Make RunnablePassthrough.assign() accept a RunnableLambda function

[zirkelc]

Currently, RunnablePassthrough.assign() needs an object / RunnableMap as input:

const sqlQueryGeneratorChain = RunnableSequence.from([
  RunnablePassthrough.assign({ // RunnableMap
    schema: async () => db.getTableInfo(),
  }),
  prompt,
  new ChatOpenAI({}).bind({ stop: ["\nSQLResult:"] }),
  new StringOutputParser(),
]);

IMHO, it would be useful to make RunnablePassthrough.assign() accept a function / RunnableLambda as input:

const sqlQueryGeneratorChain = RunnableSequence.from([
  RunnablePassthrough.assign(async () => db.getTableInfo()), // RunnableLambda
  prompt,
  new ChatOpenAI({}).bind({ stop: ["\nSQLResult:"] }),
  new StringOutputParser(),
]);

The result from RunnablePassthrough.assign() from the function would get merged with the input, the same way it is currently implemented for RunnableMap.

[arnaugomez]

Hi @zirkelc, you can achieve the same result by using the pipe method and object destructuring. Here is an example:

const sqlQueryGeneratorChain = RunnableSequence.from([
  new RunnablePassthrough().pipe(async (input) => ({
    ...input, ...db.getTableInfo(), // Input object gets merged with the new object
  })),
  prompt,
  new ChatOpenAI({}).bind({ stop: ["\nSQLResult:"] }),
  new StringOutputParser(),
]);

[zirkelc]

Thank s for your response! I think back when I asked this question, the pipe() fn didn't exist.