wehub-resource-sync
65 lines
1.6 KiB
Markdown
65 lines
1.6 KiB
Markdown
# Joining Tables
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`perspective.join()` creates a read-only `Table` by joining two source tables on
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a shared key column. The result is reactive — it updates automatically when
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either source table changes. See [`Join`](../../explanation/join.md) for
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conceptual details.
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## Basic Inner Join
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```python
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orders = perspective.table([
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{"id": 1, "product_id": 101, "qty": 5},
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{"id": 2, "product_id": 102, "qty": 3},
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{"id": 3, "product_id": 101, "qty": 7},
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])
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products = perspective.table([
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{"product_id": 101, "name": "Widget"},
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{"product_id": 102, "name": "Gadget"},
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])
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joined = perspective.join(orders, products, "product_id")
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view = joined.view()
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json = view.to_json()
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```
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## Join Types
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Pass `join_type` to select inner, left, or outer join behavior:
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```python
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# Left join: all left rows, nulls for unmatched right columns
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left_joined = perspective.join(left, right, "id", join_type="left")
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# Outer join: all rows from both tables
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outer_joined = perspective.join(left, right, "id", join_type="outer")
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```
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## Reactive Updates
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The joined table recomputes automatically when either source table is updated:
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```python
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left = perspective.table([{"id": 1, "x": 10}])
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right = perspective.table([{"id": 2, "y": "b"}])
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joined = perspective.join(left, right, "id")
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view = joined.view()
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json = view.to_json()
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# [] — no matching keys yet
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right.update([{"id": 1, "y": "a"}])
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json = view.to_json()
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# [{"id": 1, "x": 10, "y": "a"}] — new match detected
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```
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## Async Client
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The async client has the same API:
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```python
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joined = await client.join(orders, products, "product_id", join_type="left")
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```
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