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Docs: Remove separate index for leftmost column in multi-index #5595

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Oct 7, 2023
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Docs: Remove separate index for leftmost column in multi-index #5595

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4 changes: 2 additions & 2 deletions guides/contexts.md
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Original file line number Diff line number Diff line change
Expand Up @@ -621,12 +621,12 @@ We generated a new resource inside our `ShoppingCart` named `CartItem`. This sch
timestamps()
end

create index(:cart_items, [:cart_id])
- create index(:cart_items, [:cart_id])
create index(:cart_items, [:product_id])
+ create unique_index(:cart_items, [:cart_id, :product_id])
```

We used the `:delete_all` strategy again to enforce data integrity. This way, when a cart or product is deleted from the application, we don't have to rely on application code in our `ShoppingCart` or `Catalog` contexts to worry about cleaning up the records. This keeps our application code decoupled and the data integrity enforcement where it belongs – in the database. We also added a unique constraint to ensure a duplicate product is not allowed to be added to a cart. With our database tables in place, we can now migrate up:
We used the `:delete_all` strategy again to enforce data integrity. This way, when a cart or product is deleted from the application, we don't have to rely on application code in our `ShoppingCart` or `Catalog` contexts to worry about cleaning up the records. This keeps our application code decoupled and the data integrity enforcement where it belongs – in the database. We also added a unique constraint to ensure a duplicate product is not allowed to be added to a cart. As with the `product_categories` table, using a multi-column index lets us remove the separate index for the leftmost field (`cart-id`). With our database tables in place, we can now migrate up:

```console
$ mix ecto.migrate
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