Unwanted return values in lambda functions?

Question

From a previous question, I got the idea of moving boilerplate code structures into a helper function and passing in a lambda function to it.

I then applied the idea to a data access class (code below). I'm not sure how to handle the result of my ProcessDatabaseCall helper function; it seems irrelevant to my pattern of use-cases. In this example I'm returning an IEnumerable; in other cases I'm returning int, School, etc.

    public IEnumerable<School> SchoolsList(string searchChars)
    {
        DataSet ds = new DataSet();
        List<School> schools = new List<School>();
        bool cool = ProcessDatabaseCall("dbo.usp_esrvs_API_SchoolList", cmd => {
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.Add(new SqlParameter("@SearchValue", searchChars));

            SqlDataAdapter da = new SqlDataAdapter(cmd);
            da.Fill(ds);

            return true;
        });

        //Foreach row in the data set add a json array object
        foreach (DataRow row in ds.Tables[0].Rows)
        {
            schools.Add(new School((int) row["esrvs_Account_ID"], row["SchoolName"].ToString()));
        }
        return schools;
    }

    private bool ProcessDatabaseCall(string procedureName, Func<SqlCommand,bool> processor)
    {
        using (SqlConnection Mackin1Conn = new SqlConnection(connectionString))
        {
            using (SqlCommand cmd = new SqlCommand(procedureName, Mackin1Conn))
            {
                return processor(cmd);
            }
        }
    }

The function used to look like this:

public IEnumerable<School> SchoolsList(string searchChars)
    {
        DataSet ds = new DataSet();
        List<School> schools = new List<School>();
        using (SqlConnection Mackin1Conn = new SqlConnection(connectionString))
        {
            using (SqlCommand cmd = new SqlCommand("dbo.usp_esrvs_API_SchoolList", Mackin1Conn))
            {
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.Add(new SqlParameter("@SearchValue", searchChars));
                SqlDataAdapter da = new SqlDataAdapter(cmd);
                da.Fill(ds);
            }
        }
        foreach (DataRow row in ds.Tables[0].Rows)
        {
            schools.Add(new School((int) row["esrvs_Account_ID"], row["SchoolName"].ToString()));
        }
        return schools;
    }

Answer 1

Just replace Func delegate with Action delegate if you don't want return value:

private void ExecuteCommand(string commandText, Action<SqlCommand> action)
{
    using (var conn = new SqlConnection(connectionString))        
    using (var cmd = new SqlCommand(commandText, conn))
        action(cmd);
}

Then getting schools will look like (with help of LINQ you can get rid of local list of schools):

public IEnumerable<School> GetSchools(string searchChars)
{
    DataSet ds = new DataSet();

    ExecuteCommand("dbo.usp_esrvs_API_SchoolList", cmd => {
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.Add(new SqlParameter("@SearchValue", searchChars));
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        da.Fill(ds);
    });

    return from row in ds.Tables[0].AsEnumerable()
           select new School(row.Field<int>("esrvs_Account_ID"),
                             row.Field<string>("SchoolName"));
}

NOTE: Consider to use Dapper both methods above are equivalent to:

private IEnumerable<School> GetSchools(string searchChars)
{
    using (var conn = new SqlConnection(connectionString))        
        return conn.Query<School>("dbo.usp_esrvs_API_SchoolList",
                                  new { SearchValue = searchChars },
                                  commandType: CommandType.StoredProcedure);
}

Answer 2

I'd say the best course of action is to make your ProcessDatabaseCall generic:

private T ProcessDatabaseCall<T>(string procedureName, Func<SqlCommand, T> processor)
{
    using (SqlConnection Mackin1Conn = new SqlConnection(connectionString))
    {
        using (SqlCommand cmd = new SqlCommand(procedureName, Mackin1Conn))
        {
            return processor(cmd);
        }
    }
}

Your SchoolList call then turns into:

public IEnumerable<School> SchoolsList(string searchChars)
{ 
    return ProcessDatabaseCall("dbo.usp_esrvs_API_SchoolList", cmd => {
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.Add(new SqlParameter("@SearchValue", searchChars));

        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);

        var schools = new List<School>();
        //Foreach row in the data set add a json array object
        foreach (DataRow row in ds.Tables[0].Rows)
        {
            schools.Add(new School((int) row["esrvs_Account_ID"], row["SchoolName"].ToString()));
        }
        return schools;
    });
}