无法从自定义对象转换为对象或动态

Question

我有一个列表，我想用不同类型的对象填充它，试图用 object\dynamic 来完成它，但它没有，即使在转换时也是如此。使用 asp.net 核心。查看我的代码：

public Dictionary<string, Employee> getEmployees(); //This method returns a dictionary of string as a key and Employee as a value.
public Dictionary<string, customer>()> getCustomers(); //same principal


public List<Dictionary<string, object>> getDifferentItems()
{
   List<Dictionary<string, object>> listOfItems = new List<Dictionary<string, object>>();
   listOfItems.add(getEmployees()); //Error
   listOfItems.add(getCustomers()); //Error
   return listOfItems;
}

Answer 1

这里有几个问题，都与方差有关。

这行不通，因为 List<T> 或 .NET 中的任何其他 class 不支持差异。

换句话说，T 必须是特定类型，并且不像非泛型类型那样尊重继承/可替换性。

同样，对于Dictionary<TKey, TValue>，TValue不是变体，所以不能简单地使用object作为值。

另一方面，

IEnumerable<out T> 是协变的，因此您可以这样做：

public IEnumerable<IDictionary> getDifferentItems()
{
   yield return getEmployees();
   yield return getCustomers();
}

使用

IDictionary，因为它是 Dictionary<string, Employee> 和 Dictionary<string, Customer>.

的唯一共同祖先（对象除外）

这可能会满足您的要求，但您没有明确说明您要使用 getDifferentItems 方法实现的目标。

可以找到有关方差的更多信息here。

Answer 2

我会亲自制作一个界面，例如 IPerson，它具有 Employees 和 Customers 的所有属性，例如 Name、Address、ID 等

设置您的客户和员工类以实施 IPerson

然后在您的字典中使用 IPerson，您可以向其中添加对象。

这是一些代码：

public class Employee : IPerson
    {
        public int ID { get; set; }

        public string Name { get; set; }
    }

    public class Customer : IPerson
    {
        public int ID { get; set; }

        public string Name { get; set; }
    }

    public interface IPerson
    {
        int ID { get; set; }

        string Name { get; set; }
    }
    public class Test
    {
        public void MyTest()
        {
            List<Dictionary<string, IPerson>> listOfItems = new List<Dictionary<string, IPerson>>();

            Dictionary<string, IPerson> myEmployees = new Dictionary<string, IPerson>();
            string someString = "blah";
            Employee e = new Employee();
            e.Name = "Bob";
            e.ID = 1;

            myEmployees.Add(someString, e);

            Dictionary<string, IPerson> myCustomers = new Dictionary<string, IPerson>();
            string someOtherString = "blah";
            Customer c = new Customer();
            c.Name = "Robert";
            c.ID = 2;

            myCustomers.Add(someOtherString, c);

            listOfItems.Add(myEmployees);
            listOfItems.Add(myCustomers);
        }
    }

Answer 3

根据您的尝试，我可以看到两种解决方案：

创建两个不同词典的列表

    public Dictionary<string, Employee> getEmployees() {
        return new Dictionary<string, Employee>();
    }
    public Dictionary<string, Customer> getCustomers() {
        return new Dictionary<string, Customer>();
    }


    public List<Dictionary<string, object>> getDifferentItems()
    {
        List<Dictionary<string, object>> listOfItems = new List<Dictionary<string, object>>();
        listOfItems.Add(this.getEmployees().ToDictionary(entry => (string)entry.Key,
                  entry => (object)entry.Value)); 
        listOfItems.Add(this.getCustomers().ToDictionary(entry => (string)entry.Key,
                  entry => (object)entry.Value)); 
        return listOfItems;
    }

创建一个包含所有值的字典

    public Dictionary<string, Employee> getEmployees() {
        return new Dictionary<string, Employee>();
    }
    public Dictionary<string, Customer> getCustomers() {
        return new Dictionary<string, Customer>();
    }


    public Dictionary<string, object> getDifferentItems()
    {
        Dictionary<string, object> listOfItems = new Dictionary<string, object>();
        foreach (var entry in getEmployees()) {
            listOfItems.Add(entry.Key, entry.Value);
        }
        foreach (var entry in getCustomers()) {
            listOfItems.Add(entry.Key, entry.Value);
        }
        return listOfItems;
    }

Answer 4

这是另一个解决方案：

    public class Test
    {
        Dictionary<string, object> listOfItems = new Dictionary<string, object>();
        List<Employee> employees = new List<Employee>();
        List<customer> customers = new List<customer>();
        public Dictionary<string, object> getEmployees()
        {
            return employees.GroupBy(x => x.name, y => (object)y).ToDictionary(x => x.Key, y => y.FirstOrDefault());

        }//This method returns a dictionary of string as a key and Employee as a value.
        public Dictionary<string, object> getCustomers()
        {
            return customers.GroupBy(x => x.name, y => (object)y).ToDictionary(x => x.Key, y => y.FirstOrDefault());
        } //same principal 
        public Dictionary<string, object> getDifferentItems()
        {
            listOfItems = getEmployees();
            listOfItems.Concat(getCustomers());
            return listOfItems;
        }
    }
    public class Employee
    {
        public string name { get;set;}
    }
    public class customer
    {
        public string name { get;set;}
    }

无法从自定义对象转换为对象或动态

Cannot convert from custom object to object or dynamic

c#

dictionary

object

dynamicobject

asp.net-core

创建两个不同词典的列表

创建一个包含所有值的字典