Music Store Management Platform

Domain Design: Inventory

Version 1.2  |  Updated: Repair Parts Inventory, Bulk Materials, Suppliers



# 1. Overview

The Inventory domain manages all physical items in the store across three distinct inventories: sale inventory (items sold at POS), rental fleet (instruments held for rental), and repair parts inventory (materials consumed in repairs). Each inventory type has different tracking requirements, pricing models, and accounting treatment.



# 2. Inventory Types

Type

Tracking

Appears at POS

Examples

Sale — serialized

Per unit (serial #)

Yes — retail price

Guitars, trumpets, keyboards

Sale — non-serialized

Quantity on hand

Yes — retail price

Strings, reeds, books, picks

Rental fleet

Per unit (serial #)

No — rental only

Student rental instruments

Repair parts — discrete

Qty on hand (integer)

No — repair use only

Valve guides, springs, pads

Repair parts — bulk

Qty on hand (decimal)

No — repair use only

Bow hair, cork sheet, solder

Dual-use

Qty on hand (integer)

Yes — also used in repairs

Strings used in setups, valve oil

Shop supplies

Qty on hand (decimal)

No — overhead cost only

Cleaning patches, lubricant, sandpaper



# 3. Sale Inventory Schema

## 3.1 product

A product is the catalog definition — what an item is, not a specific physical unit. Applies to sale and rental fleet items.

Column

Type

Notes

id

uuid PK



company_id

uuid FK

Tenant scoping

location_id

uuid FK

Physical location — inventory is tracked per-location

sku

varchar

Store SKU

upc

varchar

Manufacturer barcode

name

varchar



description

text



brand

varchar



model

varchar



category_id

uuid FK

Product category

is_serialized

boolean

True = tracked per unit

is_rental

boolean

True = rental fleet item

is_dual_use_repair

boolean

True = also usable in repairs

cost

numeric(10,2)

Supplier cost

price

numeric(10,2)

Default retail price

min_price

numeric(10,2)

Minimum allowed sell price

rental_rate_monthly

numeric(10,2)

Default monthly rental rate

qty_on_hand

integer

Non-serialized items only

qty_reorder_point

integer

Low stock alert threshold

legacy_id

varchar

AIM inventory ID

created_at

timestamptz





## 3.2 inventory_unit

Individual physical units for serialized items and rental fleet instruments.

id, product_id, company_id, location_id, serial_number, condition (varchar — references item_condition lookup), status (varchar — references inventory_unit_status lookup), purchase_date, purchase_cost, notes, legacy_id, created_at

**Note:** `condition` and `status` are stored as varchar columns referencing slug values in lookup tables (not pgEnums). This allows stores to add custom statuses and conditions. Code references system slugs for business logic; custom values are informational.

### Lookup Tables

Both `inventory_unit_status` and `item_condition` are company-scoped lookup tables with the pattern:

Column | Type | Notes
id | uuid PK |
company_id | uuid FK | Tenant scoping
name | varchar | Display name
slug | varchar | Code-level reference (unique per company)
description | text |
is_system | boolean | True = seeded by system, cannot be deleted or deactivated
sort_order | integer | Display ordering
is_active | boolean |
created_at | timestamptz |

### System Status Values (seeded per company)

Status | Description | Set By
available | In stock, ready for sale or rental | Default, return, restock
sold | Purchased by customer | Sale transaction
rented | Out on active rental contract | Rental activation
on_trial | Out with customer on in-home trial | In-home trial checkout (07_Domain_Sales_POS.md §9)
in_repair | In repair shop for service | Repair intake
layaway | Reserved for layaway customer, not available | Layaway creation (08_Domain_Payments_Billing.md §9)
lost | Unrecovered — trial, rental, or inventory discrepancy | Overdue escalation or cycle count
retired | Permanently removed from inventory | Manual retirement

### System Condition Values (seeded per company)

Condition | Description
new | Brand new, unopened or unused
excellent | Like new, minimal signs of use
good | Normal wear, fully functional
fair | Noticeable wear, functional with minor issues
poor | Heavy wear, may need repair



# 4. Repair Parts Inventory

Repair parts are a completely separate inventory from sale items. They are never sold at POS, never appear in the sales catalog, and are tracked specifically for repair cost accounting. The repair parts inventory is accessible only through the repairs module (MOD-REPAIRS).



