Develop Reference

relationship can't be changed , foreign-keys are non-nullable

I'm running an (old) MVC3 web app on an MSSQL DB, utilizing EF 6.0 code first and the repository pattern.
the system has been running in production for the last 7 years (EF was updated about 1 year ago).
I've been encountering a very strange exception in 1 particular area of the system.
when attempting to create or update certain entities, I encounter the following exception:
The operation failed: The relationship could not be changed because
one or more of the foreign-key properties is non-nullable. When a
change is made to a relationship, the related foreign-key property is
set to a null value. If the foreign-key does not support null values,
a new relationship must be defined, the foreign-key property must be
assigned another non-null value, or the unrelated object must be
deleted.
here's one of the problematic entities:
public class BeaconAppErrorLog
{
[Key]
public int Id { get; set; }
public int EntityId { get; set; }
public string RawJson { get; set; }
public DateTime SavedAt { get; set; }
public int? EmployeeId { get; set; }
[ForeignKey("EmployeeId")]
public Employee Employee { get; set; }
public int? ContainerId { get; set; }
[ForeignKey("ContainerId")]
public Container Container { get; set; }
public int? DailyTrackId { get; set; }
[ForeignKey("DailyTrackId")]
public DailyTrack DailyTrack { get; set; }
public int? ClientId { get; set; }
[ForeignKey("ClientId")]
public Client Client { get; set; }
public string Error { get; set; }
}
here's the code for creation & saving :
DataContext.BeaconAppErrorLogs.Add(new BeaconAppErrorLog()
{
EntityId = 2,
SavedAt = DateTime.Now,
EmployeeId = activity.EmployeeId,
DailyTrackId = activity.DailytrackId,
Error = error
});
DataContext.SaveChanges();
the 'EmployeeId' and 'DailyTrackId' fields are foreign keys, they receive
valid values (i.e id's that correspond to the respective entity and exist in the DB)
an almost identical code is written hundreds of time throughout the application - and is functioning properly (even for the exact same entity).
I have no idea what is going on and why, and so far all of the solutions I've attempted did not work.
Your help will be greatly appreciated!
Thanks,
Nir

turns out the solution was someplace else entirely.
as #gregH and #tschmit007 have pointed out, EF tracks changes in entities.
once we've started moving the 'DataContext.SaveChanges()' command higher up the execution chain we've found that changes being made to one of the entities higher up were causing the issue.
the actual problem was a modification of a child collection property to the DailyTrack entity. the modification consisted of filtering the collection data (a LINQ WHERE Claus performed on the collection).
thanks, everyone for your help.

Duplicate entities when setting state within a collection in Entity Framework

I have a solution which uses Entity Framework to insert invoices to a database table. These invoices reference an order, which in turn also references an order item collection.
In this instance I am trying to add an order to the database, however the code is inside a new DbContext and so I need to attach the order and order items to the context, as these already exist in the database and shouldn't be re-added.
I've cut down the model properties for the sake of demonstration:
public class Invoice {
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int InvoiceId { get; set; }
public string OrderNumber { get; set; }
...
public virtual List<InvoiceLineItem> LineItems { get; set; }
}
public class InvoiceLineItem {
[Key]
public int Id { get; set; }
...
public ShopifyOrderItem { get; set; }
}
public class ShopifyOrder {
[Key, DatabaseGenerated(DatabaseGeneratedOption.None)]
public long Id { get; set; }
public int OrderNumber { get; set; }
...
public OrderInvoiceStatus InvoiceStatus { get; set; }
public virtual List<ShopifyOrderItem> OrderItems { get; set; }
}
public class ShopifyOrderItem {
[Key, DatabaseGenerated(DatabaseGeneratedOption.None)]
public long Id { get; set; }
...
[Required]
public virtual ShopifyOrder ShopifyOrder { get; set; }
}
In the invoice engine, I'm running the following code for each invoice to add it to the database:
ShopifyOrder order = await db.ShopifyOrders.SingleOrDefaultAsync(x => x.OrderNumber.ToString() == inv.OrderNumber);
if (order != null) {
// Attach marketplace entity to the invoice to avoid duplicate primary key exceptions
db.Marketplaces.Attach(inv.Marketplace);
db.Invoices.Add(inv);
order.InvoiceStatus = OrderInvoiceStatus.InProgress;
}
I've tried a number of methods to try and attach the states, however they all throw errors.
inv.LineItems.ForEach(li => {
db.Entry(li).State = EntityState.Unchanged;
db.Entry(li.ShopifyOrderItem).State = EntityState.Unchanged;
db.Entry(li.ShopifyOrderItem.ShopifyOrder).State = EntityState.Modified;
});
The above code returns the following error on save:
EntityFramework: Saving or accepting changes failed because more than one entity of type 'TorroModels.ShopifyOrder' have the same primary key value. Ensure that explicitly set primary key values are unique. Ensure that database-generated primary keys are configured correctly in the database and in the Entity Framework model.
What is the best way to attach the LineItems/ShopifyOrderItems without trying to attach the ShopifyOrder connected property multiple times?

