described in a join table with fluent API:
public class UserSite
{
public int UserID { get; set; }
public User User { get; set; }
public int SiteID { get; set; }
public Site Site { get; set; }
}
// Fluent API for UserSite table
builder.HasKey(us => new { us.UserID, us.SiteID });
builder.HasOne(us => us.User)
.WithMany(us => us.UserSites)
.HasForeignKey(us => us.UserID)
.OnDelete(DeleteBehavior.Cascade);
builder.HasOne(us => us.Site)
.WithMany(us => us.UserSites)
.HasForeignKey(us => us.SiteID)
.OnDelete(DeleteBehavior.Cascade);
These classes result in the following DTO's:
public class UserDTO
{
public int ID { get; set; }
public string SamAccountName { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public int GroupID { get; set; }
public bool IsEnabled { get; set; }
public IList<SiteDTO> Sites { get; set; }
}
public class SiteDTO
{
public int ID { get; set; }
public string Name { get; set; }
public string Code { get; set; }
}
What we want to know is, what is the best way to create a new user or update an existing user? Just to clarify, the data in the Sites table exists already and is static. What I mean by that is that when creating a new user or updating an existing one, a user can be assigned to one or more existing sites, but no new site is created in the process.
We already tried some things that did work but we are not sure if this is really the best way to this or if there is a far better way to do it. Here is what we tried:
The create method
// Create method
public IActionResult CreateUser(UserDTO userDTO)
{
if (ModelState.IsValid)
{
User user = _mapper.Map<User>(userDTO);
user.IsEnabled = true;
AttachSitesToUser(user.ID, user.UserSites);
_context.Users.Add(user);
_context.SaveChanges();
userViewModel = _mapper.Map<UserViewModel>(user);
}
return new JsonResult(new[] { userDTO });
}
The update method:
// Update method
public IActionResult UpdateUser(UserDTO userDTO)
{
if (ModelState.IsValid)
{
User user = _context.Users
.Include(u => u.Sites)
.ThenInclude(s => s.Site)
.Single(u => u.ID == userDTO.ID);
_mapper.Map(userViewModel, user);
AttachSitesToUser(user.ID, user.UserSites);
_context.Entry(user).State = EntityState.Modified;
_context.SaveChanges();
}
return new JsonResult(new[] { userDTO });
}
The helper method AttachSitesToUser:
// Helper method that adds the user ID and attaches the site(s) to the context
private void AttachSitesToUser(int userID, IEnumerable<UserSite> userSites)
{
foreach (UserSite userSite in userSites)
{
userSite.UserID = userID;
if (Context.Entry<Site>(userSite.Site).State == EntityState.Detached)
{
Context.Sites.Attach(userSite.Site);
Context.Entry<Site>(userSite.Site).State = EntityState.Unchanged;
}
}
}
As you can see, for the moment we have to loop through the UserSites list in the User entity and attach the sites the user was assigned to manually to the context. Is there no better way to do this or is this the official best practice?
I am implementing Chat functionality excatly like this one in asp.net.This is the model explaination
My classes are: User, Conversaiton and Message:
public class User
{
public Guid Id { get; set; }
public string Name { get; set; }
public bool Active { get; set; }
public string UserName { get; set; }
//keys
public ICollection<Conversation> Conversations { get; set; }
}
public class Conversation
{
public Guid ID { get; set; }
public ICollection<Message> Messages { get; set; }
public User RecipientUser { get; set; }
public Guid SenderUserId { get; set; }
public DateTime CreatedDate { get; set; }
public DateTime ModifiedDate { get; set; }
}
and finally,
public class Message
{
public int ID { get; set; }
public string Text { get; set; }
public bool IsDelivered { get; set; }
public bool IsSeen { get; set; }
public Guid SenderUserId { get; set; }
public Conversation Conversation { get; set; }
public DateTime CreatedDate { get; set; }
public DateTime ModifiedDate { get; set; }
}
I am using EntityTypeConfiguration using fluent Api which are:
public class UserConfig : EntityTypeConfiguration<User>
{
public UserConfig()
{
HasMany(x => x.Conversations).WithRequired(x => x.RecipientUser).HasForeignKey(x => x.SenderUserId);
}
}
public class ConversationConfig : EntityTypeConfiguration<Conversation>
{
public ConversationConfig()
{
HasKey(x => x.ID);
HasRequired(x => x.RecipientUser).WithMany(x => x.Conversations);
HasMany(x => x.Messages).WithRequired(x => x.Conversation).HasForeignKey(x => x.SenderUserId);
}
}
But I'm getting error as follows:
Multiplicity constraint violated. The role 'Conversation_RecipientUser_Target' of the relationship 'DataAcessLayer.Conversation_RecipientUser' has multiplicity 1 or 0..1.
If anyone could help me. Many thanks!!!
