A simple, lightweight NoSQL database written in pure Dart, designed for educational purposes and exploring the fundamentals of database development. This project demonstrates concepts like concurrency control, indexing, pagination, transactions, and TTL.

• Collections: Organize data into named collections, similar to tables in a relational database.
• Key-Value Storage: Store data as key-value pairs, allowing flexibility in your data structure.
• Concurrency Control: Uses the synchronized library for thread-safe access to data, with locks.
• Indexing: Supports in-memory indexing on specified fields for faster lookups.
• Pagination: Fetch data in chunks using limit and offset to improve performance.
• Transactions: Ensures atomic operations by grouping multiple changes within a transaction scope using a lock.
• TTL (Time-To-Live): Allows setting an expiry time for data, ideal for caching and temporary data management.
• Pure Dart: Built entirely in Dart, making it easy to understand and modify.
• File Persistence: Stores all data in JSON files, with a clear and well-defined structure.

1. Add the synchronized dependency:

   flutter pub add synchronized

2. Import:

   import 'package:synchronized/synchronized.dart';

3. Create a Database Instance:

   final db = Database('./my_database'); // Specify the storage path

   • The constructor argument specifies the directory where your database files will be stored.

4. Create or Access a Collection:

   final users = await db.collection('users', indexes: ['age', 'name']);

   • The first argument is the name of the collection. If a collection with that name doesn't exist it will be created.
   • The optional indexes parameter is a List<String> of properties that should be indexed. Indexing can speed up lookups based on these properties but can also slow down insertions if used too much.

5. Store Data (with optional TTL):

   await users.put('1', {'name': 'Alice', 'age': 30}, ttl: Duration(seconds: 60));

   • Use the put method to store data using a key and a value.
   • The optional ttl parameter specifies a time-to-live for the data. After that time, the data will be removed when loading from disk, or when accessing using get or getAll.

6. Retrieve Data:

   // By key
   final user = await users.get(key: '1');
   print('User by key: $user');
   
   // By index
   final usersByAge = await users.get(key: 'age', value: 30);
   print('Users by age: $usersByAge');

   • Use the get method to retrieve data using a key.
   • If you use the key parameter as a field that has been indexed you should also provide the value to filter the results.

7. Retrieve Data with Pagination:

   final pagedUsers = await users.getAll(limit: 10, offset: 0);
   print('Paged users (limit 10, offset 0): ${pagedUsers.length}');
   final allUsers = await users.getAll();
   print('Total number of users: ${allUsers.length}');

   • Use getAll with limit and offset to get data in pages.
   • The limit specifies the maximum amount of data returned, and the offset specifies which entry is the start of the page.
   • You can use the total number of users to create pagination controls.

8. Perform Operations Inside a Transaction:

   final tx = await users.startTransaction();
   await tx.put('1', {'name': 'Alice Updated', 'age': 31});
   await tx.delete('2');
   await tx.commit();

   • Transactions help group operations in one action that can be committed or rolled back if one of the operations fails.

9. Handle Errors:

   The application throws specific errors:

   • DatabaseCreateException: when the database fails to create the storage directory.
   • CollectionLoadException: when a collection fails to load from the disk.
   • CollectionSaveException: when a collection fails to save to disk.
   • CollectionNotFoundException: when a collection is not found.

   These exceptions should be caught by the application to handle specific error cases. For example:

   try {
       // your code here
   } on DatabaseCreateException catch (e) {
       print("Database creation failed ${e.toString()}");
   } on CollectionLoadException catch (e) {
       print('Error loading collection: ${e.toString()}');
   } on CollectionSaveException catch (e) {
       print('Error saving collection: ${e.toString()}');
   } on CollectionNotFoundException catch (e) {
       print("Collection not found: ${e.toString()}");
   } catch (e) {
       print('An unexpected error occurred: $e');
   }

• Database:

  • Manages the storage path and access to collections.
  • The collection method returns a collection for a specific name.

• Collection:

  • Represents a data collection and stores data as key-value pairs, with the optional ttl.
  • Methods to put, get, getAll, and delete data.
  • Manages indexing for faster lookups based on the specified fields.
  • Manages pagination for retrieving the data in chunks.
  • Provides transaction capabilities using the startTransaction method.

• Transaction:

  • Manages a transaction's state, to perform a series of operations atomically using locks.
  • Has methods put, delete, commit and rollback to manage the transaction.

The database uses custom exception classes for clear and detailed error reporting:

• DatabaseCreateException
• CollectionLoadException
• CollectionSaveException
• CollectionNotFoundException

These exceptions provide specific error messages, which you can use to provide feedback to your user, and to help debug.

Contributions are welcome! If you have ideas for enhancements or find any bugs, please feel free to:

1. Fork the repository.
2. Create a new branch for your feature or bug fix.
3. Submit a pull request with your changes.

This project is intended for educational purposes and has a few limitations:

• It is not a full-featured database.
• Indexes are stored in memory and might slow down the application with a large number of indexed fields or with big datasets.
• There is no support for complex queries or different types of storage formats.
• Transactions have a simple locking mechanism that might block operations.
• There is no scheduling for the TTL cleanup that will only happen when reading or retrieving all data.
• The code has not been thoroughly tested and might have edge cases.

This project is licensed under the MIT License - see the LICENSE file for details.