Blockchain Data Access

🌐 Blockchain Data Access: Your Window Into the Blockchain World

The Story of Getting Data

Imagine the blockchain is a giant library 📚 with millions of books (transactions). But there’s a problem—the books have no index, no catalog, and no librarian! How do you find what you need?

That’s exactly the challenge developers face. Today, we’ll discover two magical helpers that solve this problem:

1. RPC Providers — Like having a phone line directly to the library
2. The Graph Protocol — Like having a smart librarian who organizes everything for you

🔌 Part 1: RPC Providers — Your Direct Line to the Blockchain

What is an RPC Provider?

Think of an RPC provider like a telephone operator ☎️ for the blockchain.

You pick up the phone, tell the operator what you want, and they fetch it for you. Simple!

RPC = Remote Procedure Call It’s just a fancy way of saying “ask a computer to do something for me.”

The JSON-RPC API

The blockchain speaks a special language called JSON-RPC. It’s like a secret code between your app and the blockchain.

JSON = A way to write data that computers understand RPC = Ask the blockchain to do something remotely

graph TD
    A["Your App"] -->|JSON-RPC Request| B["RPC Provider"]
    B -->|Talks to| C["Blockchain Node"]
    C -->|Sends back| B
    B -->|JSON-RPC Response| A

JSON-RPC Methods: The Commands You Can Use

Here are the most common “commands” you can send:

Example: Getting an Account Balance

{
  "jsonrpc": "2.0",
  "method": "eth_getBalance",
  "params": [
    "0x742d35Cc6634C053...",
    "latest"
  ],
  "id": 1
}

Breaking it down:

• jsonrpc: "2.0" → Version of the language
• method → The command (get balance)
• params → The address to check + when (latest)
• id → A tracking number for your request

WebSocket Subscriptions: Real-Time Updates! 🔔

Sometimes you don’t want to keep asking “is there anything new?”

WebSockets are like leaving the phone line open. The blockchain can call YOU when something happens!

graph TD
    A["Your App"] -->|Subscribe| B["RPC Provider"]
    B -->|New Block!| A
    B -->|New Transaction!| A
    B -->|Event Happened!| A

What can you subscribe to?

• 🧱 newHeads — Get notified of every new block
• 📝 logs — Get notified when specific events happen
• ⏳ pendingTransactions — See transactions before they’re confirmed

Example subscription:

{
  "jsonrpc": "2.0",
  "method": "eth_subscribe",
  "params": ["newHeads"],
  "id": 1
}

Now your app gets a message every time a new block is created! Magic! ✨

📊 Part 2: The Graph Protocol — Your Smart Librarian

The Problem with RPC Alone

Imagine you want to find “all books written by Author X between 1990 and 2000.”

With just RPC (the telephone), you’d have to:

1. Call and ask about book #1
2. Call and ask about book #2
3. Call and ask about book #3
4. …repeat 10 million times! 😱

The Graph solves this by creating an organized catalog of blockchain data.

What is The Graph Protocol?

The Graph is like hiring a super-smart librarian 🧙‍♂️ who:

• Reads every single book in the library
• Creates a perfect index
• Answers complex questions instantly!

graph TD
    A["Blockchain"] -->|Raw Data| B["The Graph Indexer"]
    B -->|Organizes Into| C["Subgraph"]
    C -->|Answers| D["Your GraphQL Query"]

Subgraphs: Custom Catalogs

A subgraph is like a custom catalog for specific data you care about.

Want to track:

• All NFT sales on OpenSea? → Create a subgraph for that!
• All DeFi trades on Uniswap? → Create a subgraph for that!
• Your game’s high scores? → Create a subgraph for that!

A subgraph contains:

1. Schema — What data to store
2. Mappings — How to extract data from blockchain events
3. Data Sources — Which smart contracts to watch

Indexing Blockchain Data

Indexing = The librarian reading and organizing the books

When you deploy a subgraph:

1. Indexer nodes read blockchain history
2. They extract the data you defined
3. They store it in a searchable database
4. They keep updating as new blocks arrive

It’s like having someone constantly update the catalog as new books arrive!

GraphQL Queries: Ask Smart Questions

GraphQL is the language you use to ask your librarian questions.

Instead of:

• “Give me everything about all transactions” (too much!)

You can ask:

• “Give me the sender, amount, and time of the last 5 transactions from Alice”

Example:

{
  transfers(
    first: 5
    where: { from: "0xAlice..." }
    orderBy: timestamp
    orderDirection: desc
  ) {
    from
    to
    amount
    timestamp
  }
}

What makes GraphQL special:

• ✅ Ask for exactly what you need
• ✅ Get multiple related things in one request
• ✅ No over-fetching or under-fetching
• ✅ Strongly typed (fewer bugs!)

🎯 When to Use What?

🌟 Real-World Example: NFT Marketplace

Let’s see how both work together!

Using RPC:

→ Check if user owns NFT #42
→ Get current gas price
→ Submit purchase transaction
→ Subscribe to transaction confirmation

Using The Graph:

→ Show last 100 sales in this collection
→ Display floor price history
→ Find all NFTs owned by a user
→ Calculate volume over last 7 days

🎬 Summary: Your Blockchain Data Toolkit

graph TD
    A["Your dApp"] -->|Direct Read/Write| B["RPC Provider"]
    A -->|Complex Queries| C["The Graph"]

    B -->|One-time requests| D["JSON-RPC Methods"]
    B -->|Real-time updates| E["WebSocket Subscriptions"]

    C -->|Custom index| F["Subgraph"]
    C -->|Smart questions| G["GraphQL Queries"]

Remember:

• 🔌 RPC = Direct phone line (simple, real-time)
• 📊 The Graph = Smart librarian (complex queries, organized data)
• 🔔 WebSockets = Open line for live updates
• 📝 Subgraphs = Your custom data catalog
• 🎯 GraphQL = Ask exactly what you need

🚀 You Did It!

You now understand how dApps access blockchain data. You’ve learned:

✅ What RPC providers do ✅ How JSON-RPC methods work ✅ The magic of WebSocket subscriptions ✅ Why The Graph Protocol exists ✅ What subgraphs are and how indexing works ✅ How to query with GraphQL

Next step: Build something! Start with a simple RPC call, then try The Graph when you need complex queries.

The blockchain’s data is no longer a mystery to you! 🎉