c# - EntityFramework 中的递归查询抛出 NotSupportedException

Question

我想在EntityFramework 6.2.0中构建一个递归查询，以获取员工及其所有“直接”（一个级别）以及所有其他下属的所有层次结构。

我的观点是用来List<IQueryable<T>>构建一个完整的查询，然后只运行一次，然后对数据库进行一次往返。

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());
        }
    }
}

但我得到一个System.NotSupportedException：'无法创建'EF6.Employee' 类型的常量值。在此上下文中仅支持原始类型或枚举类型。

上面的 C# 代码试图替换下面的 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

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

这里是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; }
}

标签： c#entity-frameworklinqrecursive-query

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);
            }
        }
    }