Detailed Description

EnginioModel represents data from Enginio as a QAbstractListModel.

EnginioModel is a QAbstractListModel, together with a view it allows to show the result of a query in a convenient way. The model executes query, update and create operations asynchronously on an Enginio backend collection, which allows not only to read data from the cloud but also modify it.

The simplest type of query is:

{ "objectType": "objects.fruits" }

Assigning such a query to the model results in downloading of all objects from the "objects.fruits" collection. It is possible to append new objects, to modify or to remove them.

The query has to result in a list of objects, each object becomes an item in the model. Properties of the items are used as role names. There are a few predefined role names that will always be available (Role).

The operations are executed asynchronously, which means that user interface is not blocked while the model is initialized and updated. Every modification is divided in two steps; request and confirmation. For example when append is called EnginioModel returns immediately as if the operation had succeeded. In the background it waits for confirmation from the backend and only then the operation is really finished. It may happen that operation fails, for example because of insufficient access rights, in that case the operation will be reverted.

There are two, ways of tracking if an item state is the same in the model and backend. Each item has a role that returns a boolean SyncedRole, role name "_synced" which indicates whether the item is successfully updated on the server. This role can for example meant to be used for a busy indicator while a property is being updated. Alternatively the status of each EnginioReply returned by EnginioModel can be tracked. The operation is confirmed when the reply is finished without error.

When a reply is finished it is the user's responsibility to delete it, it can be done by connecting the finished signal to deleteLater.

QObject::connect(reply, &EnginioReply::finished, reply, &EnginioReply::deleteLater);

Note: it is not safe to use the delete operator directly in finished.

Note: EnginioClient emits the finished and error signals for the model, not the model itself.

The query can contain one or more options: The "sort" option, to get presorted data:

{
  "objectType": "objects.fruits",
  "sort": [{"sortBy":"price", "direction": "asc"}]
}

The "query" option is used for filtering:

{
  "objectType": "objects.fruits",
  "query": {"name": {"$in": ["apple", "orange", "kiwi"]}}
}

The "limit" option to limit the amount of results:

{
  "objectType": "objects.fruits",
  "limit": 10
}

The "offset" option to skip some results from the beginning of a result set:

{
  "objectType": "objects.fruits",
  "offset": 10
}

The options are valid only during the initial model population and are not enforced in anyway when updating or otherwise modifying the model data. QSortFilterProxyModel can be used to do more advanced sorting and filtering on the client side.

EnginioModel can not detect when a property of a result is computed by the backend. For example the "include" option to query fills in the original creator of and object with the full object representing the "creator".

{
  "objectType": "objects.fruits",
  "include": {"creator": {}}
}

For the model the "creator" property is not longer a reference (as it is on the backend), but a full object. But while the full object is accessible, attempts to alter the object's data will fail.