signal-desktop/js/modules/migrations/18/index.js

exports.run = (transaction) => {
  const messagesStore = transaction.objectStore('messages');

  console.log("Create message attachment metadata index: 'hasAttachments'");
  messagesStore.createIndex(
    'hasAttachments',
    ['conversationId', 'hasAttachments', 'received_at'],
    { unique: false }
  );

  ['hasVisualMediaAttachments', 'hasFileAttachments'].forEach((name) => {
    console.log(`Create message attachment metadata index: '${name}'`);
    messagesStore.createIndex(
      name,
      ['conversationId', 'received_at', name],
      { unique: false }
    );
  });
};