如何用GraphDiff更新表达式树

Question

我正在处理的对象图基本上是：

public class Resource
    {
        public string Forename { get; set; }
        public string Surname { get; set; }
        public int EmployeeNumber { get; set; }
        public ICollection<Skill> Skills { get; set; }
    }
public class Skill
    {
        public int SkillId{get; private set;}
        public Technology Technology { get; set; }
        public SkillCategory Category { get; set; }
        public SkillCompetency Competency { get; set; }    

    }

通过选择现有技术、SkillCategory、SkillCompetency的组合，可以向用户添加新的技能。我一直在努力(但失败了！)使用GraphDiff防止EF试图添加复制技术、SkillCategory、SkillCompetency记录。这似乎应该是简单的使用GraphDiff，但作为一个相对的纽比EF夫妇，只有找到GraphDiff，我正在挣扎。

有什么想法吗？

Answer 1

GraphDiff基本上区分了两种关系:拥有关系和关联关系。拥有可以解释为“是其中的一部分”，意思是拥有的任何东西都将与其所有者一起插入/更新/删除。GraphDiff处理的另一种关系是相关联的，这意味着在更新一个图时，GraphDiff只改变与而不是关联实体本身的关系。

回到您的场景:您不需要重复的Technology、Category或Competency实体，但是Skills只是这些实体的组合，所以复制Skills是可以的。要使用GraphDiff对此进行建模，您可以告诉它将Skills视为Resource (由Resource拥有)的一部分，而Technology、Category和Competency则视为Skill的关联。这个映射如下所示：

// these three entities are all managed separately and have already been saved elsewhere
Technology entityFrameworkCodeFirst;
Category objectRelationalMappers;
Competency notThatIncompetent;

using (DbContext context = new WhatEverYourContextIsNamed())
{
    Resource developer = new Resource
    {
        Skills = new List<Skill> 
        {  
            new Skill
            {
                Technology = entityFrameworkCodeFirst,
                Category = objectRelationalMappers,
                Competency = notThatIncompetent,
            }
        } 
    };
    context.UpdateGraph(developer, 
        map => map.OwnedCollection(r => r.Skills, 
            with => with.AssociatedEntity(skill => skill.Technology)
                        .AssociatedEntity(skill => skill.Category)
                        .AssociatedEntity(skill => skill.Competency)));
    context.SaveChanges();
}