Question

我想在 EntityFramework 6.2.0 中建立一个递归查询，以获取一名雇员及其所有“直接”人员（一个级别）以及所有其他下属所有层次结构。

我的意思是使用List<IQueryable<T>>建立一个完整的查询，然后一次到数据库的一次漫游就运行一次。

这是我的尝试：

private static List<IQueryable<Employee>> queryables = new List<IQueryable<Employee>>();

static void Main(string[] args)
{
    using (var db = new EmployeeContext())
    {
        IQueryable<Employee> managers = db.Employee.Where(x => x.Id == 1);
        GetSlaves(managers);

        // the System.NotSupportedException occurs in this line
        IQueryable<Employee> employees = queryables.Aggregate(Queryable.Union);

        // but throws here
        var res = (
            from e in employees
            join d in db.EmployeeDoc on e.Id equals d.EmployeeId
            select new { e.Id, e.EmployeeName, d.DocNumber }).ToList();
    }

    Console.ReadLine();
}

static void GetSlaves(IQueryable<Employee> managers)
{
    if (managers != null)
    {
        queryables.Add(managers);

        foreach (var m in managers)
        {
            Console.WriteLine($"{m.Id} {m.EmployeeName} {m.Position}");
            GetSlaves(m.Slaves.AsQueryable());
        }
    }
}

但是我得到一个 System.NotSupportedException ：“无法创建类型为'EF6.Employee'的常量值。在这种情况下，仅支持原始类型或枚举类型。'

上面的C＃代码试图替换以下SQL代码：

declare @managerId int = 1

;with Employees(Id, EmployeeName)
as
(
    select e.Id, e.EmployeeName from Employee as e
    where Id = @managerId
    union all 
    select e.Id, e.EmployeeName from Employee as e
    inner join  Employees as em on e.ManagerId = em.Id
)

select e.Id, e.EmployeeName, d.DocNumber
from Employees e
inner join EmployeeDocuments d on e.Id = d.EmployeeId

已更新：

这是我使用的SQL脚本：

create table Employee
(
    Id int not null identity(1,1) primary key,
    EmployeeName varchar(20),
    Position varchar(30),
    ManagerId int constraint FK_Employee foreign key references Employee(Id)
)

insert into Employee (EmployeeName, Position, ManagerId) values
('John', 'CEO', NULL),
('Marry', 'Head of sales division', 1),
('Mike', 'Head of HR division', 1),
('Jack', 'Sales manager', 2),
('Olivia', 'Sales manager', 2),
('Sophia', 'Sales manager', 2),
('Nadya', 'HR manager', 3),
('Tim', 'HR manager', 3),
('Jim', 'Salesman', 4),
('Sergey', 'Salesman', 4),
('Dmitry', 'Salesman', 5),
('Irina', 'Salesman', 5),
('William', 'Assistant', 8)

select * from Employee

Create table EmployeeDocuments
(
    Id int not null identity(1,1) primary key,
    DocNumber varchar(20),
    EmployeeId int not null constraint FK_Docs_Employee foreign key references Employee(Id)
)

insert into EmployeeDocuments (DocNumber, EmployeeId) values
('1/2019-01-15', 1), ('3/2019-02-25', 3), ('4/2019-01-31', 4), ('9/2019-02-28', 9)

select * from EmployeeDocuments

这是Employee类：

[Table("Employee")]
public partial class Employee
{
    public Employee()
    {
        Slaves = new HashSet<Employee>();
    }

    public int Id { get; set; }

    [StringLength(20)]
    public string EmployeeName { get; set; }

    [StringLength(30)]
    public string Position { get; set; }

    public int? ManagerId { get; set; }

    public virtual ICollection<Employee> Slaves { get; set; }

    public virtual Employee Manager { get; set; }

    public virtual ICollection<EmployeeDoc> EmployeeDocs { get; set; }
}

Answer 1

该错误是由于查询是静态的。当代码非常简单时，不确定为什么需要查询。见下文

    class Program
    {
        static void Main(string[] args)
        {
            Employee.GetSlaves();

        }
    }
    public partial class Employee
    {
        public static List<Employee> employees = new List<Employee>() {
            new Employee() {Id = 1, EmployeeName =  "John",  Position =  "CEO", ManagerId = null},
            new Employee() {Id = 2,EmployeeName =  "Marry", Position =  "Head of sales division", ManagerId = 1},
            new Employee() {Id = 3,EmployeeName =  "Mike", Position =  "Head of HR division", ManagerId = 1},
            new Employee() {Id = 4,EmployeeName =  "Jack", Position =  "Sales manager", ManagerId = 2},
            new Employee() {Id = 5,EmployeeName =  "Olivia", Position =  "Sales manager", ManagerId = 2},
            new Employee() {Id = 6,EmployeeName =  "Sophia", Position =  "Sales manager", ManagerId = 2},
            new Employee() {Id = 7,EmployeeName =  "Nadya", Position =  "HR manager", ManagerId = 3},
            new Employee() {Id = 8,EmployeeName =  "Tim", Position =  "HR manager", ManagerId = 3},
            new Employee() {Id = 9,EmployeeName =  "Jim", Position =  "Salesman", ManagerId = 4},
            new Employee() {Id = 10,EmployeeName =  "Sergey", Position =  "Salesman", ManagerId = 4},
            new Employee() {Id = 11,EmployeeName =  "Dmitry", Position =  "Salesman", ManagerId = 5},
            new Employee() {Id = 12,EmployeeName =  "Irina", Position =  "Salesman", ManagerId = 5},
            new Employee() {Id = 13,EmployeeName =  "William", Position =  "Assistant", ManagerId = 8}
        };

        public static void GetSlaves()
        {
            Employee ceo = employees.Where(x => x.ManagerId == null).First();
            GetSlavesRecursive(ceo);
        }

        public int Id { get; set; }


        public string EmployeeName { get; set; }


        public string Position { get; set; }

        public int? ManagerId { get; set; }

        public virtual ICollection<Employee> Slaves { get; set; }

        public virtual Employee Manager { get; set; }

        //public virtual ICollection<EmployeeDoc> EmployeeDocs { get; set; }

        static void GetSlavesRecursive(Employee manager)
        { 
            manager.Slaves  = employees.Where(x => x.ManagerId == manager.Id).ToList();
            foreach (Employee slave in manager.Slaves)
            {
                GetSlavesRecursive(slave);
            }
        }
    }

EntityFramework中的递归查询抛出NotSupportedException

1 个答案: