implement required fields in core

ianalyzer_readers/readers/core.py

@@ -139,6 +139,15 @@ def fieldnames(self) -> List[str]:
         '''
         return [field.name for field in self.fields]
 
+
+    @property
+    def _required_field_names(self) -> List[str]:
+        '''
+        A list of the names of all required fields
+        '''
+        return [field.name for field in self.fields if field.required]
+
+
     def sources(self, **kwargs) -> Iterable[Source]:
         '''
         Obtain source files for the Reader.
@@ -176,10 +185,12 @@ def source2dicts(self, source: Source) -> Iterable[Document]:
         if isinstance(data, AbstractContextManager):
             with data as data:
                 for document in self.iterate_data(data, metadata):
-                    yield document
+                    if self._has_required_fields(document):
+                        yield document
         else:
-            for doc in self.iterate_data(data, metadata):
-                yield doc
+            for document in self.iterate_data(data, metadata):
+                if self._has_required_fields(document):
+                    yield document
 
 
     def data_and_metadata_from_source(self, source: Source) -> Tuple[Any, Dict]:
@@ -361,3 +372,13 @@ def _reject_extractors(self, *inapplicable_extractors: extract.Extractor):
             if isinstance(field.extractor, inapplicable_extractors):
                 raise RuntimeError(
                     "Specified extractor method cannot be used with this type of data")
+
+    def _has_required_fields(self, document: Document) -> Iterable[Document]:
+        '''
+        Check whether a document has a value for all fields marked as required.
+        '''
+
+        has_field = lambda field_name: document.get(field_name, None) is not None
+        return all(
+            has_field(field_name) for field_name in self._required_field_names
+        )

ianalyzer_readers/readers/xml.py

@@ -96,9 +96,6 @@ def iterate_data(self, data: bs4.BeautifulSoup, metadata: Dict) -> Iterable[Docu
                 )
                 external_soup = None        
 
-        required_fields = [
-            field.name for field in self.fields if field.required]
-
         # iterate through entries
         top_tag = resolve_tag_specification(self.__class__.tag_toplevel, metadata)
         bowl = top_tag.find_next_in_soup(data)
@@ -129,8 +126,7 @@ def iterate_data(self, data: bs4.BeautifulSoup, metadata: Dict) -> Iterable[Docu
 
                 # yield the union of external fields and document fields
                 field_dict.update(external_dict)
-                if all(field_name in field_dict for field_name in required_fields):
-                    yield field_dict
+                yield field_dict
         else:
             logger.warning('Top-level tag not found')