Types that own disposable fields should be disposa

问题:

I tried using Run Code Analysis option in VisualStudio 2012, as a result of it I got a warning as

CA1001  Types that own disposable fields should be disposable
Implement IDisposable on 'DBConnectivity' 
because it creates members of the following IDisposable types: 'SqlConnection', 'SqlCommand'.

I referred some question in SO, but I couldn't catch the point regarding IDisposable and following is the class, responsible for this warning.

class DBConnectivity
    {
        public SqlConnection connection = null;
        public SqlCommand command = null;
        public SqlDataReader dataReader = null;
        public string connectionString = null;
        public List<MasterTableAttributes> masterTableList;
        public DBConnectivity()
        {
            connectionString = ConfigurationManager.ConnectionStrings["Master"].ConnectionString;
            connection = new SqlConnection(connectionString.ToString());

            //-----Master table results 
            connection.Open();
            string masterSelectQuery = "SELECT * FROM MASTER_TABLE";
            command = new SqlCommand(masterSelectQuery, connection);
            dataReader = command.ExecuteReader();
            masterTableList = new List<MasterTableAttributes>();

            while (dataReader.Read())
            {
                MasterTableAttributes masterTableAttribute = new MasterTableAttributes()
                {
                    fileId = Convert.ToInt32(dataReader["Id"]),
                    fileName = Convert.ToString(dataReader["FileName"]),
                    frequency = Convert.ToString(dataReader["Frequency"]),
                    scheduledTime = Convert.ToString(dataReader["Scheduled_Time"])
                };
                masterTableList.Add(masterTableAttribute);
            }
            dataReader.Close();
            connection.Close();
        }
    }

I am really confused in implementing the IDisposable. Any help appreciated?

回答1:

I fully agree with the compiler - you need to dispose your fields here, or (as already noted) - not make them fields in the first place:

class DBConnectivity : IDisposable // caveat! read below first
{
    public void Dispose() {
        if(connection != null) { connection.Dispose(); connection = null; }
        if(command != null) { command.Dispose(); command = null; }
        if(dataReader != null) { dataReader.Dispose(); dataReader = null; }
    }

Note that you would then use this type via using(...)

---

However! It looks like a static method would be more appropriate:

static class DBConnectivity
{
    public static List<MasterTableAttributes> GetMasterTableList()
    {
        var connectionString = ConfigurationManager.ConnectionStrings["Master"].ConnectionString;
        using(var connection = new SqlConnection(connectionString))
        {
            connection.Open();
            const string masterSelectQuery = "SELECT * FROM MASTER_TABLE";
            using(var command = new SqlCommand(masterSelectQuery, connection))
            using(var dataReader = command.ExecuteReader())
            {
                var masterTableList = new List<MasterTableAttributes>();

                while (dataReader.Read())
                {
                    MasterTableAttributes masterTableAttribute = new MasterTableAttributes()
                    {
                        fileId = Convert.ToInt32(dataReader["Id"]),
                        fileName = Convert.ToString(dataReader["FileName"]),
                        frequency = Convert.ToString(dataReader["Frequency"]),
                        scheduledTime = Convert.ToString(dataReader["Scheduled_Time"])
                    };
                    masterTableList.Add(masterTableAttribute);
                }
                return masterTableList;
            }
        }
    }
}

or perhaps simpler with a tool like "dapper":

static class DBConnectivity
{
    public static List<MasterTableAttributes> GetMasterTableList()
    {
        var connectionString = ConfigurationManager.ConnectionStrings["Master"].ConnectionString;
        using(var connection = new SqlConnection(connectionString))
        {
            connection.Open();
            const string sql = "SELECT Id as [FileId], FileName, Frequency, Scheduled_Time as [ScheduledTime] FROM MASTER_TABLE";
            return connection.Query<MasterTableAttributes>(sql).ToList();
        }
    }
}

回答2:

If that is you complete class you should move all the SQL variables inside the constructor. Or perhaps change the constructor to a static function that return the masterTableList