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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Add self.upstream property for pre-restricted ancestor access in make()","articleBody":"## Summary\n\nInside `make()`, provide `self.upstream` — a pre-constructed `Diagram.trace(self \u0026 key)` — as a property on auto-populated tables. This gives `make()` convenient, provenance-safe access to pre-restricted ancestor table expressions.\n\n## Context\n\nDiscussion: #1232\nDepends on: #1423 (`Diagram.trace()`)\nRelated: #242 (farfetch)\n\n## Design\n\nThe `make(self, key)` signature stays unchanged. `self.upstream` is simply a new property available during `make()` execution:\n\n```python\ndef make(self, key):\n    # Read from upstream — pre-restricted by key\n    session_date = self.upstream[Session].fetch1(\"session_date\")\n    traces = self.upstream[ExtractTraces].to_arrays(\"trace\")\n\n    # All query operators work — upstream[Table] returns a QueryExpression\n    self.upstream[Session].aggr(self.upstream[Scan], n='count(scan_id)')\n\n    # Write to self\n    self.insert1({**key, \"result\": compute(traces)})\n```\n\n**Read from `self.upstream`, write to `self`.** The read/write boundary is the provenance boundary.\n\n- `self.upstream` only exposes declared ancestors and their part tables — requesting anything else raises an error\n- `key` is passed as before — no signature changes, no redundancy\n- `make_kwargs` work unchanged\n- Existing code that doesn't use `self.upstream` is completely unaffected\n\n### Implementation\n\n- The framework sets `self.upstream = Diagram.trace(self \u0026 key)` before calling `make()`\n- `self.upstream[TableClass]` returns pre-restricted `QueryExpression` objects with full fetch capabilities\n- Requesting a table outside the declared ancestor graph raises `DataJointError`","author":{"url":"https://github.com/dimitri-yatsenko","@type":"Person","name":"dimitri-yatsenko"},"datePublished":"2026-04-04T00:50:03.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/1424/datajoint-python/issues/1424"}