c# - Entity Framework 检查 child 是否属于 parent

Question

如果一个实体属于父实体，是否有一种简短的方法可以通过 Entity Framework 找出？

例如有一些表:Manager->Project->Document。

假设这条链更长并且有很多不同的链。我可以编写一种通用方法来检查链中的最后一个子项是否属于父项(链中的第一个表)吗？

在此示例中 - 检查 Document 是否属于 Manager。这可能需要递归函数吗？

Answer 1

尝试 this solution假设我们有这样的模型并且 LazyLoading 已打开:

public class Manager
{
    public int Id { get; set; }
    public virtual ICollection<Project> Projects { get; set; }
}

public class Project
{
    public int Id { get; set; }     
    public virtual ICollection<Document> Documents { get; set; }        
    public virtual Manager Manager { get; set; }
    public int? ManagerId { get; set; }
}

public class Document
{
    public int Id { get; set; }
    public virtual Project Project { get; set; }
    public int? ProjectId { get; set; }
}

实现:

public static TParent FindParentOf<TParent, TChild>(TChild child)
    where TParent : class
    where TChild : class
{
    return FindParentOfRecursive(child, typeof(TParent)) as TParent;
}

private static object FindParentOfRecursive(object child, Type parentType)
{
    var IEnumType = typeof(IEnumerable);
    var childType = child.GetType();
    var strType = typeof(string);

    foreach (var prop in childType.GetProperties()
        .Where(x => x.PropertyType.IsClass && x.PropertyType != strType 
                    && !IEnumType.IsAssignableFrom(x.PropertyType)))
    {
        //calling to database via LazyLoading with query like: 
        //select top(1) * from dbo.Parents where Id = child.ParentId
        var parentVal = prop.GetValue(child);

        if (prop.PropertyType == parentType)
            return parentVal;
        else if(parentVal != null)
        {
            var result = FindParentOfRecursive(parentVal, parentType);
            if (result != null)
                return result;
        }
    }
    return null;
}

用法:

var manager = FindParentOf<Manager, Document>(doc);
if(manager?.Id == lookingForManagerId)
    Console.WriteLine("Belongs");