fix problem with initialization & refactor types

src/services/migrationService.ts

@@ -1,9 +1,4 @@
-type SqlValue = string | number | null | Uint8Array;
-
-export interface QueryExecResult {
-  columns: Array<string>;
-  values: Array<Array<SqlValue>>;
-}
+import { QueryExecResult } from '../interfaces/database';
 
 interface Migration {
   name: string;
@@ -36,13 +31,17 @@ export class MigrationService {
         id INTEGER PRIMARY KEY AUTOINCREMENT,
         name TEXT NOT NULL UNIQUE,
         executed_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
-      )
+      );
     `);
 
     // Get list of executed migrations
-    const result = await sqlExec('SELECT name FROM migrations');
-    const singleResult = result[0];
-    const executedMigrations = new Set(singleResult.values.map(row => row[0]));
+    const result: QueryExecResult[] = await sqlExec('SELECT name FROM migrations;');
+    let executedMigrations: Set<string> = new Set();
+    // Even with that query, the QueryExecResult may be [] (which doesn't make sense to me).
+    if (result.length > 0) {
+      const singleResult = result[0];
+      executedMigrations = new Set(singleResult.values.map((row: any[]) => row[0]));
+    }
 
     // Run pending migrations in order
     for (const migration of this.migrations) {