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Split & Promote

Split and Promote are two inverse operations on composite transactions (TRANSFER, FX_CONVERSION, CASH_TRANSFER). Both are implemented in TransactionService as atomic operations within execute_batch().

Concepts

Operation Direction Description
Split Composite → Two independent Break a linked pair into two standalone transactions
Promote Two independent → Composite Merge two standalone transactions into a linked pair

Split

What It Does

A split takes a linked pair (two transactions sharing a link_uuid) and:

  1. Detaches both legs (removes link_uuid from both)
  2. Re-types each leg according to the deterministic Split Type Map:
Source composite type From-leg becomes To-leg becomes
CASH_TRANSFER WITHDRAWAL DEPOSIT
TRANSFER ADJUSTMENT ADJUSTMENT
FX_CONVERSION WITHDRAWAL DEPOSIT
  1. Writes the two modified transactions back — in the same atomic batch

When to Use

  • A broker CSV imported a cross-currency transfer as a single row; BRIM created it as CASH_TRANSFER but the two legs actually belong to different purposes
  • A TRANSFER was created incorrectly and needs to be corrected independently

API

The split is submitted as part of the standard batch endpoint:

POST /transactions/commit
{
  "splits": [
    { "id_a": 101, "id_b": 102 }
  ]
}

Both id_a and id_b must be the two legs of the same linked pair (same link_uuid). Passing unlinked transactions raises a validation error.

Promote

What It Does

Promote merges two independent transactions (no link_uuid) into a new linked composite. The operation is atomic:

  1. Validates that the two transactions are compatible (types, currencies, brokers)
  2. Deletes the two originals
  3. Creates two new linked transactions (same data, new link_uuid, updated types)

This delete-and-recreate approach (rather than update-in-place) ensures balance validation runs cleanly from scratch on the new pair.

Promotion Rules

The allowed promotion pairs are defined in TX_TYPE_METADATA.promote_from rules:

From types Target composite Constraints
DEPOSIT + WITHDRAWAL CASH_TRANSFER Distinct brokers, same currency
DEPOSIT + WITHDRAWAL FX_CONVERSION Same or distinct brokers, different currencies
DEPOSIT + WITHDRAWAL + asset fields TRANSFER Distinct brokers, requires asset_id + quantity

Rule matching is handled by _find_promote_rule_match() and additional constraint checks in _check_promote_constraints().

Promote Suggest

Before promoting manually, clients can call the suggest endpoint to get candidate pairs:

POST /transactions/promote-suggest
{
  "items": [{ "tx_id": 101 }]
}

promote_suggest_bulk() scans accessible transactions and returns ranked candidates compatible with the input transaction, including which composite type would result.

API

POST /transactions/commit
{
  "promotes": [
    {
      "id_a": 201,
      "id_b": 202,
      "new_type": "CASH_TRANSFER"
    }
  ]
}

For TRANSFER promotion, additionally supply asset_id, quantity, and optionally cost_basis_override.

Error Handling

Both operations participate in the standard collect-all-errors pipeline:

  • Errors are reported as TXValidationIssue items in the response
  • A single error in any split or promote item rolls back the entire batch
  • The frontend receives the full set of issues to highlight every problem at once

Common errors:

Code Cause
pairTypeMismatch Split IDs do not belong to the same linked pair
pairSameBroker TRANSFER/CASH_TRANSFER promote attempted with same broker on both sides
promoteIncompatible The two transaction types cannot form any composite
missingField TRANSFER promote missing asset_id or quantity