Add UI/dropdown menu consideration to enum vs lookup table comparison

Mention that lookup tables can be queried to dynamically populate
dropdown menus in graphical interfaces and dashboards, avoiding
hardcoded values in the application.

Author: claude

book/30-design/050-relationships.ipynb

@@ -951,7 +951,7 @@
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-   "source": "## Enums vs. Lookup Tables for Valid Values\n\nIn the `Enrollment` example above, we used an **enum** to restrict `grade` to valid values: `enum('A', 'B', 'C', 'D', 'F', 'IP')`.\nAn alternative approach uses a **lookup table** to define valid grades.\n\nBoth approaches enforce data integrity, but they have different trade-offs:\n\n`````{tab-set}\n````{tab-item} Using Enum\n:sync: enum\n```python\n@schema\nclass Enrollment(dj.Manual):\n    definition = \"\"\"\n    -> Student\n    -> Course\n    ---\n    enrollment_date : date\n    grade : enum('A', 'B', 'C', 'D', 'F', 'IP')\n    \"\"\"\n```\n````\n````{tab-item} Using Lookup Table\n:sync: lookup\n```python\n@schema\nclass LetterGrade(dj.Lookup):\n    definition = \"\"\"\n    grade : char(2)\n    ---\n    grade_point = null : decimal(3,2)\n    description : varchar(30)\n    \"\"\"\n    contents = [\n        ('A', 4.00, 'Excellent'),\n        ('B', 3.00, 'Good'),\n        ('C', 2.00, 'Satisfactory'),\n        ('D', 1.00, 'Passing'),\n        ('F', 0.00, 'Failing'),\n        ('IP', None, 'In Progress'),\n    ]\n\n@schema\nclass EnrollmentWithLookup(dj.Manual):\n    definition = \"\"\"\n    -> Student\n    -> Course\n    ---\n    enrollment_date : date\n    -> LetterGrade\n    \"\"\"\n```\n````\n`````\n\n```{list-table} Enum vs. Lookup Table Comparison\n:header-rows: 1\n:widths: 15 42 43\n\n* - Aspect\n  - Enum\n  - Lookup Table\n* - **Associated data**\n  - Cannot store additional attributes (e.g., grade points)\n  - Can include related data like grade points, descriptions\n* - **Modifications**\n  - Requires `ALTER TABLE` to add/remove values\n  - Add or remove rows without schema changes\n* - **Querying**\n  - Values are inline; no join needed\n  - Requires join to access the value or related data\n* - **Referential integrity**\n  - Enforced by column type\n  - Enforced by foreign key constraint\n* - **Complexity**\n  - Simple, self-contained\n  - Additional table to manage\n* - **Reuse**\n  - Must repeat enum definition in each table\n  - Single source of truth; multiple tables can reference it\n```\n\n```{admonition} When to Use Each Approach\n:class: tip\n\n**Use enums when:**\n- The set of values is small and unlikely to change\n- No additional attributes are associated with each value\n- You want to minimize schema complexity\n\n**Use lookup tables when:**\n- Values need associated attributes (e.g., grade points, descriptions)\n- The set of values may change without requiring schema migration\n- Multiple tables reference the same set of values\n- You need to query or report on the valid values themselves\n```\n\n```{seealso}\nSee the [Lookup Tables](020-lookup-tables.ipynb) chapter for more details on creating and using lookup tables.\n```",
+   "source": "## Enums vs. Lookup Tables for Valid Values\n\nIn the `Enrollment` example above, we used an **enum** to restrict `grade` to valid values: `enum('A', 'B', 'C', 'D', 'F', 'IP')`.\nAn alternative approach uses a **lookup table** to define valid grades.\n\nBoth approaches enforce data integrity, but they have different trade-offs:\n\n`````{tab-set}\n````{tab-item} Using Enum\n:sync: enum\n```python\n@schema\nclass Enrollment(dj.Manual):\n    definition = \"\"\"\n    -> Student\n    -> Course\n    ---\n    enrollment_date : date\n    grade : enum('A', 'B', 'C', 'D', 'F', 'IP')\n    \"\"\"\n```\n````\n````{tab-item} Using Lookup Table\n:sync: lookup\n```python\n@schema\nclass LetterGrade(dj.Lookup):\n    definition = \"\"\"\n    grade : char(2)\n    ---\n    grade_point = null : decimal(3,2)\n    description : varchar(30)\n    \"\"\"\n    contents = [\n        ('A', 4.00, 'Excellent'),\n        ('B', 3.00, 'Good'),\n        ('C', 2.00, 'Satisfactory'),\n        ('D', 1.00, 'Passing'),\n        ('F', 0.00, 'Failing'),\n        ('IP', None, 'In Progress'),\n    ]\n\n@schema\nclass EnrollmentWithLookup(dj.Manual):\n    definition = \"\"\"\n    -> Student\n    -> Course\n    ---\n    enrollment_date : date\n    -> LetterGrade\n    \"\"\"\n```\n````\n`````\n\n```{list-table} Enum vs. Lookup Table Comparison\n:header-rows: 1\n:widths: 15 42 43\n\n* - Aspect\n  - Enum\n  - Lookup Table\n* - **Associated data**\n  - Cannot store additional attributes (e.g., grade points)\n  - Can include related data like grade points, descriptions\n* - **Modifications**\n  - Requires `ALTER TABLE` to add/remove values\n  - Add or remove rows without schema changes\n* - **Querying**\n  - Values are inline; no join needed\n  - Requires join to access the value or related data\n* - **Referential integrity**\n  - Enforced by column type\n  - Enforced by foreign key constraint\n* - **Complexity**\n  - Simple, self-contained\n  - Additional table to manage\n* - **Reuse**\n  - Must repeat enum definition in each table\n  - Single source of truth; multiple tables can reference it\n* - **UI integration**\n  - Values must be hardcoded in application\n  - Query the table to populate dropdown menus dynamically\n```\n\n```{admonition} When to Use Each Approach\n:class: tip\n\n**Use enums when:**\n- The set of values is small and unlikely to change\n- No additional attributes are associated with each value\n- You want to minimize schema complexity\n\n**Use lookup tables when:**\n- Values need associated attributes (e.g., grade points, descriptions)\n- The set of values may change without requiring schema migration\n- Multiple tables reference the same set of values\n- You need to query or report on the valid values themselves\n- Graphical interfaces or dashboards need to populate dropdown menus—querying a lookup table provides the options dynamically without hardcoding values in the application\n```\n\n```{seealso}\nSee the [Lookup Tables](020-lookup-tables.ipynb) chapter for more details on creating and using lookup tables.\n```",
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