fix: Silent failure in createDatabase and dropDatabase with Postgres (typeorm#7590)

* feat: implement database creation and dropping on postgres' query runner

* implement the createDatabase, dropDatabase and hasDatabase methods on postgres' query runner

Closes typeorm#6867

* test: add postgres driver on database creation and dropping tests

* Set ifNotExist=false when testing with postgres' driver

* fix: Modify ifNotExist parameter handling on postgres' database creation

* Add empty promise return when ifNotExist is true and the specified database already exists on postgres' query runner
* Set ifNotExist as true on the database creation and dropping tests

Author: PauloRSF

src/driver/postgres/PostgresQueryRunner.ts

@@ -271,7 +271,8 @@ export class PostgresQueryRunner extends BaseQueryRunner implements QueryRunner
      * Checks if database with the given name exist.
      */
     async hasDatabase(database: string): Promise<boolean> {
-        return Promise.resolve(false);
+        const result = await this.query(`SELECT * FROM pg_database WHERE datname='${database}';`);
+        return result.length ? true : false;
     }
 
     /**
@@ -320,18 +321,29 @@ export class PostgresQueryRunner extends BaseQueryRunner implements QueryRunner
 
     /**
      * Creates a new database.
-     * Postgres does not supports database creation inside a transaction block.
+     * Note: Postgres does not support database creation inside a transaction block.
      */
     async createDatabase(database: string, ifNotExist?: boolean): Promise<void> {
-        await Promise.resolve();
+        if (ifNotExist) {
+            const databaseAlreadyExists = await this.hasDatabase(database);
+            
+            if (databaseAlreadyExists)
+                return Promise.resolve();
+        }
+
+        const up = `CREATE DATABASE "${database}"`;
+        const down = `DROP DATABASE "${database}"`;
+        await this.executeQueries(new Query(up), new Query(down));
     }
 
     /**
      * Drops database.
-     * Postgres does not supports database drop inside a transaction block.
+     * Note: Postgres does not support database dropping inside a transaction block.
      */
     async dropDatabase(database: string, ifExist?: boolean): Promise<void> {
-        return Promise.resolve();
+        const up = ifExist ? `DROP DATABASE IF EXISTS "${database}"` : `DROP DATABASE "${database}"`;
+        const down = `CREATE DATABASE "${database}"`;
+        await this.executeQueries(new Query(up), new Query(down));
     }
 
     /**

test/functional/query-runner/create-and-drop-database.ts

@@ -8,7 +8,7 @@ describe("query runner > create and drop database", () => {
     before(async () => {
         connections = await createTestingConnections({
             entities: [__dirname + "/entity/*{.js,.ts}"],
-            enabledDrivers: ["mysql", "mssql", "cockroachdb"],
+            enabledDrivers: ["mysql", "mssql", "cockroachdb", "postgres"],
             dropSchema: true,
         });
     });