Generic File Importer Base Class

Problem/Question/Abstract:

Here is a useful base class to create derived classes to import data from any flat file format you can think of...

Answer:

{-----------------------------------------------------------------------------
Unit Name:     classParentDataManipulator
Author:        StewartM (Stewart Moss)

Documentation Date: 23, 08, 2002  (14:39,)

Version 1.0
-----------------------------------------------------------------------------

Compiler Directives:

Purpose:

Dependancies:

Description:

Parent Class for data manipulation
Creates the basic skelton for adding data manipulation sub-classes

Each of the inherited classes must override the ProcessData method and provide
  their own properties specific to the class (ie Invoice Number etc...)

Very useful class.

inheritance Diagram

  + -- TParentDataProcessor    // base class
       +
       |
       + --- TDerivedImporter  // sub class

Notes:

History:

Copyright 2002 by Stewart Moss.
All rights reserved.
-----------------------------------------------------------------------------}

unit classParentDataManipulator;

interface

uses Sysutils, Classes;

type
  TParentDataProcessor = class(TObject)
  private
    StringIn: string;
    LineCounter: Integer;

  public
    FieldNames,
      FieldValues,
      MultiFieldNames,
      MultiFieldValues: TStringList;

    FormName,
      FileName: string;
    Delimiters: string;
    // A list of delimiters (ie ',/[];:') used in inherited ProcessData()

    constructor create;
    destructor Destroy; override;
    procedure ProcessFile;

    function DataAtPos(S: string; StartP, EndP: Integer): string;
    // Returns the data from "StartP" to "EndP" in String "S"

    function ExpandTabs(s: string): string;
    // ExpandTabs to 8 Spaces

    procedure ProcessData(StrIn: string; LineNumber: Integer); virtual;
    // Virtual method for override in sub-classes

    procedure FieldAdd(FieldName, Data: string; GenException: Boolean);
    // Adds FieldName and FieldValue to Strings and can generate exception if
    // string is empty when required

    procedure MultiFieldAdd(FieldName, Data: string; GenException: Boolean);
    // Adds FieldName and FieldValue to Multi Field Strings and can generate exception
    // if string is empty when required

  end;

  TProcessException = Exception;

implementation

var
  F: text;
  //  Exception: TProcessException;

  { TDataProcessor }

constructor TParentDataProcessor.create;
begin
  inherited create;
  FieldNames := TStringList.Create;
  FieldValues := TStringList.Create;
  MultiFieldNames := TStringList.Create;
  MultiFieldValues := TStringList.Create;
  FieldNames.Clear;
  FieldValues.Clear;
  MultiFieldNames.Clear;
  MultiFieldValues.Clear;
end;

procedure TParentDataProcessor.ProcessFile;
begin
  if Filename = '' then
    raise Exception.Create('No Filename specified');

  try
    AssignFile(F, Filename);
    Reset(f);
  except
    try
      CloseFile(F);
    except
    end;
    raise Exception.Create('Could not open file ' + FileName);
  end;

  LineCounter := 0;

  while not eof(f) do
  begin
    Inc(LineCounter);

    try
      Readln(f, StringIn);
    except
      try
        CloseFile(f);
      except // swallow CloseFile errors
      end;

      raise Exception.Create('Could not read from file. Line number ' +
        IntToStr(LineCounter));
    end;

    StringIn := ExpandTabs(StringIn);
    // Exapnd Tabs to 8 Spaces

    ProcessData(StringIn, LineCounter);
    // Execute virutal method in sub-classes passing current line and LineNumber
  end;

  try
    closefile(f);
  except
    raise Exception.Create('Could not close file ' + FileName);
  end;
end;

procedure TParentDataProcessor.ProcessData(StrIn: string; LineNumber: Integer);
// Virtual method for override in sub-classes
begin
  //
end;

destructor TParentDataProcessor.Destroy;
begin
  FieldNames.Free;
  FieldValues.Free;
  MultiFieldNames.Free;
  MultiFieldValues.Free;
end;

function TParentDataProcessor.DataAtPos(S: string; StartP,
  EndP: Integer): string;
begin
  // Returns the data from "StartP" to "EndP" in String "S"
  Result := trim(Copy(S, StartP, EndP - StartP));
end;

function TParentDataProcessor.ExpandTabs(s: string): string;
begin
  // ExpandTabs to 8 Spaces
  Result := StringReplace(S, #09, '        ', [rfReplaceAll]);
end;

procedure TParentDataProcessor.FieldAdd(FieldName, Data: string;
  GenException: Boolean);
begin
  // Adds FieldName and FieldValue to Strings and can generate exception if
  // string is empty
  if (GenException) and (Data = '') then
    raise Exception.create('-- No ' + FieldName + ' Specified --');
  Fieldnames.add(FieldName);
  FieldValues.add(Data);
end;

procedure TParentDataProcessor.MultiFieldAdd(FieldName, Data: string;
  GenException: Boolean);

var
  loop: integer;
  flag: Boolean;
begin
  // Adds FieldName and FieldValue to Multi Field Strings and can generate exception
  // if string is empty

  if (GenException) and (Data = '') then
    raise Exception.create('-- No Multiple Field - ' + FieldName + ' Specified --');

  flag := false;
  loop := 0;
  while (loop < MultiFieldNames.count) and not flag do
  begin
    if MultiFieldNames.Strings[loop] = FieldName then
      flag := true;
    inc(Loop);
  end;

  dec(loop);

  if Flag then
    MultiFieldValues.Strings[loop] := MultiFieldValues.Strings[loop] + ';' + Data
  else
  begin
    MultiFieldNames.add(FieldName);
    MultiFieldValues.add(Data);
  end;
end;

end.