Configuring Table Write Access

Configuring Table Write Access

Everything you need to know to control access for programmable tables.

By default, the owner of a table is the only one that can modify data. However, Tableland gives you a suite of options for programming ownership in useful ways. The most feature rich way to use a controller; a smart contract that implements the ITablelandTables interface, enabling on-chain rules that govern off-chain table mutations.

Access Control with Controllers

First, it’s important to understand a controller vs. owner. The controller of a table is the address who controls the table’s access control list (”ACL”). The owner of the table is the address who originally minted the table and has the ownership. Both of these values can be a user’s account or a smart contract, but the owner is ultimately the one who can change who the controller is and transfer table ownership altogether.

There are default options that exist, but for custom access controls, you must create a contract that implements ITablelandController. Within the TablelandTables registry contract, the runSQL method is the only function that leverages the controller. The controller is used to define what an address can do to a table, including the ability to INSERT, UPDATE, and DELETE rows, plus some additional GRANT / REVOKE provisioning.

ITablelandController

The required ITablelandController interface of the TablelandController contract. Developers must implement the ITablelandController for advanced, custom access control features. Default values are implemented by the TablelandTables registry contract.

interface ITablelandController {
    /**
     * @dev Object defining how a table can be accessed.
     */
    struct Policy {
        bool allowInsert;
        bool allowUpdate;
        bool allowDelete;
        string whereClause;
        string withCheck;
        string[] updatableColumns;
    }

    /**
     * @dev Returns a {Policy} struct defining how a table can be accessed by `caller`.
     */
    function getPolicy(address caller) external payable returns (Policy memory);
}

Policy

Object defining how a table can be accessed.

allowInsert (boolean)

Whether or not the table should allow SQL INSERT statements.

allowUpdate (boolean)

Whether or not the table should allow SQL UPDATE statements.

allowDelete (boolean)

Whether or not the table should allow SQL DELETE statements.

whereClause (string)

A conditional WHERE clause used with SQL UPDATE and DELETE statements.

  • For example, a value of "foo > 0" will concatenate all SQL UPDATE and/or DELETE statements with "WHERE foo > 0". This can be useful for limiting how a table can be modified.
  • Use the Policies library’s joinClauses to include more than one condition.

withCheck (string)

A conditional CHECK clause used with SQL INSERT statements.

  • For example, a value of "foo > 0" will concatenate all SQL INSERT statements with a check on the incoming data. Namely, "CHECK (foo > 0)". This can be useful for limiting how table data ban be added.
  • Use the Policies library’s joinClauses to include more than one condition.

updatableColumns (string[])

A list of SQL column names that can be updated.

getPolicy

Returns a Policy struct, defining how a table can be accessed by caller.

Parameters

caller (address) The address to be used to check access control permissions.

Defintion

external, payable

Returns

Policy The corresponding Policy struct for the given address.

Note: The method is marked as payable. This means developers can set up access controls that require payment in order for the caller to even make a write query attempt.

Default Options

The default ownership of a table is granted to the address that creates it. Some examples include:

  • Externally Owned Account (”EOA”)
    • A developer creates a table with their Ethereum wallet → The developer’s wallet address retains default ownership of the table.
    • A user of an app built on Tableland creates a table with their Ethereum wallet → The user’s wallet address retains default ownership of the table.
  • Smart contract
    • A smart contract creates a table → The smart contract retains default ownership of the table.

Allow All Policy

Default ownership grants the owner the following “allow all” abilities:

  • allowInserttrue Allow INSERTs into the table.
  • allowUpdatetrue Allow UPDATE on all columns.
  • allowDeletetrue Allow DELETE, including using WHERE statements.
  • whereCheck"" Defaults to an empty string, meaning, no WHERE clause additions are implemented.
  • withCheck"" Defaults to an empty string, meaning, no CHECK clause additions are implemented.
  • updatableColumnsnew string[](0) Defaults to an empty list, meaning, there are no restrictions on which columns can be updated.
  • Note: Also allows GRANT and REVOKE capabilities (see below).

