c# - 如何使用 SQLite-Net Extensions 实现递归关系

Question

我有一个表Employee，它必须具有递归关系，例如。

第 1 行:EmployeeId = 1，EmployeeName = Albert，< em>SupervisorId = NULL;

第 2 行:EmployeeId = 2，EmployeeName = Leonardo，< em>SupervisorId = 1;

即EmployeeId(2) 是 EmployeeId(1) 的 child

我在 C# 中有以下代码，我在其中使用 SQLite-Net Extentions实现递归关系:

public class Employee
{
    public Employee()
    {
        Subordinates = new List<Employee>();
    }

    [PrimaryKey]
    [MaxLength(36)]
    public string EmployeeGuid { get; set; }

    public string EmployeeName { get; set; }

    [OneToMany("SupervisorGuid")]
    public List<Employee> Subordinates { get; set; }

    [ManyToOne("EmployeeGuid")]
    public Employee Supervisor { get; set; }

    [ForeignKey(typeof(Employee))]
    [MaxLength(36)]
    public string SupervisorGuid { get; set; }
}

接下来我测试代码 - 我创建了两个员工并将他们添加到表Employee:

第 1 员工

Employee employee1 = new Employee
{
    EmployeeGuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa",
    EmployeeName = "Albert"
};

Insert(employee1);

第 2 员工

Employee employee2 = new Employee
{
    EmployeeGuid = "bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb",
    EmployeeName = "Leonardo",
    SupervisorGuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"
};

Insert(employee2);

但是当我打电话的时候

GetByGuid(string guid) 

guid 是第一个员工，我收到以下错误:

Additional information: Object of type 'Project.Models.Employee' cannot be converted to type 'System.Collections.Generic.List`1

SQLite-Net 是否支持递归关系？有什么建议吗？

更新

GetByGuid() 的代码:

public T GetByGuid(string guid)
{
    return Database.GetWithChildren<T>(guid);
}

此外，当我添加 2nd 员工而不指定外键并进行调用时，它会工作...

Answer 1

在递归关系中，您必须手动指定反向关系，如下所示:

public class Employee
{
    [PrimaryKey]
    [MaxLength(36)]
    public string EmployeeGuid { get; set; }

    public string EmployeeName { get; set; }

    [OneToMany(inverseProperty: "Supervisor")]
    public List<Employee> Subordinates { get; set; }

    [ManyToOne(inverseProperty: "Subordinates")]
    public Employee Supervisor { get; set; }

    [ForeignKey(typeof(Employee))]
    [MaxLength(36)]
    public string SupervisorGuid { get; set; }
}

我已经对其进行了测试，它按预期工作。但是，我创建了 a new issue in bitbucket因为我认为这种行为可以改进，所以这种情况在不久的将来会奏效:

public class Employee
{
    [PrimaryKey]
    [MaxLength(36)]
    public string EmployeeGuid { get; set; }

    public string EmployeeName { get; set; }

    [OneToMany]
    public List<Employee> Subordinates { get; set; }

    [ManyToOne]
    public Employee Supervisor { get; set; }

    [ForeignKey(typeof(Employee))]
    [MaxLength(36)]
    public string SupervisorGuid { get; set; }
}

希望对您有所帮助。