README
This repository contains an Active Record schema to represent a bill of materials. A bill of
materials is an Assembly that may contain sub_assemblies and parts. A bill of materials does
not belong to any other assembly. Assemblies and parts can both have a unique identifier that canno
be shared by any other part or assembly.
To accomplish this goal, the schema contains three main features. First, it contains a self-join
table to connect one assembly to another. An assembly can belong to multiple parent assemblies because through this join table called AssemblyRelationship. The join table also has a sub_assembly_quantity column to track how many sub_assemblies belong to the parent assembly. Moreover, the AssemblyRelationship also has a custom validation to ensure that an assembly cannot belong to itself.
The assemblies can also have many parts through a join table called AssemblyPart. This way, a part can belong to many assemblies. This join table also has a column called part_quantity to record how many parts belong to a particular assembly.
The bill of goods can be created by loading the bill of materials with its own parts, along with all of its sub-assemblies and all of their sub-assemblies and parts, recursively. In production, I would probably write a method to eagerly load each of these components of the bill of materials.
Lastly, every part and assembly is id_taggable which means that they can have a single IdTag. Through polymorphic associations, we can track the type and id of the part or assembly that the id tag belongs to.