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68 lines
3.5 KiB
Markdown
68 lines
3.5 KiB
Markdown
# Writing your retrieval system
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Scrapling uses SQLite by default, but this tutorial shows how to write your own storage system to store element properties for the `adaptive` feature.
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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 spiders can share adaptive data with each other.
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So first, to make your storage class work, it must do the big 3:
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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.
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2. Use the decorator `functools.lru_cache` on top of the class to follow the Singleton design pattern as other classes.
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3. Implement methods `save` and `retrieve`, as you see from the type hints:
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- The method `save` returns nothing and will get two arguments from the library
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* The first one is of type `lxml.html.HtmlElement`, which is the element itself. It must be converted to a dictionary using the `element_to_dict` function in the submodule `scrapling.core.utils._StorageTools` to maintain the same format, and then saved to your database as you wish.
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* 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.
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- 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`.
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> 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
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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.
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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 :)
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## Real-World Example: Redis Storage
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Here's a more practical example generated by AI using Redis:
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```python
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import redis
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import orjson
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from functools import lru_cache
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from scrapling.core.storage import StorageSystemMixin
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from scrapling.core.utils import _StorageTools
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@lru_cache(None)
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class RedisStorage(StorageSystemMixin):
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def __init__(self, host='localhost', port=6379, db=0, url=None):
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super().__init__(url)
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self.redis = redis.Redis(
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host=host,
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port=port,
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db=db,
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decode_responses=False
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)
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def save(self, element, identifier: str) -> None:
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# Convert element to dictionary
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element_dict = _StorageTools.element_to_dict(element)
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# Create key
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key = f"scrapling:{self._get_base_url()}:{identifier}"
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# Store as JSON
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self.redis.set(
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key,
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orjson.dumps(element_dict)
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)
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def retrieve(self, identifier: str) -> dict | None:
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# Get data
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key = f"scrapling:{self._get_base_url()}:{identifier}"
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data = self.redis.get(key)
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# Parse JSON if exists
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if data:
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return orjson.loads(data)
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return None
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``` |