使用 LINQ 过滤树列表保留父级

Question

我有一个看起来像这样的模型类：

public class Employee
{ 
    public int Id {get;set;}
    public int ParentId {get;set;}
    public string Name{get;set;}
    public string Designation {get;set;}
    public List<Employee> Reportees {get;set;}
}

我用它模拟了一个带有数据的演示树列表：

var employees = new List<Employee>
{
    new Employee
    {
        Id = 1,
        ParentId = 0,
        Name = "A",
        Designation = "CEO",
        Reportees = new List<Employee>
        {
            new Employee { Id = 2, ParentId = 1,Name = "B",Designation = "Manager",Reportees = new List<Employee>
            {
                new Employee { Id = 4, ParentId = 2, Name = "D", Designation = "Lead", Reportees = new List<Employee>
                {
                    new Employee { Id = 6, ParentId = 4, Name = "F", Designation = "Developer", Reportees = new List<Employee>() },
                    new Employee { Id = 7, ParentId = 4, Name = "G", Designation = "Developer", Reportees = new List<Employee>() }
                }},
                new Employee { Id = 3, ParentId = 1,Name = "C",Designation = "Manager",Reportees = new List<Employee>
                {
                    new Employee { Id = 5, ParentId = 3, Name = "E", Designation = "Lead", Reportees = new List<Employee>
                    {
                        new Employee { Id = 8, ParentId = 5, Name = "H", Designation = "Developer", Reportees = new List<Employee>() }
                    }}
                }}
            }}
        }
    }
};

如果孩子满足过滤条件，我需要过滤上面的列表以显示父对象。这里还有一个问题是如果它是满足条件的父级，而子级不满足，则将其省略。

是否有可用的扩展或者我可以使用 LINQ 来执行此操作？

为了更清楚，如果过滤器搜索条件是 ID 6 和 7，这是预期的过滤列表：

var employees = new List<Employee>
{
    new Employee {Id = 1, ParentId = 0, Name = "A",Designation = "CEO", Reportees = new List<Employee>
    {
        new Employee {Id = 2, ParentId = 1, Name = "B",Designation = "Manager", Reportees = new List<Employee>
        {
            new Employee {Id = 4, ParentId = 2, Name = "D", Designation = "Lead", Reportees = new List<Employee>
            {
                new Employee {Id = 6, ParentId = 4, Name = "F", Designation = "Developer", Reportees = new List<Employee>() },
                new Employee {Id = 7, ParentId = 4, Name = "G", Designation = "Developer", Reportees = new List<Employee>() }
            }}
        }}
    }}
};

如果要过滤的 Id 是 6：

new List<Employee> employees
{
    new Employee{Id = 1,ParentId = 0,Name = "A",Designation = "CEO",Reportees = new List<Employee>{
      new Employee{Id = 2,ParentId = 1,Name = "B",Designation = "Manager",Reportees = new List<Employee>{
        new Employee{Id = 4, ParentId = 2, Name = "D", Designation = "Lead", Reportees = new List<Employee>
            {
                new Employee{Id = 6, ParentId = 4, Name = "F", Designation = "Developer", Reportees = new List<Employee> () }
            } 
        }
    }
};

如果要过滤的 Id 是 2：

new List<Employee> employees
{
    new Employee{Id = 1,ParentId = 0,Name = "A",Designation = "CEO",Reportees = new List<Employee>{
      new Employee{Id = 2,ParentId = 1,Name = "B",Designation = "Manager",Reportees = new List<Employee>()}
    }
};C#

Answer 1

这是您需要的方法：

List<Employee> FilterEmployees(List<Employee> source, Func<Employee, bool> predicate) =>
    source
        .Select(e => new { employee = e, reportees = FilterEmployees(e.Reportees, predicate) })
        .Where(x => predicate(x.employee) || x.reportees.Any())
        .Select(x => new Employee
        {
            Id = x.employee.Id,
            ParentId = x.employee.ParentId,
            Name = x.employee.Name,
            Designation = x.employee.Designation,
            Reportees = x.reportees,
        })
        .ToList();

此方法的两个关键行是第一行Select 和Where。

第一个Select 跟踪当前employee 并递归调用FilterEmployees 以获取任何匹配的Reportees。

Where 决定我们是否要保留当前的employee - 标准是员工是否满足谓词或满足其任何Reportees。

最后，它只是构建新的Employee 来返回。

对于FilterEmployees(employees, e => e.Id == 6 || e.Id == 7)，我们得到：

对于FilterEmployees(employees, e => e.Id == 6)，我们得到：

对于FilterEmployees(employees, e => e.Id == 2)，我们得到：

Answer 2

我有两个解决方案：

1)创建一个函数以从其 ID 访问员工对象

2) 创建一个 childsID 属性，如：

new Employee{Id = 1,ParentId = 0, childsID=new list<int>(){2,4,6,7}, ...}

在两者之后，您可以使用 linq 轻松完成这项工作