fix(schema): do not cache knex instance

When a database is missing, the ensuring mechanism is reconnecting, hence the cached
knex instance becomes outdated. Instead of replacing it, it's better to use a getter
and always have up to date value.

Closes #3713

packages/knex/src/schema/SchemaGenerator.ts

@@ -13,7 +13,6 @@ import { SchemaComparator } from './SchemaComparator';
 export class SchemaGenerator extends AbstractSchemaGenerator<AbstractSqlDriver> {
 
   private readonly helper = this.platform.getSchemaHelper()!;
-  private readonly knex = this.connection.getKnex();
   private readonly options = this.config.get('schemaGenerator');
 
   /** @deprecated use `dropSchema` and `createSchema` commands respectively */
@@ -586,4 +585,8 @@ export class SchemaGenerator extends AbstractSchemaGenerator<AbstractSqlDriver>
     return tmp ? tmp + append : '';
   }
 
+  private get knex() {
+    return this.connection.getKnex();
+  }
+
 }

packages/migrations/src/MigrationStorage.ts

@@ -7,7 +7,6 @@ import type { MigrationRow } from './typings';
 export class MigrationStorage implements UmzugStorage {
 
   private readonly connection = this.driver.getConnection();
-  private readonly knex = this.connection.getKnex();
   private readonly helper = this.driver.getPlatform().getSchemaHelper()!;
   private masterTransaction?: Transaction;
 
@@ -110,4 +109,8 @@ export class MigrationStorage implements UmzugStorage {
     return { tableName, schemaName };
   }
 
+  private get knex() {
+    return this.connection.getKnex();
+  }
+
 }