Add database structure documentation

README.md

@@ -90,6 +90,10 @@ The application is setup for deployment on Fly.io - just make sure you edit
 
 See the `.github` folder.
 
+## Architecture
+
+See the `docs` folder.
+
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docs/database_structure.md

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+# Database Structure
+
+This document describes the database structure of the Music Library application.
+
+## Entity Relationship Diagram
+
+```mermaid
+erDiagram
+    RECORDS {
+        uuid id PK
+        string type
+        string format
+        string title
+        uuid musicbrainz_id
+        string[] genres
+        string cover_url
+        blob cover_data
+        string cover_hash
+        map musicbrainz_data
+        string[] release_ids
+        string[] included_release_group_ids
+        datetime purchased_at
+        string release
+        map artists
+        datetime inserted_at
+        datetime updated_at
+    }
+
+    RECORDS_SEARCH_INDEX {
+        uuid id PK
+        string type
+        string format
+        string title
+        uuid musicbrainz_id
+        string[] genres
+        string[] release_ids
+        string[] included_release_group_ids
+        string cover_hash
+        datetime purchased_at
+        string release
+        map artists
+    }
+
+    ARTIST_RECORDS {
+        uuid musicbrainz_id
+        uuid record_id
+        map artist
+    }
+
+    RECORDS ||--o{ RECORDS_SEARCH_INDEX : "syncs via triggers"
+    RECORDS ||--o{ ARTIST_RECORDS : "extracted from artists JSON"
+```
+
+## Tables Description
+
+### Records
+
+The main table storing music records. Key features:
+
+- Uses UUID as primary key
+- Stores basic record information (title, type, format, year)
+- Includes MusicBrainz integration with IDs and additional data
+- Stores cover image data and URLs
+- Embeds artists data directly in a JSON field
+- Includes timestamps for record keeping
+
+### Records Search Index
+
+A virtual FTS5 (Full Text Search) table that mirrors the records table for efficient searching:
+
+- Automatically synced with the records table via triggers
+- Optimized for full-text search operations
+- Contains most fields from the records table
+- Some fields are marked as UNINDEXED for efficiency
+
+### Views
+
+#### Artist Records View
+
+A view that extracts artist information from the embedded JSON in the records table:
+
+```sql
+CREATE VIEW artist_records AS
+  SELECT json_extract(json_each.value, '$.musicbrainz_id') AS musicbrainz_id,
+  records.id AS record_id,
+  json_each.value as artist
+  FROM records,
+  json_each(records.artists)
+```
+
+### Triggers
+
+The following triggers maintain the search index:
+
+1. `records_search_index_before_update`: Removes old record data from search index before updates
+2. `records_search_index_before_delete`: Removes record data from search index before deletion
+3. `records_after_insert`: Inserts new record data into search index after record creation
+4. `records_after_update`: Updates record data in search index after record updates
+
+### Indices
+
+The following indices are maintained for performance:
+
+1. On `records`:
+   - `format`
+   - `title`
+   - `musicbrainz_id`
+   - `purchased_at`
+   - `included_release_group_ids`
+   - `release_ids`
+
+## Notes
+
+1. The database uses SQLite as the primary database.
+2. Artists data is embedded directly in the records table as JSON/map data, rather than having a separate table.
+3. The search index is implemented using SQLite's FTS5 extension for efficient full-text search capabilities.
+4. Where needed queries use SQLite's `unicode` extension to filter/sort over UTF-8 data.
+5. The database supports both collection and wishlist functionality through the `purchased_at` field:
+   - Records with `purchased_at IS NOT NULL` are in the collection
+   - Records with `purchased_at IS NULL` are in the wishlist
+