如何创建和查询向量存储
info
前往集成查看与第三方向量存储的内置集成文档。
存储和搜索非结构化数据的最常见方法之一是将其嵌入并存储生成的嵌入向量，然后在查询时嵌入非结构化查询并检索与嵌入查询“最相似”的嵌入向量。向量存储负责为您存储嵌入数据并执行向量搜索。
开始使用
本指南展示了与向量存储相关的基本功能。使用向量存储的一个关键部分是创建要放入其中的向量，这通常是通过嵌入创建的。因此，建议您在深入了解此内容之前，先熟悉文本嵌入模型接口。
在使用向量存储之前，我们需要加载一些数据并初始化一个嵌入模型。
我们想要使用OpenAIEmbeddings，所以我们必须获取OpenAI API密钥。
import os
import getpass
os.environ['OPENAI_API_KEY'] = getpass.getpass('OpenAI API Key:')
from langchain_community.document_loaders import TextLoader
from langchain_openai import OpenAIEmbeddings
from langchain_text_splitters import CharacterTextSplitter
# Load the document, split it into chunks, embed each chunk and load it into the vector store.
raw_documents = TextLoader('state_of_the_union.txt').load()
text_splitter = CharacterTextSplitter(chunk_size=1000, chunk_overlap=0)
documents = text_splitter.split_documents(raw_documents)
有许多优秀的向量存储选项，这里有一些是免费的、开源的，并且完全在您的本地机器上运行。查看所有集成以了解许多优秀的托管服务。
- Chroma
- FAISS
- Lance
本教程使用chroma向量数据库，它作为一个库在您的本地机器上运行。
pip install langchain-chroma
from langchain_chroma import Chroma
db = Chroma.from_documents(documents, OpenAIEmbeddings())
本教程使用FAISS向量数据库，该数据库利用了Facebook AI相似性搜索（FAISS）库。
pip install faiss-cpu
from langchain_community.vectorstores import FAISS
db = FAISS.from_documents(documents, OpenAIEmbeddings())
API Reference:FAISS
本笔记本展示了如何使用基于Lance数据格式的LanceDB向量数据库的相关功能。
pip install lancedb
from langchain_community.vectorstores import LanceDB
import lancedb
db = lancedb.connect("/tmp/lancedb")
table = db.create_table(
"my_table",
data=[
{
"vector": embeddings.embed_query("Hello World"),
"text": "Hello World",
"id": "1",
}
],
mode="overwrite",
)
db = LanceDB.from_documents(documents, OpenAIEmbeddings())
API Reference:LanceDB
相似性搜索
所有向量存储都暴露了一个similarity_search方法。
这将接收传入的文档，创建它们的嵌入，然后找到所有具有最相似嵌入的文档。
query = "What did the president say about Ketanji Brown Jackson"
docs = db.similarity_search(query)
print(docs[0].page_content)
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.
向量相似性搜索
也可以使用similarity_search_by_vector来搜索与给定嵌入向量相似的文档，该函数接受嵌入向量作为参数，而不是字符串。
embedding_vector = OpenAIEmbeddings().embed_query(query)
docs = db.similarity_search_by_vector(embedding_vector)
print(docs[0].page_content)
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.
异步操作
向量存储通常作为一个需要一些IO操作的独立服务运行，因此它们可能会被异步调用。这带来了性能上的好处，因为您不会浪费时间等待外部服务的响应。如果您使用异步框架（如FastAPI），这也可能很重要。
LangChain 支持在向量存储上进行异步操作。所有的方法都可以使用它们的异步对应方法调用，前缀为 a，表示 async。
docs = await db.asimilarity_search(query)
docs
[Document(page_content='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. \n\nTonight, 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. \n\nOne of the most serious constitutional responsibilities a President has is nominating someone to serve on the United States Supreme Court. \n\nAnd 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.', metadata={'source': 'state_of_the_union.txt'}),
Document(page_content='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. \n\nAnd if we are to advance liberty and justice, we need to secure the Border and fix the immigration system. \n\nWe can do both. At our border, we’ve installed new technology like cutting-edge scanners to better detect drug smuggling. \n\nWe’ve set up joint patrols with Mexico and Guatemala to catch more human traffickers. \n\nWe’re putting in place dedicated immigration judges so families fleeing persecution and violence can have their cases heard faster. \n\nWe’re securing commitments and supporting partners in South and Central America to host more refugees and secure their own borders.', metadata={'source': 'state_of_the_union.txt'}),
Document(page_content='And for our LGBTQ+ Americans, let’s finally get the bipartisan Equality Act to my desk. The onslaught of state laws targeting transgender Americans and their families is wrong. \n\nAs I said last year, especially to our younger transgender Americans, I will always have your back as your President, so you can be yourself and reach your God-given potential. \n\nWhile it often appears that we never agree, that isn’t true. I signed 80 bipartisan bills into law last year. From preventing government shutdowns to protecting Asian-Americans from still-too-common hate crimes to reforming military justice. \n\nAnd soon, we’ll strengthen the Violence Against Women Act that I first wrote three decades ago. It is important for us to show the nation that we can come together and do big things. \n\nSo tonight I’m offering a Unity Agenda for the Nation. Four big things we can do together. \n\nFirst, beat the opioid epidemic.', metadata={'source': 'state_of_the_union.txt'}),
Document(page_content='Tonight, I’m announcing a crackdown on these companies overcharging American businesses and consumers. \n\nAnd as Wall Street firms take over more nursing homes, quality in those homes has gone down and costs have gone up. \n\nThat ends on my watch. \n\nMedicare is going to set higher standards for nursing homes and make sure your loved ones get the care they deserve and expect. \n\nWe’ll also cut costs and keep the economy going strong by giving workers a fair shot, provide more training and apprenticeships, hire them based on their skills not degrees. \n\nLet’s pass the Paycheck Fairness Act and paid leave. \n\nRaise the minimum wage to $15 an hour and extend the Child Tax Credit, so no one has to raise a family in poverty. \n\nLet’s increase Pell Grants and increase our historic support of HBCUs, and invest in what Jill—our First Lady who teaches full-time—calls America’s best-kept secret: community colleges.', metadata={'source': 'state_of_the_union.txt'})]