Return objects with populated list properties from stored procedure

Question

I\'m new to SQL Server stored procedures, so apologies if I\'m being an idiot. I would like to use a stored procedure to return a list of objects, each of which has a property c

Answer 1

Here is your most basic type of ORM mapper.

Well, most basic, with some maintainability and readability in mind.

I would hit the database ONCE, but have multiple resultsets in your stored procedure. And look into the IDataReader.NextResult

(as seen here LINK )

Below is some basic ORM.

[Serializable]
public partial class Answer
{
    public int AnswerKey { get; set; }                   
    public int ParentQuestionID { get; set; }
    public string AnswerText { get; set; }                   

    public Question ParentQuestion  { get; set; }    

}

internal static class AnswerDefaultLayout
{
    public static readonly int AnswerKey = 0;
    public static readonly int ParentQuestionID = 1;
    public static readonly int AnswerText = 2;

}

public class AnswerSerializer
{
    public ICollection<Answer> SerializeAnswers(IDataReader dataReader)
    {
        Answer item = new Answer();
        ICollection<Answer> returnCollection = new List<Answer>();

            int fc = dataReader.FieldCount;//just an FYI value

            int counter = 0;//just an fyi of the number of rows

            while (dataReader.Read())
            {

                if (!(dataReader.IsDBNull(AnswerDefaultLayout.AnswerKey)))
                {
                    item = new Answer() { AnswerKey = dataReader.GetInt32(AnswerDefaultLayout.AnswerKey) };

                    if (!(dataReader.IsDBNull(AnswerDefaultLayout.ParentQuestionID)))
                    {
                        item.ParentQuestionID = dataReader.GetInt32(AnswerDefaultLayout.ParentQuestionID);
                    }

                    if (!(dataReader.IsDBNull(AnswerDefaultLayout.AnswerText)))
                    {
                        item.AnswerText = dataReader.GetString(AnswerDefaultLayout.AnswerText);
                    }


                    returnCollection.Add(item);
                }

                counter++;
            }

            return returnCollection;

    }
    }


[Serializable]
public class Question
{
    public int QuestionID { get; set; }
    public string Question { get; set; }
    public ICollection<Answer> Answers { get; set; }
}

internal static class QuestionDefaultLayout
{
    public static readonly int QuestionID = 0;
    public static readonly int QuestionText = 1;
}


public class QuestionSerializer
{
    public ICollection<Question> SerializeQuestions(IDataReader dataReader)
    {
        Question item = new Question();
        ICollection<Question> returnCollection = new List<Answer>();


            int fc = dataReader.FieldCount;//just an FYI value

            int counter = 0;//just an fyi of the number of rows

            while (dataReader.Read())
            {

                if (!(dataReader.IsDBNull(QuestionDefaultLayout.QuestionID)))
                {
                    item = new Question() { QuestionID = dataReader.GetInt32(QuestionDefaultLayout.QuestionID) };

                    if (!(dataReader.IsDBNull(QuestionDefaultLayout.LAST_NAME)))
                    {
                        item.LastName = dataReader.GetString(QuestionDefaultLayout.LAST_NAME);
                    }



                    returnCollection.Add(item);
                }

                counter++;
            }

            return returnCollection;


    }
}






public class QuestionManager
{

    public ICollection<Question> GetAllQuestionsWithChildAnswers()
    {

    String myConnString  = "User ID=<username>;password=<strong password>;Initial Catalog=pubs;Data Source=myServer";
    SqlConnection myConnection = new SqlConnection(myConnString);
    SqlCommand myCommand = new SqlCommand();
    SqlDataReader myReader ;

    myCommand.CommandType = CommandType.StoredProcedure;
    myCommand.Connection = myConnection;
    myCommand.CommandText = "dbo.uspQuestionAndAnswersGetAll";
    int RecordCount=0; 

    try
    {
        myConnection.Open();
        myReader = myCommand.ExecuteReader();

        ICollection<Question> questions = new QuestionSerializer().SerializeQuestions(myReader);

        myReader.NextResult();

        ICollection<Answer> answers = new AnswerSerializer().SerializeAnswers(myReader);

        questions = this.MergeQuestionObjectGraphs(questions, answers);

    catch(Exception ex) 
    {
       MessageBox.Show(ex.ToString());
    }
    finally
    {
    if (null != myReader)
    {
        myReader.Close();
    }
    if (null != myConnection)
    {
        myConnection.Close();
    }
    }
    }

        private ICollection<Question> MergeQuestionObjectGraphs(ICollection<Question> qtions, ICollection<Answer> aners)
        {
            if (null != qtions && null != aners)
            {
                foreach (Question qtn in qtions)
                {
                    IEnumerable<Answer> foundLinks = aners.Where(lnk => lnk.ParentQuestionId == qtn.QuestionId);
                    if (null != foundLinks)
                    {
                        foreach (Answer link in foundLinks)
                        {
                            link.ParentQuestion = qtn;
                        }

                        qtn.Answers = foundLinks.ToList();
                    }
                }
            }

            return qtions;
        }

}

TSQL

CREATE PROC dbo.uspQuestionAndAnswersGetAll
AS
    SELECT QuestionId, QuestionText FROM dbo.Question
    SELECT AnswerId, QuestionId, AnswerText FROM dbo.Answer
GO 

Answer 2

Actually a stored procedure delivers a relational result rather than objects. As an alternative, you could return XML using FOR XML and deserialize it into objects. Mapping this to objects is usually done using an O/R mapper.

You can use datasets and table adapters to get the relational data into your applications. Once loaded into the dataset, you can populate your Question and Answer objects.

Here is a sample toy code to fill the result of a stored procedure into a data set:

var ds = new DataSet();

using (var cn = new SqlConnection())
using (var cmd = new SqlCommand("myStoredProcedure", cn))
{
    cmd.CommandType = CommandType.StoredProcedure;

    using (var adapter = new SqlDataAdapter(cmd))
    {
        adapter.TableMappings.Add("Table0", "Answers");
        adapter.TableMappings.Add("Table1", "Questions");

        adapter.Fill(ds);
    }
}

For actual development I'd suggest you to use a Typed Dataset and a proper SqlConnection. However, as comments pointed out too, use EF or another O/R mapper if you can.