Entity framework.. self referencing table.. get records of Depth =x?

问题

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; }
}

回答1:

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.

来源：https://stackoverflow.com/questions/15634586/entity-framework-self-referencing-table-get-records-of-depth-x

标签

ASP.NET

sql

entity-framework

self-reference