Bugfix: $sort field set incorrectly in GET_LIST handler

[nicholasnelson]

In testing Websocket compatibility, I've found the following issue.

Feathers documentation shows the query format for $sort in GET_LIST as follows:

// Find the 10 newest messages
app.service('messages').find({
  query: {
    $limit: 10,
    $sort: {
      createdAt: -1
    }
  }
});

ra-data-feathers currently provides the $sort param like this:

query: {
  '$sort[createdAt]': '-1'
}

This works for the REST transport, but not for Websocket.

I suspect this is because the REST transport on the server side parses $sort[createdAt]: '-1' to $sort: { createdAt: '-1' } when the query string is parsed. When Websocket is being used, the query is not parsed (because it is sent directly as an object rather than a string).

For example in my project which is backed by Sequelize, this results in a SQL query like ... WHERE '$sort[createdAt]' = '-1' ... which then gives an error about the field '$sort[createdAt]' not existing.

Updating GET_LIST to set the $sort parameter as in the Feathers documentation example above should resolve this issue.