如何创建和查询向量存储

info

请前往 Integrations 查看关于内置第三方向量存储集成的文档。

存储和搜索非结构化数据最常见的方法之一是将其嵌入为向量，然后存储生成的嵌入向量。在查询时，将非结构化查询嵌入为向量，并检索与嵌入查询“最相似”的嵌入向量。向量存储负责存储嵌入数据并为您执行向量搜索。

开始

本指南展示了与向量存储相关的基本功能。使用向量存储的关键部分是创建要放入其中的向量，而向量通常是通过嵌入创建的。因此，建议您在深入研究之前，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。

我们想使用 OpenAIEmbeddings，所以我们需要获取 OpenAI API Key。

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

# 加载文档，将其分割成块，嵌入每个块，并将其加载到向量存储中。
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)

API Reference:TextLoader | OpenAIEmbeddings | CharacterTextSplitter

有许多优秀的向量存储选项，以下是一些免费、开源且完全在本地机器上运行的选项。请查看所有集成以了解许多优秀的托管服务。

Chroma
FAISS
Lance

本次演练使用 chroma 向量数据库，它作为库在本地机器上运行。

pip install langchain-chroma

from langchain_chroma import Chroma

db = Chroma.from_documents(documents, OpenAIEmbeddings())

API Reference:Chroma

本次演练使用 FAISS 向量数据库，它利用了 Facebook AI Similarity Search (FAISS) 库。

pip install faiss-cpu

from langchain_community.vectorstores import FAISS

db = FAISS.from_documents(documents, OpenAIEmbeddings())

API Reference:FAISS

本教程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

所有向量存储都公开了一个 similarity_search 方法。这将接受传入的文档，为其创建嵌入，然后查找所有与嵌入最相似的文档。

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.

按向量进行相似性搜索

还可以使用 similarity_search_by_vector 对给定嵌入向量的相似文档进行搜索，它接受一个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

向量存储通常作为需要一些 IO 操作的独立服务运行，因此它们可能被异步调用。这可以带来性能优势，因为您不必浪费时间等待外部服务的响应。如果您使用的是异步框架，例如 FastAPI，这可能也很重要。

LangChain 支持向量存储上的异步操作。所有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'})]

开始​

相似性搜索​

按向量进行相似性搜索​

异步操作​

开始

相似性搜索

按向量进行相似性搜索

异步操作