## 4.1 Part Types

Part Type

Description

Invoice Treatment

billable

Parts charged to customer. Tracked at cost and bill rate.

Appears as line item on invoice at bill_rate

shop_supply

Consumed in repairs but not billed individually. Overhead cost.

Does not appear on invoice

dual_use

Also exists in sale inventory. Repair use decrements sale stock.

Billed at repair rate or retail

flat_rate_material

Material bundled into a flat-rate service charge. E.g. bow hair in a rehair service.

Included in flat rate line item — not itemized



## 4.2 Discrete vs Bulk Parts

Material Type

Tracked As

Examples

Discrete

Integer quantity — whole units only

Valve guides, pad sets, bridge blanks, spring sets

Bulk

Decimal quantity — fractional units allowed

Bow hair (hank), cork sheet, solder (spool), varnish (ml)

Bulk consumable

Decimal — consumed by drops/grams/ml

Lubricant, pad cement, shellac, jewelers rouge



## 4.3 repair_part

Column

Type

Notes

id

uuid PK



company_id

uuid FK

Tenant scoping

location_id

uuid FK

Physical location — repair parts stock is per-location

name

varchar

e.g. 'Bow Hair — Natural White (Standard)'

description

text



part_number

varchar

Manufacturer or supplier part number

part_type

enum

billable | shop_supply | dual_use | flat_rate_material

is_bulk

boolean

True = fractional qty tracking

unit_of_measure

varchar

each | hank | sheet | roll | spool | ml | gram | drop

qty_on_hand

numeric(10,3)

Decimal supports fractional bulk quantities

qty_reorder_point

numeric(10,3)

Low stock alert threshold

cost_per_unit

numeric(10,4)

What store pays per unit — 4 decimal places for small fractions

bill_rate_per_unit

numeric(10,2)

Nullable — what customer is charged per unit if billed per unit

billing_type

enum

per_unit | flat_rate | shop_supply

product_id

uuid FK

Nullable — links to sale inventory for dual_use parts

supplier_id

uuid FK

Primary supplier for reorders

instrument_categories

text[]

Which instrument types use this part

notes

text



is_active

boolean



created_at

timestamptz





## 4.4 repair_part_usage_template

Predefined templates define how much of a bulk material a specific job consumes. Technicians select a template rather than entering quantities manually. Particularly important for bow hair where qty varies by instrument size.



Column

Type

Notes

id

uuid PK



company_id

uuid FK

Tenant scoping

repair_part_id

uuid FK

Which part this template applies to

template_name

varchar

e.g. 'Full size violin bow rehair'

instrument_type

varchar

violin | viola | cello | bass | fractional | other

instrument_size

varchar

4/4 | 3/4 | 1/2 | 1/4 | 1/8 | full

qty_used

numeric(10,3)

Amount consumed e.g. 1.0 hank, 0.67 hank

billing_type

enum

per_unit | flat_rate | shop_supply

flat_rate_desc

varchar

Customer-facing description if flat rate

flat_rate_amount

numeric(10,2)

Nullable — flat rate bill amount

sort_order

integer

Display order in picker UI

created_at

timestamptz





### Default Bow Hair Templates (System Seeded)

Template Name

Instrument

Qty Used

Typical Flat Rate

Full size violin/viola rehair

violin/viola

1.0 hank

$45-55 (store sets)

Cello bow rehair

cello

0.67 hank

$65-80

Bass bow rehair

bass

0.75 hank

$85-100

3/4 violin rehair

violin

0.75 hank

$35-45

1/2 violin rehair

violin

0.60 hank

$30-40

1/4 violin rehair

violin

0.50 hank

$25-35

1/8 and smaller

violin

0.40 hank

$20-30



## 4.5 repair_part_usage

Records each part consumed in a repair ticket. One record per part type per ticket. Referenced by repair_ticket for invoice generation and cost accounting.

Column

Type

Notes

id

uuid PK



repair_ticket_id

uuid FK



repair_part_id

uuid FK

Nullable for custom flat-rate entries

template_id

uuid FK

Nullable — set if selected from template

qty_used

numeric(10,3)

Actual quantity consumed

unit_of_measure

varchar

Recorded at time of use

unit_cost

numeric(10,4)

Cost at time of use — historical accuracy

total_cost

numeric(10,2)

qty_used * unit_cost

billing_type

enum

per_unit | flat_rate | shop_supply

billed_amount

numeric(10,2)

Amount on invoice — 0 for shop_supply

invoice_description

varchar

Customer-facing line item description

created_at

timestamptz





## 4.6 Bulk Material Examples

Material

Unit

Type

Notes

Bow hair — natural white standard

hank

flat_rate_material

Used via templates by bow size

Bow hair — natural white premium

hank

flat_rate_material

Higher grade — higher flat rate

Bow hair — black

hank

flat_rate_material

Bass/cello preference

Cork sheet — 1mm

sheet

billable

Cut to size for neck corks etc

Cork sheet — 2mm

sheet

billable

Thicker applications

Solder — silver bearing

spool

shop_supply

Overhead — not billed

Pad leather — natural

sheet

billable

Cut to size per pad

Shellac flakes

gram

shop_supply

Overhead

Pad cement

ml

shop_supply

Overhead

Valve oil (bulk)

bottle

shop_supply

Overhead — retail valve oil is separate sale item

Cleaning patches

each

shop_supply

Discrete but overhead

Abrasive paper — 220 grit

sheet

shop_supply

Overhead

Resonators — mylar

sheet

billable

Tone holes — billed per replacement

Fingerboard ebony blank

each

billable

Discrete — billed per blank used

Jewelers rouge

gram

shop_supply

Overhead



# 5. Supplier Management

Suppliers are the vendors from whom the store purchases repair parts and sale inventory. Common music repair suppliers include RS Musical, Ferree's Tools, and Allied Supply. Supplier records enable reorder tracking and purchase order generation.



## 5.1 supplier

Column

Type

Notes

id

uuid PK



company_id

uuid FK

Tenant scoping

name

varchar

e.g. 'RS Musical', 'Ferree’s Tools'

contact_name

varchar

Primary contact

email

varchar



phone

varchar



website

varchar



account_number

varchar

Store’s account number with this supplier

payment_terms

varchar

e.g. Net 30, COD, prepaid

notes

text



is_active

boolean



created_at

timestamptz





# 6. Repair Parts Reporting

- Parts on hand — current stock levels across all repair parts

- Low stock alerts — parts at or below reorder point

- Parts usage by period — which parts consumed most frequently

- Parts cost per repair ticket — material cost breakdown

- Technician material usage — parts consumed per technician

- Shop supply expense by period — overhead cost tracking

- Gross margin per repair — revenue vs labor cost vs parts cost

- Bow hair usage analysis — hanks used per month, yield per hank by bow type

- Reorder suggestions — parts below reorder point with preferred supplier



# 7. Business Rules

- Repair parts never appear in sale inventory search or POS catalog

- Dual-use parts decrement sale inventory qty_on_hand when used in repair

- Bulk qty_on_hand uses numeric(10,3) — supports fractional units down to 0.001

- cost_per_unit uses numeric(10,4) — supports very small per-unit costs for bulk materials

- Usage templates are store-configurable — seeded defaults provided, store can modify

- Shop supply parts reduce qty_on_hand but generate no invoice line item

- Flat-rate billing combines material + labor into one customer-facing line item

- Parts cost always recorded at time of use — price changes do not affect historical records

- Negative qty_on_hand not permitted — system warns technician when stock is insufficient



# 8. Instrument Sizing

String instruments come in fractional sizes — critical for rentals, school orders, and customer matching. Size is tracked on both the product catalog and individual inventory units.

