Fixed #373 -- Added CompositePrimaryKey.

Thanks Lily Foote and Simon Charette for reviews and mentoring
this Google Summer of Code 2024 project.

Co-authored-by: Simon Charette <charette.s@gmail.com>
Co-authored-by: Lily Foote <code@lilyf.org>

2 files changed, 71 insertions, 12 deletions

diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index 49263d5944..053bdc09d5 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -7,7 +7,9 @@ from itertools import chain
 from django.core.exceptions import EmptyResultSet, FieldError, FullResultSet
 from django.db import DatabaseError, NotSupportedError
 from django.db.models.constants import LOOKUP_SEP
-from django.db.models.expressions import F, OrderBy, RawSQL, Ref, Value
+from django.db.models.expressions import ColPairs, F, OrderBy, RawSQL, Ref, Value
+from django.db.models.fields import composite
+from django.db.models.fields.composite import CompositePrimaryKey
 from django.db.models.functions import Cast, Random
 from django.db.models.lookups import Lookup
 from django.db.models.query_utils import select_related_descend
@@ -283,6 +285,9 @@ class SQLCompiler:
                 # Reference to a column.
                 elif isinstance(expression, int):
                     expression = cols[expression]
+                # ColPairs cannot be aliased.
+                if isinstance(expression, ColPairs):
+                    alias = None
                 selected.append((alias, expression))
 
         for select_idx, (alias, expression) in enumerate(selected):
@@ -997,6 +1002,7 @@ class SQLCompiler:
         # alias for a given field. This also includes None -> start_alias to
         # be used by local fields.
         seen_models = {None: start_alias}
+        select_mask_fields = set(composite.unnest(select_mask))
 
         for field in opts.concrete_fields:
             model = field.model._meta.concrete_model
@@ -1017,7 +1023,7 @@ class SQLCompiler:
                 # parent model data is already present in the SELECT clause,
                 # and we want to avoid reloading the same data again.
                 continue
-            if select_mask and field not in select_mask:
+            if select_mask and field not in select_mask_fields:
                 continue
             alias = self.query.join_parent_model(opts, model, start_alias, seen_models)
             column = field.get_col(alias)
@@ -1110,9 +1116,10 @@ class SQLCompiler:
                 )
             return results
         targets, alias, _ = self.query.trim_joins(targets, joins, path)
+        target_fields = composite.unnest(targets)
         return [
             (OrderBy(transform_function(t, alias), descending=descending), False)
-            for t in targets
+            for t in target_fields
         ]
 
     def _setup_joins(self, pieces, opts, alias):
@@ -1504,13 +1511,25 @@ class SQLCompiler:
         return result
 
     def get_converters(self, expressions):
+        i = 0
         converters = {}
-        for i, expression in enumerate(expressions):
-            if expression:
+
+        for expression in expressions:
+            if isinstance(expression, ColPairs):
+                cols = expression.get_source_expressions()
+                cols_converters = self.get_converters(cols)
+                for j, (convs, col) in cols_converters.items():
+                    converters[i + j] = (convs, col)
+                i += len(expression)
+            elif expression:
                 backend_converters = self.connection.ops.get_db_converters(expression)
                 field_converters = expression.get_db_converters(self.connection)
                 if backend_converters or field_converters:
                     converters[i] = (backend_converters + field_converters, expression)
+                i += 1
+            else:
+                i += 1
+
         return converters
 
     def apply_converters(self, rows, converters):
@@ -1524,6 +1543,24 @@ class SQLCompiler:
                 row[pos] = value
             yield row
 
+    def has_composite_fields(self, expressions):
+        # Check for composite fields before calling the relatively costly
+        # composite_fields_to_tuples.
+        return any(isinstance(expression, ColPairs) for expression in expressions)
+
+    def composite_fields_to_tuples(self, rows, expressions):
+        col_pair_slices = [
+            slice(i, i + len(expression))
+            for i, expression in enumerate(expressions)
+            if isinstance(expression, ColPairs)
+        ]
+
+        for row in map(list, rows):
+            for pos in col_pair_slices:
+                row[pos] = (tuple(row[pos]),)
+
+            yield row
+
     def results_iter(
         self,
         results=None,
@@ -1541,8 +1578,10 @@ class SQLCompiler:
         rows = chain.from_iterable(results)
         if converters:
             rows = self.apply_converters(rows, converters)
-            if tuple_expected:
-                rows = map(tuple, rows)
+        if self.has_composite_fields(fields):
+            rows = self.composite_fields_to_tuples(rows, fields)
+        if tuple_expected:
+            rows = map(tuple, rows)
         return rows
 
     def has_results(self):
@@ -1863,6 +1902,18 @@ class SQLInsertCompiler(SQLCompiler):
                     )
                 ]
                 cols = [field.get_col(opts.db_table) for field in self.returning_fields]
+            elif isinstance(opts.pk, CompositePrimaryKey):
+                returning_field = returning_fields[0]
+                cols = [returning_field.get_col(opts.db_table)]
+                rows = [
+                    (
+                        self.connection.ops.last_insert_id(
+                            cursor,
+                            opts.db_table,
+                            returning_field.column,
+                        ),
+                    )
+                ]
             else:
                 cols = [opts.pk.get_col(opts.db_table)]
                 rows = [
@@ -1876,8 +1927,10 @@ class SQLInsertCompiler(SQLCompiler):
                 ]
         converters = self.get_converters(cols)
         if converters:
-            rows = list(self.apply_converters(rows, converters))
-        return rows
+            rows = self.apply_converters(rows, converters)
+        if self.has_composite_fields(cols):
+            rows = self.composite_fields_to_tuples(rows, cols)
+        return list(rows)
 
 
 class SQLDeleteCompiler(SQLCompiler):
@@ -2065,6 +2118,7 @@ class SQLUpdateCompiler(SQLCompiler):
         query.add_fields(fields)
         super().pre_sql_setup()
 
+        is_composite_pk = meta.is_composite_pk
         must_pre_select = (
             count > 1 and not self.connection.features.update_can_self_select
         )
@@ -2079,7 +2133,8 @@ class SQLUpdateCompiler(SQLCompiler):
             idents = []
             related_ids = collections.defaultdict(list)
             for rows in query.get_compiler(self.using).execute_sql(MULTI):
-                idents.extend(r[0] for r in rows)
+                pks = [row if is_composite_pk else row[0] for row in rows]
+                idents.extend(pks)
                 for parent, index in related_ids_index:
                     related_ids[parent].extend(r[index] for r in rows)
             self.query.add_filter("pk__in", idents)
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index b7b93c235a..cca11bfcc2 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -627,8 +627,12 @@ class Query(BaseExpression):
         if result is None:
             result = empty_set_result
         else:
-            converters = compiler.get_converters(outer_query.annotation_select.values())
-            result = next(compiler.apply_converters((result,), converters))
+            cols = outer_query.annotation_select.values()
+            converters = compiler.get_converters(cols)
+            rows = compiler.apply_converters((result,), converters)
+            if compiler.has_composite_fields(cols):
+                rows = compiler.composite_fields_to_tuples(rows, cols)
+            result = next(rows)
 
         return dict(zip(outer_query.annotation_select, result))