PseudoPotentialFamily: add the pseudo_type extra

Since pseudopotential families can now optionally support many
pseudopotential formats, although each instance only supports one format
at a time, it should be easy to determine which format any particular
family hosts.

The `pseudo_type` property is added to `PseudoPotentialFamily` which
returns the entry point name of the `PseudoPotentialData` subclass that
is used by the pseudopotentials that it contains. For example, if the
family hosts only `UpfData` nodes, whose entry point string is defined
as `aiida.data:pseudo.upf`, it will return `pseudo.upf`. Note that the
entry point group `aiida.data` is stripped as it is redundant
information.

The `pseudo_type` is stored as an extra on the family instance and is
updated after the node contents are mutated, i.e. after `add_nodes`,
`remove_nodes` and `clear. Having this information stored as an extra
and not calculated each time on the fly, not only helps efficiency but
it also makes it queryable, which is important if one needs to find a
family with pseudos of a particular type.

The class does not provide a `pseudo_type` setter as this only ever
needs to be set by the class itself. Users can of course always change
the value through the `set_extra` method of the `Group` class, causing
inconsistency in the data, but there is nothing one can do to protect
against this.

aiida_pseudo/groups/family/pseudo.py

@@ -25,6 +25,7 @@ class PseudoPotentialFamily(Group):
     hosted by setting ``_pseudo_types`` to a tuple of ``PseudoPotentialData`` subclasses.
     """
 
+    _key_pseudo_type = '_pseudo_type'
     _pseudo_types = (PseudoPotentialData,)
     _pseudos = None
 
@@ -174,6 +175,26 @@ def create_from_folder(cls, dirpath, label, *, description='', pseudo_type=None,
 
         return family
 
+    @property
+    def pseudo_type(self):
+        """Return the type of the pseudopotentials that are hosted by this family.
+
+        :return: the pseudopotential type or ``None`` if none has been set yet.
+        """
+        return self.get_extra(self._key_pseudo_type, None)
+
+    def update_pseudo_type(self):
+        """Update the pseudo type, stored as an extra, based on the current nodes in the family."""
+        pseudo_types = {pseudo.__class__ for pseudo in self.pseudos.values()}
+
+        if pseudo_types:
+            assert len(pseudo_types) == 1, 'Family contains pseudopotential data nodes of various types.'
+            entry_point_name = tuple(pseudo_types)[0].get_entry_point_name()
+        else:
+            entry_point_name = None
+
+        self.set_extra(self._key_pseudo_type, entry_point_name)
+
     def add_nodes(self, nodes):
         """Add a node or a set of nodes to the family.
 
@@ -203,6 +224,7 @@ def add_nodes(self, nodes):
             pseudos[pseudo.element] = pseudo
 
         self.pseudos.update(pseudos)
+        self.update_pseudo_type()
 
         super().add_nodes(nodes)
 
@@ -218,11 +240,13 @@ def remove_nodes(self, nodes):
 
         removed = [node.pk for node in nodes]
         self._pseudos = {pseudo.element: pseudo for pseudo in self.pseudos.values() if pseudo.pk not in removed}
+        self.update_pseudo_type()
 
     def clear(self):
         """Remove all the pseudopotentials from this family."""
         super().clear()
         self._pseudos = None
+        self.update_pseudo_type()
 
     @property
     def pseudos(self):

tests/groups/family/test_pseudo.py

@@ -37,6 +37,26 @@ class CustomFamily(PseudoPotentialFamily):
         CustomFamily(label='custom')
 
 
+@pytest.mark.usefixtures('clear_db')
+def test_pseudo_type(get_pseudo_potential_data):
+    """Test ``PseudoPotentialFamily.pseudo_type`` property."""
+    family = PseudoPotentialFamily(label='label').store()
+    assert family.pseudo_type is None
+
+    pseudo = get_pseudo_potential_data('Ar').store()
+    family.add_nodes((pseudo,))
+    assert family.pseudo_type == pseudo.get_entry_point_name()
+
+    family.clear()
+    assert family.pseudo_type is None
+
+    family.add_nodes((pseudo,))
+    assert family.pseudo_type == pseudo.get_entry_point_name()
+
+    family.remove_nodes(pseudo)
+    assert family.pseudo_type is None
+
+
 @pytest.mark.usefixtures('clear_db')
 def test_construct():
     """Test the construction of `PseudoPotentialFamily` works."""