20 / 26Part 5: Blockchain state and transactions explainedBeginner

Walking through an example

With the setup complete, you can now submit a few transactions and query both the state and the transaction history to see how the two relate.

Start from a clean node. If the Chromia Node is running, stop it with Ctrl+C first, then wipe its data with this command:

shell

chr node start --wipe

The command deletes every transaction on the blockchain and resets the current state. To confirm, run:

shell

chr query get_all_books

You should get an empty array, which means the current state contains no books.

Now submit a transaction that creates a book. Misspell "Chromia" on purpose so you have something to fix later with an update:

shell

chr tx create_book "ISBN001" "Crhomia 101" "Alice" --key-id "book_admin" --await

Expected output:

shell

transaction with rid DF94A07EACBA673CC4ECA4A43D70CDA4FD30E4335E124B7153FB12A78FDD8CE9 was posted CONFIRMED

tip

To avoid passing --key-id on every transaction, set a default key in a .chromia/config file:

ini

key.id = book_admin

The file can live in either of two places:

Global config: ~/.chromia/config — used by every project unless something overrides it
Project config: .chromia/config inside your project folder — takes priority over the global file

With the default key configured, CLI transactions no longer need --key-id:

bash

chr tx create_book "ISBN001" "Crhomia 101" "Alice" --await

The CLI picks up the configured key on its own.

For the complete rules on which config file wins, read Key pair reading flow

Once the transaction is in, list every book with the get_all_books command:

shell

chr query get_all_books

You should see:

json

[  {    "author": "Alice",    "isbn": "ISBN001",    "title": "Crhomia 101"  }]

The new book now appears in the state/table. Next, query the transactions stored on the blockchain:

shell

chr query get_transactions

The output is:

json

[  [    "body": [      "blockchain_rid": x"B52F0A078993374201853649F807FDEDD6516A424557F311E2AF769761F89D40",      "operations": [        [          "args": [            "ISBN001",            "Crhomia 101",            "Alice"          ],          "name": "create_book"        ]      ],      "signers": [        x"035A25AB32B85E6A5B58A31A71CC709CED159096194984243159492CBA0FADF82F"      ]    ],    "signatures": [      x"91EFC02C2958698E71C41D2B020F9E4EF81F6C427FAA98667D6FF4B87857809E1ECE4C9C923B1E5659177B8D0635711E47A4EBB502217A437D3FFC89741E74DD"    ]  ]]

This shows the transaction was recorded on the blockchain and the state changed to match.

To fix the misspelled title, you need an operation that updates a book's title. First, make the title field mutable in the book entity:

src/main/entities.rell

entity book {  key isbn: text;  mutable title: text;  author: text;}

Then add the update operation:

src/main/operations.rell

operation update_book(isbn: text, title: text){  val adminPubkey = chain_context.args.admin_pubkey;  require(op_context.is_signer(adminPubkey), "Only admin can update books");  update book @ { .isbn == isbn }( .title = title );}

The running node does not yet know about this operation. Update the Chromia Node with the following command and wait for the next block before testing:

shell

chr node update

When the update is done, send a transaction that changes the book's title:

shell

chr tx update_book "ISBN001" "Chromia 101" --key-id "book_admin" --await

Query the state and the blockchain transactions once more:

shell

chr query get_all_books

The state now returns the corrected title:

json

[  {    "author": "Alice",    "isbn": "ISBN001",    "title": "Chromia 101"  }]

Query the blockchain transactions the same way:

shell

chr query get_transactions

The output is:

json

[  [    "body": [      "blockchain_rid": x"B52F0A078993374201853649F807FDEDD6516A424557F311E2AF769761F89D40",      "operations": [        [          "args": [            "ISBN001",            "Crhomia 101",            "Alice"          ],          "name": "create_book"        ]      ],      "signers": [        x"035A25AB32B85E6A5B58A31A71CC709CED159096194984243159492CBA0FADF82F"      ]    ],    "signatures": [      x"91EFC02C2958698E71C41D2B020F9E4EF81F6C427FAA98667D6FF4B87857809E1ECE4C9C923B1E5659177B8D0635711E47A4EBB502217A437D3FFC89741E74DD"    ]  ],  [    "body": [      "blockchain_rid": x"B52F0A078993374201853649F807FDEDD6516A424557F311E2AF769761F89D40",      "operations": [        [          "args": [            "ISBN001",            "Chromia 101"          ],          "name": "update_book"        ]      ],      "signers": [        x"035A25AB32B85E6A5B58A31A71CC709CED159096194984243159492CBA0FADF82F"      ]    ],    "signatures": [      x"FD9402B45ED52A238B0C756AFA1ABA5BD2F89C9AE44343E58FE76E207F4672CF0AF5C37F7209E5D9A474491671000FAFA9753A4BF2B5D16AE7C5C48CFA18A8E1"    ]  ]]

The blockchain now holds two transactions: the one that created the book and the one that changed its title.

The state is the combined result of both transactions. Because every transaction affecting this book is recorded, you can trace back through the history and see exactly how the current state came to be.

To build and maintain decentralized applications well, you need a clear picture of how Rell, Chromia, the blockchain, and the state work together.

Written for this site from Chromia’s public course. Code samples are the course’s own.