In other words, if a custom TablelandController contract has not been set, the default values for the Policy are those defined above. There are a few additional things to note:

  • If the controller is never explicitly set (default setting), the controller is automatically defined as the 0x0 address. This means that a table owner has the default “allow all” permissions.
    • In other words, the owner is the only one who can call a runSQL function by default; it’s the only address that can perform any SQL write queries.
  • If the owner sets the controller to an EOA, the caller of a runSQL function must be the controller of the table. This controller EOA address will now have the default “allow all” permissions, removing all query permissions from the table owner.
    • For example, user address_1 mints a table and sets the controller to user address_2.
    • Before setting the controller, address_1 had full “allow all” permissions and ownership of the table; address_1 could perform any SQL write operations and was the owner of the ERC721 token (e.g., can still set the controller, transfer ownership, etc.).
    • After address_1 set the controller to address_2, address_1 no longer has the “allow all” permissions. The controller address_2 has the “allow all” permission, but the owner still owns the table (e.g., can set/change the controller, transfer ownership, etc.).
  • If the controller is set to a contract address, it must implement ITablelandController.
    • It is technically possible to set a controller to a contract address that doesn’t implement the controller interface. However, this would lead to issues.
    • There is logic that checks if the runSQL caller is a contract. If so, the registry contract makes a getPolicy call on this calling controller contract — which, if ITablelandController isn’t implemented, will cause the call to revert.

GRANT & REVOKE

Rather than a smart contract defined ACL, mutating SQL statements can provision access to certain addresses using the GRANT or REVOKE keywords. Only the owner can make a write query with the following:

  • GRANT ⇒ Allows the caller to grant an address permissions for INSERT, UPDATE, or DELETE abilities on a table.
  • REVOKE ⇒ Removes any privileges that were enabled for an address using GRANT.

It’s important to note that when the owner explicitly sets the controller (using setController), any GRANT provisions will no longer be valid. The action of setting a controller causes previously defined GRANT abilities to be “ignored.” Upon removing (”unsetting”) the controller, those permissions are fully respected.

The act of “unsetting” — recall the default controller is defined as the 0x0 address. To unset an existing controller, simply update the table’s controller using this address:

// Set some controller address, and previous `GRANT`s no longer work.
setController(0xAbCdEf1234567890AbCdEf1234567890AbCdEf12)
// "Unset" the controller, and `GRANT`s are back in action & work again.
setController(0x0000000000000000000000000000000000000000)

Example SQL Statements

To grant permissions for all table mutation abilities, you can execute a runSQL write query that resembles something like the following:

GRANT INSERT, UPDATE, DELETE ON <tableName> TO '<0x_address_value>'

Perhaps at a point in the future, you decide to remove the permission to DELETE rows via a write query:

REVOKE DELETE ON <tableName> FROM '<0x_address_value>'

For more information on GRANT and REVOKE, see the SQL Specification.

Registry Controller Methods

The TablelandTables registry smart contract has three dedicated controller methods, which are helpful to understand within this context.

getController(uint256 tableId)

setController(address caller, uint256 tableId, address controller)

lockController(address caller, uint256 tableId)

Creating a TablelandController

A TablelandController compliant contract is one that implements ITablelandController, meaning, it supports a getPolicy read method that returns the ITablelandController’s Policy struct. This method can include on-chain rules as logical checks prior to the Policy being returned (e.g., conditional logic to check ownership of a token or certain balance).

How It Works

As noted, the default controller is the 0x0 address. Optionally, a table owner can register the TablelandController's address via the TablelandTables contract’s setController method. Once registered, Tableland will check any INSERT, UPDATE, or DELETE statement against the getPolicy response to ensure it is a valid modification.

Writing the TablelandController

The following example shows how to import the ITablelandController interface and then create a policy that only allows INSERTs on a table, from any address.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.12;

import "@tableland/evm/contracts/ITablelandController.sol";
import "@tableland/evm/contracts/policies/Policies.sol";

contract ExamplePolicy {
  function getPolicy(address sender)
      public
      payable
      override
      returns (ITablelandController.Policy memory)
  {

      /*
      * Add any custom ACL check here.
      */

      // Return allow-insert policy
      return
          ITablelandController.Policy({
              allowInsert: true,
              allowUpdate: false,
              allowDelete: false,
              whereClause: Policies.joinClauses(new string[](0)),
              withCheck: Policies.joinClauses(new string[](0)),
              updatableColumns: new string[](0)
          });
  }
}

Alternatively, you could lock down your table to “allow none” for now, and then unlock your policy with a modification later. A dynamic policy could be interesting in cases such as post-reveal during your NFT launch.

