Object Oriented Persistence Middleware in Praxis

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Object Oriented Persistence Middleware in Praxis
A Motivation B Concept C Objects for DB
operations D Mapper and Parameters E
Attribute mapping F building the SQL
Statements

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Motivation (initial architecture)

• low cost of implementation at first

• change on DB may result in massive change on
  program
• bound to one type of DB

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Motivation (new architecture)

• change on DB results only in change on access
  layer
• only SQL builder is bound to type of DB

• high cost of implementation at first

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Concept
2-Way Concept

• 1. Select a List of Indexes of Table

• 2. Select/Insert/Update/Delete Data Row by Row

• business object holds all relevant data of a table

• navigation with First, Next, Last, Prev

• LoadAll for loading of objects, internally only
  keys

• when operating with object call to functions
  LoadCurrentObject, SaveCurrentObject,
  DeleteCurrentObject

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Objects for DB operations

• to perform BD operations with help of Mapper

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SQL

• z.B. SELECT
• SELECT Table.Column AS ColumnName,
• FROM Table,
• WHERE Table.Column X AND
• (ORDER BY Table.Column, )

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Mapper and Parameters

• to perform BD operations with help of Mapper

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Attribute mapping

• Table
• Key 1 2 3

• one attribute object represents one column
• attributes name, columnname, tablename,
  datatype, iskeyattribute isprimarykey,
  joinattribute nullcolumn
• all attributes to one table are stored in one list

must have unique property on single Column
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Attribute mapping
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building the SQL Statements
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example code

• procedure TIvuSelectSqlStatement.SetSqlSelect(aSql
  Objecte TObjectList)
• var
• i integer // interner Zähler
• begin
• Select Initalisieren
• FSqlSelect ''
• (Select-liste)
• for i 0 to aSqlObjecte.Count - 2
• do begin
• if TSqlParameter(aSqlObjecte.Itemsi).Verbind
  ungsTyp svtAs
• then begin
• if TSqlParameter(aSqlObjecte.Itemsi).Wert.
  Count gt 0
• then begin
• FSqlSelect FSqlSelect
• // Bezeichner
• TSqlParameter(aSqlObjecte.It
  emsi).Bezeichner ' '
• // AS
• GetSqlStatementAs
  ' '

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screenshots
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screenshots