Sorry to say but it seems that you need to follow the best practice first when constructing a relationship. You may follow this link :
http://www.entityframeworktutorial.net/entity-relationships.aspx
In short :
Avoid using only "Id" in every entity, or you can use attributes to map between the physical name and the property name
It seems that you have circular references here, so maybe you could simplify it first
Next, you can read this link :
http://www.entityframeworktutorial.net/EntityFramework5/attach-disconnected-entity-graph.aspx
if you need to know more about what's the best practice of attaching entities, but in my opinion, just don't abuse this feature, because using normal CRUD should be sufficient most of the time.
I'm sorry I cannot help you more than this, because of lack of information I may need, and with my reputation I still cannot comment directly in your post to ask for it.

Why EF navigation property return null?

I have two model
1)
public class Indicator
{
public long ID { get; set; }
public string Name { get; set; }
public int MaxPoint { get; set; }
public string Comment { get; set; }
public DateTime DateChanged { get; set; }
public DateTime DateCreated { get; set; }
public virtual IList<CalculationType> CalculationTypes { get; set; }
public virtual IList<TestEntity> TestEntitys { get; set; }
public virtual IndicatorGroup IndicatorGroup { get; set; }
}
2)
public class CalculationType
{
public long ID { get; set; }
public string UnitName { get; set; }
public int Point { get; set; }
public DateTime DateCreated { get; set; }
public DateTime DateChanged { get; set; }
public virtual Indicator Indicator { get; set; }
public virtual IList<Сalculation> Calculations { get; set; }
}
I executing this code
var indicator = DataContext.Indicators.FirstOrDefault(i => i.ID == indicatorID);
var test = DataContext.CalculationTypes.FirstOrDefault();
first line return null on navigation property CalculationTypes
Second line return empty collection. Why?
UPDATE
snapshot database
project link https://github.com/wkololo4ever/Stankin
added Calculation
public class Сalculation
{
public long ID { get; set; }
public virtual CalculationType CalculationType { get; set; }
public virtual ApplicationUser Creator { get; set; }
}

1) Is Lazy Loading enabled? If not, you need to explicitly load your navigation properties with the '.Include' syntax.
2) Are you sure EF should be able to detect that relation? Did you use Code First or Database First?
Edit: 3) Are you sure there is data in your database and that the foreign key from Indicator to IndicatorGroup has a value for that specific record? I am saying this because the value "null" is valid if there is simply no data.
P.S. If you do not see a foreign key on Indicator called "IndicatorGroupId", there might be an "IndicatorId" on the table "IndicatorGroup", in which case - going from the names you provided - your database is misconfigured and you will need to use fluent syntax or data attributes to instruct EF on how to make the foreign keys.

Try this:
DbContext.Configuration.ProxyCreationEnabled = true;
DbContext.Configuration.LazyLoadingEnabled = true;
If DbContext.Configuration.ProxyCreationEnabled is set to false, DbContext will not load child objects for some parent object unless Include method is called on parent object. Setting DbContext.Configuration.LazyLoadingEnabled to true or false will have no impact on its behaviours.
If DbContext.Configuration.ProxyCreationEnabled is set to true, child objects will be loaded automatically, and DbContext.Configuration.LazyLoadingEnabled value will control when child objects are loaded.
I think this is problem:
Edit: 3) Are you sure there is data in your database and that the
foreign key from Indicator to IndicatorGroup has a value for that
specific record? I am saying this because the value "null" is valid if
there is simply no data.
P.S. If you do not see a foreign key on Indicator called
"IndicatorGroupId", there might be an "IndicatorId" on the table
"IndicatorGroup", in which case - going from the names you provided -
your database is misconfigured and you will need to use fluent syntax
or data attributes to instruct EF on how to make the foreign keys.
Try to this and make sure foreign key is corrected.
public class CalculationType
{
public long ID { get; set; }
public string UnitName { get; set; }
public int Point { get; set; }
public DateTime DateCreated { get; set; }
public DateTime DateChanged { get; set; }
[ForeignKey("IndicatorID")]
public string IndicatorId { get; set; } //this is the foreign key, i saw in your database is: Indicator_ID, avoid this, rename it to IndicatorID or IndicatorId
public virtual Indicator Indicator { get; set; }
public virtual IList<Сalculation> Calculations { get; set; }
}

Same behavior, but different root cause than selected answer:
Navigation property can also be null if you turned off myContext.Configuration.AutoDetectChangesEnabled
Very obvious, but this got me when I was implementing some performance improvments.

