Prevent username reusing

migration/1563757595828-UsedUsername.ts

@@ -0,0 +1,13 @@
+import {MigrationInterface, QueryRunner} from "typeorm";
+
+export class UsedUsername1563757595828 implements MigrationInterface {
+
+    public async up(queryRunner: QueryRunner): Promise<any> {
+        await queryRunner.query(`CREATE TABLE "used_username" ("username" character varying(128) NOT NULL, "createdAt" TIMESTAMP WITH TIME ZONE NOT NULL, CONSTRAINT "PK_78fd79d2d24c6ac2f4cc9a31a5d" PRIMARY KEY ("username"))`);
+    }
+
+    public async down(queryRunner: QueryRunner): Promise<any> {
+        await queryRunner.query(`DROP TABLE "used_username"`);
+    }
+
+}