创建一个通用函数，该通用函数在C＃中返回通用类型列表

Question

I have two Model classes, one is Person and the other is Department . What I want to achieve is I want to create a generic function which can be used to retrieve generic type data in the form of List for eg one call will return Person List , another call will return Department List . More specifically I want to return data in the form of a List.

The below is the Person Class.

public class Person {

    public Int16 Personid{ get; set; }
    public string Personname { get; set; }
    public string Personaddress { get; set; }

}

The below is the Department class.

public class Department {

     public Int16 Departmentid { get; set; }
     public string Departmentname { get; set; }
     public string Departmentsection { get; set; }

}

The below are the calling function where One time I make a call with CallingMethodPerson() and other with CallingMethodDepartment() .

public class CallingClass {

   public void CallingMethodPerson() {

      CalledClass calling = new CalledClass();
      Calling. CalledMethod();

   }

    public void CallingMethodDepartment() {

      CalledClass calling = new CalledClass();
      Calling. CalledMethod();

    }
}

The below blue print is the CalledClass where it does some manipulation and return List of either Person or Department .

public class CalledClass {

    public void CalledMethod() {
      //this is a generic method wherein returns the list of either a Person 
      or Department whenever called.

    }
}

To summarise I want to implement a common function that return generic type data. The trick is actually I want build one generic function that has a SQL Read command , so I will call the same function again and again with different models, execute the query, retrieve the data from the database , store it into a list of type generic and return back to the callingmethod .

Answer 1

Your CalledClass should accept T as generic.

Both your Person and Department should have atleast and Interface in common (if you need to do things with those objects.)

public class CalledClass<T> where T : IAmAClassObject {

    public List<T> CalledMethod() {
         //create your objects and do something
         return objects.ToList();
    }
}

Another way of handling this is to make the CalledMethod handle the generic public class CalledClass {

    public List<T> CalledMethod<T>() {
         //create your objects and do something
         return objects.ToList();
    }
}

This way you should instantiate the CalledClass once in the CallingClass class, and just call the CallMethod giving the right T type.

Answer 2

Looks like you could benefit from entity framework. It has the method you need, it is called using DbContext , DbSet<T> and Linq-to-sql.

Answer 3

The correct syntax to do this is the following:

public class CalledClass<T>
{
    public List<T> CalledMethod()
    {
         return objects.ToList();
    }
}

But this will not allow you to modify the list entries, because there are of type object .

Tour example shows that your objects are quite similar, so i would suggest extracting a common interface:

1. Remove the prefix Person and Department this information is already given with the class
2. Then moving those properties in an interface

This will leave you with the following hierarchy

public interface IEntity
{
    string Name {set;get;}
    string Id {set;get;}
}

public class Person : IEntity 
{   
    string Name {set;get;}
    string Id {set;get;}
    string Address {set;get;}
}

public class Department : IEntity 
{   
    string Name {set;get;}
    string Id {set;get;}
    string Section {set;get;}
}

You can now add a constraint that your generic function only takes a child of IEntity

public class CalledClass<TEntity>
    where TEntity : IEntity
{
    public List<TEntity> CalledMethod()
    {
         // You can access Name and Id here
         foreach(var entity in entities) // i know the code is not useful ;) 
             entity.Id = "Unique ID";    // only for demonstration purposes
             entity.Name = "Random Name";
         }

         return entities.ToList();
    }
}