ERC-721 Approve Facet

Manage ERC-721 approvals within a diamond

Key Features

• Exposes external functions for ERC-721 approval management.
• Interacts with shared diamond storage via ERC721Storage.
• Supports approve and setApprovalForAll operations.
• Provides exportSelectors for discovery within a diamond.

Overview

This facet provides external functions for managing ERC-721 token approvals within a diamond. It interacts with shared diamond storage to track token ownership and approvals. Developers integrate this facet to enable external calls for approving token transfers and operator permissions, ensuring upgradeability and composability.

Storage

ERC721Storage

Definition

struct ERC721Storage {
  mapping(uint256 tokenId => address owner) ownerOf;
  mapping(address owner => uint256 balance) balanceOf;
  mapping(address owner => mapping(address operator => bool approved)) isApprovedForAll;
  mapping(uint256 tokenId => address approved) approved;
}

State Variables

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

Functions

approve

Approves another address to transfer the given token ID.

function approve(address _to, uint256 _tokenId) external;

Parameters:

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

---

setApprovalForAll

Approves or revokes permission for an operator to manage all caller's assets.

function setApprovalForAll(address _operator, bool _approved) external;

Parameters:

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

---

exportSelectors

Exports the function selectors of the ERC721ApproveFacet This function is use as a selector discovery mechanism for diamonds

function exportSelectors() external pure returns (bytes memory);

Returns:

Property	Type	Description
-	bytes	selectors The exported function selectors of the ERC721ApproveFacet

Events

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 ERC721NonexistentToken(uint256 _tokenId);

Signature:

error ERC721InvalidApprover(address _approver);

Signature:

error ERC721InvalidOperator(address _operator);

Best Practices

Best Practice

• Initialize the facet and its associated storage correctly during diamond deployment.
• Ensure that access control for state-changing functions aligns with your diamond's security model.
• When upgrading, verify that the storage slot STORAGE_POSITION is compatible with previous versions to prevent data loss.

Security Considerations

Security

The approve function reverts with ERC721NonexistentToken if the token ID does not exist, and ERC721InvalidApprover if the caller is not the owner or approved delegate. The setApprovalForAll function reverts with ERC721InvalidOperator if the operator is the caller. Follow standard Solidity security practices for input validation and access control.

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Last updated:March 13, 2026