ERC721EnumerableFacet

ERC-721 token ownership and metadata management

Key Features

• Implements core ERC-721 enumerable functionality.
• Exposes external functions for diamond routing.
• Utilizes diamond storage for state management.
• Compatible with ERC-2535 diamond standard.

Overview

This facet implements ERC-721 token functionality, including ownership tracking and metadata retrieval, within a diamond proxy. It exposes standard ERC-721 functions externally, allowing interaction with token data via the diamond's unified interface. Developers integrate this facet to provide NFT capabilities while leveraging the diamond's upgradeability and composability.

---

Storage

ERC721EnumerableStorage

Definition

struct ERC721EnumerableStorage {
  mapping(uint256 tokenId => address owner) ownerOf;
  mapping(address owner => uint256[] ownerTokens) ownerTokens;
  mapping(uint256 tokenId => uint256 ownerTokensIndex) ownerTokensIndex;
  uint256[] allTokens;
  mapping(uint256 tokenId => uint256 allTokensIndex) allTokensIndex;
  mapping(address owner => mapping(address operator => bool approved)) isApprovedForAll;
  mapping(uint256 tokenId => address approved) approved;
  string name;
  string symbol;
  string baseURI;
}

State Variables

Property	Type	Description
STORAGE_POSITION	bytes32	Diamond storage slot position for this module (Value: keccak256("compose.erc721.enumerable"))

Functions

name

Returns the name of the token collection.

function name() external view returns (string memory);

Returns:

Property	Type	Description
-	string	The token collection name.

---

symbol

Returns the symbol of the token collection.

function symbol() external view returns (string memory);

Returns:

Property	Type	Description
-	string	The token symbol.

---

tokenURI

Provide the metadata URI for a given token ID.

function tokenURI(uint256 _tokenId) external view returns (string memory);

Parameters:

Property	Type	Description
_tokenId	uint256	tokenID of the NFT to query the metadata from

Returns:

Property	Type	Description
-	string	the URI providing the detailed metadata of the specified tokenID

---

totalSupply

Returns the total number of tokens in existence.

function totalSupply() external view returns (uint256);

Returns:

Property	Type	Description
-	uint256	The total supply of tokens.

---

balanceOf

Returns the number of tokens owned by an address.

function balanceOf(address _owner) external view returns (uint256);

Parameters:

Property	Type	Description
_owner	address	The address to query.

Returns:

Property	Type	Description
-	uint256	The balance (number of tokens owned).

---

ownerOf

Returns the owner of a given token ID.

function ownerOf(uint256 _tokenId) public view returns (address);

Parameters:

Property	Type	Description
_tokenId	uint256	The token ID to query.

Returns:

Property	Type	Description
-	address	The address of the token owner.

---

tokenOfOwnerByIndex

Returns a token ID owned by a given address at a specific index.

function tokenOfOwnerByIndex(address _owner, uint256 _index) external view returns (uint256);

Parameters:

Property	Type	Description
_owner	address	The address to query.
_index	uint256	The index of the token.

Returns:

Property	Type	Description
-	uint256	The token ID owned by _owner at _index.

---

getApproved

Returns the approved address for a given token ID.

function getApproved(uint256 _tokenId) external view returns (address);

Parameters:

Property	Type	Description
_tokenId	uint256	The token ID to query.

Returns:

Property	Type	Description
-	address	The approved address for the token.

---

isApprovedForAll

Returns whether an operator is approved for all tokens of an owner.

function isApprovedForAll(address _owner, address _operator) external view returns (bool);

Parameters:

Property	Type	Description
_owner	address	The token owner.
_operator	address	The operator address.

Returns:

Property	Type	Description
-	bool	True if approved for all, false otherwise.

---

approve

Approves another address to transfer a specific token ID.

function approve(address _to, uint256 _tokenId) external;

Parameters:

Property	Type	Description
_to	address	The address being approved.
_tokenId	uint256	The token ID to approve.

---

setApprovalForAll

Approves or revokes an operator to manage all tokens of the caller.

function setApprovalForAll(address _operator, bool _approved) external;

Parameters:

Property	Type	Description
_operator	address	The operator address.
_approved	bool	True to approve, false to revoke.

---

transferFrom

Transfers a token from one address to another.

function transferFrom(address _from, address _to, uint256 _tokenId) external;

Parameters:

Property	Type	Description
_from	address	The current owner of the token.
_to	address	The recipient address.
_tokenId	uint256	The token ID to transfer.

---

safeTransferFrom

Safely transfers a token, checking for receiver contract compatibility.

function safeTransferFrom(address _from, address _to, uint256 _tokenId) external;

Parameters:

Property	Type	Description
_from	address	The current owner of the token.
_to	address	The recipient address.
_tokenId	uint256	The token ID to transfer.

---

safeTransferFrom

Safely transfers a token with additional data.

function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes calldata _data) external;

Parameters:

Property	Type	Description
_from	address	The current owner of the token.
_to	address	The recipient address.
_tokenId	uint256	The token ID to transfer.
_data	bytes	Additional data to send to the receiver contract.

Events

Signature:

event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);

Signature:

event Approval(address indexed _owner, address indexed _to, uint256 indexed _tokenId);

Signature:

event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);

Errors

Signature:

error ERC721InvalidOwner(address _owner);

Signature:

error ERC721NonexistentToken(uint256 _tokenId);

Signature:

error ERC721IncorrectOwner(address _sender, uint256 _tokenId, address _owner);

Signature:

error ERC721InvalidSender(address _sender);

Signature:

error ERC721InvalidReceiver(address _receiver);

Signature:

error ERC721InsufficientApproval(address _operator, uint256 _tokenId);

Signature:

error ERC721InvalidApprover(address _approver);

Signature:

error ERC721InvalidOperator(address _operator);

Signature:

error ERC721OutOfBoundsIndex(address _owner, uint256 _index);

Best Practices

Best Practice

• Initialize the name, symbol, and baseURI during diamond setup.
• Enforce access control on state-changing functions like approve and transferFrom if custom logic requires it.
• Ensure storage compatibility when upgrading to new versions of this facet.

Security Considerations

Security

Follow standard Solidity security practices. Input validation for token IDs and addresses is critical. The safeTransferFrom functions include checks for receiver contract compatibility. Ensure that any custom access control added to state-changing functions is robust.

Related Documentation

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ERC721EnumerableMod

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Last updated:December 30, 2025