Join chat

Meta

Logux stores metadata for every action in separated object:

log = [
  [action1, meta1],
  [action2, meta2],
  …
]

Meta contains Logux-related data. It should not contain anything related to application state.

Meta has unique action’s ID, creating time, processing status and many other things. Meta is open structure, applications can set custom keys to meta object.

{
  added: 5,
  id: "1564508138460 380:R7BNGAP5:px3-J3oc 0",
  reasons: ['amplifr/lastPrices'],  ​
  subprotocol: '0.6.2',
  time: 1564508138460
}

Setting Meta

Most of methods to add action accept meta as second arguments:

store.dispatch.sync(action, meta)
client.log.add(action, meta)
server.log.add(action, meta)
ctx.sendBack(action, meta)

Logux Redux has the only method without meta argument: store.dispatch(action). Use store.dispatch.local(action, meta) to set meta for local-tab actions.

Changing Meta

In Logux architecture, you can change application state only by adding new action to the log. This is why you can’t change action or action’s order.

Since meta doesn’t contain anything related to application state, you can change meta if it will not affect action’s order.

  • store.log.changeMeta(actionId, {
      reasons: []
    })

    You can not change meta’s keys related to action’s order: id, time, added.

    On the server you can set channels, users, clients and nodes keys (and singular versions) for new action from the client by resend callback:

  • server.type('users/rename', {
      …,
      resend (ctx, action, meta) {
        return { channel: `users/${ action.userId }` }
      },
      …
    })

    Meta Synchronization

    Logux synchronizes only 3 meta’s keys:

    All other meta keys are local and both server and client do not send them.

    ID and Time

    Each action has unique ID. This ID is unique on all machines.

    "1564508138460 380:R7BNGAP5:px3-J3oc 0"

    To generate ID unique across all nodes in Logux cluster, Logux combines 3 values:

    log.generateId() //=> "1564508138460 380:R7BNGAP5:px3-J3oc 0"
    log.generateId() //=> "1564508138460 380:R7BNGAP5:px3-J3oc 1"
    log.generateId() //=> "1564508138461 380:R7BNGAP5:px3-J3oc 0"

    In real world, every node will have own time. For instance, user could set wrong time on own phone. This is why you should not use meta.id as a time. Logux has special meta.time, which will use time of current node. During the connection client and server will calculate time difference between them and change meta.time during synchronization. As result, meta.time could be different on different nodes.

    const time = new Date(meta.time) //=> Date 2019-07-30T17:35:38.460Z

    meta.time is a timestamp. Few actions can have the same meta.time if these actions was generated very fast in the same millisecond. Logux has isFirstOlder helper, which uses both meta.time and meta.id to always be sure what action was generated later.

    import isFirstOlder from '@logux/core/is-first-older'
    
    if (isFirstOlder(meta1, meta2)) {
      lastName = action1.name
    } else {
      lastName = action2.name
    }

    Common Meta Keys

    These meta’s keys are available on client and server:

    Client Meta Keys

    Server Meta Keys