Table of Contents
Valentina Database Link
Working with tables, a database designer often establishes links between two or more tables.
Starting with Valentina 2.0 the Valentina Database Model extends the traditional relational model by adding the new abstraction: Link.
The adding of the Valentina Link (VLink object) means that developers can use both API and SQL commands to create, delete and modify links between tables, as well as link/unlink records, use links for joins and other database operations - in a new and highly efficient way.
Links are very easy to understand and could probably be considered a reincarnation of links from The Network Database Model.
It is easy to see that links should provide the following features:
- Each link has an unique ID.
- Each link has a unique name in the scope of the database. Link names and table names are in the same scope.
- The database knows about each of its links.
- Each table knows about each of its links.
- You can access a table link by name or index.
- Each link knows what tables it links and how.
Description of Links
Valentina currently offers three kinds of links between 2 tables that implement the VLink2 interface:
Comparison of Links
You can compare the types of Valentina links here:
Links in SQL
- Link Functions - COUNT_LINKED(), MAX_LINKED(), MIN_LINKED(), SUM_LINKED(), etc …
- Operator -> - for M:1 links, as ObjectPtr and ForeignKey.
Refactoring of Links
During the development developer can change the type of a link to better fit its task-specific requirements. This section describes how to change one kind of link into another using Valentina's built-in refactoring features.