reports: Add RelatedPostings.group_by_first_meta_link() method.

conservancy_beancount/reports/accrual.py

@@ -694,7 +694,7 @@ def main(arglist: Optional[Sequence[str]]=None,
 
     returncode = 0
     postings = filter_search(data.Posting.from_entries(entries), args.search_terms)
-    groups: PostGroups = dict(AccrualPostings.group_by_meta(postings, 'invoice'))
+    groups: PostGroups = dict(AccrualPostings.group_by_first_meta_link(postings, 'invoice'))
     for error in load_errors:
         bc_printer.print_error(error, file=stderr)
         returncode |= ReturnFlag.LOAD_ERRORS

conservancy_beancount/reports/core.py

@@ -46,7 +46,6 @@ from typing import (
     Any,
     BinaryIO,
     Callable,
-    DefaultDict,
     Dict,
     Generic,
     Iterable,
@@ -255,6 +254,17 @@ class RelatedPostings(Sequence[data.Posting]):
         else:
             self._postings = list(source)
 
+    @classmethod
+    def _group_by(cls: Type[RelatedType],
+                  postings: Iterable[data.Posting],
+                  key: Callable[[data.Posting], T],
+    ) -> Iterator[Tuple[T, RelatedType]]:
+        mapping: Dict[T, List[data.Posting]] = collections.defaultdict(list)
+        for post in postings:
+            mapping[key(post)].append(post)
+        for value, posts in mapping.items():
+            yield value, cls(posts, _can_own=True)
+
     @classmethod
     def group_by_meta(cls: Type[RelatedType],
                       postings: Iterable[data.Posting],
@@ -268,11 +278,27 @@ class RelatedPostings(Sequence[data.Posting]):
         The values are RelatedPostings instances that contain all the postings
         that had that same metadata value.
         """
-        mapping: DefaultDict[Optional[MetaValue], List[data.Posting]] = collections.defaultdict(list)
-        for post in postings:
-            mapping[post.meta.get(key, default)].append(post)
-        for value, posts in mapping.items():
-            yield value, cls(posts, _can_own=True)
+        def key_func(post: data.Posting) -> Optional[MetaValue]:
+            return post.meta.get(key, default)
+        return cls._group_by(postings, key_func)
+
+    @classmethod
+    def group_by_first_meta_link(
+            cls: Type[RelatedType],
+            postings: Iterable[data.Posting],
+            key: MetaKey,
+    ) -> Iterator[Tuple[Optional[str], RelatedType]]:
+        """Relate postings by the first link in metadata
+
+        This method takes an iterable of postings and returns a mapping.
+        The keys of the mapping are the values of
+        post.meta.first_link(key, None).
+        The values are RelatedPostings instances that contain all the postings
+        that had that same first metadata link.
+        """
+        def key_func(post: data.Posting) -> Optional[MetaValue]:
+            return post.meta.first_link(key, None)
+        return cls._group_by(postings, key_func)
 
     def __repr__(self) -> str:
         return f'<{type(self).__name__} {self._postings!r}>'

tests/test_reports_related_postings.py

@@ -63,6 +63,27 @@ def two_accruals_three_payments():
         (-550, 'EUR'),
     ))
 
+@pytest.fixture
+def link_swap_posts():
+    retval = []
+    meta = {
+        'rt-id': 'rt:12 rt:16',
+        '_post_type': data.Posting,
+        '_meta_type': data.Metadata,
+    }
+    for n in range(1, 3):
+        n = Decimal(n)
+        retval.append(testutil.Posting(
+            'Assets:Receivable:Accounts', n * 10, metanum=n, **meta,
+        ))
+    meta['rt-id'] = 'rt:16 rt:12'
+    for n in range(1, 3):
+        n = Decimal(n)
+        retval.append(testutil.Posting(
+            'Liabilities:Payable:Accounts', n * -10, metanum=n, **meta,
+        ))
+    return retval
+
 def test_initialize_with_list(credit_card_cycle):
     related = core.RelatedPostings(credit_card_cycle[0].postings)
     assert len(related) == 2
@@ -313,3 +334,35 @@ def test_group_by_meta_many_single_posts(two_accruals_three_payments):
     actual = dict(core.RelatedPostings.group_by_meta(postings, 'metanumber'))
     assert set(actual) == {post.units.number for post in postings}
     assert len(actual) == len(postings)
+
+def test_group_by_first_meta_link_zero():
+    assert not list(core.RelatedPostings.group_by_first_meta_link([], 'foo'))
+
+def test_group_by_first_meta_link_no_key(link_swap_posts):
+    actual = dict(core.RelatedPostings.group_by_first_meta_link(
+        iter(link_swap_posts), 'Nonexistent',
+    ))
+    assert len(actual) == 1
+    assert list(actual[None]) == link_swap_posts
+
+def test_group_by_first_meta_link_bad_type(link_swap_posts):
+    assert all(post.meta.get('metanum') for post in link_swap_posts), \
+        "did not find metadata required by test"
+    actual = dict(core.RelatedPostings.group_by_first_meta_link(
+        iter(link_swap_posts), 'metanum',
+    ))
+    assert len(actual) == 1
+    assert list(actual[None]) == link_swap_posts
+
+def test_group_by_first_meta_link(link_swap_posts):
+    actual_all = dict(core.RelatedPostings.group_by_first_meta_link(
+        iter(link_swap_posts), 'rt-id',
+    ))
+    assert len(actual_all) == 2
+    for key, expect_account in [
+            ('rt:12', 'Assets:Receivable:Accounts'),
+            ('rt:16', 'Liabilities:Payable:Accounts'),
+    ]:
+        actual = actual_all.get(key, '')
+        assert len(actual) == 2
+        assert all(post.account == expect_account for post in actual)