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feat: add piece_count and piece_size fields to BomItem for cut-to-length parts - #12422

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feat: add piece_count and piece_size fields to BomItem for cut-to-length parts#12422
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Summary

Addresses #10274

Manufacturing BOMs frequently require multiple pieces of a specific size cut from continuous stock (cables, tubing,
structural profiles). Currently the only way to express "10 pieces of 250mm cable" is to enter the total length (2.5m)
as quantity, which loses the piece-count information that purchasing and production need.

Changes

Adds two optional fields to BomItem:

  • piece_count: number of discrete pieces required (default: 1)
  • piece_size: size/length of each piece (e.g. "250 mm")

When piece_size is specified, the total quantity is auto-calculated as piece_count × piece_size, maintaining full
backward compatibility (existing items effectively have piece_count=1 and empty piece_size).

Backend

  • New model fields with migration
  • Updated recalculate_quantity() to compute total from piece_count × piece_size when piece_size is set
  • Added fields to BOM item hash for validation checksum

API

  • Serializer exposes piece_count and piece_size fields

Frontend

  • BOM creation/edit form includes the new fields
  • BOM table shows piece_count and piece_size as optional (hidden by default) columns

Example

A BOM line for "10 pieces of 250mm aluminum profile" (part units: m):

  • piece_count: 10
  • piece_size: "250 mm"
  • Auto-calculated quantity: 2.5 (meters)

This preserves the per-piece information for production while correctly computing total material requirement for
purchasing.

…gth parts

Manufacturing BOMs frequently require multiple pieces of a specific size
cut from continuous stock (cables, tubing, structural profiles). Currently
the only way to express "10 pieces of 250mm cable" is to enter the total
length (2.5m) as quantity, which loses the piece-count information that
purchasing and production need.

This adds two optional fields to BomItem:
- piece_count: number of discrete pieces required (default: 1)
- piece_size: size/length of each piece (e.g. "250 mm")

When piece_size is specified, the total quantity is auto-calculated as
piece_count × piece_size, maintaining full backward compatibility (existing
items effectively have piece_count=1 and empty piece_size).

Changes:
- Backend: new model fields, migration, updated recalculate_quantity()
  logic, hash_fields for BOM validation
- API: serializer exposes piece_count and piece_size
- Frontend: BOM form includes the new fields, BOM table shows them as
  optional columns

Addresses inventree#10274
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@SchrodingersGat

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@amanjain57-gif an interesting idea here, thanks for submitting.

I think that you can achieve this with a single additional field, not two.

If you remove the "piece_size" field and just use quantity, then the additional "piece_count" field can be used to reflect multiple pieces.

e.g. a BOM with multiple lengths of wire

Field Value Description
quantity 200mm Length of individual cut wires
piece_count 10 10x separate multiples of 200mm

Thus the total requirement is 2m of wire, but we can see it is in 10x pieces of 200mm

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Reduce to a single additional field as discussed

Remove the piece_size field entirely. The existing quantity field already
represents the per-piece size/length, so piece_count multiplied by
quantity gives the total material requirement.

Example: quantity=200mm, piece_count=10 → total 2m of wire in 10 pieces.

Changes:
- Remove piece_size model field, serializer field, and frontend column/form
- Update migration to only add piece_count
- Update get_required_quantity() to multiply by piece_count
- Restore original recalculate_quantity() without piece_size logic
@amanjain57-gif

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Thanks for the feedback! Simplified to a single piece_count field as suggested. quantity now represents per-piece size, and total material = quantity × piece_count. Removed piece_size from model, migration, serializer, and frontend.

@SchrodingersGat

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@amanjain57-gif thanks for the updates.

Can you please also add some unit tests here, for (at least) the following:

  • Expected "quantity required" calculations based on the new field
  • API GET / POST tests for the new field

@SchrodingersGat

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You will also need to add comprehensive documentation for the new extension

@amanjain57-gif

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@SchrodingersGat Working on both requests:

  1. Unit tests — Adding tests for get_required_quantity() calculations with piece_count, API GET/POST/PATCH tests for the new field, and validation tests (default=1, positive-only).
  2. Documentation — Adding a section to the BOM docs explaining piece_count with examples (e.g., quantity=200mm, piece_count=10, total=2m of wire).

Will push shortly.

@amanjain57-gif

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Done — pushed unit tests and documentation:

Tests added (11 total):

  • 6 model-level tests: default value, quantity multiplier calculation, interactions with attrition/setup_quantity/rounding, and validation (rejects 0 and negatives)
  • 5 API tests: GET returns piece_count, POST with/without piece_count, PATCH updates, invalid values return 400

Documentation:

  • Added piece_count to the BOM Line Items table in docs/docs/manufacturing/bom.md
  • Added a "Piece Count (Cut-to-Length Parts)" section with the formula, two worked examples (wire harness, hydraulic tubing with attrition), and usage tips
  • Added to BOM Checksum fields list

@amanjain57-gif

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Fixed ruff check failure — replaced Unicode multiplication sign (×) with plain x in docstrings (RUF002).

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2 participants