I created a project using .NET 6 Entity Framework Core. I have 2 entities that are related one-to-many like this:
public partial class ProductImage
{
public Guid Id { get; set; }
public Guid ProductId { get; set; }
public string? ImageUrl { get; set; }
public virtual Product Product { get; set; } = null!;
}
public partial class Product
{
public Product()
{
ProductImages = new HashSet<ProductImage>();
}
public Guid Id { get; set; }
public string? Name { get; set; }
public Guid CategoryId { get; set; }
public decimal? Price { get; set; }
public virtual ICollection<ProductImage> ProductImages { get; set; }
}
I try get data from ICollection<ProductImage> ProductImages by using Include() and I get an error response like that
System.Text.Json.JsonException: A possible object cycle was detected. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 32. Consider using ReferenceHandler.Preserve on JsonSerializerOptions to support cycles.
Path: $.Data.ProductImages.Product.ProductImages.Product.ProductImages.Product.ProductImages.Product.ProductImages.Product.ProductImages.Product.ProductImages.Product.ProductImages.Product.ProductImages.Product.ProductImages.Id.
Is there any way to load data from the ICollection?
Related
I want to add two properties from the city model:
after migration this error shows up:
Unable to determine the relationship represented by navigation
'City.Orders' of type 'ICollection'. Either manually configure
the relationship, or ignore this property using the '[NotMapped]'
attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.
here is my code :
public class Order
{
public virtual City FromCity { get; set; }
public virtual City ToCity { get; set; }
}
public class City
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Order> Orders { get; set; }
}
I suppose your model is more complicated than just FromCity and ToCity because I don't think it's a good idea to store such information in a different table. Yet, You can use inheritance in this case.
The table-per-hierarchy (TPH) pattern is used by default to map the inheritance in EF. TPH stores the data for all types in the hierarchy in a single table.
However, for your scenario, you can have a base class that holds all related attributes.
public class CityBase
{
public int Id { get; set; }
public string Name { get; set; } = string.Empty;
}
Then suppose you need two entities as per your scenario:
public class FromCity : CityBase
{
public virtual ICollection<Order> Orders { get; set; } = null!;
}
public class ToCity : CityBase
{
public virtual ICollection<Order> Orders { get; set; } = null!;
}
And the order entity:
public class Order
{
public int Id { get; set; }
public string OrderTitle { get; set; } = string.Empty;
public virtual FromCity FromCity { get; set; } = null!;
public virtual ToCity ToCity { get; set; } = null!;
}
This approach can solve your problem with a One-to-Many relationship between Orders and FromCity, ToCity as per below diagram:
Let's say I have a bike shops that sell various types of bikes: pro, kids, youth, leisure and any mixture. So I have a table of shops that refers/relates to a table of possible types. Now these shops also host events with the same types: events for pros, kids etc again any mixture. And so I have another table of events that also need to refer/relate to the same table of types:
I need to be able in a single quick query get a list of all bike types for a shop or event.
So I figured I'd have 3 main tables: Shops, Events, BikeTypes and two intermediate to link shops and events to bike types:
And I organized my models as:
public class BikeShop
{
public long Id { get; set; }
public string name { get; set; }
public string address { get; set; }
public string phone { get; set; }
}
public class BikeEvent
{
public long Id { get; set; }
public string name { get; set; }
public string description { get; set; }
public DateTime date { get; set; }
public string location { get; set; }
}
public class BikeType
{
public long Id { get; set; }
public string name { get; set; }
public string code { get; set; }
}
public class ShopBikeTypes
{
public long Id { get; set; }
public BikeShop shop { get; set; }
public BikeType biketype { get; set; }
}
public class EventBikeTypes
{
public long Id { get; set; }
public BikeEvent bikeevent { get; set; }
public BikeType biketype { get; set; }
}
With DataCotext:
public class DataContext : DbContext
{
public DbSet<BikeShop> Shops { get; set; }
public DbSet<BikeEvent> Events { get; set; }
public DbSet<BikeType> BikeTypes { get; set; }
public DbSet<ShopBikeTypes> ShopBikeTypes { get; set; }
public DbSet<EventBikeTypes> EventBikeTypes { get; set; }
}
Migration creates correct database structure just as my diagram. Great!
Now how do I make a straight forward query:
get list of all bike types for a shop
get list of all bike types for an event
Is my structure even correct?
Do I need some List<> in the main object models BikeShop and BikeEvent?
EF's include and theninclude seem to require some list?
This feels like such a typical scenario. What's the right way of doing this?
Thank you.
Those are the linq queries that you are asked but when i look at that your class models, i can say they are wrong. U need to define first which relation theyre having. if all of that relation has based on one-to-one, u wont gonna need any List<> in your class models. but if u have one-to-many relation,u gonna need them.
