带有Id和对象的实体框架导航属性失败

本文关键字：框架 导航 属性 失败 实体 Id 对象 带有 | 更新日期: 2023-09-27 18:11:22

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。

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();
        }
    }
}

将Entry State更改为add时出现问题。错误Conflicting changes to the role 'Child_TheOnlyParent_Target' of the relationship 'ConsoleAppEFAttaching.Child_TheOnlyParent' have been detected.引发。

如果我放一个Console。在子元素中写入一行。onlyparent属性，我看到该方法在状态变化期间多次设置和获取。我认为这个问题可能是由于返回的对象不相同而引起的，但即使我创建了这个对象一次(只实例化第一次，然后返回相同的实例)，它也有同样的问题。

如果我不使用父元素。在子对象中创建。onlyparent，它起作用了。但是，我想使用我们的逻辑(与Create方法)来定义类的情况下，我们想限制包括为性能原因的id。

所以我的问题分为两个:为什么它在更改状态期间多次调用Getter和Setter，为什么我对角色有冲突的更改?

带有Id和对象的实体框架导航属性失败

由于context.Entry(c1)方法调用而调用getter和setter。这里发生的事情是，当您为一个分离对象调用这个方法时，ChangeTracker将整个对象图(对象及其所有导航属性)递归地附加到上下文。这就是调用getter的原因。

如果导航属性与已经附加的对象匹配，ChangeTracker也会尝试修复它们。如果你有DbContext和一个Parent。Id = 1已经附加到您的上下文，并且您附加了Child with Child。ParentId = 1和Child。在context.Entry(c1)调用Child之后，父导航属性= null。属性将自动填充。这就是为什么要调用setter

正如您所假设的那样，您的问题是每次访问getter时都会创建Parent对象的新实例。对于EF来说，这基本上就像拥有具有相同主键的对象的多个实例，而ChangeTracker根本无法处理。像这样更改导航和外键属性应该可以工作。

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;
        }
    }
}

我有一些东西需要改变，使它工作

首先，我们需要Child来返回对象。原因是，如果有人将可导航性设置为Null，我们可以在属性为Null的同时保持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);
        }
    }
}

第二件事是在处理实体时。我可以将TheOnlyParent设置为null并保留Id，或者我可以使用上下文的Entry并设置为Unchanged。

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，这里是完整的代码:

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();
    }
}
相关文章：