How can I use LangChain with external data sources?

LangChain enables integration with external data sources through document loaders, text processing, and retrieval augmented generation. The framework provides tools to load data from various formats (PDFs, databases, APIs), process it into usable chunks, and connect it to language models for context-aware responses. This process typically involves embedding the data for efficient similarity search and storing it in vector databases for quick retrieval during queries.

First, use LangChain’s document loaders to import data. For example, the CSVLoader reads CSV files, UnstructuredFileLoader processes PDFs or Word docs, and WebBaseLoader scrapes webpage content. Once loaded, split the text into manageable chunks using text splitters like RecursiveCharacterTextSplitter, which preserves context while avoiding token limits. These chunks are converted into embeddings (vector representations) using models like OpenAI’s text-embedding-ada-002. Store the embeddings in a vector database such as FAISS, Chroma, or Pinecone. During a query, LangChain retrieves the most relevant chunks based on semantic similarity and feeds them to the language model as context. For instance, a RetrievalQA chain combines retrieval and generation steps to answer questions using the external data.

Developers can customize this workflow. For APIs or real-time data, use APIFetcher tools or build custom loaders. LangChain Agents extend functionality by dynamically choosing when to query external data. For example, an agent could first check a database for product inventory before answering a customer query. You can also fine-tune retrieval parameters, like chunk size or metadata filtering, to improve relevance. By combining these components, LangChain creates flexible pipelines that ground language model outputs in external data, ensuring accuracy and reducing hallucinations.