Comparing RPG to C# and SQL

Question

In an RPG program (One of IBM's languages on the AS/400) I can "chain" out to a file to see if a record (say, a certain customer record) exists in the file. If it does, then I can update that record instantly with new data. If the record doesn't exist, I can write a new record. The code would look like this:

Customer  Chain CustFile   71 ;turn on indicator 71 if not found
          if    *in71         ;if 71 is "on"
          eval  CustID = Customer;
          eval  CustCredit = 10000;
          write CustRecord
          else                ;71 not on, record found.
          CustCredit = 10000;
          update CustRecord
          endif

Not being real familiar with SQL/C#, I'm wondering if there is a way to do a random retrieval from a file (which is what "chain" does in RPG). Basically I want to see if a record exists. If it does, update the record with some new information. If it does not, then I want to write a new record. I'm sure it's possible, but not quite sure how to go about doing it. Any advice would be greatly appreciated.

Answer 1

RPG has intrinsic connectivity to the database tables on the system. That makes it easy to write such succinct operations.

C#, on the other hand, requires you to implement your own database routines (or use a framework like LINQ).

If I was doing this, I would create a class responsible for database manipulation using the System.OLEDB objects.

Some methods might be (general idea, not actual code):

public boolean CheckExists(string TableName, string ColumnName, int ID) {
  //Connect to database
  // Create Command with query  "SELECT COUNT(1) FROM " + TableName.Replace(";","") + " WHERE " + ColumnName.Replace(";","") + " = " + ID 

  Return int.Parse(myQuery.ExecuteScalar) > 0

 //disconnect

}


 public boolean UpdateCredit(int CustID, int newCredit) {
  //Connect to database
  // Create Command with query  "UPDATE CustTable SET CustCredit = " + newCredit.ToString() + " WHERE = CustId = " + CustID 

  myQuery.ExecuteNonQuery

//disconnect

}

public boolean CreateCredit(int CustID, int newCredit) {
  //Connect to database
  // Create Command with query  "INSERT INTO CustTable (CustID, CustCredit) VALUES (" + CustId.ToString + ", " + newCredit.ToString + ")"

  myQuery.ExecuteNonQuery

  //disconnect
}

Then your main method world read something like

If (CheckExists("CustTable", "CustId", CustID)) {
    UpdateCredit(CustID, 10000)
} else {
    CreateCredit(CustId, 10000)
}