## 8.1 Size Values

Size | Instruments | Notes
4/4 (full) | Violin, viola, cello, bass, guitar | Default adult size
3/4 | Violin, cello, bass, guitar | Older students, smaller adults
1/2 | Violin, cello, bass | Intermediate students
1/4 | Violin, cello | Younger students
1/8 | Violin | Beginner young students
1/10 | Violin | Smallest common size
1/16 | Violin | Rare — very young students
15" | Viola | Measured in inches for viola
15.5" | Viola | Common intermediate
16" | Viola | Full-size standard
16.5" | Viola | Large full-size

## 8.2 Schema Changes

**product** — add column:

Column | Type | Notes
instrument_size | varchar | Nullable — only set for sized instruments. Free text to support both fractional (1/2) and inch (15.5") formats.

**inventory_unit** — add column:

Column | Type | Notes
instrument_size | varchar | Nullable — size of this specific physical unit. May differ from product default (e.g. product "Yamaha Model 5 Violin" has units in multiple sizes).

## 8.3 Business Rules

- Size is optional — only relevant for sized instruments (strings, some guitars)
- Product-level size is the default/catalog size — inventory units can override per-unit
- Size is searchable and filterable in product lists and POS lookup
- Rental matching: when a student needs a size, search filters by instrument_size
- Size changes on rental returns are common (student grew) — logged in rental history



# 9. Inventory Cycle Counts

Physical inventory reconciliation ensures system counts match actual shelf counts. Cycle counts can be full-store or targeted (by category, location area, or supplier).

## 9.1 count_session

Column | Type | Notes
id | uuid PK |
company_id | uuid FK | Tenant scoping
location_id | uuid FK | Which location is being counted
name | varchar | e.g. "Q1 2025 Full Count", "Guitar Room Spot Check"
count_type | enum | full | category | spot
status | enum | draft | in_progress | review | completed | cancelled
category_id | uuid FK | Nullable — set if count_type = category
started_by | uuid FK | Employee who initiated
started_at | timestamptz | When counting began
completed_at | timestamptz | When finalized
notes | text |
created_at | timestamptz |

## 9.2 count_entry

One row per product counted in a session. For serialized products, one row per unit.

Column | Type | Notes
id | uuid PK |
count_session_id | uuid FK |
product_id | uuid FK |
inventory_unit_id | uuid FK | Nullable — set for serialized items
expected_qty | integer | System qty at time count started
counted_qty | integer | Physical count entered by staff
variance | integer | counted_qty - expected_qty (computed)
counted_by | uuid FK | Employee who counted this item
counted_at | timestamptz | When this entry was recorded
notes | text | Explanation for variance
created_at | timestamptz |

## 9.3 count_adjustment

When a count session is completed, variances are applied as inventory adjustments. Each adjustment is an auditable record.

Column | Type | Notes
id | uuid PK |
count_session_id | uuid FK |
count_entry_id | uuid FK |
product_id | uuid FK |
inventory_unit_id | uuid FK | Nullable
previous_qty | integer | qty_on_hand before adjustment
adjusted_qty | integer | qty_on_hand after adjustment
adjustment_reason | enum | cycle_count | damaged | stolen | found | data_entry_error
approved_by | uuid FK | Manager who approved the adjustment
approved_at | timestamptz |
created_at | timestamptz |

