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Handling Nested Objects in Entity Framework

I am struggling a bit to wrap my head around Entity Framework and It's driving me crazy. I have an target object that I'd like to populate:
public class ApiInvitationModel
{
public int Id { get; set; }
public EventModel Event { get; set; }
public UserModel InvitationSentTo { get; set; }
public UserModel AttendingUser { get; set; }
}
The schemas of the above models are:
public class EventModel {
public int Id? { get; set; }
public string Name { get; set; }
public DateTime? StartDate { get; set; }
public DateTime? EndDate { get; set }
public OrganizationModel HostingOrganization { get; set; }
public Venue Venue { get; set; }
public string Price { get; set; }
}
public class UserModel {
public int Id? { get; set; }
public string Name { get; set; }
public string PhoneNumber { get; set; }
public string MobileNumber { get; set; }
public List<OrganizationModel> Organizations { get; set; }
}
public class OrganizationModel {
public int Id? { get; set; }
public stirng Name { get; set; }
public string Address { get; set; }
public UserModel PrimaryContact { get; set; }
}
The above schemas are simplified for the purpose of the question and are the models we intend to return via API.
The problem is the origin schemas in the database is very different and I'm trying to map the database objects to these objects via Entity Framework 6.
My attempted solution was to try and nest the models via a query but that didn't work and I'm not sure where to go from here besides making numerous calls to the database.
public List<ApiInvitationModel> GetInvitations(int userId) {
using (var entities = new Entities()) {
return entities.EventInvitations
.Join(entities.Users, invitation => invitiation.userId, user => user.id, (invitation, user) => new {invitation, user})
.Join(entities.Events, model => model.invitation.eventId, ev => ev.id, (model, ev) => new {model.invitation, model.user, ev})
.Join(entities.organization, model => model.user.organizationId, organization => organization.id, (model, organization) => new ApiInvitationModel
{
Id = model.invitation.id,
Event = new EventModel {
Id = model.event.id,
Name = model.event.name,
StartDate = model.event.startDate,
EndDate = model.event.endDate,
HostingOrganization = new OrganizationModel {
Id = model.invitation.hostingId,
Name = model.event.venueName,
Address = model.event.address,
PrimaryContact = new UserModel {
Name = model.event.contactName,
PhoneNumber = model.event.contactNumber,
}
}
...
},
InvitedUser = {
}
}
).ToList();
}
}
As you can see above, there's quite a bit of nesting going on but this doesn't work in Entity Framework 6 as far as I am aware. I keep getting the following errors:
"The type 'Entities.Models.API.UserModel' appears in two structurally incompatible initializations within a single LINQ to Entities query. A type can be initialized in two places in the same query, but only if the same properties are set in both places and those properties are set in the same order.",
Based on the above error, I assumed that each of the model initiatilizations would need to be the same (i.e. initializing the values as the same ApiInvitationModel in each join in the same order) but that produces the same error.
What would be the best approach to handling this, keepign in mind the source database doesn't have foreign keys implemented?

How to create list of object as foreign keys in Entity Framework and fill the database

