I am developing a MVC Project with Entity framework and i have a category table like this :
public partial class Categories
{
public Categories()
{
this.Categories1 = new HashSet<Categories>();
}
public int CategoryId { get; set; }
public string CategoryName { get; set; }
public Nullable<int> RelatedCategoryId { get; set; }
public virtual ICollection<Categories> Categories1 { get; set; } //Children
public virtual Categories Categories2 { get; set; } //Parent
}
When i get table data with EF, it gives me the object i want. Parents with children.
class Program
{
static Entities db = new Entities();
static void Main(string[] args)
{
List<Categories> categories = db.Categories.Where(item => item.RelatedId == null).ToList();
}
}
With relatedId == null part, i get the main categories which has no parent.
There is no problem this far. But i want to cast categories object which ef returned to another class which is :
public class NewCategories
{
public int Id { get; set; }
public string Name { get; set; }
private List<NewCategories> _subCategories;
public NewCategories()
{
_subCategories= new List<NewCategories>();
}
public List<NewCategories> SubCategories { get { return _subCategories; } }
}
And i want new List<NewCategories> newCategories object.
How can i accomplish that?
Thanks.
I think you have to create a recursive method to convert Categories to NewCategories, something like this (I'm not sure if it works, but it's worth trying):
public NewCategories ConvertToNewCategories(Categories cat){
NewCategories nc = new NewCategories {Id = cat.CategoryId, Name = cat.CategoryName};
nc.SubCategories.AddRange(cat.Categories1.Select(c=>ConvertToNewCategories(c)));
return nc;
}
//Then
List<NewCategories> categories = db.Categories.Where(item => item.RelatedId == null)
.Select(item=>ConvertToNewCategories(item))
.ToList();
Related
I have these:
public class FamilyHead
{
public Guid HeadId { get; set; }
public string Name { get; set; }
}
public class Citizen
{
public Guid Id { get; set; }
public string Name { get; set; }
public short Age { get; set; }
// more properties
[ForeignKey("FamilyHead")]
public Guid HeadId { get; set; }
public virtual FamilyHead FamilyHead { get; set; }
}
public class CitizenDTO
{
public Guid Id { get; set; }
public string Name { get; set; }
public short Age { get; set; }
public Guid HeadId
public string HeadName { get; set; }
}
I can manually map it via extension method if it is a single instance:
public static CitizenDTO ToDTO(this Citizen citizen)
{
if (citizen == null) return null;
return new CitizenDTO {
Id = citizen.Id,
Name = citizen.Name,
HeadId = citizen.HeadId,
HeadName = citizen.FamilyHead.Name
}
}
var dto = aCitizen.ToDTO();
But how to map a list of citizens? I think Select() might do the work but I only know how to do it if the model and the dto have a same structure. Like this example:
IEnumerable<int> integers = new List<int>() { 1, 2, 3, 4, 5 };
IEnumerable<string> strings = integers.Select(i => i.ToString());
So how to map a list of it?
You can use Linq Select() as you used for string in your question, no need to write long extension method
IEnumerable<CitizenDTO> dto = citizens.Select(x => x.ToDTO());
I found the answer before finishing my question. Just iterate through the list and add mapped DTO to it. Silly me
// Extension method
public static IEnumerable<CitizenDTO> ToDTO(this IEnumerable<Citizen> citizens)
{
if (citizen == null) return null;
var dto = new List<CitizenDTO>();
foreach(var citizen in citizens) {
dto.Add(citizen.ToDTO());
}
return dto;
}
// How to use
IEnumerable<CitizenDTO> result = listOfCitizens.ToDTO();
How to correctly handle computed properties in EF model?
My try bellow will fail because of "The entity or complex type 'Invoice' cannot be constructed in a LINQ to Entities query."
Consider method "GetInvoice" as WebApi method with allowed querystring.
static void Main(string[] args)
{
var invs = GetInvoice();
invs.FirstOrDefault();
}
public static IQueryable<Invoice> GetInvoice()
{
var model = new Model();
IQueryable<Invoice> inv = model.Invocies.Include(t => t.Items).SelectInvoiceData();
return inv;
}
public static class ExtHelper
{
public static IQueryable<Invoice> SelectInvoiceData(this IQueryable<Invoice> item)
{
return item.Select(c => new Invoice
{
LatestItemName = c.Items.FirstOrDefault().Name
});
}
}
public class Item
{
public int Id { get; set; }
public string Name { get; set; }
public DateTime CreatedAt { get; set; }
}
public class Invoice
{
public int Id { get; set; }
public DateTime CreatedAt { get; set; }
public string Issuer { get; set; }
[NotMapped]
public string LatestItemName { get; set; }
private ICollection<Item> _items;
public virtual ICollection<Item> Items
{
get { return _items ?? (_items = new Collection<Item>()); }
set { _items = value; }
}
}
EntityFramework 6 does not support creating partial entities like this. Either use anonymous type:
return item.Select(c => new
{
LatestItemName = c.Items.FirstOrDefault().Name
});
Or some DTO class that does not belong to context:
return item.Select(c => new InvoiceDTO
{
LatestItemName = c.Items.FirstOrDefault().Name
});
However in EF Core it is possible to create entities like in your example.
