Need help sorting the main abstract headache in my DAL

Question

I myself have a bit of a problem with my level of data access. In this particular case, I have a table that contains potentially 5 types of "entities". This is mainly a company, client, website, etc. The type is dictated by PositionTypeId in the table. All of them are in the same table, since they all have the same data structure; PositionId, Description and Code.

I have a main abstract class as follows:

public abstract class PositionProvider<T> : DalProvider<T>, IDalProvider where T : IPositionEntity
{
    public static PositionProvider<T> Instance
    {
        get
        {
            if (_instance == null)
            {
                // Create an instance based on the current database type
            }
            return _instance;
        }
    }
    private static PositionProvider<T> _instance;

    public PositionType PositionType
    {
        get
        {
            return _positionType;
        }
    }
    private PositionType _positionType;

    // Gets a list of entities based on the PositionType enum value.
    public abstract List<T> GetList();

    internal void SetPositionType(RP_PositionType positionType)
    {
        _positionType = positionType;
    }

}

I want me to be able to put all the common code in an inheritance class that is based on SQL or Oracle. This is my SQL implementation:

public class SqlPositionProvider<T> : PositionProvider<T> where T : IPositionEntity
{
        public override List<T> GetList()
        {
            int positionTypeId = (int)this.PositionType;
            using (SqlConnection cn = new SqlConnection(Globals.Instance.ConnectionString))
            {
                SqlCommand cmd = new SqlCommand("Get_PositionListByPositionTypeId", cn);
                cmd.Parameters.Add("@PositionTypeId", SqlDbType.Int).Value = positionTypeId;
                cmd.CommandType = CommandType.StoredProcedure;
                cn.Open();
                return this.GetCollectionFromReader(this.ExecuteReader(cmd));
            }
        }
}

Then I create a class for each type as follows (this is an example of CustomerProvider):

public class CustomerProvider
{
    public static PositionProvider<CustomerEntity> Instance
    {
        get
        {
            if ((int)PositionProvider<CustomerEntity>.Instance.PositionType == 0)
            {
                PositionProvider<CustomerEntity>.Instance.SetPositionType(PositionType.Customer);
            }
            return PositionProvider<CustomerEntity>.Instance;
        }
    }
}

... , , . ( IPositionType) .

:

public abstract List<CustomerEntity> GetCustomersByUserPermission(Guid userId);

, , PositionProvider, , /.

SqlPositionProvider?

Edit:

, , , PositionProvider ClientProvider, SiteProvider . .Provider:

public abstract class CustomerProvider
{

    public CustomerProvider()
    {
        this.Common.SetPositionType(PositionType.Customer);
    }

    public PositionProvider<CustomerEntity> Common
    {
        get
        {
            if (_common == null)
            {
                DalHelper.CreateInstance<PositionProvider<CustomerEntity>>(out _common);
            }
            return _common;
        }
    }
    private PositionProvider<CustomerEntity> _common;

    public static CustomerProvider Instance
    {
        get
        {
            if (_instance == null)
            {
                DalHelper.CreateInstance<CustomerProvider>(out _instance);
            }
            return _instance;
        }
    }
    private static CustomerProvider _instance;

    public abstract List<CustomerEntity> GetCustomersByUserPermission(Guid userId);

}

CustomerProvider.Instance.MyNonGenericMethod(), PositionProvider, CustomerProvider.Instance.Common.GetList()... .

Answer 1

. Inheriting :

public abstract class CustomerProvider : PositionProvider<CustomerEntity>
{

        public CustomerProvider() { }

        public new static CustomerProvider Instance
        {
            get
            {
                if (_instance == null)
                {
                    DalHelper.CreateInstance<CustomerProvider>(out _instance);
                }
                return _instance;
            }
        }
        private static CustomerProvider _instance;

        public override List<CustomerEntity> GetList()
        {
            return PositionProvider<CustomerEntity>.Instance.GetList();
        }

        public abstract List<CustomerEntity> GetCustomersByUserPermission(Guid userId);

}

:

public class SqlCustomerProvider : CustomerProvider
{
    public override List<CustomerEntity> GetCustomersByUserPermission(Guid userId)
    {
        using (SqlConnection cn = new SqlConnection(Globals.Instance.ConnectionString))
        {
            SqlCommand cmd = new SqlCommand("GetRP_CustomersByUser", cn);
            cmd.Parameters.Add("@UserId", SqlDbType.UniqueIdentifier).Value = userId;
            cmd.CommandType = CommandType.StoredProcedure;
            cn.Open();
            return this.GetCollectionFromReader(this.ExecuteReader(cmd));
        }
    }
}

PositionProvider , , CustomerProvider, SqlPositionProvider .

