Karim shoair
66 lines
3.4 KiB
Markdown
66 lines
3.4 KiB
Markdown
Scrapling uses SQLite by default, but this tutorial covers writing your storage system to store element properties there for auto-matching.
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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 the spiders will share 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_adaptors.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 function `element_to_dict` in submodule `scrapling.core.utils._StorageTools` to keep the same format and save it 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 auto-match 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_adaptors.py) file
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If your class meets these criteria, the rest is easy. 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_adaptors.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_adaptors 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:
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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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``` |