保存动态定义导航属性的实体时会导致问题。
这是一个更复杂的代码的复制品。
namespace ConsoleAppEFAttaching
{
public class MyContext : DbContext
{
public MyContext()
: base("MyContextConnectionString")
{
base.Configuration.LazyLoadingEnabled = false;
base.Configuration.AutoDetectChangesEnabled = false;
base.Configuration.ProxyCreationEnabled = false;
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Parent>();
modelBuilder.Entity<Child>();
}
}
public class Parent
{
public int Id { get; set; }
public string NameParent { get; set; }
public static Parent Create(int id)
{
return new Parent { Id = id };
}
}
public class Child
{
private Parent theOnlyParent;
public int Id { get; set; }
public string NameChild { get; set; }
public Parent TheOnlyParent {
get { return Parent.Create(TheOnlyParentId); }
set { TheOnlyParentId = value.Id; }
}
public int TheOnlyParentId { get; set; }
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Start create database");
Database.SetInitializer(new DropCreateDatabaseAlways<MyContext>());
Console.WriteLine("Start adding Parent");
var p1 = new Parent {NameParent = "Test Parent Name#1"};
int parentCreatedId;
Console.WriteLine("Context");
using (var context = new MyContext())
{
context.Set<Parent>().Add(p1);
context.SaveChanges();
parentCreatedId = p1.Id;
}
Console.WriteLine("Start adding a child from a different context");
var c1 = new Child { NameChild= "Child #1" };
c1.TheOnlyParentId = parentCreatedId;
c1.TheOnlyParent = new Parent {Id = parentCreatedId};
Console.WriteLine("Context");
using (var context = new MyContext())
{
Console.WriteLine("*Change State Child");
context.Entry(c1).State = EntityState.Added; // !!! Error : Conflicting changes to the role 'Child_TheOnlyParent_Target' of the relationship 'Child_TheOnlyParent' have been detected.
Console.WriteLine("*Change State Child->Parent Navigability Property");
context.Entry(c1.TheOnlyParent).State = EntityState.Detached;
Console.WriteLine("*Save Changes");
context.SaveChanges();
}
Console.WriteLine("End");
Console.ReadLine();
}
}
}
问题在于将Entry State更改为Added。错误Conflicting changes to the role 'Child_TheOnlyParent_Target' of the relationship 'ConsoleAppEFAttaching.Child_TheOnlyParent' have been detected.
会引发。
如果我将一个Console.WriteLine放在Child.TheOnParent属性中,我看到该方法已设置并在状态更改期间多次获取。我虽然问题可能是由于返回的对象不一致引起的,但即使我创建了一次(仅实例化第一次然后返回相同的实例)它也有同样的问题。
如果我不在Child.OnlyParent中使用Parent.Create,它可以工作。但是,我想使用我们的逻辑(使用Create方法)仅在我们要为性能原因限制Include的情况下通过id定义类。
所以我的问题分为两部分:为什么在更改状态期间它会多次调用Getter和Setter?为什么我对角色进行了相互冲突的更改?
