reports: Add RelatedPostings.meta_values() method.

This corresponds to the ledtag_onevalue check in the
payment-report and income-report scripts.

conservancy_beancount/reports/core.py

@@ -29,9 +29,14 @@ from typing import (
     Mapping,
     Optional,
     Sequence,
+    Set,
     Tuple,
     Union,
 )
+from ..beancount_types import (
+    MetaKey,
+    MetaValue,
+)
 
 class Balance(Mapping[str, data.Amount]):
     """A collection of amounts mapped by currency
@@ -134,3 +139,9 @@ class RelatedPostings(Sequence[data.Posting]):
             return balance
         except NameError:
             return Balance()
+
+    def meta_values(self,
+                    key: MetaKey,
+                    default: Optional[MetaValue]=None,
+    ) -> Set[Optional[MetaValue]]:
+        return {post.meta.get(key, default) for post in self}

tests/test_reports_related_postings.py

@@ -106,3 +106,64 @@ def test_iter_with_balance_credit_card(credit_card_cycle):
 
 def test_iter_with_balance_two_acccruals(two_accruals_three_payments):
     check_iter_with_balance(two_accruals_three_payments)
+
+def test_meta_values_empty():
+    related = core.RelatedPostings()
+    assert related.meta_values('key') == set()
+
+def test_meta_values_no_match():
+    related = core.RelatedPostings()
+    related.add(testutil.Posting('Income:Donations', -1, metakey='metavalue'))
+    assert related.meta_values('key') == {None}
+
+def test_meta_values_no_match_default_given():
+    related = core.RelatedPostings()
+    related.add(testutil.Posting('Income:Donations', -1, metakey='metavalue'))
+    assert related.meta_values('key', '') == {''}
+
+def test_meta_values_one_match():
+    related = core.RelatedPostings()
+    related.add(testutil.Posting('Income:Donations', -1, key='metavalue'))
+    assert related.meta_values('key') == {'metavalue'}
+
+def test_meta_values_some_match():
+    related = core.RelatedPostings()
+    related.add(testutil.Posting('Income:Donations', -1, key='1'))
+    related.add(testutil.Posting('Income:Donations', -2, metakey='2'))
+    assert related.meta_values('key') == {'1', None}
+
+def test_meta_values_some_match_default_given():
+    related = core.RelatedPostings()
+    related.add(testutil.Posting('Income:Donations', -1, key='1'))
+    related.add(testutil.Posting('Income:Donations', -2, metakey='2'))
+    assert related.meta_values('key', '') == {'1', ''}
+
+def test_meta_values_all_match():
+    related = core.RelatedPostings()
+    related.add(testutil.Posting('Income:Donations', -1, key='1'))
+    related.add(testutil.Posting('Income:Donations', -2, key='2'))
+    assert related.meta_values('key') == {'1', '2'}
+
+def test_meta_values_all_match_one_value():
+    related = core.RelatedPostings()
+    related.add(testutil.Posting('Income:Donations', -1, key='1'))
+    related.add(testutil.Posting('Income:Donations', -2, key='1'))
+    assert related.meta_values('key') == {'1'}
+
+def test_meta_values_all_match_default_given():
+    related = core.RelatedPostings()
+    related.add(testutil.Posting('Income:Donations', -1, key='1'))
+    related.add(testutil.Posting('Income:Donations', -2, key='2'))
+    assert related.meta_values('key', '') == {'1', '2'}
+
+def test_meta_values_many_types():
+    expected = {
+        datetime.date(2020, 4, 1),
+        Decimal(42),
+        testutil.Amount(5),
+        'rt:42',
+    }
+    related = core.RelatedPostings()
+    for index, value in enumerate(expected):
+        related.add(testutil.Posting('Income:Donations', -index, key=value))
+    assert related.meta_values('key') == expected