FEATURES

General Information
Schema issues
ModelGenerator
Selections and Manipulations
Database transformation
Supported platforms

General Information

The Database Access Library is a C++ Class Library that stores C++ objects in relational databases. It takes care of all issues related to the transformation of C++ objects to SQL-relations without compromising the features of the object-oriented paradigm.

Schema issues

• Easy persistency for C++ Classes
  You can make any C++ class persistent by making it a subclass of the supplied class Instance and adding three simple methods.
• Support for many different datatypes
  The database access library supports the following datatypes for persistent attributes: signed/unsigned int, signed/unsigned long, float, double float, bool and the supplied fullfeatured classes: String, Timestamp and Blob.
• Simple to use bidirectional associations
  The database access library supplies classes for support of associations between classes. These associations can be indicated as one-to-many relations or many-to-many relations. They are bidirectional. This means that if two instances A and B are related you can find A from B and B from A. The library will make sure these associations are always consistent. In fact it is only necessary to set one side of the association the library will set the other.
• Support for restricted or cascading removal of associated instances
  One-to-Many associations can be indicated as restricted or cascading. A restricted association wil make sure that if you try to remove an instance that is related via this association to one or more other instances the removal of the instance is prohibited by the library. If the association is cascading the associated instances will be removed with it.
• Inheritance between classes
  The library supports single inheritence between classes. In this case a subclass will inherit all attributes and associations of its superclass.
• Abstract classes
  You can indicate a class as abstract. Such a class can not have persistent instances.
• Versioning mechanism
  The library supports a schema versioning mechanism. Both the whole model as the inidividual classes have a version that is used to generate and update schema's in the underlying database.
• Object-Identity through surrogates
  Each instance is automatically given a database wide unique identity that will stay unchanged during the lifetime of the instance.

ModelGenerator

• Maintain your class model interactively
  The Database Access Library comes with an application called the ModelGenerator that can define and manipulate your class model.
• Generate headerfile for use with the library
  The ModelGenerator can generate C++-header files that define your class model for the Database Access Library.
• Build with DALC++ itself
  The ModelGenerator is build with the DALC++ itself so it can use all database that you have drivers for, supports a multi-user environment has multilevel undo/redo, etc. The source code is included so you can see for yourself how easy it is to build such an application with the Database Access Library.

Selections and Manipulations

• Add, update, associate and remove instances
  You can add, update, associate and remove instances with one statement.
• Full transaction support with client-side commit and rollback
  The library fully supports transactions. All changes made will be stored in the database when you specify a commit command or rollbacked on request. When something goes wrong during the commit, the transaction will be automatically aborted. When a transaction is rollbacked all changes made in the transaction will be undone both in the database and in the client.
• C++ Query language
  You can use C++ as a flexible and easy to use query language to select instances from the database.
• Polymorphic Selections
  Specified queries will take the inheritance relations into account. This means that when you select instances of a superclass, you will also receive instances of its subclasses.
• Navigational Selections
  The library will automatically select associated instances when you navigate over associations.
• Client-side Cache
  The library will manage a client-side cache to increase performance of navigational style selections.
• Garbage Collection of persistent instances
  The library will take care of the memory management of the persistent instances. It is never necessary to delete allocated memory for persistent instances. For this the library makes use of smart pointers. It is NOT based on a reference count mechanism, so there are no problems with cycles in associations. The garbage collection mechanism can also be activated explicitely.
• Support for the Subject-Observer design pattern with events
  Persistent Instances will issue events for changes that have taken place. This makes it possible for multiple observers to keep track of changes to these objects.
• Multilevel undo/redo mechanism
  With one statement you can undo and redo previous transactions

Database transformation

• Driver mechanism to support multiple databases
  You can switch from one kind of database to the other with just changing the parameters for one statement.
• Optimized drivers
  The driver mechanism makes it possible to utilize all features of the specific database to optimize performance. For instance when possible it will make use of stored procedures.
• Automatic schema creation
  The library will create tables, indices and stored procedures when connecting to a database where the right version of these tables are not available. This does not exclude the option for DBA's to tune the database objects.
• Optimistic Locking Strategy
  Through a mechanism of instance versions the library will track changes made by others. When it detect a multi-user conflict it will rollback the transaction automatically and alert the user to the incident.
• Optional Explicit Locking
  Instances can be locked explicitely to prevent a possible rollback when necessary.
• Referential integrity
  The library will make sure that the referential integrity in the database is not violated.

Supported platforms

• Operating systems
  Win32 platforms (Windows 95/98/NT/2000).
• Databases
  MS-Access, MS-SQLServer and Oracle 8 or higher.
• Compilers
  MS-Visual C++, Borland C++ Builder.