New item/attr setter for Dict nodes

[ramirezfranciscof]

Fixes #2883

The following two ways for setting (key:val) pairs in the dicts stored inside a Dict node were failing (the first one silently, the second one with an error message) but are now valid:

dict_node = Dict()
dict_node.dict.x = 'Set a value for x'
dict_node['x'] = 'Overwrite the value for x'

[codecov]

Codecov Report

Merging #4351 into develop will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #4351      +/-   ##
===========================================
- Coverage    79.15%   79.15%   -0.00%     
===========================================
  Files          468      468              
  Lines        34616    34620       +4     
===========================================
+ Hits         27397    27399       +2     
- Misses        7219     7221       +2     

Flag	Coverage Δ
#django	72.77% <100.00%> (+0.01%)	⬆️
#sqlalchemy	71.96% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiida/orm/nodes/data/dict.py	85.00% <100.00%> (+0.79%)	⬆️
aiida/orm/utils/managers.py	92.07% <100.00%> (+0.27%)	⬆️
aiida/engine/daemon/runner.py	79.32% <0.00%> (-3.44%)	⬇️
aiida/transports/plugins/local.py	81.29% <0.00%> (-0.25%)	⬇️

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[sphuber]

Thanks @ramirezfranciscof . Have some suggestions

[sphuber]

Although I see the point of adding this, given that this was not clear for you either, this does not just apply to the Dict nodes, but to all nodes. All node specific data are stored as attributes in the database. So although this may help clear things up, it may also confuse, since it may suggest that this is behavior specific to the Dict plugin.

I would propose a text something like:

    The dictionary contents of a `Dict` node are stored in the database as attributes. The dictionary can be initialized
    through the `dict` argument in the constructor. After construction, values can be retrieved and updated through the
    item getters and setters, respectively:

        node['key'] = 'value'

    Alternatively, the `dict` property returns an instance of the `AttributeManager` that can be used to get and set
    values through attribute notation:

        node.dict.key = 'value'

    Note that trying to set dictionary values directly on the node, e.g. `node.key = value`, will not work as intended.
    It will merely set the `key` attribute on the node instance, but will not be stored in the database. As soon as the
    node goes out of scope, the value will be lost.

    Finally, all dictionary mutations will be forbidden once the node is stored.

[ramirezfranciscof]

Ok, would it still be ok to add something like this between the last two paragraphs?

    node goes out of scope, the value will be lost.

    Note that here it becomes apparent the difference in something being an "attribute of a node" (in
    the sense that it is stored in the "attribute" column of the database when the node is stored) and
    something being an "attribute of a python object" (in the sense of being able to modify and access
    it as if it was a property of the variable, e.g. `node.key = value`). This is true of all types of
    nodes, but it becomes more relevant for `Dict` nodes where one is constantly manipulating these
    attributes.

    Finally, all dictionary mutations will be forbidden once the node is stored.

[sphuber]

Thanks a lot @ramirezfranciscof !