## 9.4 Cycle Count Workflow

1. Manager creates count session — selects scope (full, category, or spot check)
2. System snapshots expected quantities for all products in scope
3. Staff count physical inventory — enter counts per product/unit
4. System calculates variances and flags discrepancies
5. Manager reviews variances — adds reason codes for each
6. Manager approves adjustments — qty_on_hand updated, adjustment records created
7. Session marked completed — immutable after completion

## 9.5 Business Rules

- Count sessions lock affected products from sale/receiving while in_progress — prevents count drift
- Variances above a configurable threshold (default: 5% or $50 value) require manager approval
- All adjustments are append-only audit records — never modified after creation
- Serialized items: count confirms unit is present and in expected status
- Completed sessions cannot be reopened — start a new session to re-count
- Spot checks do not lock inventory — used for quick verification without disrupting sales



# 10. Purchase Orders

Formal purchase order workflow extends the existing stock_receipt flow. POs track what was ordered, what was received, and flag discrepancies.

## 10.1 purchase_order

Column | Type | Notes
id | uuid PK |
company_id | uuid FK | Tenant scoping
location_id | uuid FK | Receiving location
po_number | varchar | Human-readable PO number (auto-generated)
supplier_id | uuid FK |
status | enum | draft | submitted | partial | received | cancelled
order_date | date | When PO was sent to supplier
expected_date | date | Expected delivery date
received_date | date | When fully received
subtotal | numeric(10,2) | Sum of line totals
shipping_cost | numeric(10,2) |
tax | numeric(10,2) |
total | numeric(10,2) |
notes | text | Internal notes or special instructions
created_by | uuid FK | Employee who created
created_at | timestamptz |
updated_at | timestamptz |

## 10.2 purchase_order_line

Column | Type | Notes
id | uuid PK |
purchase_order_id | uuid FK |
product_id | uuid FK |
supplier_sku | varchar | Supplier's SKU for this product
description | varchar | Line item description
qty_ordered | integer |
qty_received | integer | Updated as items arrive — default 0
unit_cost | numeric(10,2) | Agreed cost per unit
line_total | numeric(10,2) | qty_ordered * unit_cost
created_at | timestamptz |

## 10.3 Three-Way Match

When receiving against a PO, the system compares:
1. **PO line** — what was ordered (qty_ordered, unit_cost)
2. **Packing slip** — what supplier says they shipped (entered by staff at receiving)
3. **Physical count** — what actually arrived (counted by staff)

Discrepancies flagged: short shipment, over shipment, wrong item, cost mismatch.

## 10.4 PO → Stock Receipt Flow

- Receiving against a PO auto-creates stock_receipt records for each line received
- stock_receipt.purchase_order_id links receipt back to originating PO
- Partial receives update PO status to "partial" — remaining lines stay open
- Final receive updates PO status to "received"

## 10.5 Business Rules

- POs in draft status are editable — submitted POs are locked (create new revision if needed)
- Supplier auto-populated from product's preferred supplier if set
- Unit cost defaults to last stock_receipt cost for that product from that supplier
- PO approval workflow optional — configurable threshold requiring manager sign-off
- Cancelled POs retained for audit — soft cancel with reason code
- Reorder report: products below qty_reorder_point generate suggested PO lines grouped by preferred supplier



# 11. Product Bundles & Kits

Bundles group multiple products into a single sellable item at a package price. Common in music retail: instrument + case + accessories starter packs.

## 11.1 product_bundle

Column | Type | Notes
id | uuid PK |
company_id | uuid FK | Tenant scoping
product_id | uuid FK | The bundle's parent product record (is_bundle = true)
created_at | timestamptz |

## 11.2 product_bundle_item

Column | Type | Notes
id | uuid PK |
bundle_id | uuid FK | References product_bundle
component_product_id | uuid FK | The included product
qty | integer | How many of this component per bundle (default 1)
sort_order | integer | Display order in bundle breakdown
created_at | timestamptz |

## 11.3 Schema Changes

**product** — add column:

Column | Type | Notes
is_bundle | boolean | Default false. True = this product is a bundle of other products.

