Fix review comments

- Combine the various exported types; the only API surface is now the
  `PluginDatabaseClientFactory` which is a free function.
- Rename to the SingleConnectionManager class.
- Refactor the PluginEnvironment type to use databaseClientFactory for
  clarity.
- Fix mergeDatabaseConfig to not override the input dictionary.

packages/create-app/templates/default-app/packages/backend/src/index.ts

@@ -8,14 +8,12 @@
 
 import Router from 'express-promise-router';
 import {
-  ensureDatabaseExists,
   createServiceBuilder,
   loadBackendConfig,
   getRootLogger,
   useHotMemoize,
   notFoundHandler,
-  SingleDatabaseConfiguration,
-  SingleDatabaseManager,
+  SingleConnectionManager,
   SingleHostDiscovery,
   UrlReaders,
 } from '@backstage/backend-common';
@@ -34,15 +32,20 @@ function makeCreateEnv(config: ConfigReader) {
 
   root.info(`Created UrlReader ${reader}`);
 
-  const databaseConfig = new SingleDatabaseConfiguration(
-    config.getConfig('backend.database'),
-  )
-  const databaseManager = new SingleDatabaseManager(databaseConfig);
+  const databaseManager = new SingleConnectionManager(
+    config.getConfig('backend.database')
+  );
 
   return (plugin: string): PluginEnvironment => {
     const logger = root.child({ type: 'plugin', plugin });
-    const databaseFactory = databaseManager.getDatabaseFactory(plugin);
-    return { logger, database: databaseFactory, config, reader, discovery };
+    const databaseFactory = databaseManager.getDatabaseClientFactory(plugin);
+    return {
+      logger,
+      databaseClientFactory: databaseFactory,
+      config,
+      reader,
+      discovery
+    };
   };
 }
 
@@ -50,11 +53,6 @@ async function main() {
   const configs = await loadBackendConfig();
   const configReader = ConfigReader.fromConfigs(configs);
   const createEnv = makeCreateEnv(configReader);
-  await ensureDatabaseExists(
-    configReader.getConfig('backend.database'),
-    'backstage_plugin_catalog',
-    'backstage_plugin_auth',
-  );
 
   const catalogEnv = useHotMemoize(module, () => createEnv('catalog'));
   const scaffolderEnv = useHotMemoize(module, () => createEnv('scaffolder'));

packages/create-app/templates/default-app/packages/backend/src/plugins/auth.ts

@@ -3,9 +3,14 @@ import { PluginEnvironment } from '../types';
 
 export default async function createPlugin({
   logger,
-  database,
+  databaseClientFactory,
   config,
   discovery,
 }: PluginEnvironment) {
-  return await createRouter({ logger, config, database, discovery });
+  return await createRouter({
+    logger,
+    config,
+    database: databaseClientFactory,
+    discovery
+  });
 }

packages/create-app/templates/default-app/packages/backend/src/plugins/catalog.ts

@@ -14,11 +14,14 @@ export default async function createPlugin({
   logger,
   config,
   reader,
-  database,
+  databaseClientFactory,
 }: PluginEnvironment) {
   const locationReader = new LocationReaders({ logger, reader, config });
 
-  const db = await DatabaseManager.createDatabase(database, { logger });
+  const db = await DatabaseManager.createDatabase(
+    await databaseClientFactory(),
+    { logger },
+  );
   const entitiesCatalog = new DatabaseEntitiesCatalog(db);
   const locationsCatalog = new DatabaseLocationsCatalog(db);
   const higherOrderOperation = new HigherOrderOperations(

packages/create-app/templates/default-app/packages/backend/src/types.ts

@@ -1,11 +1,14 @@
-import Knex from 'knex';
 import { Logger } from 'winston';
 import { Config } from '@backstage/config';
-import { PluginEndpointDiscovery, UrlReader } from '@backstage/backend-common';
+import {
+  PluginDatabaseClientFactory,
+  PluginEndpointDiscovery,
+  UrlReader
+} from '@backstage/backend-common';
 
 export type PluginEnvironment = {
   logger: Logger;
-  database: Knex;
+  databaseClientFactory: PluginDatabaseClientFactory;
   config: Config;
   reader: UrlReader
   discovery: PluginEndpointDiscovery;