实体框架..自我引用表..得到深度= x的记录？ [英] Entity framework.. self referencing table.. get records of Depth =x?

问题描述

我成功地用在实体框架自我引用表。
但我无法弄清楚如何获得所需深度的记录？

应该是什么逻辑呢？

---

型号：

 公共类FamilyLabel
{
    公共FamilyLabel（）
    {
        this.Children =新的收集和LT; FamilyLabel＆GT;（）;
        this.Families =新的收集和LT;家庭＆GT;（）;
    }    [键]
    [DatabaseGenerated（DatabaseGeneratedOption.Identity）
    公众诠释FamilyLabelId {搞定;组; }
    公共字符串FamilyLabelName {搞定;组; }    公共虚拟FamilyLabel家长{搞定;组; }    公众诠释JamaatId {搞定;组; }
    公共虚拟Jamaat的Jamaat的{搞定;组; }    公共虚拟的ICollection＆LT;家庭＆GT;家庭{搞定;组; }
    公共虚拟的ICollection＆LT; FamilyLabel＆GT;儿童{搞定;组; }
}
 

解决方案

理论上你可以创建动态构建根据指定的深度级别的查询前pression的方法：

  context.FamilyLabels.Where（X =＆GT;
    x.Parent。 ... .Parent = NULL＆放大器;！＆安培;
    x.Parent.Parent ... .Parent == NULL）;
 

下面执行的伎俩：

 公共静态的IList＆LT; FamilyLabel＆GT;获取（的DbConnection连接，诠释深度）
{
    变种p值=前pression.Parameter（typeof运算（FamilyLabel））;
    防爆pression电流= P;    的for（int i = 0; I＆LT;深;我++）
    {
        电流=前pression.Property（目前，父）;
    }    VAR nullConst =前pression.Constant（空的typeof（FamilyLabel））;    VAR predicate =前pression.Lambda＆LT;＆Func键LT; FamilyLabel，布尔＆GT;＆GT;（
        防爆pression.AndAlso（
            防爆pression.NotEqual（电流，nullConst）
            防爆pression.Equal（前pression.Property（目前，父），nullConst）），P）;    使用（MyDbContext上下文=新MyDbContext（连接））
    {
        返回context.FamilyLabels.Where（predicate）.ToList（）;
    }
}
 

不过，presumably这将创建一批加入前pressions的，所以也许这不是最优化的方式。

I am successfully using a self referencing table in entity framework. But I can't figure out how to get the records of the desired depth ?

What should be the logic for this ?

---

Model :

public class FamilyLabel
{
    public FamilyLabel()
    {
        this.Children = new Collection<FamilyLabel>();
        this.Families = new Collection<Family>();
    }

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int FamilyLabelId { get; set; }
    public string FamilyLabelName { get; set; }

    public virtual FamilyLabel Parent { get; set; }

    public int JamaatId { get; set; }
    public virtual Jamaat Jamaat { get; set; }

    public virtual ICollection<Family> Families { get; set; }
    public virtual ICollection<FamilyLabel>  Children { get; set; }
}

解决方案

Theoretically you can create a method that builds query expression dynamically based on the specified depth level:

context.FamilyLabels.Where(x => 
    x.Parent. ... .Parent != null &&
    x.Parent.Parent ... .Parent == null);

The following implementation does the trick:

public static IList<FamilyLabel> Get(DbConnection connection, int depth)
{
    var p = Expression.Parameter(typeof(FamilyLabel));
    Expression current = p;

    for (int i = 0; i < deep; i++)
    {
        current = Expression.Property(current, "Parent");
    }

    var nullConst = Expression.Constant(null, typeof(FamilyLabel));

    var predicate = Expression.Lambda<Func<FamilyLabel, bool>>(
        Expression.AndAlso(
            Expression.NotEqual(current, nullConst),
            Expression.Equal(Expression.Property(current, "Parent"), nullConst)), p);

    using (MyDbContext context = new MyDbContext(connection))
    {
        return context.FamilyLabels.Where(predicate).ToList();
    }
}

However, presumably this will create a bunch of join expressions, so maybe this is not the most optimal way.

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