feat: add postgres connection option applicationName (#7989)

docs/connection-options.md

@@ -191,6 +191,8 @@ See [SSL options](https://github.com/mysqljs/mysql#ssl-options).
 
 * `installExtensions` - A boolean to control whether to install necessary postgres extensions automatically or not (default: `true`)
 
+* `applicationName` - A string visible in statistics and logs to help referencing an application to a connection (default: `undefined`)
+
 ## `sqlite` connection options
 
 * `database` - Database path. For example "./mydb.sql"

src/driver/postgres/PostgresConnectionOptions.ts

@@ -67,4 +67,10 @@ export interface PostgresConnectionOptions extends BaseConnectionOptions, Postgr
      * Automatically install postgres extensions
      */
      readonly installExtensions?: boolean;
+
+    /**
+     * sets the application_name var to help db administrators identify
+     * the service using this connection. Defaults to 'undefined'
+     */
+    readonly applicationName?: string;
 }

src/driver/postgres/PostgresDriver.ts

@@ -1101,7 +1101,8 @@ export class PostgresDriver implements Driver {
             database: credentials.database,
             port: credentials.port,
             ssl: credentials.ssl,
-            connectionTimeoutMillis: options.connectTimeoutMS
+            connectionTimeoutMillis: options.connectTimeoutMS,
+            application_name: options.applicationName
         }, options.extra || {});
 
         // create a connection pool

test/functional/driver/postgres/specific-options.ts

@@ -0,0 +1,24 @@
+import "reflect-metadata";
+import { createTestingConnections, closeTestingConnections, reloadTestingDatabases } from "../../../utils/test-utils";
+import { Connection } from "../../../../src/connection/Connection";
+import { expect } from "chai";
+
+describe("postgres specific options", () => {
+  let connections: Connection[];
+  before(async () => connections = await createTestingConnections({
+    enabledDrivers: ["postgres"],
+    driverSpecific: {
+      applicationName: "some test name"
+    }
+  }));
+  beforeEach(() => reloadTestingDatabases(connections));
+  after(() => closeTestingConnections(connections));
+
+  it("should set application_name", () => Promise.all(connections.map(async connection => {
+    const result = await connection.query(
+      "select current_setting('application_name') as application_name"
+    );
+    expect(result.length).equals(1);
+    expect(result[0].application_name).equals("some test name");
+  })));
+});