Evolution of data query in C#...

One of the most common operation in programming is data query. In C# 1.2, normally I would use a custom collection class that derived from System.Collections. But for sake of example here, I'll show it with an ArrayList instead.

Here's a class that'll become an element of the collection (yes, I know Auto-Implemented Properties).

    public class Student
    {
        private int _id;
        private string _name;
        private string _gender;

        public Student()
        {
        }

        public int Id
        {
            get { return _id; }
            set { _id = value; }
        }

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }

        public string Gender
        {
            get { return _gender; }
            set { _gender = value; }
        }
    }

This is how I normally code in C# 1.2 (.NET Framework 1.1) with an ArrayList.

    private ArrayList SomeFilterMethod(ArrayList myList)
    {
        ArrayList result = new ArrayList();
        
        for (int x = 0; x < myList.Count; x++)
        {
            if (((Student)myList[x]).Gender == "Male")
            {
                result.Add(myList[x]);
            }
        }

        return result;
    }

Generic list with action and predicate was introduced in C# 2.0 (.NET Framework 2.0). This is how my code will look like.

    private List<Student> SomeFilterMethod(List<Student> myList)
    {
        return mylist.FindAll(GetMaleStudents); 
    }

    private bool GetMaleStudents(Student item)
    {
        return item.Gender == "Male";
    }

Not to forget an anonymous methods.

    private List<Student> SomeFilterMethod(List<Student> myList)
    {
        return mylist.FindAll( delegate(Student item) { return item.Gender == "Male"; } ); 
    }

In C# 3.0 (.NET Framework 3.5), there's LINQ with 2 flavours.
1) Lambda Expression

    private List<Student> SomeFilterMethod(List<Student> myList)
    {
        return mylist.FindAll( item => item.Gender == "Male" ); 
    }

2) Query Expression

    private List<Student> SomeFilterMethod(List<Student> myList)
    {
        return (from student in mylist
            where student.Gender == "Male"
            select student).ToList<Student>();
    }

Between the two, personally I prefer the former.