Summary:

If you want common behavior, you need an interface. And from the first one is a small step to re-organizing the program.

Body:

When you make a component for other people, you must make the possibility for those to

1. customize your software with their software

2. provide a default implementation

For the messaging component, the first customization is to provide a way for the site using the messaging to use their users.

The first step is to create a custom project which can provide guidance to the users that want to implement. VS provides XML documentation –I have checked and put also “warnings as error”

Next , I have create the User interface:

/// <summary>
    /// the user that can send messages
    /// TODO version 2: make pagination
    /// </summary>
    /// <typeparam name="UserPrimaryKey">the type of primary key</typeparam>
    public interface IUser<UserPrimaryKey>
    {
        /// <summary>
        /// the user primary key
        /// </summary>
        UserPrimaryKey Key { get; set; }
        /// <summary>
        /// the user name to be displayed
        /// </summary>
        string UserNameToDisplay { get; set; }
        /// <summary>
        /// other info for the user
        /// </summary>
        string OtherInfo { get; set; }

        /// <summary>
        /// find friends
        /// </summary>
        /// <param name="search">find user by name</param>
        /// <returns></returns>
        IEnumerable<KVPNew<UserPrimaryKey, string>> FindFriends(string search);

        /// <summary>
        /// find friends online
        /// </summary>
        /// <param name="search"></param>
        /// <returns></returns>
        IEnumerable<KVPNew<UserPrimaryKey, string>> FindFriendsOnline(string search);

        /// <summary>
        /// sends a message
        /// </summary>
        /// <param name="message"></param>
        void SendMessage(IUserMessage<IUser<UserPrimaryKey>, UserPrimaryKey> message);

    }
 

Two methods are interesting : SendMessage and FindFriends

Let’s take first SendMessage. It was obviously clear that I need another interface – the message to be sent. So the next interface created:

/// <summary>
    /// the message to be sent to the user
    /// TODO version 2: allow messaging for more than 1 user
    /// TODO version 2: message importance
    /// </summary>
    /// <typeparam name="TheUser">user interface</typeparam>
    ///  /// <typeparam name="UserPrimaryKey">user primary key</typeparam>
    public interface IUserMessage<TheUser, UserPrimaryKey>
        where TheUser : IUser<UserPrimaryKey>
    {
        /// <summary>
        /// subject of the message
        /// </summary>
        string Subject { get; set; }
        /// <summary>
        /// body of the message
        /// </summary>
        string Body { get; set; }
        /// <summary>
        /// to the user
        /// </summary>
        TheUser To { get; set; }
        /// <summary>
        /// from the user
        /// </summary>
        TheUser From { get; set; }
        /// <summary>
        /// cc - as in email
        /// </summary>
        TheUser CC { get; set; }

        /// <summary>
        /// date of message
        /// </summary>
        DateTime DateInserted { get; set; }

        /// <summary>
        /// if recipient have read
        /// </summary>
        bool MessageRead { get; set; }
        // <summary>
        // bcc - as in email
        // </summary>
        //TheUser BCC { get; set; }

    }

Let’s take the other : IEnumerable<KVPNew<UserPrimaryKey, string>> FindFriends(string search);

It is clear that a user can send emails to friends( maybe to anybody if we make an intranet site for an enterprise) and I must somehow have the names and id’s of the friends. I could use KeyValuePair – but it is a struct and can not be compared with null . More, usually I need more data to be transferred – so I have created long ago a KVPNew class:

 /// <summary>
    /// this is the correspondent class of KeyValuePair structure from .net
    /// The features:
    /// 1. it is a class-  can be compared fastly with null
    /// 2. can be used in a search and display <paramref name="AdditionalData">AdditionalData </paramref>
    /// </summary>
    /// <typeparam name="TKEY">Key - it is compared in equals and GetHashCode</typeparam>
    /// <typeparam name="TValue">Value to be displayed</typeparam>
    public class KVPNew<TKEY, TValue>
    {
        public KVPNew() { }
        public KVPNew(TKEY key, TValue value):this()
        {
            this.Key = key;
            this.Value = value;

        }
        public TKEY Key { get; set; }
        public TValue Value { get; set; }
        public string AdditionalData { get; set; }
        public override bool Equals(object obj)
        {
            if (obj == null)
                return false;

            var o = obj as KVPNew<TKEY, TValue>;
            if (o == null)
                return false;
            return this.Key.Equals(o.Key);

        }
        public override int GetHashCode()
        {
            return this.Key.GetHashCode();
        }
    }

And, being to interfaces, I have created also an interface for admin people to find users

/// <summary>

/// used by application to load plugins to find users

/// because each application can have it’s own way to find users

/// <summary>
    /// used by application to load plugins to find users
    /// because each application can have it's own way to find users
    /// used by admins to find users
    /// Improvement version 2 : pagination
    /// </summary>
    /// <typeparam name="T">user </typeparam>
    /// <typeparam name="UserKey">user key </typeparam>
    public interface IUsersFind<T,UserKey>
        where T:IUser<UserKey>
    {
        /// <summary>
        /// used to find users online to send message
        /// </summary>
        /// <param name="UserThatMakesTheSearch"> the user that makes the search </param>
        /// <param name="Search">search string - could be null</param>
        /// <returns> a list of users</returns>
        IEnumerable<KVPNew<T, string>> FindUsersOnline(T UserThatMakesTheSearch, string Search);
        /// <summary>
        /// used to find users (online or not )to send message
        /// </summary>
        /// <param name="UserThatMakesTheSearch"> the user that makes the search </param>
        /// <param name="Search">search string - could be null</param>
        /// <returns> a list of users</returns>
        IEnumerable<KVPNew<T, string>> FindUsers(T UserThatMakesTheSearch, string Search);
        /// <summary>
        /// find a user by his key
        /// </summary>
        /// <param name="key">the user key</param>
        /// <returns></returns>
        IUser<UserKey> FindUser(UserKey key);

    }

/// <summary>
    /// operations with the database
    /// </summary>
    /// <typeparam name="User"></typeparam>
    /// <typeparam name="UserPrimaryKey"></typeparam>
    public interface IUserList<User, UserPrimaryKey>: IDisposable
        where User : IUser<UserPrimaryKey>
    {
        /// <summary>
        /// fast delete all from database - good for testing
        /// </summary>
        void FastDeleteAll();

        /// <summary>
        /// add to internal list
        /// </summary>
        /// <param name="u">the user to be added </param>
        void Add(User u);

        /// <summary>
        /// save changes for new and old members
        /// </summary>
        void SaveNew();
        /// <summary>
        /// save changes for old members
        /// </summary>
        void SaveExisting();

        /// <summary>
        /// for retrieving
        /// </summary>
        /// <param name="i"></param>
        /// <returns></returns>
        User Find(int i);

    }

The final interfaces are in this picture:

Next time we will create the database EF4.1 files from DatabaseFirst and we will modify .tt templates to behave nicely with relationships.

Homework:

• Add to IUserMessage a BCC field
• What if To from IUserMessage will be directed to more than one person ?How do you implement it?
• Do you think that is something missed from KVPNew class?( Hint == operator and GetHashCode)

Tags: ASP.NET MVC, Simple messaging system