anchor.diff:    Library buildOrmBaseLibrary(AssetId inputId, OrmBuildContext ctx) {
       return new Library((lib) {
         // Necessary imports
  -      lib.directives.addAll([
  -        new Directive.import('dart:async'),
  -        new Directive.import(p.basename(inputId.uri.path)),
  -      ]);
  +      var imports = new SplayTreeSet<String>.from(
  +          ['dart:async', p.basename(inputId.uri.path)]);
  +
  +      switch (ctx.ormAnnotation.type) {
  +        case OrmType.mongoDB:
  +          imports.add('package:mongo_dart/mongo_dart.dart');
  +          break;
  +        case OrmType.postgreSql:
  +          imports.add('package:postgres/postgres.dart');
  +          break;
  +        default:
  +          break;
  +      }
  +
  +      lib.directives.addAll(imports.map((url) => new Directive.import(url)));
   
         // Add the corresponding `part`
         String dbExtension;
  
positive.code:           throw 'Unsupported ORM type: ${ctx.ormAnnotation.type}';
        }
  
        var dbFile =
            p.setExtension(p.basename(inputId.uri.path), '.$dbExtension.orm.g.dart');
  
        lib.body.add(new Code("part '$dbFile';"));
  
  
negative.code: import 'dart:async';
  import 'dart:collection';
  import 'package:analyzer/dart/element/element.dart';
  import 'package:angel_orm/angel_orm.dart';
  import 'package:build/build.dart';
  