1- get list of all bike types for a shop
return DbContext.Shops
.Include(x>=x.ShopBikeTypes)
.ThenInclude(x=>x.BikeTypes).ToList();
2- get list of all bike types for an event
return DbContext.Events
.Include(x=>x.EventBikeTypes)
.ThenInclude(x=>x.BikeTypes).ToList();
3- Get all data in that relation
return DbContext.BikeTypes
.Include(x>=x.EventBikeTypes)
.ThenInclude(x=>x.Events).AsSplitQuery()
.Include(x=>x.ShopBikeTypes)
.ThenInclude(x>=x.Shops).AsSplitQuery()
.ToList();
it can be a tough query, do not try to use AsNoTracking() because it can cause Cartesian Explosion.
#BerkGarip: thank you for your help. I ended up with this models structure:
public class AShop
{
public long Id { get; set; }
public string name { get; set; }
public string address { get; set; }
public string phone { get; set; }
public List<AShopType> aTypes { get; set; }
}
public class AEvent
{
public long Id { get; set; }
public string name { get; set; }
public string description { get; set; }
public DateTime date { get; set; }
public string location { get; set; }
public List<AEventType> aTypes { get; set; }
}
public class AType
{
public long Id { get; set; }
public string name { get; set; }
public string code { get; set; }
}
public class AShopType
{
public long Id { get; set; }
public AType aType { get; set; }
}
public class AEventType
{
public long Id { get; set; }
public AType aType { get; set; }
}
In order to achieve what I needed using answer from #BerkGarip I figured out that the trick there was to have lists in the 'shop' and 'event' models to the intermediate objects which in turn have a single reference to 'type'. This way database layout is the same and it is many-to-many relationship and I can use 'include' and 'thenInclude' exactly as expected:
return await _context.AShops.Where(x => x.name == "Z")
.Include(x => x.aTypes)
.ThenInclude(y => y.aType)
.ToListAsync();
Is it possible to store an IEnumerable<string> in Entity Framework?
I'm using code-first in ASP.NET MVC5 and I have a model that looks a little like this, but ImageUris does not appear as a column in my database (all the other properties do).
public class Product
{
[Key]
public int Id { get; set; }
public string Title { get; set; }
public string Description { get; set; }
public string Condition { get; set; }
public decimal Price { get; set; }
public IEnumerable<string> ImageUris { get; set; }
}
PS: In case you are interested in why I'm storing Uris rather than images themselves, they are uris to Azure Storage Blobs.
You cannot save multiple records in single column of the relational database. There is no such data type that supports this.
You can create a separate table for Image Uris and then store your image Uris there.
Your entity code would look something like this:
public class Product
{
[Key]
public int Id { get; set; }
public string Title { get; set; }
public string Description { get; set; }
public string Condition { get; set; }
public decimal Price { get; set; }
public virtual ICollection<ImageUri> ImageUris { get; set; }
}
public class ImageUri
{
[Key]
public int Id { get; set; }
public string Uri { get; set; }
}
Here are my models
public class Driver
{
public int Id { get; set; }
public String Name { get; set; }
public int VehicleId { get; set; }
public virtual Vehicle Vehicle { get; set; }
}
public class Vehicle
{
public int Id { get; set; }
public String Name { get; set; }
public virtual Driver Driver { get; set; }
public int VehicleGroupId { get; set; }
public virtual VehicleGroup Vehicles { get; set; }
}
I'm getting the following error on updating database:
Unable to determine the principal end of an association between the types 'AppName.Models.Vehicle' and 'AppName.Models.Driver'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.
I wish to solve the issue using data annotations. I've tried putting foreign key attribute over Driver Navigation property in vehicle model. But no success. Any help is much appreciated.
To solve your problem you need to explicitly set the end of the association like this :
public class Vehicle
{
[Key, ForeignKey("Driver")]
public int Id { get; set; }
public String Name { get; set; }
public virtual Driver Driver { get; set; }
public int VehicleGroupId { get; set; }
public virtual VehicleGroup Vehicles { get; set; }
}
I think your model is inccorect because a driver can use many vehicles in real life ;)
I added just two tables into my database, using as always update-database command. Everything went nice, without any errors.
But now, when I try to generate Entity Data Model (Entity Framework > View Entity Data Model), I get an window with an error:
Exception has been thrown by the target of an invocation
Why? How to repair it? Reinstall Entity Framework Power Tools is not helpful at all.
Regards
EDIT:
Context:
public DbSet<Order> Order { get; set; }
public DbSet<Product> Product { get; set; }
Model:
[Table("Product")]
public class Product
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int ProductId { get; set; }
public string name { get; set; }
public DateTime AddDate { get; set; }
public bool del { get; set; }
public virtual List<Order> OrderList { get; set; }
}
[Table("Order")]
public class Order
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int OrderId { get; set; }
public int ProductId { get; set; }
public string desc { get; set; }
public virtual Product product { get; set; }
}
Without this code below, everything works nice - what is wrong?