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4 Component

4.1 Component introduction

TjanSQL is a Delphi freeware component with source code released under the MOZILLA PUBLIC LICENSE Version 1.1. In fact TjanSQL is not a component but derived from TObject.

4.2 Installation

Please the supplied source files in any folder (e.g. components\jansoft\janSQL) and include the folder in the Delphi library path.

  • janSQL.pas
  • janSQLExpression2.pas
  • janSQLTokenizer.pas
  • janSQLStrings.pas
  • mwStringHashList.pas

Then you create the component as described in TjanSQL Creation.

4.3 janSQLStrings

A small unit with usefull string routines.

4.4 TjanSQL

4.4.1 TjanSQL overview

TjanSQL was designed for ease of use. With just a few methods you can manage a database and display selected data:

function SQLDirect(value:string):integer;
function ReleaseRecordset(arecordset:integer):boolean;
function Error:string;

property RecordSets[index:integer]:TjanRecordSet read getrecordset;
property RecordSetCount:integer read getRecordSetCount;
SQLDirect

Will process a value that consists of one or more semi-colon ; seperated SQL statements and returns 0 in case of failure, -1 in case of valid execution with no resultset, and the number of the result recordset in case of a SELECT statement.

Recordsets

Read-only property to retrieve a reference to a recordset. In janSQL, all collection (records, fields) are 0-based, except for the recordsets collection which is 1-based. In case of a select statement, SQLDirect will return the index of the generated result set.

See Retrieving Data for example code.

ReleaseRecordset

Allows you to release a recordset given the 1-based index of the recordset. You will normally use this after a SELECT resultset has been processed. Returns false in case of failure and true when the recordset was deleted.

RecordSetCount

Returns the number of recordsets. Can be used together with the RecordSets property and the ReleaseRecordset method to clear all recordsets.

Notes

TjanSQL and all helper components clean-up any resources they use automatically when freed.

4.4.2 TjanSQL creation

You do not place TjanSQL on the component palette but create it in e.g. the FormCreate event of your form, and free it in the FormDestroy event of the form. Include janSQL in the uses clause of the interface part of the form.

var
  janSQLDemoF: TjanSQLDemoF;
  appldir:string;
  thefile:string;
  db:TjanSQL;

procedure TjanSQLDemoF.FormCreate(Sender: TObject);
begin
  db:=TjanSQL.create;
end;

procedure TjanSQLDemoF.FormDestroy(Sender: TObject);
begin
  db.free;
end;

4.5 TjanRecordSet

4.5.1 TjanRecordSet Overview

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4.6 TjanRecord

4.6.1 TjanRecord Overview

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4.7 TjanRecordSetList

4.7.1 TjanRecordSetList Overview

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4.8 TjanRecordList

4.8.1 TjanRecordList Overview

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4.9 TjanSQLExpression2

4.9.1 TjanSQLExpression2 Overview

This expression evaluator semi-compiles the expression that you assign, allowing for very fast evaluation.

This component was derived from several other evaluators I wrote in the past. It includes InFix to PostFix conversion. It is tailered for use with TjanSQL, but can be modified for general purpose use.

The evaluator uses only a single data type: variant, and uses a stack for calculations.

When you assign an expression it is tokenized using the TjanSQLTokenizer tokenizer.

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