答案 0 :(得分:1)
由于context.Entry(c1)方法调用而调用getter和setter。 这里发生的是,当你为一个分离的对象调用这个方法时,ChangeTracker将整个对象图(该对象及其所有的navigationproperties递归地)附加到Context。这就是吸气者被召唤的原因。
如果匹配,ChangeTracker还会尝试修复已附加对象的导航属性。因此,如果您的DbContext已将Parent.Id = 1附加到您的上下文,并且在context.Entry(c1)调用Child.Parent之后附加Child with Child.ParentId = 1且Child.Parent navigation property = null财产自动填写。这就是调用setter的原因。
正如您所假设的,您的问题是每次访问getter时都会创建一个新的Parent对象实例。对于EF来说,基本上就像具有相同主键的对象的多个实例一样,ChangeTracker无法处理。 更改这样的导航和外键属性应该有效。
public Parent TheOnlyParent
{
get
{
if (theOnlyParent == null) {
theOnlyParent = Parent.Create(TheOnlyParentId);
}
return theOnlyParent;
}
set
{
If(theOnlyParent != value){
theOnlyParent = value;
if (value != null) {
TheOnlyParentId = value.Id;
}
}
}
}
private int theOnlyParentId;
public int TheOnlyParentId
{
get
{
return theOnlyParentId;
}
set
{
if (theOnlyParentId != value) {
theOnlyParentId = value;
theOnlyParent = null;
}
}
}
答案 1 :(得分:0)
我需要改变一些东西以使其有效。
首先,我们需要让Child返回对象。原因是,如果有人将导航设置为Null,我们可以将属性设置为Null并同时保留ID。
public class Child
{
private Parent theOnlyParent;
private int theOnlyParentId;
public int Id { get; set; }
public string NameChild { get; set; }
[Required]
public Parent TheOnlyParent
{
get
{
return theOnlyParent;
}
set
{
theOnlyParent = value;
if (value != null)
TheOnlyParentId = value.Id;
}
}
public int TheOnlyParentId
{
get { return theOnlyParentId; }
set {
theOnlyParentId = value;
theOnlyParent = Parent.Create(value);
}
}
}
第二件事是与实体合作。我可以将TheOnlyParent设置为null并保持Id或我可以使用上下文的Entry并设置为Unchanged。两者现在都有效。
using (var context = new MyContext())
{
Console.WriteLine("*Change State Child");
context.Entry(c1).State = EntityState.Added; // Conflicting changes to the role 'Child_TheOnlyParent_Target' of the relationship 'Child_TheOnlyParent' have been detected.
Console.WriteLine("*Change State Child->Parent Navigability Property");
context.Entry(c1.TheOnlyParent).State = EntityState.Unchanged; // We do not want to create but reuse
Console.WriteLine("*Save Changes");
context.SaveChanges();
}
如果有人想尝试整个解决方案,请输入以下完整代码:
public class MyContext : DbContext
{
public MyContext()
: base("MyContextConnectionString")
{
base.Configuration.LazyLoadingEnabled = false;
base.Configuration.AutoDetectChangesEnabled = false;
base.Configuration.ProxyCreationEnabled = false;
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Parent>();
modelBuilder.Entity<Child>();
}
}
public class Parent
{
public int Id { get; set; }
public string NameParent { get; set; }
public static Parent Create(int id)
{
return new Parent { Id = id };
}
}
public class Child
{
private Parent theOnlyParent;
private int theOnlyParentId;
public int Id { get; set; }
public string NameChild { get; set; }
[Required]
public Parent TheOnlyParent
{
get
{
return theOnlyParent;
}
set
{
theOnlyParent = value;
if (value != null)
TheOnlyParentId = value.Id;
}
}
public int TheOnlyParentId
{
get { return theOnlyParentId; }
set {
theOnlyParentId = value;
theOnlyParent = Parent.Create(value);
}
}
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Start create database");
Database.SetInitializer(new DropCreateDatabaseAlways<MyContext>());
Console.WriteLine("Start adding Parent");
var p1 = new Parent {NameParent = "Test Parent Name#1"};
int parentCreatedId;
Console.WriteLine("Context");
using (var context = new MyContext())
{
context.Set<Parent>().Add(p1);
context.SaveChanges();
parentCreatedId = p1.Id;
}
Console.WriteLine("Start adding a child from a different context");
var c1 = new Child { NameChild= "Child #1" };
c1.TheOnlyParentId = parentCreatedId;
c1.TheOnlyParent = new Parent {Id = parentCreatedId};
Console.WriteLine("Context");
using (var context = new MyContext())
{
Console.WriteLine("*Change State Child");
context.Entry(c1).State = EntityState.Added; // Conflicting changes to the role 'Child_TheOnlyParent_Target' of the relationship 'Child_TheOnlyParent' have been detected.
Console.WriteLine("*Change State Child->Parent Navigability Property");
context.Entry(c1.TheOnlyParent).State = EntityState.Unchanged; // We do not want to create but reuse
Console.WriteLine("*Save Changes");
context.SaveChanges();
}
Console.WriteLine("End");
Console.ReadLine();
}
}