JUNCTION OBJECT/ INTERSECTION OBJECT IN SALESFORCE

This post talks about how to create M:M relationship in Salesforce.

Salesforce platform has a funny way of maintaining M:M relationship.

In general, for many-to-many related objects, everybody would think, when we pick/ map data from one object, the system would create an association and maintain the relationship. But in case of standard page layouts, we will have to create the association link manually. We're gonna see how.

Requirement: Cases may have multiple Bugs; Bugs may have multiple Cases.

Solution: Create a junction Object.

Cool thing to say, heh. But u wont find a junction object anywhere in your set up. Then how would you create it?
Please do the steps from the following link, directly from salesforce.
https://ap1.salesforce.com/help/doc/en/relationships_manytomany.htm

The real thing behind the scenes is that, we are manually creating the record that holds the relationship.

Let me put it this way for you.

In general, the m:m relationship is dealt in the following way.

Objects A and B have m:m relationship. The intersection table C is created. The child records of B appear under A, and Child records of A appear under B, when they are identified, the system automatically creates a record in C holding primary keys from both the tables.

But in salesforce we are clearly opening intersection table (junction object) and manually creating the record  there. Like in the previous example, BugCaseAssociation is the proof of it. There is no escape from it. we have to create it, add it has a child and map the other table record from a look-up.

Hope that gives better understanding.