Check this out: Navigation Property With Code First . It mentions about why navigation property is null and the solutions of it.
By default, navigation properties are null, they are not loaded by
default. For loading navigation property, we use “include” method of
IQuearable and this type of loading is called Eager loading.
Eager loading: It is a process by which a query for one type of entity
loads the related entities as a part of query and it is achieved by
“include” method of IQueryable.

I experienced this issue, where navigation properites were not loaded, even when the Include statement was present.
The problem was caused by string-comparison differences between SQL Server and EF6 using .NET. I was using a VARCHAR(50) field as the primary key in my customers table and also, as a foreign key field in my audit_issues table. What I did not realize was that my keys in the customers table had two additional white space characters on the end; these characters were not present in my audit_issues table.
However, SQL Server will automatically pad whitespace for string comparisons. This applies for WHERE and JOIN clauses, as well as for checks on FOREIGN KEY constraints. I.e. the database was telling me string were equivalent and the constraint passed. Therefore I assumed that they actually were exactly equal. But that was false. DATALENGTH of one field = 10, while the DATALENGTH of the other = 8.
EF6 would correctly compose the SQL query to pull the foreign key related fields and I would see them both in the generated Sql query and in the results. However, EF6 would silently fail when loading the Navigation Properties because .NET does not consider those strings equal. Watch out for whitespace in string-type foreign key fields!.

This article helped me.
In sum :
Install-Package Microsoft.EntityFrameworkCore.Proxies
In Startup.cs
using Microsoft.EntityFrameworkCore;
public void ConfigureServices(IServiceCollection services)
{
...
services.AddDbContext<MyDbContext>(builder =>
{
builder.UseLazyLoadingProxies(); // <-- add this
}, ServiceLifetime.Singleton);

This is a variant of Keytrap's answer. Using .NET 6 and EF Core 6, I created a ContextPartials.cs for any custom configurations that I don't want EF's Scaffold command to overwrite:
Required Package:
Install-Package Microsoft.EntityFrameworkCore.Proxies
Code (ContextPartials.cs):
// NOTE: I am not using the new file-scoped namespace on purpose
namespace DataAccess.Models.MyDatabase
{
// NOTE: This is a partial outside of the generated file from Scaffold-DbContext
public partial class MyDatabaseContext
{
// NOTE: This enables foreign key tables to become accessible
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
=> optionsBuilder.UseLazyLoadingProxies();
}
}

Fluent NHibernate Relation Without Foreign Key

I'm trying so simplify my problem here, but basically I'm trying to map 2 entities however i don't have a Foreign Key in the database set, since the column could be null. When I try to do an insert on the parent, I'm getting the following error:
object references an unsaved transient instance - save the transient
instance before flushing or set cascade action for the property to
something that would make it autosave.
This is what I have so far:
My entities
public class DocumentDraft
{
public virtual Guid Id { get; set; }
public virtual string Subject { get; set; }
public virtual string ReferenceNo { get; set;}
public virtual DocumentType DocumentType { get; set; }
}
public class DocumentType
{
public virtual short Id { get; set; }
public virtual string Description { get; set; }
}
Mapping
public class DocumentDraftMap : ClassMap<DocumentDraft>
{
public DocumentDraft()
{
// other mappings ...
References(x => x.DocumentType)
.Columns("DocumentTypeId")
.Nullable()
.Not.LazyLoad()
.NotFound.Ignore(); // <-- added this since the value could be null and it throws an error
}
}
I tried specifying Cascade.None() in the mapping, but I'm getting the same result. Basically what happens is that a null value is attempted at being inserted in the DocumentType, and I don't want this (I want to insert null in the parent table, but I don't want to touch the child tables at all, I don't want this to cascade).
I've also tried: .Not.Insert(), but that didn't work either.
I'd appreciate it if someone could help me out on this one.

I guess the property DocumentType is not really null when saving.
It seems there is an instance and without Cascade.All() on the reference it can not be saved.

Map parameter to ignored property in service stack?

I have a DB entity like:-
public class DBThing
{
public int Id { get; set; }
public string Name { get; set; }
}
The Id maps to the DB primary key. I then have a service DTO like:-
public class Thing
{
[IgnoreDataMember]
public int Id { get; set; }
public string Identity { get; set; }
public string Name { get; set; }
}
The Identity field here contains a REST friendly ID like /things/1, made from the DB Id. I had to call it something differennt from Id, because I'm using TranslateTo and it breaks going from Thing to DBThing if the string Id is "" and it tries to map to int Id, such as when a POST occurs.
The problem I have is that my route [Route("/things/{Id}", "PUT")] fails saying it can't find the Id property on Thing. If I remove [IgnoreDataMember] from the class it works fine. I can imagine why this would be (using shared code with ServiceStack serialization internally?) but I can't see how to fix this. I don't want the internal DB numeric Id serialized to the web services if at all possible.
Can anyone help please?

You can use a int? Id which if it's null it doesn't get serialized by default in JSON / JSV Serializers.