Concepts of OOP

Question

I saw a project, i need explaination of this code

public class Grades : RepositoryBase<GEN_Grades>, IGrades
{
    public Grades() : this(new sCMSRepositoryContext())
    {
     // some code here
    }

 }

Where as the RepositoryBase Class is below

  public class sCMSRepositoryContext : IRepositoryContext
    {
        private const string OBJECT_CONTEXT_KEY = "sCMS.Dal.EntityModels";
        public IObjectSet<T> GetObjectSet<T>() 
            where T : class
        {
            return ContextManager.GetObjectContext(OBJECT_CONTEXT_KEY).CreateObjectSet<T>();
        }

        /// <summary>
        /// Returns the active object context
        /// </summary>
        public ObjectContext ObjectContext
        {
            get
            {
                return ContextManager.GetObjectContext(OBJECT_CONTEXT_KEY);
            }
        }

        public int SaveChanges()
        {
            return this.ObjectContext.SaveChanges();
        }

        public void Terminate()
        {
            ContextManager.SetRepositoryContext(null, OBJECT_CONTEXT_KEY);
        }

    }

// and here is the irepository class

public interface IRepositoryContext
{

    IObjectSet<T> GetObjectSet<T>() where T : class;

    ObjectContext ObjectContext { get; }

    /// <summary>
    /// Save all changes to all repositories
    /// </summary>
    /// <returns>Integer with number of objects affected</returns>
    int SaveChanges();

    /// <summary>
    /// Terminates the current repository context
    /// </summary>
    void Terminate();
}

i need explaination of constructor on the Grades Class that what is a meaning of this statement

public Grades() : this(new sCMSRepositoryContext())

why and when we need this???

As we know that we use ":" operator for inheritance But not getting why it has inherited the object of class also both the sCMSRepositoryContext and Grades Class don't have such a relation (ie inheritance)

thanks in advance

Answer 1

It is simple. You just explicitly call second constructor when invoked a first one.

Imagine something like:

public class Repository {
     //FIRST CONSTRUCTOR
     public Repository() : this(null) { //NULL OR SOME OTHER DEFAULT VALUE
     }


     //SECOND CONSTRUCTOR
     public Repository(DBObject ob) {
         //DRAMATICALLY IMPORTANT INTIALIZATION CODE
     }
}

In some cases when consumer of your class use a simple ctor, it's guaranteed that the second constructor will be invoked too , so important intialization will be executed too.

//THIS CODE WILL EXECUTE BOTH CONSTRUCTORS
Repository re = new Repository(); 

Why all this? You can invoke important initialization code in single functions (ctor) and avoid code duplication, which makes easier testing and maintaining of your code in the future.