I didn't get the exception when I used your model, but that doesn't matter much, because you've got to make some changes anyway.
First, this configuration in UserConfig ...
HasMany(x => x.Conversations).WithRequired(x => x.RecipientUser)
.HasForeignKey(x => x.SenderUserId);
... doesn't make sense to me. This means that the conversations belong to the recipient, not to the sender, which in itself is somewhat unexpected. But the name of the foreign key is SenderUserId. If you save objects into this model, SenderUserId will get the value of the recipient's ID!
Second, assuming the previous point was an error, you make it harder than necessary by defining ...
public User RecipientUser { get; set; }
public Guid SenderUserId { get; set; }
This means that you can only navigate from Conversation to the sender User by an explicit join over SenderUserId. Conversely, you can only set the recipient by setting RecipientUser, not by simply setting a foreign key value.
Third, you shouldn't have this SenderUserId in Message. It should be ConversationId instead. You can find a Message's sender through the Conversation it belongs to.
All in all, I changed your model into this, reducing it to the bare-bone minimum, and using int for ID, just because it's easier reading:
public class User
{
public int ID { get; set; }
public string Name { get; set; }
public ICollection<Conversation> Conversations { get; set; }
}
public class Conversation
{
public int ID { get; set; }
public int SenderUserID { get; set; }
public User SenderUser { get; set;}
public int RecipientUserID { get; set; }
public User RecipientUser { get; set; }
public ICollection<Message> Messages { get; set; }
}
public class Message
{
public int ID { get; set; }
public string Text { get; set; }
public int ConversationID { get; set; }
public Conversation Conversation { get; set; }
}
And the only configuration:
public class ConversationConfig : EntityTypeConfiguration<Conversation>
{
public ConversationConfig()
{
HasKey(c => c.ID);
HasRequired(c => c.SenderUser).WithMany(u => u.Conversations)
.HasForeignKey(c => c.SenderUserID).WillCascadeOnDelete(true);
HasRequired(c => c.RecipientUser).WithMany()
.HasForeignKey(c => c.RecipientUserID).WillCascadeOnDelete(false);
HasMany(c => c.Messages).WithRequired(x => x.Conversation)
.HasForeignKey(x => x.ConversationID);
}
}
(One of the foreign keys doesn't have cascaded delete because that will cause a SQL-Server error: multiple cascade paths).
A simple test:
using (DbContext db = new DbContext(connectionString))
{
var send = new User { Name = "Sender" };
db.Set<User>().Add(send);
var rec = new User { Name = "Recipient" };
var messages = new[] { new Message { Text = "a" }, new Message { Text = "b" } };
var conv = new Conversation { SenderUser = send, RecipientUser = rec, Messages = messages };
db.Set<User>().Add(rec);
db.Set<Conversation>().Add(conv);
db.SaveChanges();
}
Result:
Users:
ID Name
1 Recipient
2 Sender
Converstions:
ID RecipientUserID SenderUserID
11 1 2
Messages:
ID Text ConversationID
21 a 11
22 b 11
Given Conversation has 1 User foreign key-column which called SenderUserId
// Here you set the user key for the old user!
conversation.RecipientUser = user;
// Here you are trying to change Conversation.SenderUserId from other user (currentUser)
currentUser.Conversations.Add(conversation);
As you seen the added user into collection is not the same which you have assigned to the Conversation 1..n can not be working in this way correctly.
EF try to say to you with the exception, that you are trying to add/change more then entity for the releshinship one-to-zero-or-one, the error message is a little bit foggy I would say the error message should be like "One-to-many navigation properties should using the same entity"
solution 1)
// conversation.RecipientUser = user; remove this line why you need it?!
solution 2)
Create a new property in conversation one for CurrentUser and the other one for User
public class User
{
public User()
{
Conversations = new List<Conversation>();
CurrentUserConversations = new List<Conversation>();
}
public Guid Id { get; set; }
public string Name { get; set; }
public bool Active { get; set; }
public string UserName { get; set; }
public ICollection<Conversation> Conversations { get; set; }
public ICollection<Conversation> CurrentUserConversations { get; set; }
}
public class Conversation
{
public Conversation()
{
Messages = new List<Message>();
}
public Guid ID { get; set; }
public User RecipientUser { get; set; }
public Guid SenderUserId { get; set; }
public User CurrentUser { get; set; }
public Guid? CurrentUserId { get; set; }
public ICollection<Message> Messages { get; set; }
}
public class UserConfig : EntityTypeConfiguration<User>
{
public UserConfig()
{
HasMany(x => x.Conversations).WithRequired(x => x.RecipientUser).HasForeignKey(x => x.SenderUserId);
HasMany(x => x.CurrentUserConversations).WithOptional(x => x.CurrentUser).HasForeignKey(x => x.CurrentUserId);
}
}
How to use it:
var user = myDbContext.Users.First();
var currentUser = new User { Active = true, Id = Guid.NewGuid() };
myDbContext.Users.Add(currentUser);
var message = new Message { IsDelivered = true };
var conversation = new Conversation() { ID = Guid.NewGuid() };
conversation.Messages.Add(message);
conversation.CurrentUser = user;
currentUser.Conversations.Add(conversation);
myDbContext.Conversations.Add(conversation);
myDbContext.SaveChanges();
I have a annoying problem with my code.