Example of Allow None

ITablelandController.Policy({
  allowInsert: false,
  allowUpdate: false,
  allowDelete: false,
  whereClause: Policies.joinClauses(new string[](0)),
  withCheck: Policies.joinClauses(new string[](0)),
  updatableColumns: new string[](0)
});

Setting the Policy

The owner of a contract needs to call the Tableland registry’s setController method to register a deployed policy on-chain.

function setController(
  address caller,     // The table owner's address.
  uint256 tableId,    // Unique `tableId`, as defined in `prefix_chainId_tableId`
  address controller  // Contract address that implements `ITablelandController`
)

Smart Contract Calls

In cases where a table is owned by a smart contract, you can also call the setController method from the smart contract. Here, adding a policy update method that can be called after deploy (where the onlyOwner modifier is from a useful Ownable OpenZeppelin contract):

function updateController() onlyOwner {
   _tableland.setController(
      address(this),
      _tableId,
      address(this)
    );
}

Dev Environment

If you are using a development framework, like hardhat, or simply using a library like ethers, you can make smart contact calls directly to the Tableland registry smart contract to set the controller.

Manually

If you are just playing around, you can also call the setController method on Etherscan by going to the Tableland registry contract directly (you’ll need to call the method from the address of the table owner). You can find the list of live contracts here.

Using a Smart Contract Only

When you create tables directly from your smart contract, you are not required to use the TablelandController since all updates need to come from your smart contract. In these cases, you can write various abstractions around SQL updates and build them into your app.

Take the example from

where the smart contract dynamically inserts token metadata into a table at the time of token minting.

Dynamic INSERTs

function safeMint(address to) public returns (uint256) {
    uint256 newItemId = _tokenIds.current();
    _tableland.runSQL(
      address(this),
			SQLHelpers.toInsert(
				_tablePrefix, // prefix
				_metadataTableId, // table id
			  // column names
				"id, external_link, x, y",
			  // values
				string.concat(
					Strings.toString(newItemId),
					", 'not.implemented.xyz', 0, 0)"
				)
      )
    );
    _safeMint(to, newItemId, "");
    _tokenIds.increment();
    return newItemId;
}

Because the contract sending the runSQL command has full ownership over the table, the query will run. If any other contract or end-user attempts to make the same call, it will fail!

Later on in that same example

, we run an UPDATE command to dynamically update the data for a single NFT. You can see that in the example, we allow only the NFT owner to change only the row in the table that records their NFT’s metadata. Pretty cool, the smart contract is driving the ACL here.

User Controlled UPDATEs

function makeMove(uint256 tokenId, uint256 x, uint256 y) public {
  // Check token ownership
  require(this.ownerOf(tokenId) == msg.sender, "Invalid owner");
  // Simple on-chain gameplay enforcement
  require(x < 512 && 0 <= x, "Out of bounds");
  require(y < 512 && 0 <= y, "Out of bounds");
  // Update the row in tableland
  _tableland.runSQL(
    address(this),
		SQLHelpers.toUpdate(
			_tablePrefix, //prefix
			_metadataTableId, //table id
      // setters
			string.concat(
	      "x = ",
	      Strings.toString(x),
	      ", y = ",
	      Strings.toString(y),
			),
			// where conditions
			string.concat(
	      "id = ",
	      Strings.toString(tokenId)
			)
    )
  );
}

Dynamic ACL

The power of the TablelandController and pure smart contract approach is that they allow you to create ACLs that evolve with your project. Perhaps you have an NFT where users have a window of time where they can update metadata, and then your project will lock it down. To do this, you can simply update the TablelandController or change the logic in your smart contract to enforce the new rules. It's that easy.