Question

I have been tasked with a project at work of writing a class to connect to multiple different databases such as Oracle, SQL Server, Spatialite etc and get and set data values and I was wondering which of the two in the title you would recommend for this.

I have created a class that utilises OLE functionality in order to make connections and set and retrieve data as I thought ADO was more of an SQL Server specific technology. Is this the case or can ADO.NET be used for a variety of data sources? I have researched it quite a lot and most places that I have seen recommend OLE for multiple possible data sources whereas they recommend ADO for SQL Server.

Thanks

Answer 1

I can’t see how OLE is going to provide a magic bullet for unifying the DAL. You want to use the data access framework that best suits the data source and abstract the implementation away from the application.

My guess is that you’re hoping that using OLE will allow some unification of syntax. But this is not the case. Once you attempt to do something like paging, each data source is going to have its own quirks and how you connect to the source is not going to help unify the syntax differences. For example, in the case of paging, SQLite usings SKIP, TAKE. Oracle uses ROWNUM. Sql Server uses TOP.

I would approach the problem by creating a DAL that abstracts the entity classes away from the data source. Then you can use the connection type that is most suitable for the data source. For example, suppose my application wants to retrieve “Products” from a data source. My application would only know about the ProductFactory interface, not the specifics of the data source type. For example,

string id = "0000001";
IProductFactory factory = FactoryManager.GetProductFactory();
Product p = factory.Get(id);

In the example below, I implement the Oracle data access tier for the Product interfaces using ODP.Net (the best data access components for an Oracle data source). Then the data access tier looks like this:

IProductFactory:

public interface IProductFactory: IEntityFactory
{
    Product Get(string productId);
    IList<Product> GetAll();
    int GetAllCount();
}

Product:

public class Product : IEntity<Product>
{
    public string ProductId { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }

    #region IEntity<Product> Members

    public Product MapData(System.Data.IDataReader reader)
    {
        return new Product
        {
            Name = reader["name"] as string,
            Description = reader["description"] as string
        };
    }

    #endregion
}

Oracle ProductFactory

public class ProductFactory : EntityFactory, IProductFactory
{
    #region IProductFactory Members

    public Product Get(string productId)
    {
        Product p = null;
        using (OracleConnection conn = new OracleConnection(ConnectionString))
        {
            using (OracleCommand cmd = new OracleCommand())
            {
                cmd.CommandText = "select * from product where productId = :productId";
                cmd.Parameters.Add("productId", productId);
                using (IDataReader reader = cmd.ExecuteReader())
                {
                    p = new Product();
                    p.MapData(reader);
                }
            }
        }
        return p;
    }

    public IList<Product> GetAll()
    {
        throw new NotImplementedException();
    }


    public int GetAllCount()
    {
        throw new NotImplementedException();
    }

    #endregion
}