C++ Object Persistency Using Object/Relational Databases
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C++ Object Persistency Using Object/Relational Databases


Master's Thesis

Petr Čermák

Charles University in Prague
Faculty of Mathematics and Physics

April 2009

Abstract

This thesis deals with design and implementation of a library providing object-relational mapping services for programs written in C++. Emphasis is put on its transparency and ease of its use. To achieve these goals the library uses GCCXML, a XML output extension to GCC. GCCXML helps the library to get description of the class model used in the user application and to simulate the reflection.

For the mapping purposes, new object-relational database features are discussed and a new mapping type is proposed.

Implementation of the library is based on three related projects - the POLiTe, POLiTe 2 and IOPC libraries. The proposed and implemented library unifies them into one solid, flexible and extensible platform. Thanks to its modular architecture, the resulting library can be used in several configurations providing subsets of implemented services - database access, reflection and object-relational mapping.

Table of Contents

1. Introduction
2. Persistence layer requirements
The identity of persistent objects
Database mapping requirements
Object-relational databases
Database mapping requirements continued
Querying
Caching
Reflection
Library architecture
Conclusion
3. Evolution of the IOPC 2 library
POLiTe
Architecture
The data access layer
Metamodel and object-relational mapping.
Persistent object manipulation
Querying
Conclusion
POLiTe 2
Architecture of the POLiTe 2 library
The cache layer
Persistent object manipulation
Querying
Conclusion
IOPC
Features of the library
Architecture of the library
IOPC SP
IOPC DBSC
IOPC LIB
Conclusion
Library comparison
4. Basic concepts of the IOPC 2 library
Library architecture
Obtaining metamodel description
Object relational mapping in the IOPC 2 library
Base classes
ADT mapping
Mapping algorithm prerequisites
The mapping algorithm
Conclusion
5. Architecture of the IOPC 2 library
Architecture overview
Common services
Thread synchronization classes
Class metadata
Utilities
Database access
Basic classes
Driver features
The metamodel
The metamodel classes
Enhanced data types
Class metadata
iopcsp
Usage transparency differences from IOPC
The persistence layer - iopclib
Database mapping
Persistent object manipulation
The cache layer
Querying
6. Conclusion
References
A. User's guide
Library initialization and termination
Inspecting objects with reflection
Class metadata
Basic database access
Driver features
Driver implementation
Persistent object manipulation
Querying persistent objects
Caching
B. Sample schema SQL scripts
C. Metadata overview
D. DVD content

List of Figures

1.1. IOPC 2 evolution
2.1. Example class hierarchy
2.2. Vertical mapping tables
2.3. Horizontal mapping tables
2.4. Filtered mapping tables
2.5. Combined mapping tables
2.6. Proposed architecture of the O/R mapping library
3.1. Architecture of the POLiTe library
3.2. POLiTe persistent object states
3.3. POLiTe references
3.4. Architecture of the POLiTe 2 library
3.5. Caches in the POLiTe 2 library
3.6. States of the POLiTe 2 objects
3.7. Dereferencing DbPtr in POLiTe 2
3.8. The IOPC library workflow
3.9. POLiTe library components used in IOPC LIB
3.10. Structure of the IOPC LIB
4.1. Reflection using the GCCXML
4.2. IOPC 2 base classes
4.3. SQL schema generated from classes using combined mapping
4.4. Top-level part of the object-relational mapping algorithm
4.5. Description of the Insert_Row method. Not used for ADT mapping.
4.6. Inserting objects using filtered mapping
4.7. Iterative loading algorithm
5.1. Overview of the IOPC 2 architecture
5.2. Basic classes of the database layer
5.3. Using the decorator pattern
5.4. Oracle 10g database driver extensions and driver features
5.5. The iopcmeta classes
5.6. Structure of the enhanced data type classes
5.7. Classes involved in the database mapping process
5.8. Classes manipulating with persistent objects
5.9. The bePersistent operation
5.10. Database pointer and cache pointer interaction
5.11. Interaction with the O/R mapping services
5.12. Basic classes of the cache layer. VoidCache architecture.
5.13. Extended interface of the cache layer.
5.14. The Query classes

 

List of Tables

A.1. Library configurations and their initialization/termination routines

 

List of Examples

2.1. Using object types in Oracle
2.2. Accessing objects in Oracle
2.3. Nested tables in Oracle
2.4. References in Oracle
2.5. A polymorphic query using object-relational features of the Oracle database.
3.1. Definition of a class in the POLiTe library
3.2. Associations in the POLiTe library
3.3. Persistent object manipulation
3.4. Queries in the POLiTe library
3.5. Persistent object manipulation in the POLiTe 2 library
3.6. Executing queries in the POLiTe 2 library
3.7. Definition of persistent classes in IOPC
3.8. XML metamodel description file
4.1. Basic persistent class definition in IOPC 2
4.2. GCCXML output
4.3. IOPC SP output
4.4. DatabaseObject usage
4.5. SQL schema generated for DatabaseObject subclasses.
4.6. SQL schema generated for OidObject subclasses.
4.7. Using the ADT mapping.
4.8. SQL schema from classes that use ADT mapping.
4.9. Loading objects using ADTs from an Oracle database
5.1. Connecting to an Oracle database in IOPC 2
5.2. Type traits
5.3. Using the reflection interface
5.4. Enhanced datatype usage
5.5. Java annotations and C# attributes
5.6. Example usage of metadata in the IOPC 2 library
5.7. Friend type description declaration
5.8. Using the ScriptsGenerator to create required database schema.
5.9. Using the bePersistent method
5.10. Example query in IOPC 2
Next
Chapter 1. Introduction