I'm new to Entity Framework and I'm trying to create database for my Android application using Entity Framework with a code-first approach (I think).
My database would look like this:
In the Restaurant table, I would like to have a list of Dish table elements and same for Groceries in the Dish table.
I tried to do it like this:
https://entityframework.net/knowledge-base/41048304/entity-framework-class-with-list-of-object
But I can't see the FK in migration or in the database.
Next I tried it like this code below (here are my classes) :
public class Restaurant
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int IdRestaurant { get; set; }
[Required]
public String NameOfRestaurant { get; set; }
[Required]
public String Location { get; set; }
[Required]
public String PictureOfRestaurant { get; set; }
public virtual ICollection<Dish> Dishes { get; set; }
[Required]
public String UserId { get; set; }
public ApplicationUser User { get; set; }
}
public class Dish
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int IdDish { get; set; }
[Required]
public String NameOfDish { get; set; }
[Required]
public String PictureOfDish { get; set; }
[Required]
public Double Price { get; set; }
[Required]
public Double CalorieValue { get; set; }
public virtual int? IdRestaurant { get; set; }
public virtual Restaurant Restaurant { get; set; }
public virtual ICollection<Grocery> Groceries{ get; set; }
[Required]
public String UserId { get; set; }
public ApplicationUser User { get; set; }
}
public class Grocery
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int IdGrocery { get; set; }
[Required]
public String NameOfGrocery { get; set; }
[Required]
public String PictureOfGrocery { get; set; }
[Required]
public Double CalorieValue { get; set; }
public virtual int? IdDish { get; set; }
public virtual Dish Dish { get; set; }
[Required]
public String UserId { get; set; }
public ApplicationUser User { get; set; }
}
But it didn't work.
After I solve this problem, I would like to add some elements in database. Tried it like this (just to test if it works, but with no success) :
internal sealed class Configuration : DbMigrationsConfiguration<Restaurants.Models.MojDbContext>
{
public Configuration()
{
AutomaticMigrationsEnabled = false;
}
protected override void Seed(Restaurants.Models.MojDbContext context)
{
// This method will be called after migrating to the latest version.
// You can use the DbSet<T>.AddOrUpdate() helper extension method
// to avoid creating duplicate seed data.
context.Groceries.AddOrUpdate(x => x.IdGrocery,
new Grocery()
{
NameOfGrocery = "Carrot",
PictureOfGrocery = "anhnahdagd",
CalorieValue = 55
},
new Grocery()
{
NameOfGrocery = "Tomato",
PictureOfGrocery = "wqeqwewqeewqqew",
CalorieValue = 89
},
new Grocery()
{
NameOfGrocery = "Potato",
PictureOfGrocery = "zuuuiitutuitu",
CalorieValue = 110
}
);
context.SaveChanges();
}
}
And when I add a migration with:
Add-Migration SeedMigration
it just creates a blank migration :
public partial class SeedMigration : DbMigration
{
public override void Up()
{
}
public override void Down()
{
}
}
So how can I add data into the table?

Create foreign key
To create a foreign key, you have to add a line that is an [Index], with a name (in this example) U_FK and then add [Required] at the end.
[Index]
public int U_FK { get; set; } // Foreign Key - User
[Required]
Create list of foreign key
To create a foreign key, you have to add a line that is an [Index], with a name (in this example) U_FK and then add [Required] at the end.
[Index]
public List<int> U_FK { get; set; } // Foreign Key - User List
[Required]
Add elements to database
To add elements you first call the class name and create a new instance of it, in this case exp. Then you assign it's values (as long as they aren't required you don't have to). After that you load your context and save it in ExampleList you created (will show example below).
Example exp = new Example
{
Active = true,
Titel = InputTitel,
Views = 0,
};
using(var context = new ForumDbContext())
{
context.Examples.Add(exp);
context.SaveChanges();
}
Create a Context (if you don't already have one)
In your specific case you can replace Context with your already existing seed migration.
public class GlobalRef
{
public static string dbConnectionString = "Data Source = (localdb)\\MSSQLLocalDB; Initial Catalog = FForumDB; Integrated Security = True; MultipleActiveResultSets=True";
}
public class ForumDbContext : DbContext
{
public ForumDbContext() : base(GlobalRef.dbConnectionString) {}
public DbSet<Example> Examples{ get; set; }
}
Get Value from database
To get for example the ID of another Datatable. You first get the context again. Then you loop through each element in that Database where it's active and order it by views. You can also add .First() to only get the first element that was returned.
using(ForumDbContext context = new ForumDbContext())
{
foreach(Example example in context.Examples.SqlQuery("SELECT * FROM Examples WHERE Active='1' ORDER BY Views" ).ToList<Example>())
{
int exampleid = example.E_ID;
}
}
Get all Values from database and put them in a List
List<int> exampleFKs = new List<int>;
using(ForumDbContext context = new ForumDbContext())
{
foreach(Example example in context.Examples.SqlQuery("SELECT * FROM Examples WHERE Active='1' ORDER BY Views" ).ToList<Example>())
{
exampleFKs.Add(example.E_ID);
}
}

