tests/form_pages/test_item_field.py

@@ -310,7 +310,7 @@ def test_form_autosave_item_field_data_source_error(pub):
     with mock.patch.object(NamedDataSource, 'get_structured_value', lambda *args: None):
         autosave_resp = app.post('/test/autosave', params=resp.form.submit_fields())
     assert autosave_resp.json == {
-        'reason': 'form deserialization failed: a datasource is unavailable (field id: 1)',
+        'reason': 'form deserialization failed: no matching value in datasource (field id: 1, value: \'1\')',
         'result': 'error',
     }
 

tests/form_pages/test_live.py

@@ -2147,7 +2147,7 @@ def test_field_live_condition_data_source_error(pub):
     with mock.patch.object(NamedDataSource, 'get_structured_value', lambda *args: None):
         live_resp = app.post('/foo/live', params=resp.form.submit_fields())
         assert live_resp.json == {
-            'reason': 'form deserialization failed: a datasource is unavailable (field id: 1)',
+            'reason': 'form deserialization failed: no matching value in datasource (field id: 1, value: \'2\')',
             'result': 'error',
         }
 

tests/workflow/test_backoffice_field.py

@@ -685,10 +685,28 @@ def test_set_backoffice_field_item(pub):
     item.perform(formdata)
 
     formdata = formdef.data_class().get(formdata.id)
-    assert formdata.data['bo1'] == 'foobar'
+    assert formdata.data['bo1'] is None
     assert formdata.data.get('bo1_display') is None
     assert formdata.data.get('bo1_structured') is None
 
+    # check with unknown value but no datasource
+    wf.backoffice_fields_formdef.fields[0].data_source = None
+    wf.store()
+    formdata = formdef.data_class()()
+    formdata.data = {}
+    formdata.just_created()
+    formdata.store()
+
+    item = SetBackofficeFieldsWorkflowStatusItem()
+    item.parent = st1
+    item.fields = [{'field_id': 'bo1', 'value': 'foobar'}]
+    item.perform(formdata)
+
+    formdata = formdef.data_class().get(formdata.id)
+    assert formdata.data['bo1'] == 'foobar'
+    assert formdata.data.get('bo1_display') == 'foobar'
+    assert formdata.data.get('bo1_structured') is None
+
 
 def test_set_backoffice_field_card_item(pub):
     CardDef.wipe()

wcs/fields.py

@@ -2557,6 +2557,18 @@ class ItemField(WidgetField, MapOptionsMixin, ItemFieldMixin, ItemWithImageField
                 widget.extra_css_class = self.extra_css_class
         return widget
 
+    def set_value(self, data, value, raise_on_error=False):
+        data_source = data_sources.get_object(self.data_source)
+        if raise_on_error and value and data_source and data_source.type != 'jsonp':
+            # check value (this looks up on id only, not text, convert_value_from_anything()
+            # can be called before if the value may be a text value, as it's done in the
+            # wf/backoffice_fields.py action.
+            if not data_source.get_structured_value(value):
+                raise SetValueError(
+                    'no matching value in datasource (field id: %s, value: %r)' % (self.id, value)
+                )
+        super().set_value(data, value, raise_on_error=raise_on_error)
+
     def store_display_value(self, data, field_id, raise_on_error=False):
         value = data.get(field_id)
         if not value:

wcs/wf/backoffice_fields.py

@@ -187,7 +187,7 @@ class SetBackofficeFieldsWorkflowStatusItem(WorkflowStatusItem):
                     continue
 
             try:
-                formdef_field.set_value(formdata.data, new_value)
+                formdef_field.set_value(formdata.data, new_value, raise_on_error=True)
             except SetValueError as e:
                 summary = _('Failed to set %(kind)s field (%(id)s), error: %(exc)s') % {
                     'kind': formdef_field.get_type_label(),