My model :
public class Option
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Conference> Conference { set; get; }
}
public partial class Conference
{
[Key, ForeignKey("User")]
public int UserId { get; set; }
public virtual Option Option { set; get; }
public virtual User User { get; set; }
}
public partial class User
{
public int Id {get; set; }
public string Name { get; set; }
public virtual Conference Conference { get; set; }
}
And now i`m getting Option object from Db by dbSet.Find(id) (RepositoryFactory) and what i want to do is to save newly created User, but with selected Option.
If i do like that:
var option = dbSet.Find(id);
var user = new User()
{
Name = "Name",
Conference = new Conference
{
Option = option
}
};
//...
context.SaveChanges();
I`m getting an exception:
An entity object cannot be referenced by multiple instances of IEntityChangeTracker.
What I`m doing wrong?
Edit: I Tried to create Mapping, but this doesn`t seems to work too.
modelBuilder.Entity<Conference>()
.HasKey(x => x.UserId)
.HasRequired(x => x.User)
.WithOptional(user => user.Conference);
modelBuilder.Entity<Option>()
.HasMany(option => option.Conferences)
.WithRequired(conference => conference.Option)
.HasForeignKey(conference => conference.UserId);
Are you trying to achieve a 1:1 relationship between User and Conference? If so, you need to add an Id (key) property to User. Please see the comments I added to the code sample below regarding the 1:1 relationship. I would advise further evaluation of your domain layer to ensure this is what you are trying to achieve...
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity;
namespace Stackoverflow
{
public class EntityContext : DbContext
{
public IDbSet<Conference> Conferences { get; set; }
public IDbSet<Option> Options { get; set; }
public IDbSet<User> Users { get; set; }
}
public class Option
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Conference> Conference { set; get; }
}
public class Conference
{
// In one-to-one relation one end must be principal and second end must be dependent.
// User is the one which will be inserted first and which can exist without the dependent one.
// Conference end is the one which must be inserted after the principal because it has foreign key to the principal.
[Key, ForeignKey("User")]
public int UserId { get; set; }
public int OptionId { get; set; }
public virtual Option Option { set; get; }
public virtual User User { get; set; }
}
public class User
{
// user requires a key
public int Id { get; set; }
public string Name { get; set; }
public virtual Conference Conference { get; set; }
}
class Program
{
static void Main(string[] args)
{
using (var entityContext = new EntityContext())
{
// added to facilitate your example
var newOption = new Option {Name = "SomeOptionName"};
entityContext.Options.Add(newOption);
entityContext.SaveChanges();
var option = entityContext.Options.Find(newOption.Id);
var user = new User
{
Name = "Name",
Conference = new Conference
{
Option = option
}
};
// need to add the user
entityContext.Users.Add(user);
//...
entityContext.SaveChanges();
}
}
}
}
PROBLEM:
I am very new to EF and to LINQ, so please bear with me.
I am trying to create a EF6 model using the database first approach. Simply speaking, I have 2 database tables tblUser and tblMilkMan which have a foreign key relationship on the UserID column.
To avoid cyclic references and to shape the entity data I have created DTO classes for both the models.
I made the MilkManDTO class contain a reference to a UserDTO instance.(This is probably stupid, if so, please guide me to the right way).My aim is to be able to load a milkmen and the related User data
Anyway in my API call, when I try to load a MilkMan by ID, I do not know how to load the related UserDTO. I found examples online on how to load related Entities but not related DTOs.
DB Schema:
Models:
MilkMan Model and DTO:
namespace MilkMan.Models
{
using System;
using System.Collections.Generic;
public partial class tblMilkMan
{
public int RecordID { get; set; }
public int UserID { get; set; }
public bool IsMyTurn { get; set; }
public int RoundRobinOrder { get; set; }
public virtual tblUser tblUser { get; set; }
}
public class MilkManDTO
{
public int RecordID { get; set; }
public int UserID { get; set; }
public bool IsMyTurn { get; set; }
public int RoundRobinOrder { get; set; }
public virtual UserDTO User { get; set; }
}
}
User Model and DTO:
public partial class tblUser
{
public tblUser()
{
this.tblMilkMen = new HashSet<tblMilkMan>();
}
public int UserID { get; set; }
public string LogonName { get; set; }
public string Password { get; set; }
public int PasswordExpiresAfter { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
:
// more fields
:
public virtual ICollection<tblMilkMan> tblMilkMen { get; set; }
}
public class UserDTO
{
public int UserID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
Web API Controller Method:
// GET api/MilkMan/5
[ResponseType(typeof(MilkManDTO))]
public async Task<IHttpActionResult> GettblMilkMan(int id)
{
//tblMilkMan tblmilkman = await db.tblMilkMen.FindAsync(id);
MilkManDTO milkMan = await db.tblMilkMen.Select(b => new MilkManDTO()
{
RecordID = b.RecordID,
UserID = b.UserID,
IsMyTurn = b.IsMyTurn,
RoundRobinOrder = b.RoundRobinOrder,
User = //???? Error//
}).SingleOrDefaultAsync(b => b.RecordID == id);
if (milkMan == null)
{
return NotFound();
}
return Ok(milkMan);
}
You can nest a new UserDTO and use the same initialization list technique.
MilkManDTO milkMan = await db.tblMilkMen.Select(b => new MilkManDTO()
{
RecordID = b.RecordID,
UserID = b.UserID,
IsMyTurn = b.IsMyTurn,
RoundRobinOrder = b.RoundRobinOrder,
User = new UserDTO {
UserID = b.User.UserID,
FirstName = b.User.FirstName,
LastName = b.User.LastName,
}
}).SingleOrDefaultAsync(b => b.RecordID == id);
This code may throw a null reference exception on b.User.UserID if there is not associated User and thus User could be null. You would need to deal with this with either a ?? coalesce, ternary (b.User == null ? "DefaultFirstName" : b.User.FirstName) or omit the entire reference User = (b.User == null ? (UserDTO)null : new UserDTO { ... }). null's make this kind of thing fun.
With C# 6 we have null reference operator .? that makes this much more succinct.
UPDATED: I understood I should not use a DbSet so I changed the implementation to an ICollection as suggested by Erenga
Please consider the following classes:
[Table("Tenant")]
public class Tenant : IEntity
{
public int Id { get; set; }
public string Name { get; set; }
[Key]
public string Guid { get; set; }
public virtual ICollection<User> Users { get; set; }
}
[Table("User")]
public class User : IEntity
{
public int Id { get; set; }
public string Name { get; set; }
public string EmailAddress { get; set; }
public string Password { get; set; }
}
The first test creates a new Tenant and a new User and stores them in the appropriate tables.
[Test]
public void CreateNewUserForNewTenant()
{
var user = _applicationContext.Users.Create();
user.Name = "barney";
user.EmailAddress = "barney#flinstone.com";
var tenant = _applicationContext.Tenants.Create();
tenant.Name = "localhost";
tenant.Guid = Guid.NewGuid().ToString();
tenant.Users.Add(user); // NullReferenceException, I expected the EF would LazyLoad the reference to Users?!
_tenantRepository.Add(tenant);
_applicationContext.SaveChanges();
}
This test will fail on a NullReferenceException since the property Users is not initialized.
How should I change my code that I can rely on LazyLoading provided with EF?
There are 2 problems I see here.
As #SimonWhitehead mentioned, reference types are initialized as null by default. Lazy loading works only on entities created by EF. These are actually sub classes of your class that contain addtional logic to lazy load.
DbSet is not a collection type that is supported on entities. You need to change the type to ICollection, ISet, or IList.
Here's a working example
[Table("Tenant")]
public class Tenant : IEntity
{
public int Id { get; set; }
public string Name { get; set; }
[Key]
public string Guid { get; set; }
public virtual ICollection<User> Users { get; set; }
}
[Table("User")]
public class User : IEntity
{
public int Id { get; set; }
public string Name { get; set; }
public string EmailAddress { get; set; }
public string Password { get; set; }
}
[Test]
public void CreateNewUserForNewTenant()
{
var user = _applicationContext.Users.Create();
user.Name = "barney";
user.EmailAddress = "barney#flinstone.com";
var tenant = _applicationContext.Tenents.Create();
tenant.Name = "localhost";
tenant.Guid = Guid.NewGuid().ToString();
tenant.Users = new List<User> { user };
_tenantRepository.Add(tenant);
_applicationContext.SaveChanges();
}
var tenant = new Tenant
{
Name = "localhost",
Guid = Guid.NewGuid().ToString(),
Users = new List<User> { user }
};
I think you were expecting something like this (not threadsafe):
[Table("Tenant")]
public class Tenant : IEntity
{
private DbSet<User> _users;
public int Id { get; set; }
public string Name { get; set; }
[Key]
public string Guid { get; set; }
public virtual ICollection<User> Users
{
get
{
if (_users == null)
_users = new List<Users>();
return _users;
}
set { _users = value; }
}
}
I'm sure the Lazy<T> class could be utilised somehow too but I am not familiar with that class.