Question

I am begging in c# .
What is mean “where” in all this class?
Why i am used “where” in code?
what is benefit about Where Keyword ?

public abstract class AbstractEntity
    {
    }

 public abstract class AbstractControl<E> where E: AbstractEntity
    {
        public abstract void Add(E entity);
        public abstract void Modify(E entity);
        public abstract void Remove(E entity);
    }    


public abstract class AbstractSQLServerControl<E> : AbstractControl<E> where E : AbstractEntity
        {
            protected SQLServerConnectionManager connectionManager;
            public AbstractSQLServerControl(string connectionString)
            {
                connectionManager = new SQLServerConnectionManager(connectionString);
            }


        }

Answer 1

where is known as a constraint. It makes sure that your Type Parameter E is derived from AbstractEntity. If an interface was specified after the where, E would need to implement that interface.