I am trying to list some food items with a controller. I use Repository pattern with UnitOfWork for the data in another assembly and referenced it in a BaseApiController. The Data property is my UnitOfWork instance.
var result = Data.Food
.FindAll()
.Select(FoodItemViewModel.Create);
return result;
and here is my ViewModel:
public static Expression<Func<FoodItem, FoodItemViewModel>> Create
{
get
{
return fi => new FoodItemViewModel
{
Id = fi.Id,
Description = fi.Description,
DiaryEntries = fi.DiaryEntries
.Select(s => new DiaryEntityViewModel()
{
Id = s.Id,
Quantity = s.Quantity
}
};
}
}
But all I get is:
"The specified type member 'DiaryEntries' is not supported in LINQ to
Entities. Only initializers, entity members, and entity navigation
properties are supported."
My DiaryEntries member in the ViewModel is
IEnumerable<DiaryEntityViewModel>
and my DiaryEntries member in the Data instance is
IRepository<DiaryEntry>
and DiaryEntry is my model class
and here is my FoodItem model class:
public class FoodItem
{
private IEnumerable<Measure> measures;
private IEnumerable<DiaryEntry> diaryEntries;
public FoodItem()
{
this.measures = new HashSet<Measure>();
this.diaryEntries = new HashSet<DiaryEntry>();
}
public int Id { get; set; }
public string Description { get; set; }
public virtual IEnumerable<DiaryEntry> DiaryEntries
{
get
{
return this.diaryEntries;
}
set
{
this.diaryEntries = value;
}
}
public virtual IEnumerable<Measure> Measures
{
get
{
return this.measures;
}
set
{
this.measures = value;
}
}
}
Change you FoodItem class to the one below, IEnumerable<T> is not supported as a type for a navigation collection :
public class FoodItem
{
public FoodItem()
{
this.Measures = new HashSet<Measure>();
this.DiaryEntries = new HashSet<DiaryEntry>();
}
public int Id { get; set; }
public string Description { get; set; }
public virtual ICollection<DiaryEntry> DiaryEntries
{
get;
set;
}
public virtual ICollection<Measure> Measures
{
get;
set;
}
}
How can i select all levels of a self-referencing table as a view model. if max level was 2 or 3 then i can do that by calling Select multiple times but i have 4-5 level menus and i think there should be a better solution for doing that and select all levels.
this is my viewmodel:
public class MenuViewModel
{
public MenuViewModel()
{
Childs = new HashSet<MenuViewModel>();
}
public int Id{ get; set; }
public string Title { get; set; }
public string Url { get; set; }
public ICollection<MenuViewModel> Childs { get; set; }
}
and this is my Menu class:
public class Menu
{
public Menu()
{
Childs = new HashSet<Menu>();
}
public int Id{ get; set; }
public string Title { get; set; }
public string Url { get; set; }
public string Description { get; se; }
public byte[] Icon { get; set; }
public int Order { get; set; }
public ICollection<Menu> Childs { get; set; }
}
var viewModel = _dataContext.Menus
.Select(x => new MenuViewModel
{
Id = x.Id,
Title = x.Title,
Child = ???
}
.ToList();
When you are using EF , you can do like following way:
public class BlogComment
{
public int Id { set; get; }
[MaxLength]
public string Body { set; get; }
public virtual BlogComment Reply { set; get; }
public int? ReplyId { get; set; }
public ICollection<BlogComment> Children { get; set; }
}
using (var ctx = new MyContext())
{
var list = ctx.BlogComments
//.where ...
.ToList() // fills the childs list too
.Where(x => x.Reply == null) // for TreeViewHelper
.ToList();
}
with this way you don't need to use recursive queries but As far as I know,when use view model for fetch data , the dynamic proxy of EF Is destroyed.
about above example:
just select one list of comments and with
.Where(x=>x.Reply==null).Tolist()
EF fill children property of Comments.
Reference
Assuming that Id property is unique you can do it in two passes:
Create viewmodel items without children, but with associated children ids. From that data create the Dictionary that will allow you to get any viewmodel by its id. Values in this dictionary will be the created viewmodels alongside their children ids.
For each viewmodel item get the associated view model items using the children ids.
Something like:
var tempModels = _dataContext
.Menus
.Select(menu => new
{
childrenIds = menu.Childs.Select(item => item.Id).ToArray(),
viewModel =
new MenuViewModel
{
Id = menu.Id,
Title = menu.Title
}
})
.ToDictionary(
keySelector: item => item.viewModel.Id);
var viewModels = tempModels
.Select(kv =>
{
var viewModel = kv.Value.viewModel;
viewModel.Childs = kv
.Value
.childrenIds
.Select(childId =>
tempModels[childId].viewModel)
.ToList();
return viewModel;
})
.ToList();
for depth problem you can use one int property like Depth in your Model then you can fetch data like this :
public class BlogComment
{
public int Id { set; get; }
[MaxLength]
public string Body { set; get; }
public int Depth{get;set}
public virtual BlogComment Reply { set; get; }
public int? ReplyId { get; set; }
public ICollection<BlogComment> Children { get; set; }
}
using (var ctx = new MyContext())
{
var list = ctx.BlogComments
.Where(a=>a.Depth<2)
.ToList() // fills the childs list too
.Where(x => x.Reply == null) // for TreeViewHelper
.ToList();
}
for using viewModel in this senario , I Test with AutoMapper,but when select data with viewModel , the dyamic proxy that EF generate is Destroyed .
Please Note this Issue
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
}
}