, .

// Returns a list of customers still using the PositionProvider
CustomerProvider.Instance.GetList(); 

// Returns my specific customer data
CustomerProvider.Instance.GetCustomersByUserPermission();

// Returns a list of sites still using the PositionProvider
SiteProvider.Instance.GetList(); 

// Not part of the SiteProvider!
SiteProvider.Instance.GetCustomersByUserPermission(); 

Answer 2

"" Repository. .

:

public static class Repository {
    public static List<CustomerEntity> GetCustomersByUserPermission(
        PositionProvider<CustomerEntity> source, Guid userId)
    {
        // query source and return results
    }
}

"" .

Answer 3

, , .

, , , ().

- ( ).

[: , ]

public class PositionProviderRepository
{
    public List<T> GetList()
        {
            int positionTypeId = (int)this.PositionType;
            using (SqlConnection cn = new SqlConnection(Globals.Instance.ConnectionString))
            {
                SqlCommand cmd = new SqlCommand("Get_PositionListByPositionTypeId", cn);
                cmd.Parameters.Add("@PositionTypeId", SqlDbType.Int).Value = positionTypeId;
                cmd.CommandType = CommandType.StoredProcedure;
                cn.Open();
                return this.GetCollectionFromReader(this.ExecuteReader(cmd));
            }
        }
    public List<CustomerEntity> GetCustomersByUserPermission(Guid userId) {
      //TODO: implementation
    }
}

, CustomerEntity.

SqlPositionProvider<T>, , , .

Answer 4

- :

public IEnumerable<T> GetItems(Predicate<T> match)
{
    foreach (T item in GetList())
    {
        if (match(item))
           yield return item;  
    }
}

SetPositionType(...), ( , GetList()?)

, , :

customerProvider.GetItems(customer => customer.Id == someId);

(, .Net 2.0)

customerProvider.GetItems(delegate(Customer c)
{
     return c.Id == someId;
});

Answer 5

-,.NET BCL , System.Data.Common. DbConnection SqlConnection/OracleConnection, DbCommand SqlCommand/OracleCommand .. ( gotchas, , ).

-, IMHo - .

public class CustomerProvider
{
    PositionProvider<CustomerEntity> _provider;
    PositionProvider<CustomerEntity> Instance // we don't need it public really.
    {
        get
        {
            if ((int)PositionProvider<CustomerEntity>.Instance.PositionType == 0)
            {
                _provider = new PositionProvider<CustomerEntity>(); // PositionType is set in .ctor
                // we can also use a factory to abstract away DB differences
            }
            return _provider;
        }
    }
    // one way of implementing custom query
    public List<CustomerEntity> GetCustomersByUserPermission(Guid userId){
        return _provider.GetListWithCriteria(Criteria.Argument("UserId", userId));
    }
}

GetListWithCriteria :

public List<CustomerEntity> GetListWithCriteria(params ICriterion[] criterias){
        int positionTypeId = (int)this.PositionType;
        using (DbConnection cn = OpenConnection()) // creates DbConnection and opens it
        using (DbCommand cmd = cn.CreateCommand())
        {
            // ... setting command text ...
            foreach(ICriterion c in criterias){
                DbParameter p = cmd.CreateParameter();
                p.DbType = c.DbType;
                p.Name = Encode(c.Name); // add '@' for MS SQL, ':' for Oracle
                p.Value = c.Value;
                cmd.AddParameter(p);
            }
            return this.GetCollectionFromReader(this.ExecuteReader(cmd));
        }        
}

, PositionProvider , CustomerProviders .