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.

Valentina currently offers three kinds of links between 2 tables that implement the VLink2 interface:

1. Foreign Key Link.
2. ObjectPtr Link.
3. Binary Link.

• Link Terminology - Discusses such terms of the Link abstraction as Branches, Power, Owner, …
• Pointer Links - Discusses the pointer nature of Foreign Key and ObjectPtr links.
• Valentina Links on Diagrams - Explains how three kinds of Valentina links are shown on diagrams.

You can compare the types of Valentina links here:

• ObjectPtr + RecID Advantages
• Binary Link Advantages
• Foreign Key Advantages

• VLink Class
  • VLink2 Class
    • VBinaryLink Class
    • VObjectPtr Class

• CREATE LINK statement
• ALTER LINK
• DROP LINK statement

• LINK/UNLINK Records
• JOIN ON link_name

• HIERARCHICAL (RECURSIVE) QUERIES

• Link Functions - COUNT_LINKED(), MAX_LINKED(), MIN_LINKED(), SUM_LINKED(), etc …
• Operator -> - for M:1 links, as ObjectPtr and ForeignKey.

• Valentina Link Properties

• SHOW LINKS
• SHOW PROPERTIES OF LINK

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.

• Link Refactoring Overview

• Convert or Copy Foreign Key to ObjectPtr
• Convert ObjectPtr to Foreign Key

• Convert ForeignKey to BinaryLink
• Convert BinaryLink to ForeignKey

• Convert ObjectPtr to BinaryLink
• Convert BinaryLink to ObjectPtr

• Convert M:M Table to BinaryLink M:M
• BinaryLink to MM Table with ObjectPtr
• BinaryLink to MM Table with FK

• Convert 1:M Link to M:M Table

• Foreign Key Manual Optimization
• Automatic Optimization