LangChain Document Loaders & Vector Stores: Powering RAG Applications

Unlock the power of Retrieval-Augmented Generation (RAG) by combining external knowledge with LLMs using LangChain’s document loaders and vector stores.

🔍 What Are Document Loaders in LangChain?

Document loaders let you ingest data from various formats such as:

• PDFs
• Web pages
• YouTube transcripts
• Notion, Slack, Confluence
• Markdown, CSV, DOCX

They convert raw input into clean Document objects containing:

• .page_content
• .metadata

✂️ Splitting Text into Chunks

Large documents are split into smaller chunks using TextSplitter, allowing each chunk to be embedded and indexed individually.

Common strategies:

• RecursiveCharacterTextSplitter
• TokenTextSplitter

Why split?

• LLMs have token limits
• Improves retrieval relevance
• Faster indexing and searching

🧠 What Are Vector Stores?

Vector stores are databases optimized for similarity search using embeddings. LangChain supports:

• FAISS (local, fast)
• ChromaDB (lightweight, local)
• Pinecone (cloud-hosted)
• Weaviate, Qdrant, Milvus (enterprise-scale)

These stores map text chunks to high-dimensional vectors using an embedding model (e.g., OpenAI, HuggingFace).

🔁 Retrieval-Augmented Generation (RAG)

RAG = Query → Retrieve → Generate

You retrieve relevant chunks from your vector store based on user input, then feed that context into an LLM to generate grounded, factual responses. Common RAG flow:

• Load documents
• Split into chunks
• Embed + store in vector DB
• Query vector store
• Inject retrieved context into LLM prompt

🧪 Example: Load Documents + Store in FAISS

from langchain.document_loaders import PyPDFLoader
from langchain.text_splitter import RecursiveCharacterTextSplitter
from langchain.embeddings import OpenAIEmbeddings
from langchain.vectorstores import FAISS

# 1. Load the document
loader = PyPDFLoader("sample.pdf")
documents = loader.load()

# 2. Split into chunks
splitter = RecursiveCharacterTextSplitter(chunk_size=500, chunk_overlap=50)
chunks = splitter.split_documents(documents)

# 3. Embed and store in FAISS
embedding = OpenAIEmbeddings()
vectorstore = FAISS.from_documents(chunks, embedding)

# 4. Save locally (optional)
vectorstore.save_local("faiss_index")

This example shows how to prepare documents for a Retrieval-Augmented Generation (RAG) setup.

✅ Use Cases

Below are some famous usecases:

• Internal knowledge bots
• Legal document assistants
• Financial report summarization
• Q&A over policy documents or handbooks
• YouTube or podcast summarizers

📦 LangChain Integrations

LangChain supports loading documents from:

• PyPDFLoader, UnstructuredPDFLoader
• WebBaseLoader, NotionDBLoader, YouTubeLoader
• DirectoryLoader to bulk load files

You can then use:

• FAISS or Chroma for local indexing
• RetrievalQAChain to tie everything together with an LLM

🔗 Related Blogs

📘 LangChain Mastery Series

🧠 LangChain Memory Guide

🔧 LangChain Chains & Workflows

🚀 TL;DR

• Document loaders turn files into retrievable chunks
• Vector stores let you semantically search those chunks
• Together, they enable powerful RAG apps grounded in your data

LangChain makes it easy to go from unstructured documents to searchable, LLM-augmented assistants.