World
Querying

Querying

The query utility allows Systems to ask questions about keys in the World. These queries are evaluated left to right and can include fragments like "Give me all keys in the CanFly table" and "Then keep keys in the Position table with value {x: 1, y: 43}".

query is simply a view function, but it can only be used with tables that have the relevant modules installed:

  • For Has or Not fragments, the corresponding table needs to have KeysInTable.
  • For HasValue or NotValue fragments, the corresponding table needs to have KeysWithValue.

Let's walk through an example of using query in a simple game, where we check that a position is unoccupied before allowing a playing to move into it.

Creating tables

First, we define some tables. Here, the Player table is a boolean flag; storing whether a key corresponds to a player. Position stores the (x, y) coordinate of a key.

import { mudConfig } from "@latticexyz/world/register";
 
export default mudConfig({
  tables: {
    Player: "bool",
    Position: { schema: { x: "int32", y: "int32" } },
  },
});

Installing the indexing modules

Next, we install the necessary modules for our use case. We will be querying for all keys in the Player table, so it requires KeysInTable. Conversely, will be filtering by a specific position, so Position requires KeysWithValue.

import { mudConfig } from "@latticexyz/world/register";
import { resolveTableId } from "@latticexyz/config";
 
export default mudConfig({
  tables: {
    ...
  },
  modules: [
    {
      name: "KeysInTableModule",
      root: true,
      args: [resolveTableId("Player")],
    },
    {
      name: "KeysWithValueModule",
      root: true,
      args: [resolveTableId("Position")],
    },
  ],
});

Using query

Now the modules are installed, we can we construct the QueryFragment, then call query like so:

QueryFragment[] memory fragments = new QueryFragment[](2);
 
// Specify the more restrictive filter first for performance reasons
fragments[0] = QueryFragment(QueryType.HasValue, PositionTableId, abi.encode(x, y));
 
// The value argument is ignored in Has query fragments
fragments[1] = QueryFragment(QueryType.Has, PlayerTableId, new bytes(0));
 
bytes32[][] memory keyTuples = query(fragments);

Here is the full system, which queries for all players at a position to check if it occupied.

import { System } from "@latticexyz/world/src/System.sol";
import { query, QueryFragment, QueryType } from "@latticexyz/world/src/modules/keysintable/query.sol";
import { PlayerTableId, Position, PositionTableId } from "../codegen/Tables.sol";
 
contract MoveSystem is System {
  function move(int32 x, int32 y) public {
    QueryFragment[] memory fragments = new QueryFragment[](2);
 
    // Specify the more restrictive filter first for performance reasons
    fragments[0] = QueryFragment(QueryType.HasValue, PositionTableId, abi.encode(x, y));
 
    // The value argument is ignored in Has query fragments
    fragments[1] = QueryFragment(QueryType.Has, PlayerTableId, new bytes(0));
 
    bytes32[][] memory keyTuples = query(fragments);
 
    require(keyTuples.length == 0, "There is a player at the given position");
 
    Position.set(bytes32(msg.sender), x, y);
  }
}
Community ComputersInternal tables & systems