1. Basic CodeGen
* Many-to-Many Relationships
<< * Reverse Relationships (One-to-One and One-to-Many)   |   Back to Main   |   Defining Relationships without Foreign Keys >>

View Source
will open in a new window
Using Association Tables
Qcodo also supports handling many-to-many relationships. Typically, many-to-many relationships are mapped in the database using an Association Table (sometimes also called a Mapping or a Join Table). It is basically a two-column table where both columns are Foreign Keys to two different tables.

Qcodo allows you to define a set suffix for all Association Tables (the default is "_assn"). Whenever the code generator sees any table that ends in "_assn", it will mark it as a special table to be used/analyzed as an Association Table, associating two objects together in a many-to-many relationship. With the Association Table in place, Qcodo will generate five methods each for the two classes involved in this many-to-many relationship. In our example, we created a team_member_project_assn table to represent a many-to-many relationship between Person and Project.

Qcodo will generate the following five methods in Person to deal with this many-to-many relationship: Qcodo will also generate the following five methods in Project to deal with this many-to-many relationship: Note that the structure of these five methods are very similar for both objects (get, count, associate, unassociate, and unassociate all). In fact, you will also notice that this is the same structure as the reverse one-to-many relationship in our previous example. This especially makes sense considering that for all three examples, the object is dealing with the "-to-many" side of the relationship. Regardless if it is a one-"to-many" or a many-"to-many", the five methods dealing with "-to-many" is consistent.

Also, similar to our previous example, note that the "AsTeamMember" token in all these methods are there because we named the Association Table in the database team_member_project_assn. If we simply named it person_project_assn, then the methods would be named without the "AsTeamMember" token (e.g. "GetProjectArray", "AssociatePerson", etc.)

Person's Many-to-Many Relationship with Project (via team_member_project_assn)

Person ID: 2
First Name: Kendall
Last Name: Public

Listing of the Project(s) that This Person is a Team Member of
• ACME Website Redesign
• State College HR System
• ACME Payment System

There are 3 project(s) that this person is a team member of.


Project's Many-to-Many Relationship with Person (via team_member_project_assn)

Project ID: 1
Project Name: ACME Website Redesign

Listing of the Person(s) that This Project has as Team Members
• Kendall Public
• Alex Smith
• Wendy Smith
• Karen Wolfe
• Samantha Jones

There are 5 person(s) that this project has as team members.