Add support for jobs & queueables, migrations

- Create migration directives & migrators
- Modify Cache classes to support array manipulation
- Create Redis unit and RedisCache implementation
- Create Queueable base class and Queue class that uses Cache backend

src/orm/connection/Connection.ts

@@ -1,4 +1,4 @@
-import {ErrorWithContext} from '../../util'
+import {Awaitable, ErrorWithContext} from '../../util'
 import {QueryResult} from '../types'
 import {SQLDialect} from '../dialect/SQLDialect'
 import {AppClass} from '../../lifecycle/AppClass'
@@ -68,6 +68,13 @@ export abstract class Connection extends AppClass {
      */
     public abstract schema(name?: string): Schema
 
+    /**
+     * Execute all queries logged to this connection during the closure
+     * as a transaction in the database.
+     * @param closure
+     */
+    public abstract asTransaction<T>(closure: () => Awaitable<T>): Awaitable<T>
+
     /**
      * Fire a QueryExecutedEvent for the given query string.
      * @param query

src/orm/connection/PostgresConnection.ts

@@ -2,7 +2,7 @@ import {Connection, ConnectionNotReadyError} from './Connection'
 import {Client} from 'pg'
 import {Inject} from '../../di'
 import {QueryResult} from '../types'
-import {collect} from '../../util'
+import {Awaitable, collect} from '../../util'
 import {SQLDialect} from '../dialect/SQLDialect'
 import {PostgreSQLDialect} from '../dialect/PostgreSQLDialect'
 import {Logging} from '../../service/Logging'
@@ -70,6 +70,17 @@ export class PostgresConnection extends Connection {
         }
     }
 
+    public async asTransaction<T>(closure: () => Awaitable<T>): Promise<T> {
+        if ( !this.client ) {
+            throw new ConnectionNotReadyError(this.name, { config: JSON.stringify(this.config) })
+        }
+
+        await this.client.query('BEGIN')
+        const result = await closure()
+        await this.client.query('COMMIT')
+        return result
+    }
+
     public schema(name?: string): Schema {
         return new PostgresSchema(this, name)
     }