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Revise link table guidelines in DESIGN-PRINCIPLES.md #238

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Revise link table guidelines in DESIGN-PRINCIPLES.md #238

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9 changes: 3 additions & 6 deletions DESIGN-PRINCIPLES.md
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Expand Up @@ -239,12 +239,9 @@ The following columns should be present in all tables unless there is a compelli

## Link Tables

- Link tables should have an `id` column that is separate from the foreign keys.
- Often, this column is not used, but consistency is preferred over eliminating redundancy.
- Link tables should have a `link_` prefix, and the table names should be singular or plural depending on the relationship. e.g.:
- one-to-one: `link_apple_orange`
- one-to-many: `link_apple_oranges`
- many-to-many: `link_apples_oranges`
- Link tables should NOT have an `id` column that is separate from the foreign keys.
- This key is often redundant and never used -- a link table is typically referenced by the two linking tables.
- Link tables should always be in the format of `link_{table_a}__{table_b}`, and the tables should always be in alphabetical order, to avoid confusion when remembering which comes first.
- Link tables should have unique constraints reflective of the particular relationship:
- one-to-one: separate unique constraints on each foreign key column
- one-to-many: unique constraint on the `one` column
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