การสร้างสายงานด้วย LCEL

from langchain_openai import ChatOpenAI
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.output_parsers import StrOutputParser

prompt = ChatPromptTemplate.from_template(
    'Write a product description for: {product}'
)
model = ChatOpenAI(model='gpt-4o-mini', temperature=0.7)
parser = StrOutputParser()

chain = prompt | model | parser

result = chain.invoke({'product': 'noise-cancelling headphones'})
print(result)

# Inspect chain structure
print('Steps:', chain.steps)
print('Input schema:', chain.input_schema.schema())
print('Output schema:', chain.output_schema.schema())

# Named run for observability
result = chain.invoke(
    {'product': 'coffee maker'},
    config={'run_name': 'product-desc-run', 'tags': ['production']}
)

import asyncio
from langchain_openai import ChatOpenAI
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.output_parsers import StrOutputParser

chain = ChatPromptTemplate.from_template('Explain {topic}') | ChatOpenAI() | StrOutputParser()

async def main():
    # Async invocation
    result = await chain.ainvoke({'topic': 'quantum computing'})
    print(result)

asyncio.run(main())

chain = (
    ChatPromptTemplate.from_template('Tell me about {topic} in detail.')
    | ChatOpenAI(model='gpt-4o-mini')
    | StrOutputParser()
)

# Print each token as it arrives
for chunk in chain.stream({'topic': 'neural networks'}):
    print(chunk, end='', flush=True)
print()  # newline at end

# Async streaming
async def stream_async():
    async for chunk in chain.astream({'topic': 'transformers'}):
        print(chunk, end='', flush=True)

products = [
    {'product': 'laptop'},
    {'product': 'tablet'},
    {'product': 'smartwatch'},
    {'product': 'earbuds'},
]

# Process all 4 concurrently
results = chain.batch(products, config={'max_concurrency': 4})

for product, description in zip(products, results):
    print(f'{product["product"]}: {description[:80]}...')

from langchain_core.runnables import RunnablePassthrough, RunnableLambda

def word_count(text: str) -> str:
    count = len(text.split())
    return f'{text}\n\n[Word count: {count}]'

chain = (
    ChatPromptTemplate.from_template('Write about {topic}')
    | ChatOpenAI(model='gpt-4o-mini')
    | StrOutputParser()
    | RunnableLambda(word_count)  # Add word count to output
)

result = chain.invoke({'topic': 'climate change'})
print(result)

from langchain_core.runnables import RunnablePassthrough

# Fake retriever for illustration
def retrieve_docs(question: str):
    return ['Doc 1 content', 'Doc 2 content']

retriever = RunnableLambda(retrieve_docs)

rag_chain = (
    RunnablePassthrough.assign(context=retriever)  # adds 'context' key
    | ChatPromptTemplate.from_template(
        'Context: {context}\n\nAnswer: {question}'
    )
    | ChatOpenAI()
    | StrOutputParser()
)

result = rag_chain.invoke({'question': 'What is machine learning?'})

from langchain_openai import ChatOpenAI
from langchain_anthropic import ChatAnthropic

primary_chain = (
    ChatPromptTemplate.from_template('Answer: {question}')
    | ChatOpenAI(model='gpt-4o')
    | StrOutputParser()
)

fallback_chain = (
    ChatPromptTemplate.from_template('Answer: {question}')
    | ChatAnthropic(model='claude-3-haiku-20240307')
    | StrOutputParser()
)

robust_chain = primary_chain.with_fallbacks([fallback_chain])
# If OpenAI fails, automatically tries Anthropic

from langchain.globals import set_verbose, set_debug

# Verbose: logs LLM inputs/outputs
set_verbose(True)

# Debug: logs everything including prompts, parsers, and runnables
set_debug(True)

result = chain.invoke({'product': 'smart watch'})

# Or per-chain verbose config
chain_debug = chain.with_config({'verbose': True})
result = chain_debug.invoke({'product': 'laptop'})

from langchain_core.runnables import ConfigurableField

llm = ChatOpenAI(model='gpt-4o-mini').configurable_fields(
    temperature=ConfigurableField(
        id='temperature',
        name='LLM Temperature',
        description='Controls output creativity'
    )
)

chain = ChatPromptTemplate.from_template('Write about {topic}') | llm | StrOutputParser()

# Low temperature for factual output
factual = chain.invoke(
    {'topic': 'history of Rome'},
    config={'configurable': {'temperature': 0.0}}
)