feat: Optimise langchain calls in batching mode (#15243)

packages/@n8n/nodes-langchain/nodes/chains/InformationExtractor/processItem.ts

@@ -0,0 +1,39 @@
+import type { BaseLanguageModel } from '@langchain/core/language_models/base';
+import { HumanMessage } from '@langchain/core/messages';
+import { ChatPromptTemplate, SystemMessagePromptTemplate } from '@langchain/core/prompts';
+import type { OutputFixingParser } from 'langchain/output_parsers';
+import type { IExecuteFunctions } from 'n8n-workflow';
+
+import { getTracingConfig } from '@utils/tracing';
+
+import { SYSTEM_PROMPT_TEMPLATE } from './constants';
+
+export async function processItem(
+	ctx: IExecuteFunctions,
+	itemIndex: number,
+	llm: BaseLanguageModel,
+	parser: OutputFixingParser<object>,
+) {
+	const input = ctx.getNodeParameter('text', itemIndex) as string;
+	const inputPrompt = new HumanMessage(input);
+
+	const options = ctx.getNodeParameter('options', itemIndex, {}) as {
+		systemPromptTemplate?: string;
+	};
+
+	const systemPromptTemplate = SystemMessagePromptTemplate.fromTemplate(
+		`${options.systemPromptTemplate ?? SYSTEM_PROMPT_TEMPLATE}
+{format_instructions}`,
+	);
+
+	const messages = [
+		await systemPromptTemplate.format({
+			format_instructions: parser.getFormatInstructions(),
+		}),
+		inputPrompt,
+	];
+	const prompt = ChatPromptTemplate.fromMessages(messages);
+	const chain = prompt.pipe(llm).pipe(parser).withConfig(getTracingConfig(ctx));
+
+	return await chain.invoke(messages);
+}