In this tutorial we will retrieve the history of a data contract created in the Register a Data Contract tutorial. Only contracts that have enabled the keepsHistory option during contract creation will store revision information.

Prerequisites

• General prerequisites (Node.js / Hellar SDK installed)
• A Hellar Platform contract ID for a contract configured to keep history: Tutorial: Register a Data Contract

Code

Retrieving data contract history

`const Hellar = require('hellar');

const client = new Hellar.Client({ network: 'mainnet' });

const retrieveContractHistory = async () => { const contractId = '8cvMFwa2YbEsNNoc1PXfTacy2PVq2SzVnkZLeQSzjfi6' return await client.platform.contracts.history(contractId, 0, 10, 0); };

retrieveContractHistory() .then((d) => { Object.entries(d).forEach(([key, value]) => { client.platform.hpp.dataContract .createFromObject(value) .then((contract) => console.dir(contract.toJSON(), { depth: 5 })); }); }) .catch((e) => console.error('Something went wrong:\n', e)) .finally(() => client.disconnect());`

Example data contract history

The following example response shows a retrieved contract history:

[ { "$format_version": "0", "id": "BWgzcW4XRhmYKzup1xY8fMi3ZHGG1Hf8fD9Rm3e3bopm", "config": { "$format_version": "0", "canBeDeleted": false, "readonly": false, "keepsHistory": true, "documentsKeepHistoryContractDefault": false, "documentsMutableContractDefault": true, "requiresIdentityEncryptionBoundedKey": null, "requiresIdentityDecryptionBoundedKey": null }, "version": 1, "ownerId": "DKFKmJ58ZTDddvviDJwDyCznDMxd9Y6bsJcBN5Xp8m5w", "schemaDefs": null, "documentSchemas": { "note": { "type": "object", "properties": { "message": { "type": "string" } }, "additionalProperties": false } } }, { "$format_version": "0", "id": "BWgzcW4XRhmYKzup1xY8fMi3ZHGG1Hf8fD9Rm3e3bopm", "config": { "$format_version": "0", "canBeDeleted": false, "readonly": false, "keepsHistory": true, "documentsKeepHistoryContractDefault": false, "documentsMutableContractDefault": true, "requiresIdentityEncryptionBoundedKey": null, "requiresIdentityDecryptionBoundedKey": null }, "version": 2, "ownerId": "DKFKmJ58ZTDddvviDJwDyCznDMxd9Y6bsJcBN5Xp8m5w", "schemaDefs": null, "documentSchemas": { "note": { "type": "object", "properties": { "message": { "type": "string" }, "author": { "type": "string" } }, "additionalProperties": false } } } ]

📘 Please refer to the data contract reference page for more comprehensive details related to contracts and documents.

What’s Happening

After we initialize the Client, we request a contract’s history. The platform.contracts.history method method takes four arguments: a contract ID, timestamp to start at, number of revisions to retrieve, and a number to offset the start of the records. After the contract history is retrieved, it is displayed on the console.