Scrapling uses SQLite by default, but this tutorial covers writing your storage system to store element properties there for `adaptive` feature.

You might want to use FireBase, for example, and share the database between multiple spiders on different machines. It's a great idea to use an online database like that because the spiders will share with each other.

So first, to make your storage class work, it must do the big 3:

1. Inherit from the abstract class `scrapling.core.storage.StorageSystemMixin` and accept a string argument, which will be the `url` argument to maintain the library logic.
2. Use the decorator `functools.lru_cache` on top of the class to follow the Singleton design pattern as other classes.
3. Implement methods `save` and `retrieve`, as you see from the type hints:
    - The method `save` returns nothing and will get two arguments from the library
        * The first one is of type `lxml.html.HtmlElement`, which is the element itself. It must be converted to a dictionary using the function `element_to_dict` in submodule `scrapling.core.utils._StorageTools` to keep the same format and save it to your database as you wish.
        * The second one is a string, the identifier used for retrieval. The combination result of this identifier and the `url` argument from initialization must be unique for each row, or the `adaptive` data will be messed up.
    - The method `retrieve` takes a string, which is the identifier; using it with the `url` passed on initialization, the element's dictionary is retrieved from the database and returned if it exists; otherwise, it returns `None`.

> If the instructions weren't clear enough for you, you can check my implementation using SQLite3 in [storage_adaptors](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/core/storage.py) file

If your class meets these criteria, the rest is straightforward. If you plan to use the library in a threaded application, ensure your class supports it. The default used class is thread-safe.

Some helper functions are added to the abstract class if you want to use them. It's easier to see it for yourself in the [code](https://github.com/D4Vinci/Scrapling/blob/main/scrapling/core/storage.py); it's heavily commented :)


## Real-World Example: Redis Storage

Here's a more practical example generated by AI using Redis:

```python
import redis
import orjson
from functools import lru_cache
from scrapling.core.storage import StorageSystemMixin
from scrapling.core.utils import _StorageTools

@lru_cache(None)
class RedisStorage(StorageSystemMixin):
    def __init__(self, host='localhost', port=6379, db=0, url=None):
        super().__init__(url)
        self.redis = redis.Redis(
            host=host,
            port=port,
            db=db,
            decode_responses=False
        )
        
    def save(self, element, identifier: str) -> None:
        # Convert element to dictionary
        element_dict = _StorageTools.element_to_dict(element)
        
        # Create key
        key = f"scrapling:{self._get_base_url()}:{identifier}"
        
        # Store as JSON
        self.redis.set(
            key,
            orjson.dumps(element_dict)
        )
        
    def retrieve(self, identifier: str) -> dict:
        # Get data
        key = f"scrapling:{self._get_base_url()}:{identifier}"
        data = self.redis.get(key)
        
        # Parse JSON if exists
        if data:
            return orjson.loads(data)
        return None
```