Multiple database support in C#

Question

My application need to support multiple databases. Currently, it supports Postgres now I am adding support for Orcle and may be SqlServer in upcoming days.

Before asking any question lets look at codes.

IDbParser :

public interface IDbParser
{
    IDbConnection GetDbConnection(string ServerName, string DbPortNumber, string Username, string Password, string DatabaseName);
    IDbCommand GetDbCommand(string query, IDbConnection sqlConnection);
    IDataParameter CreateParameter(string key, object value);
    string GetDbQuery(DbQueries query);
}

OracleDbParser :

public class OracleParser : IDbParser
{
    #region >>> Queries
    private string SELECTGROUPSESSIONS = "....";
    ........
    #endregion

    public IDbCommand GetDbCommand(string query, IDbConnection sqlConnection)
    {
        var command = new OracleCommand();
        command.CommandText = query;
        command.Connection = (OracleConnection)sqlConnection;
        command.CommandType = CommandType.Text;
        command.CommandTimeout = 300;
        return command;
    }

    public IDataParameter CreateParameter(string key, object value)
    {
        return new OracleParameter(key, value);
    }        

    public IDbConnection GetDbConnection(string ServerName, string DbPortNumber, string Username, string Password, string DatabaseName)
    {
        connString = String.Format("Data Source=(DESCRIPTION = (ADDRESS_LIST = (ADDRESS=(PROTOCOL=TCP)(HOST={0})(PORT={1})))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME={2}))); Connection Timeout=60; User Id={3};Password={4};",
                                                ServerName, DbPortNumber, DatabaseName, Username, Password);
        return new OracleConnection(connString);
    }

    public string GetDbQuery(DbQueries query)
    {
        switch (query)
        {                
            case DbQueries.SELECTGROUPSESSIONS:
                return SELECTGROUPSESSIONS;
            ................
            ..............
            default:
                return String.Empty;
        }
    }
}

Similarly, there is parser for Postgres :

public class PostgresParser : IDbParser
{
    #region >>> Queries
    private string SELECTGROUPSESSIONS = "....";
    ........
    #endregion

   public IDbCommand GetDbCommand(string query, IDbConnection sqlConnection)
    {
        var command = new NpgsqlCommand();
        command.CommandText = query;
        command.Connection = (NpgsqlConnection)sqlConnection;
        command.CommandType = CommandType.Text;
        return command;
    }

    public IDataParameter CreateParameter(string key, object value)
    {
        return new NpgsqlParameter(key, value);
    }       

    public IDbConnection GetDbConnection(string ServerName, string DbPortNumber, string Username, string Password, string DatabaseName)
    {
        string connString = String.Format("Server={0};Port={1};Timeout=60;CommandTimeout=300;" +
                                            "User Id={2};Password={3};Database={4};",
                                            ServerName, DbPortNumber, Username, Password, DatabaseName);
        return new NpgsqlConnection(connString);
    }


    public string GetDbQuery(DbQueries query)
    {
        switch (query)
        {                
            case DbQueries.SELECTGROUPSESSIONS:
                return SELECTGROUPSESSIONS;
            ................
            ..............
            default:
                return String.Empty;
        }
    }
}

DatabaseParserFactory:

 public class DatabaseParserFactory
{
    public static IDbParser GetDbParser(string dbType)
    {
        CUCMDbType dbTypeName;
        Enum.TryParse(dbType.ToLower(), out dbTypeName);
        switch (dbTypeName)
        {
            case CUCMDbType.oracle:
                return new OracleParser();
            case CUCMDbType.postgres:
                return new PostgresParser();
            default:
                return new PostgresParser();
        }
    }
}

Query execution :

 public void Query(string queryStatement, DbParameterColl parameters, Action<IDataReader> processReader)
    {
        using (SqlConnection)
        {
            IDbCommand selectCommand = null;                
            selectCommand = _factory.GetDbCommand(queryStatement, SqlConnection);                     
            selectCommand.Parameters.Clear();

            using (selectCommand)
            {
                if (parameters != null)
                {
                    foreach (var param in parameters)
                    {
                        selectCommand.Parameters.Add(_factory.CreateParameter(param.Key, param.Value));                           
                    }
                }

                try
                {                 
                    using (var reader = selectCommand.ExecuteReader())
                    {
                        processReader(reader);
                    }

                }
                catch (Exception ex)
                {
                    Logger.DebugFormat("Unable to execute the query. Query : {0} . Exception: {1}", queryStatement, ex);
                    Debug.WriteLine("\n\n>> Error on executing reader. Exception :\n " + ex);
                }
            }
        }
    }

FYI: There will only be SELECT queries and no other commands.

I am passing parameter's value as an object. Well, currently there is no problem assigning the parameters and executing the query. But in most of the blogs and in stackoverflow I could see that people have been suggesting to specify the Input direction, and most specifically Input type/DbType. Do I need to specify DbType ? Currently, my code runs fine with no errors. But I am afraid, it might break down in production.

Moreover I have no control over the type of parameter, it could be anything. So what do you guys suggest? Or is there any better approach of doing this ?

Answer 1

First, you should take a look at DbProviderFactories - most of your code duplicates that already-existing standard functionality. Note that it is not yet available in .NET Core (but will be).

Regarding your question, in general you don't need to specify the parmeter direction - it's assumed to be the default. Database drivers can typically infer the database type from the CLR value you assign to a parameter, but it's a good idea to explicitly specify DbType just to be sure.