## 11.4 Pricing Models

Model | Description
fixed | Bundle has a set price — component prices ignored at POS
sum_discount | Bundle price = sum of component prices minus a bundle discount (percent or fixed)

Bundle price is stored on the parent product.price field. The pricing model determines how the discount is displayed on receipts (single line vs itemized with discount).

## 11.5 Inventory Behavior

- Bundle does not have its own qty_on_hand — availability derived from component stock
- Bundle is "in stock" only if ALL components are in stock at required quantities
- Selling a bundle decrements each component product's qty_on_hand (or marks serialized units as sold)
- Stock receipt never targets a bundle directly — components are received individually
- Low stock alert triggers if any component falls below its reorder point

## 11.6 Business Rules

- A bundle component cannot itself be a bundle (no nesting)
- Bundles appear in POS search like any product — clearly labeled as bundle
- Receipt shows bundle name and price, with component breakdown below
- Returning a bundle returns all components — partial bundle returns handled as individual item returns
- Bundle price must be less than or equal to sum of component prices (enforced at creation)



# 12. Barcode Label Printing

Bulk label printing for inventory receiving, repricing, and cycle count preparation.

## 12.1 Label Templates

Template | Use Case | Content
standard_price | Shelf labels | SKU, name, price, barcode (UPC or SKU)
serialized | Individual units | Serial number, SKU, name, barcode (serial)
clearance | Sale items | SKU, name, original price (struck), sale price, barcode
receiving | Incoming stock | SKU, name, price, received date, barcode
bundle | Bundle items | Bundle name, bundle price, component list, barcode

## 12.2 Print Jobs

Label printing is triggered from:
- **Stock receipt** — auto-prompt to print labels for received items
- **Price change** — bulk print updated labels for repriced items
- **Cycle count prep** — print labels for products missing barcodes
- **Manual** — select products from inventory list, choose template, print

## 12.3 Technical

- Labels rendered server-side as PDF (ZPL support planned for thermal printers)
- Standard label sizes: 1.25" x 0.875" (Dymo), 2" x 1" (thermal roll), 4" x 6" (shipping)
- Barcode formats: Code 128 (SKU-based), UPC-A (manufacturer UPC), QR code (serial number)
- Print queue supports batching — up to 500 labels per job



# 13. Backorders

Customer order queue for out-of-stock items. Tracks demand and notifies customers when stock arrives.

## 13.1 backorder

Column | Type | Notes
id | uuid PK |
company_id | uuid FK | Tenant scoping
location_id | uuid FK |
product_id | uuid FK | What was requested
account_id | uuid FK | Who wants it
member_id | uuid FK | Nullable — specific member on account
qty | integer | Quantity requested
status | enum | pending | ordered | received | fulfilled | cancelled
purchase_order_line_id | uuid FK | Nullable — linked to PO when ordered from supplier
deposit_transaction_id | uuid FK | Nullable — if deposit collected
notes | text |
requested_date | date | When customer placed backorder
fulfilled_date | date | When customer received item
created_by | uuid FK | Employee who took the order
created_at | timestamptz |
updated_at | timestamptz |

## 13.2 Workflow

1. Customer wants an out-of-stock product — staff creates backorder
2. Optional: collect deposit via POS (deposit_transaction_id recorded)
3. When creating next PO for that supplier, backorder quantities surfaced as suggested lines
4. Stock receipt against PO triggers backorder match — status updated to "received"
5. Staff notified to contact customer — notification sent via preferred channel
6. Customer picks up item — backorder marked "fulfilled", deposit applied to sale

## 13.3 Business Rules

- Multiple backorders can exist for the same product — filled in request date order (FIFO)
- Backorder quantities included in reorder report alongside reorder point calculations
- Cancelled backorders refund any deposit collected
- Backorder demand report: shows products with pending backorders — informs purchasing decisions