Query the blockchain using postchain-client

This lesson shows you how to query the Chromia blockchain for information about transactions and about the current state of your dapp's table.

postchain-client keeps queries simple. The example below fetches every book and walks through how the call works.

Start by declaring a Book type to describe each book's data:

type Book = {  isbn: string;  title: string;  author: string;};

Then add a function that fetches all books and prints them:

const getAllBooks = async () => {  const bookList = await client.query<Book[]>("get_all_books", {});  console.log("Book list:", bookList);};

The function runs the query through the client and its query command. You pass the expected return type as a generic, here Book[].

Function arguments

First argument: queryFunctionName

The name of the query function on the blockchain. It matches a function in your Rell script that returns every book record.

Second argument: queryArguments

Passing an empty object ({}) means the query runs without arguments. When a blockchain function needs input to filter or process its results, you put those parameters in this object.

Handling the response

client.query returns a promise. Once it resolves, you get an array of books (Book[]) that you can display, process, or use however your application requires. This example logs them to the console.

Call getAllBooks(); from your main function as shown below, then run the client again to see the book you added. To restart and test the example from a clean state, run chr node start --wipe, which starts a new node with no existing data.

async function main() {  client = await createClient({    nodeUrlPool: "http://localhost:7740",    blockchainRid: blockchainRID,  });  console.log("Creating a new book transaction");  await client.signAndSendUniqueTransaction(    { name: "create_book", args: ["ISBN1", "Chromia 101", "John Doe"] },    bookKeeperSignatureProvider  );  getAllBooks();}