WPF Entity Framework Foreign key won't load it's value in a DataGrid

I am using Entity Framework code first with fluent API I have an items table with foreign keys from users and units tables
but when I load the table to ObservableCollection then bind it to a datagrid the table normal column load it's data normally into the datagrid excpet for the foreign keys which show nothing but when i insert a break point to see the data inside the ObservableCollection I can see that every thing from Users and Units table is there
private void MainContentsWindow_ContentRendered(object sender, EventArgs e)
{
using (var db2 = new DataContext())
{
var AllItems2 = new ObservableCollection<Model.Items.Item>(db2.Items);
ItemsDataGrid.ItemsSource = AllItems2;
}
}
Users
public class User
{
public User()
{
Id = Guid.NewGuid();
IsActive = false;
}
public Guid Id { get; set; }
public string Name { get; set; }
public string Password { get; set; }
public UserGroup Group { get; set; }
public bool IsActive { get; set; }
public virtual ICollection<Items.Item> Items { get; set; } = new List<Items.Item>();
}
public enum UserGroup
{
Administrator = 1,
User,
Unknown
}
base
public class NormalBaseModel : CommonBase
{
public NormalBaseModel()
{
Id = new Guid();
CreateDate = DateTime.Now;
EditDate = null;
}
public Guid Id { get; set; }
public string Notes { get; set; }
public virtual User CreateBy { get; set; }
public DateTimeOffset? CreateDate { get; set; }
public virtual User EditBy { get; set; }
public DateTimeOffset? EditDate { get; set; }
}
items
public class Item : NormalBaseModel
{
public string NameAr { get; set; }
public string NameEn { get; set; }
public int? ManualId { get; set; }
public string Barcode { get; set; }
public byte?[] Image { get; set; }
public virtual Unit Unit { get; set; }
public string MadeIn { get; set; }
public bool IsSerail { get; set; }
public bool IsExpire{ get; set; }
}
Here is a test project on Github
https://github.com/ahmedpiosol/psychic-parakeet.git
https://imgur.com/a/zimd4

When you load your items via EF it needs to create new instances of User and Item. Behind the scenes, EF will call the constructor for each new instance. Your problem is in your constructors:
public User()
{
Id = Guid.NewGuid(); // <- here
}
Your constructor reassigns a new ID each time an instance is created, this will break the referential integrity and cause all sorts of other problems.
Your code doesn't know the difference between creating a new User and recreating a User instance from the database.
I suggest removing the assignments from inside your constructor and placing this either in a static Create method or place wherever you are creating a new User or Item.
p.s. WPF is irrelevant to your problem here.

Fluent API needs to specify foreign key in code, something like
modelBuilder.Entity<Items>()
.HasRequired(o => o.User)
.WithMany(c => c.Items)
.HasForeignKey(o => o.UserId);

Object doesn't add with children - EF Code First

It's been quite a while since I last used EF. I've never had any problems using it before. Now I'm attempting to insert an object that has a one-many relationship with another object. But in the API call, the collection array of the child object is shown to be empty however the parent object can be seen in the api call of the child object.
I have my models as below:
Conversation Table
public class Conversation
{
public Conversation()
{
this.ChatMessages = new List<ChatMessage>();
this.DeletedConversations = new List<ConversationDeleted>();
}
public int ConversationID { get; set; }
public string toUser { get; set; }
public string FromUser { get; set; }
[InverseProperty("Conversation")]
public ICollection<ChatMessage> ChatMessages { get; set; }
public ICollection<ConversationDeleted> DeletedConversations { get; set; }
public DateTime CreatedAt { get; set; }
public int UserID { get; set; }
}
ChatMessage Table
public class ChatMessage
{
public int ChatMessageID { get; set; }
public string fromUser { get; set; }
public string toUser { get; set; }
public string Message { get; set; }
public bool DeliveryStatus { get; set; }
public DateTime CreatedAt { get; set; }
public Guid UniqueID { get; set; }
public int ConversationID { get; set; }
[ForeignKey("ConversationID")]
public virtual Conversation Conversation { get; set; }
public ICollection<MessageDeleted> MessagesDeleted { get; set; }
public int UserId { get; set; }
}
My Fluent API looks like this:
modelBuilder.Entity<ChatMessage>()
.HasRequired(x => x.Conversation)
.WithMany(x => x.ChatMessages)
.HasForeignKey(x => x.ConversationID);
I'm trying to create a conversation entity and add a chat object to it's collection. I do it like so:
public IHttpActionResult CreateConversation()
{
ChatMessage msg = new ChatMessage { CreatedAt = DateTime.UtcNow, DeliveryStatus = true, fromUser = "annettehiggs", toUser = "terrydriscoll", Message = "Hum tum", UniqueID = Guid.NewGuid(), UserId = 43 };
Conversation conv = new Conversation();
conv.ChatMessages.Add(msg);
conv.CreatedAt = DateTime.UtcNow;
conv.FromUser = "annettehiggs";
conv.toUser = "terrydriscoll";
DataModel db = new DataModel();
db.Conversations.Add(conv);
db.SaveChanges();
return Ok(conv);
}
and this is how I retrieve the conversation object:
public IQueryable<Conversation> GetConversations()
{
return db.Conversations;
}
As a result, ChatMessage API call shows the conversation it's associated to but the Conversation object doesn't show the chat in it's collection. What am I doing wrong here?

The add code is working properly (otherwice you'll not be able to see the new chat message). The problem is with your data retrieval code.
Since your ChatMessage.Conversation property is marked as virtual, most probably it gets lazy loaded, that's why you see it populated.
At the same time, your Conversation.ChatMessages is not virtual, hence you need to explicitly eager load it using the Inlclude method, or depending on your requirements, mark it virtual to get the lazy load behavior like the inverse navigation property.

EF6 Interceptor to set a value on Insert or Update

I am having troubles trying to figure out how to use the EF6 interceptors to set a value on Insert/Update.
What I wanted to do is to have an interceptor to automatically create a new instance of Audit like so:
public class FooContext : DbContext
{
public DbSet<Invoice> Invoices { get; set; }
public DbSet<Audit> Audits { get; set; }
}
public class Invoice
{
public int Id { get; set; }
public string Name { get; set; }
public Audit AuditAndConcurrencyKey { get; set; }
}
public class InvoiceItem
{
public int Id { get; set; }
public Invoice Header { get; set; }
public string Name { get; set; }
public decimal Price { get; set; }
//For legacy reasons. I know this design is wrong :(
public Audit AuditAndConcurrencyKey { get; set; }
}
public class Audit
{
public int Id { get; set; }
public int InstanceId { get; set; }
public string Message { get; set; }
}
[Test]
public void WillCreateAudit()
{
using (var db = new FooContext())
{
var inv = new Invoice {Name = "Foo Invoice"};
var invLine = new InvoiceItem {Header = inv, Price = 1, Name = "Apple"};
db.Invoices.Add(inv);
db.SaveChanges();
//Inceptors should figure out that we are working with "Invoice" and "InvoiceLine"
//And automatically create an "Audit" instance
Assert.That(inv.AuditAndConcurrencyKey != null);
Assert.That(invLine.AuditAndConcurrencyKey != null);
Assert.That(inv.AuditAndConcurrencyKey == invLine.AuditAndConcurrencyKey)
}
}
The first thing I checked is this example for SoftDeleteInterceptor. I don't think this is what I want because it looks like at the point where we are already generating the expression tree, we are no longer aware of the type of object you are working with.
I checked this example as well, but again, it looks like we are injecting strings instead of setting object references.
Ideally I want something like this:
public class AuditInterceptor
{
public void Intercept(object obj)
{
if (!(obj is Invoice) && !(obj is InvoiceItem))
return; //not type we are looking for, by-pass
//Set the audit here
}
}