LangGraph Architecture Uncovered: A Step-by-Step Guide

Originally published on Medium.

I spent three weeks building a LangGraph-based project because I was frustrated with the limitations of traditional machine learning models. I had tried using Hugging Face and FastAPI to build a simple chatbot, but I quickly realized that I needed a more robust framework to handle complex conversations. That's when I discovered LangGraph, and it changed everything. In this article, you'll learn how to build a LangGraph-based project from scratch, and by the end of it, you'll have a solid understanding of nodes, edges, and state in LangGraph.

My journey with LangGraph started with a simple goal: to build a conversational AI that could understand and respond to user queries. I had tried using pydantic and TypedDict to define my data models, but I soon realized that I needed a more flexible framework to handle the complexities of natural language processing. That's when I started exploring LangGraph, and I was amazed by its simplicity and power.

In this article, we'll take a deep dive into the LangGraph architecture, covering nodes, edges, and state. You'll learn how to build a LangGraph-based project from scratch, and by the end of it, you'll have a solid understanding of how to use LangGraph to build your next AI project.

Table of Contents

Introduction to LangGraph Architecture
The Problem: Understanding Nodes, Edges, and State
The Solution: LangGraph Architecture
Implementation: Core Code
The Key Insight: Deep Dive into Nodes and Edges
Running It: Results and Benchmarks

Introduction to LangGraph Architecture

LangGraph is a powerful framework for building conversational AI models. At its core, LangGraph is a graph-based architecture that consists of nodes, edges, and state. Nodes represent entities or concepts in the conversation, edges represent relationships between nodes, and state represents the current context of the conversation.

To understand LangGraph, you need to understand how nodes, edges, and state work together to enable complex conversations. In the next section, we'll dive deeper into the problem of understanding nodes, edges, and state.

The Problem: Understanding Nodes, Edges, and State

Understanding nodes, edges, and state is crucial to building effective LangGraph-based models. Here are some common issues that developers face when working with LangGraph:

Node Definition: Defining nodes that accurately represent entities or concepts in the conversation.
Edge Definition: Defining edges that accurately represent relationships between nodes.
State Management: Managing state to ensure that the conversation context is accurately represented.

Key insight: The key to building effective LangGraph-based models is to understand how nodes, edges, and state work together to enable complex conversations.

The Solution: LangGraph Architecture

The LangGraph architecture consists of three stages:

Stage 1: Node Definition

In this stage, you define nodes that represent entities or concepts in the conversation. Nodes can be defined using pydantic models or TypedDict types.

Stage 2: Edge Definition

In this stage, you define edges that represent relationships between nodes. Edges can be defined using pydantic models or TypedDict types.

Stage 3: State Management

In this stage, you manage state to ensure that the conversation context is accurately represented. State can be managed using pydantic models or TypedDict types.

Architecture diagram:

graph TD
    A[Node Definition] --> B[Edge Definition]
    B --> C[State Management]
    C --> D[Conversation Context]

Implementation: Core Code

Here's the complete code for a simple LangGraph-based model:

from typing_extensions import TypedDict
from pydantic import BaseModel, Field
import operator
from typing import Annotated, List

class Node(BaseModel):
    id: int = Field(description="Unique identifier for the node")
    name: str = Field(description="Name of the node")

class Edge(BaseModel):
    id: int = Field(description="Unique identifier for the edge")
    node1: Node = Field(description="First node in the edge")
    node2: Node = Field(description="Second node in the edge")

class State(TypedDict):
    nodes: List[Node] = Field(description="List of nodes in the conversation")
    edges: List[Edge] = Field(description="List of edges in the conversation")
    context: str = Field(description="Conversation context")

class ReportState(TypedDict):
    topic: str = Field(description="Report topic")
    sections: List[Section] = Field(description="List of report sections")
    completed: Annotated[List[Section], operator.add] = Field(description="List of completed sections")
    final_report: str = Field(description="Final compiled report")

class Section(BaseModel):
    name: str = Field(description="Name of the section")
    research: bool = Field(description="Whether to perform web search")
    content: str = Field(description="Content of the section")

Let me explain the key design decisions here. Node Definition: We define nodes using pydantic models to ensure that they are accurately represented. Edge Definition: We define edges using pydantic models to ensure that they are accurately represented. State Management: We manage state using pydantic models and TypedDict types to ensure that the conversation context is accurately represented.

Typed State Management: You define state as TypedDict — LangGraph enforces types at runtime. Annotated merge: The Annotated[List[Section], operator.add] pattern tells LangGraph how to merge parallel results.

The Key Insight: Deep Dive into Nodes and Edges

Let's take a closer look at how nodes and edges work together to enable complex conversations. Here's a small focused code example:

Define a node
node1 = Node(id=1, name="Entity1")

Define an edge
edge1 = Edge(id=1, node1=node1, node2=node1)

Define state
state = State(nodes=[node1], edges=[edge1], context="Initial context")

This line is deceptively powerful. Let me explain what's happening. When we define a node, we are creating an entity that can be used in the conversation. When we define an edge, we are creating a relationship between two nodes. When we define state, we are creating a context that represents the current state of the conversation.

In LangGraph, nodes and edges are used to represent entities and relationships in the conversation. State is used to manage the conversation context. By using pydantic models and TypedDict types, we can ensure that our nodes, edges, and state are accurately represented and enforced at runtime.

Running It: Results and Benchmarks

To run the LangGraph-based model, you can use the following code:

Run the model
result = main_function(input)
print(result)

The results will depend on the specific model and data used. However, in general, LangGraph-based models can achieve high accuracy and efficiency in conversational AI tasks.

In the next part of this series, we'll explore how to build a real-world project using LangGraph. We'll cover how to build a customer support bot using LangGraph and Gradio.

What's Next

In the next part of this series, we'll dive deeper into building a real-world project using LangGraph. We'll cover how to build a customer support bot using LangGraph and Gradio. If you're interested in learning more about LangGraph and conversational AI, I encourage you to check out the previous parts of this series.

If you're building something similar, what's the hardest part for you? Are you struggling with node definition, edge definition, or state management? Let me know in the comments below.

You can find the previous parts of this series here: