brotherton-erpnext/erpnext/stock/spec/README.md

Implementation notes for Stock Ledger

Important files

• stock/stock_ledger.py
• controllers/stock_controller.py
• stock/valuation.py

What is in an Stock Ledger Entry (SLE)?

Stock Ledger Entry is a single row in the Stock Ledger. It signifies some modification of stock for a particular Item in the specified warehouse.

• item_code: item for which ledger entry is made
• warehouse: warehouse where inventory is affected
• actual_qty: change in qty
• qty_after_transaction: quantity available after the transaction is processed
• incoming_rate: rate at which inventory was received.
• is_cancelled: if 1 then stock ledger entry is cancelled and should not be used for any business logic except for the code that handles cancellation.
• posting_date & posting_time: Specify the temporal ordering of stock ledger entries. Ties are broken by creation timestamp.
• voucher_type: Many transaction can create SLE, e.g. Stock Entry, Purchase Invoice
• voucher_no: name of the transaction that created SLE
• voucher_detail_no: name of the child table row from parent transaction that created the SLE.
• dependant_sle_voucher_detail_no: cross-warehouse transfers need this reference in order to update dependent warehouse rates in case of change in rate.
• recalculate_rate: if this is checked in/out rates are recomputed on transactions.
• valuation_rate: current average valuation rate.
• stock_value: current total stock value
• stock_value_difference: stock value difference made between last and current entry. This value is booked in accounting ledger.
• stock_queue: if FIFO/LIFO is used this represents queue/stack maintained for computing incoming rate for inventory getting consumed.
• batch_no: batch no for which stock entry is made; each stock entry can only affect one batch number.
• serial_no: newline separated list of serial numbers that were added (if actual_qty > 0) or else removed. Currently multiple serial nos can have single SLE but this will likely change in future.

Implementation of Stock Ledger

Stock Ledger Entry affects stock of combinations of (item_code, warehouse) and optionally batch no if specified. For simplicity, lets avoid batch no. for now.

Stock Ledger Entry table stores stock ledger for all combinations of item_code and warehouse. So whenever any operations are to be performed on said item-warehouse combination stock ledger is filtered and sorted by posting datetime. A typical query that will give you individual ledger looks like this:

select *
from `tabStock Ledger Entry` as sle
where
    is_cancelled = 0  --- cancelled entries don't affect ledger
    and item_code = 'item_code' and warehouse = 'warehouse_name'
order by timestamp(posting_date, posting_time), creation

New entry is just an update to the last entry which is found by looking at last row in the filter ledger.

Serial nos

Serial numbers do not follow any valuation method configuration and they are consumed at rate they were produced unless they are grouped in which case they are consumed at weighted average rate.

Batch Nos

Batches are currently NOT consumed as per batch wise valuation rate, instead global FIFO queue for the item is used for valuation rate.

Creation process of SLEs

• SLE creation is usually triggered by Stock Transactions using a method conventionally named update_stock_ledger() This might not be defined for stock transaction and could be specified somewhere in inheritance hierarchy of controllers.
• This method produces SLE objects which are processed by make_sl_entries in stock_ledger.py which commits the SLE to database.
• update_entries_after class is used to process ONLY the inserted SLE's queue and valuation.
• The change in qty is propagated to future entries immediately. Valuation and queue for future entries is processed in background using repost item valuation.

Accounting impact

• Accounting impact for stock transaction is handled by get_gl_entries() method on controllers. Each transaction has different business logic for booking the accounting impact.