Account Model

Cadence-or other resource-oriented smart contract languages like Move-completely differentiate themselves from central ledger-based languages such as Solidity.

Instead of storing user data inside the contract, data is stored in the form of Resources inside user accounts. This means users completely own and control their data once it is in their account, unless the user explicity allows their data to be accessed/modified through published Capabilities.

Solidity vs. Cadence

In the Solidity world, all data is stored inside of the contract. The contract acts as a central ledger.

Furthermore, assets such as NFTs are represented as simple integers. If we wanted to know who owned a specific NFT (with ‘id’ == 4), we would go inside the contract and ask “what is the address associated with ‘id’ == 4?”

However in Cadence, two things differ:

1. Data is stored in user accounts, not the contract
2. Assets such as NFTs are represented as actual objects (“resources”) that can store their own data and functions

This has a lot of benefits. Namely, resources have built-in properties that make them extremely secure. They cannot be copied or lost.

Let’s take a look at an NFT example in Cadence:

While definitions of the NFT resource and Collection are made in the contract, the user actually stores a Collection resource inside their account.

Example Implementation

Below is an example smart contract & associated transaction leveraging the resource-oriented nature of Cadence, and showing how they get stored in accounts.

		
			pub contract Test {

  // define a new Profile resource
  pub resource Profile {
    pub let id: UInt64
    pub let name: String
    pub let favoriteNumber: Int

    init(name: String, favoriteNumber: Int) {
      self.id = self.uuid // a unique identifier for every resource in existence
      self.name = name
      self.favoriteNumber = favoriteNumber
    }
  }

  // public function to create a Profile
  pub fun createProfile(name: String, favoriteNumber: Int): @Profile {
    return <- create Profile(name: name, favoriteNumber: favoriteNumber)
  }

}
		 
	

		
			import Test from 0x01

transaction(name: String, favoriteNumber: Int) {
  prepare(signer: AuthAccount) {
    // a new 'Profile' resource is created
    let newProfile <- Profile.createProfile(name: name, favoriteNumber: favoriteNumber)
    // the 'Profile' gets stored in the user's account
    signer.save(<- newProfile, to: /storage/TestProfile)
  }
}