返回作为参数传递的同一对象的方法

Question

Is it acceptable practice to pass an object into a method, then return the same object rather than creating a new object inside of the method itself?

As an example: if have an entity class as follows:

class UserDetails {
    int UserID { get; set; }
    string UserName { get; set; }
    string UserAge { get; set; }
}

And then I pass an instance of this class to a method, as follows:

UserDetails UserInfo = new UserDetails();
UserInfo = Get_Details(UserInfo);

Is it reasonable for the method to do the following?

public UserDetails Get_Details(UserDetails user) {
    // SQL Operations...
    user.age = 32;
    return user;
}

Answer 1

IMO, there is no need to return the object . Since it is passed to the method by reference , the caller already has a reference to the same object (with the updated values after the method completes).

On the other hand, what can be useful in some situations is a fluent-interface, where instance-methods of a class return the instance again, eg:

class X
{
  public X DoThis(int number)
  {
    // do something
    return this;
  }
  public X DoThat(string name)
  {
    // do something else
    return this;
  }
}

This allows to write very readable code, such as:

var x = new X().DoThis(23).DoThat("asdf");

Answer 2

This can be useful with the builder pattern (when you want to build a complex object step by step).

As a very bad example:

class FooBuilder {
  FooBuilder WithAge(int age);
  FooBuilder WithUrl(Url url);

  Foo ToFoo();
}

new FooBuilder().WithAge(12).WithUrl(new Url("http://www.happybirthday.com/").ToFoo();

In your particular case, I'd prefer to initialize everything in one go with the initializer syntax.

new User { Age = 45, UserName = "Bob", Id = 101 };

Answer 3

There is nothing horribly wrong with this but a couple of observations;

• You are setting details inside of a method called get perhaps load is more appropriate.
• If you are only passing in UserDetails because you want the id for your then the parameter should just be id instead. This keeps the interface cohesive.
• It is generally considered bad form to modify a parameter object within a method, ie, mutation principle.

Answer 4

This is a possible approach and when you have only ONE item to work one, the best, too. You might also consider to use ref , which creates a reference to the passed parameter

public void Get_Details(ref UserDetails user)
{
    // SQL Operations. . .
    user.age= 32;
}

this way, you don't pass a copy, but reference the object you passed in. But this can become quite obscure and is unnecessary in your case. See here for an insight.

Answer 5

You might do well to look up the concepts of the Repository Pattern and OOD. In general, I prefer projections or fully loaded entities.

public UserDetailsProjection GetDetailsByUserId(Guid userID)
{
   // Code goes here
   return user;
}

Note: ref is not required, because all objects are passed by reference.

Answer 6

Doing it like that is rather pointless, as the assignment that you do doesn't change anything.

Calling it like this:

UserInfo = Get_Details(UserInfo);

gives the same result as calling it and ignoring the return value:

Get_Details(UserInfo);

Returning the reference may only be confusing, leading someone to believe that the method returns a new instance, as that would be the only logical reason to return a reference.

It would make more sense to have that method in the class, so that you call it as:

UserInfo.Get_Details();

If your method is supposed to initialise the object, you would rather put the code it the constructor than calling it after creating the instance:

class UserDetails {

  int UserID { get; set; }
  string UserName { get; set; }
  string UserAge { get; set; }

  public UserDetails() {
    Get_Details(this);
  }

}

Then you just create the instance, and the constructor loads the data:

UserDetails UserInfo = new UserDetails();

Answer 7

You can fill your entity in its constructor method or another method inside entity class. It will be ready to use when created.

public class SomeClass
{
    public string Field_1;
    public int Field_2;

    public SomeClass(int ID)
    {
        // Sql operations by ID or another value
        // set fields
    }

    public AnotherMethod(int ID)
    {
        // Sql operations by ID or another value
        // set fields
    }
}