Add nullables to candidate_subclass()

CHANGELOG.rst

@@ -18,6 +18,9 @@ Added
 * `@wajdikhattel`_: Add multinary candidates.
   (`#455 <https://github.com/HazyResearch/fonduer/issues/455>`_)
   (`#456 <https://github.com/HazyResearch/fonduer/pull/456>`_)
+* `@HiromuHota`_: Add ``nullables`` to :func:`candidate_subclass()` to allow NULL mention in a candidate.
+  (`#496 <https://github.com/HazyResearch/fonduer/issues/496>`_)
+  (`#497 <https://github.com/HazyResearch/fonduer/pull/497>`_)
 
 Changed
 ^^^^^^^

src/fonduer/candidates/candidates.py

@@ -265,8 +265,11 @@ def apply(  # type: ignore
                     enumerate(
                         # a list of mentions for each mention subclass within a doc
                         getattr(doc, mention.__tablename__ + "s")
+                        + ([None] if nullable else [])
+                    )
+                    for mention, nullable in zip(
+                        candidate_class.mentions, candidate_class.nullables
                     )
-                    for mention in candidate_class.mentions
                 ]
             )
             # Get a set of stable_ids of candidates.
@@ -286,15 +289,16 @@ def apply(  # type: ignore
 
                 # TODO: Make this work for higher-order relations
                 if self.arities[i] == 2:
-                    ai, a = (cand[0][0], cand[0][1].context)
-                    bi, b = (cand[1][0], cand[1][1].context)
+                    ai, a = (cand[0][0], cand[0][1].context if cand[0][1] else None)
+                    bi, b = (cand[1][0], cand[1][1].context if cand[1][1] else None)
 
                     # Check for self-joins, "nested" joins (joins from context to
                     # its subcontext), and flipped duplicate "symmetric" relations
                     if not self.self_relations and a == b:
                         logger.debug(f"Skipping self-joined candidate {cand}")
                         continue
-                    if not self.nested_relations and (a in b or b in a):
+                    # Skip the check if either is None as None is not iterable.
+                    if not self.nested_relations and (a and b) and (a in b or b in a):
                         logger.debug(f"Skipping nested candidate {cand}")
                         continue
                     if not self.symmetric_relations and ai > bi:
@@ -306,7 +310,8 @@ def apply(  # type: ignore
                     candidate_args[arg_name] = cand[j][1]
 
                 stable_ids = tuple(
-                    cand[j][1].context.get_stable_id() for j in range(self.arities[i])
+                    cand[j][1].context.get_stable_id() if cand[j][1] else None
+                    for j in range(self.arities[i])
                 )
                 # Skip if this (temporary) candidate is used by this candidate class.
                 if (

src/fonduer/candidates/models/candidate.py

@@ -74,6 +74,7 @@ def candidate_subclass(
     table_name: Optional[str] = None,
     cardinality: Optional[int] = None,
     values: Optional[List[Any]] = None,
+    nullables: Optional[List[bool]] = None,
 ) -> Type[Candidate]:
     """Create new relation.
 
@@ -95,6 +96,10 @@ def candidate_subclass(
     :param cardinality: The cardinality of the variable corresponding to the
         Candidate. By default is 2 i.e. is a binary value, e.g. is or is not
         a true mention.
+    :param values: A list of values a candidate can take as their label.
+    :param nullables: The number of nullables must match that of args.
+        If nullables[i]==True, a mention for ith mention subclass can be NULL.
+        If nullables=``None`` (by default), no mention can be NULL.
     """
     if table_name is None:
         table_name = camel_to_under(class_name)
@@ -124,6 +129,12 @@ def candidate_subclass(
     elif cardinality is not None:
         values = list(range(cardinality))
 
+    if nullables:
+        if len(nullables) != len(args):
+            raise ValueError("The number of nullables must match that of args.")
+    else:
+        nullables = [False] * len(args)
+
     class_spec = (args, table_name, cardinality, values)
     if class_name in candidate_subclasses:
         if class_spec == candidate_subclasses[class_name][1]:
@@ -153,6 +164,7 @@ def candidate_subclass(
             # Helper method to get argument names
             "__argnames__": [_.__tablename__ for _ in args],
             "mentions": args,
+            "nullables": nullables,
         }
         class_attribs["document_id"] = Column(
             Integer, ForeignKey("document.id", ondelete="CASCADE")
@@ -166,10 +178,12 @@ def candidate_subclass(
         # Create named arguments, i.e. the entity mentions comprising the
         # relation mention.
         unique_args = []
-        for arg in args:
+        for arg, nullable in zip(args, nullables):
             # Primary arguments are constituent Contexts, and their ids
             class_attribs[arg.__tablename__ + "_id"] = Column(
-                Integer, ForeignKey(arg.__tablename__ + ".id", ondelete="CASCADE")
+                Integer,
+                ForeignKey(arg.__tablename__ + ".id", ondelete="CASCADE"),
+                nullable=nullable,
             )
             class_attribs[arg.__tablename__] = relationship(
                 arg.__name__,

src/fonduer/utils/utils.py

@@ -61,7 +61,7 @@ def get_set_of_stable_ids(
         set_of_stable_ids.update(
             set(
                 [
-                    tuple(m.context.get_stable_id() for m in c)
+                    tuple(m.context.get_stable_id() for m in c) if c else None
                     for c in getattr(doc, candidate_class.__tablename__ + "s")
                 ]
             )

tests/candidates/test_candidates.py

@@ -541,3 +541,34 @@ def test_pickle_subclasses():
     pickle.loads(pickle.dumps(part))
     pickle.loads(pickle.dumps(temp))
     pickle.loads(pickle.dumps(parttemp))
+
+
+def test_candidate_with_nullable_mentions():
+    """Test if mentions can be NULL."""
+    docs_path = "tests/data/html/112823.html"
+    pdf_path = "tests/data/pdf/112823.pdf"
+    doc = parse_doc(docs_path, "112823", pdf_path)
+
+    # Mention Extraction
+    MentionTemp = mention_subclass("MentionTemp")
+    temp_ngrams = MentionNgramsTemp(n_max=2)
+    mention_extractor_udf = MentionExtractorUDF(
+        [MentionTemp],
+        [temp_ngrams],
+        [temp_matcher],
+    )
+    doc = mention_extractor_udf.apply(doc)
+
+    assert len(doc.mention_temps) == 23
+
+    # Candidate Extraction
+    CandidateTemp = candidate_subclass("CandidateTemp", [MentionTemp], nullables=[True])
+    candidate_extractor_udf = CandidateExtractorUDF(
+        [CandidateTemp], [None], False, False, True
+    )
+
+    doc = candidate_extractor_udf.apply(doc, split=0)
+    # The number of extracted candidates should be that of mentions + 1 (NULL)
+    assert len(doc.candidate_temps) == len(doc.mention_temps) + 1
+    # Extracted candidates should include one with NULL mention.
+    assert None in [c[0] for c in doc.candidate_temps]