langchain-sdk-patterns

# LangChain SDK Patterns ## Overview Production-grade patterns every LangChain application should use: type-safe structured output, provider fallbacks, async batch processing, streaming, caching, and retry logic. ## Pattern 1: Structured Output with Zod ```typescript import { ChatOpenAI } from "@langchain/openai"; import { ChatPromptTemplate } from "@langchain/core/prompts"; import { z } from "zod"; const ExtractedData = z.object({ entities: z.array(z.object({ name: z.string(), type: z.enum(["person", "org", "location"]), confidence: z.number().min(0).max(1), })), language: z.string(), summary: z.string(), }); const model = new ChatOpenAI({ model: "gpt-4o-mini" }); const structuredModel = model.withStructuredOutput(ExtractedData); const prompt = ChatPromptTemplate.fromTemplate( "Extract entities from this text:\n\n{text}" ); const chain = prompt.pipe(structuredModel); const result = await chain.invoke({ text: "Satya Nadella announced Microsoft's new AI lab in Seattle.", }); // result is fully typed: { entities: [...], language: "en", summary: "..." } ``` ## Pattern 2: Provider Fallbacks ```typescript import { ChatOpenAI } from "@langchain/openai"; import { ChatAnthropic } from "@langchain/anthropic"; const primary = new ChatOpenAI({ model: "gpt-4o", maxRetries: 2, timeout: 10000, }); const fallback = new ChatAnthropic({ model: "claude-sonnet-4-20250514", }); // Automatically falls back on any error (rate limit, timeout, 500) const...