如何使用父文档检索器
在分割文档以进行检索时，常常存在相互冲突的愿望：
- 您可能希望文档较小，以便它们的嵌入能够最准确地反映其含义。如果文档过长，嵌入可能会失去意义。
- 您希望文档足够长，以便每个块的上下文得以保留。
ParentDocumentRetriever 通过分割和存储小块数据来达到这种平衡。在检索过程中，它首先获取小块数据，然后查找这些块的父ID并返回那些较大的文档。
请注意，“父文档”指的是小块内容来源的文档。这可以是整个原始文档或更大的块。
from langchain.retrievers import ParentDocumentRetriever
API Reference:ParentDocumentRetriever
from langchain.storage import InMemoryStore
from langchain_chroma import Chroma
from langchain_community.document_loaders import TextLoader
from langchain_openai import OpenAIEmbeddings
from langchain_text_splitters import RecursiveCharacterTextSplitter
loaders = [
TextLoader("paul_graham_essay.txt"),
TextLoader("state_of_the_union.txt"),
]
docs = []
for loader in loaders:
docs.extend(loader.load())
检索完整文档
在这种模式下，我们希望检索完整的文档。因此，我们只指定了一个子分割器。
# This text splitter is used to create the child documents
child_splitter = RecursiveCharacterTextSplitter(chunk_size=400)
# The vectorstore to use to index the child chunks
vectorstore = Chroma(
collection_name="full_documents", embedding_function=OpenAIEmbeddings()
)
# The storage layer for the parent documents
store = InMemoryStore()
retriever = ParentDocumentRetriever(
vectorstore=vectorstore,
docstore=store,
child_splitter=child_splitter,
)
retriever.add_documents(docs, ids=None)
这应该会产生两个键，因为我们添加了两个文档。
list(store.yield_keys())
['9a63376c-58cc-42c9-b0f7-61f0e1a3a688',
'40091598-e918-4a18-9be0-f46413a95ae4']
现在让我们调用向量存储搜索功能 - 我们应该看到它返回的是小块（因为我们存储的是小块）。
sub_docs = vectorstore.similarity_search("justice breyer")
print(sub_docs[0].page_content)
Tonight, I’d like to honor someone who has dedicated his life to serve this country: Justice Stephen Breyer—an Army veteran, Constitutional scholar, and retiring Justice of the United States Supreme Court. Justice Breyer, thank you for your service.
One of the most serious constitutional responsibilities a President has is nominating someone to serve on the United States Supreme Court.
现在让我们从整体检索器中检索。这应该会返回大文档——因为它返回的是包含较小块的文档。
retrieved_docs = retriever.invoke("justice breyer")
len(retrieved_docs[0].page_content)
38540
检索更大的块
有时，完整的文档可能太大，无法直接检索。在这种情况下，我们真正想做的是首先将原始文档分割成较大的块，然后再将其分割成较小的块。然后我们对较小的块进行索引，但在检索时我们检索较大的块（但仍然不是完整的文档）。
# This text splitter is used to create the parent documents
parent_splitter = RecursiveCharacterTextSplitter(chunk_size=2000)
# This text splitter is used to create the child documents
# It should create documents smaller than the parent
child_splitter = RecursiveCharacterTextSplitter(chunk_size=400)
# The vectorstore to use to index the child chunks
vectorstore = Chroma(
collection_name="split_parents", embedding_function=OpenAIEmbeddings()
)
# The storage layer for the parent documents
store = InMemoryStore()
retriever = ParentDocumentRetriever(
vectorstore=vectorstore,
docstore=store,
child_splitter=child_splitter,
parent_splitter=parent_splitter,
)
retriever.add_documents(docs)
我们可以看到，现在有超过两个文档 - 这些是较大的块。
len(list(store.yield_keys()))
66
让我们确保底层的向量存储仍然能够检索到小的数据块。
sub_docs = vectorstore.similarity_search("justice breyer")
print(sub_docs[0].page_content)
Tonight, I’d like to honor someone who has dedicated his life to serve this country: Justice Stephen Breyer—an Army veteran, Constitutional scholar, and retiring Justice of the United States Supreme Court. Justice Breyer, thank you for your service.
One of the most serious constitutional responsibilities a President has is nominating someone to serve on the United States Supreme Court.
retrieved_docs = retriever.invoke("justice breyer")
len(retrieved_docs[0].page_content)
1849
print(retrieved_docs[0].page_content)
In state after state, new laws have been passed, not only to suppress the vote, but to subvert entire elections.
We cannot let this happen.
Tonight. I call on the Senate to: Pass the Freedom to Vote Act. Pass the John Lewis Voting Rights Act. And while you’re at it, pass the Disclose Act so Americans can know who is funding our elections.
Tonight, I’d like to honor someone who has dedicated his life to serve this country: Justice Stephen Breyer—an Army veteran, Constitutional scholar, and retiring Justice of the United States Supreme Court. Justice Breyer, thank you for your service.
One of the most serious constitutional responsibilities a President has is nominating someone to serve on the United States Supreme Court.
And I did that 4 days ago, when I nominated Circuit Court of Appeals Judge Ketanji Brown Jackson. One of our nation’s top legal minds, who will continue Justice Breyer’s legacy of excellence.
A former top litigator in private practice. A former federal public defender. And from a family of public school educators and police officers. A consensus builder. Since she’s been nominated, she’s received a broad range of support—from the Fraternal Order of Police to former judges appointed by Democrats and Republicans.
And if we are to advance liberty and justice, we need to secure the Border and fix the immigration system.
We can do both. At our border, we’ve installed new technology like cutting-edge scanners to better detect drug smuggling.
We’ve set up joint patrols with Mexico and Guatemala to catch more human traffickers.
We’re putting in place dedicated immigration judges so families fleeing persecution and violence can have their cases heard faster.
We’re securing commitments and supporting partners in South and Central America to host more refugees and secure their own borders.