Fixed #29771 -- Support database-specific syntax for bulk_update

django/db/backends/base/features.py

@@ -302,6 +302,9 @@ class BaseDatabaseFeatures:
     # Does this backend require casting the results of CASE expressions used
     # in UPDATE statements to ensure the expression has the correct type?
     requires_casted_case_in_updates = False
+    # Does this backend require casting the results of a VALUES expression used
+    # in UPDATE statements to ensure the expression has the correct type?
+    requires_casted_case_in_values_updates = False
 
     # Does the backend support partial indexes (CREATE INDEX ... WHERE ...)?
     supports_partial_indexes = True

django/db/backends/mysql/compiler.py

@@ -22,6 +22,17 @@ class SQLInsertCompiler(compiler.SQLInsertCompiler, SQLCompiler):
     pass
 
 
+class SQLBulkUpdateCompiler(compiler.SQLBulkUpdateCompiler, SQLCompiler):
+    def get_update_clause(self, values):
+        qn = self.quote_name_unless_alias
+        values_sql, value_params = self.compile(values)
+        update_sql = f"UPDATE {qn(self.query.base_table)}, ({values_sql}) as subquery"
+        return update_sql, tuple(value_params)
+
+    def get_subquery_from_clause(self, values):
+        return None, tuple()
+
+
 class SQLDeleteCompiler(compiler.SQLDeleteCompiler, SQLCompiler):
     def as_sql(self):
         # Prefer the non-standard DELETE FROM syntax over the SQL generated by

django/db/backends/postgresql/features.py

@@ -60,6 +60,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         )
     """
     requires_casted_case_in_updates = True
+    requires_casted_case_in_values_updates = True
     supports_over_clause = True
     supports_frame_exclusion = True
     only_supports_unbounded_with_preceding_and_following = True

django/db/models/expressions.py

@@ -2140,3 +2140,72 @@ class ValueRange(WindowFrame):
 
     def window_frame_start_end(self, connection, start, end):
         return connection.ops.window_frame_range_start_end(start, end)
+
+
+class RowTuple(ExpressionList):
+    template = "(%(expressions)s)"
+
+    def as_mysql(self, compiler, connection, **extra_context):
+        # MySQL requires the ROW() function to be used for tuples in VALUES clauses.
+        if not connection.mysql_is_mariadb:
+            extra_context["template"] = "ROW(%(expressions)s)"
+        return self.as_sql(compiler, connection, **extra_context)
+
+    def __str__(self):
+        values = self.arg_joiner.join(str(arg) for arg in self.source_expressions)
+        return self.template % {"expressions": values}
+
+    def __getitem__(self, item):
+        return self.source_expressions[item]
+
+
+class RowTupleValues(ExpressionList):
+    template = "VALUES %(expressions)s"
+
+    def __init__(self, expression_list, pk_field, field_list, **extra):
+        expressions = (
+            (
+                RowTuple(*expressions)
+                if not isinstance(expressions, RowTuple)
+                else expressions
+            )
+            for expressions in expression_list
+        )
+        self.pk_field = pk_field
+        self.field_list = field_list
+        super().__init__(*expressions, **extra)
+
+    def as_mysql(self, compiler, connection, **extra_context):
+        # MySQL doesn't support aliases in VALUES clauses. The workaround is to use a
+        # UNION as the first column
+        # SELECT 1 AS x ,2 AS y
+        # UNION VALUES (3,4),(5,6);
+        first_row = self.source_expressions.pop()
+
+        class MySQLJoiner:
+            def join(self, expressions):
+                return ", ".join(
+                    f"{col_sql} AS column{idx}"
+                    for idx, col_sql in enumerate(expressions, 1)
+                )
+
+        sql, params = first_row.as_sql(
+            compiler,
+            connection,
+            template="%(expressions)s",
+            **extra_context,
+            arg_joiner=MySQLJoiner(),
+        )
+        sql = f"SELECT {sql}"
+        if self.source_expressions:
+            rest_sql, rest_params = super().as_sql(
+                compiler, connection, **extra_context
+            )
+            sql += f" UNION {rest_sql}"
+            params += rest_params
+
+        return sql, params
+
+    def __str__(self):
+        values = self.arg_joiner.join(str(arg) for arg in self.source_expressions)
+        return self.template % {"expressions": values}

django/db/models/query.py

@@ -23,7 +23,7 @@ from django.db import (
 from django.db.models import AutoField, DateField, DateTimeField, Field, sql
 from django.db.models.constants import LOOKUP_SEP, OnConflict
 from django.db.models.deletion import Collector
-from django.db.models.expressions import Case, F, Value, When
+from django.db.models.expressions import Case, F, RowTuple, RowTupleValues, Value, When
 from django.db.models.functions import Cast, Trunc
 from django.db.models.query_utils import FilteredRelation, Q
 from django.db.models.sql.constants import CURSOR, GET_ITERATOR_CHUNK_SIZE
@@ -890,31 +890,73 @@ class QuerySet(AltersData):
         max_batch_size = connection.ops.bulk_batch_size(["pk", "pk"] + fields, objs)
         batch_size = min(batch_size, max_batch_size) if batch_size else max_batch_size
         requires_casting = connection.features.requires_casted_case_in_updates
+        requires_casting_in_values = (
+            connection.features.requires_casted_case_in_values_updates
+        )
         batches = (objs[i : i + batch_size] for i in range(0, len(objs), batch_size))
         updates = []
+
+        has_related_fields = any(f.model is not self.model for f in fields)
+        has_field_references = False
         for batch_objs in batches:
-            update_kwargs = {}
-            for field in fields:
-                when_statements = []
-                for obj in batch_objs:
+            row_tuples = []
+            for obj in batch_objs:
+                values = [Value(getattr(obj, "pk"))]
+                for field in fields:
                     attr = getattr(obj, field.attname)
-                    if not hasattr(attr, "resolve_expression"):
+                    if hasattr(attr, "resolve_expression"):
+                        has_field_references = True
+                    else:
                         attr = Value(attr, output_field=field)
-                    when_statements.append(When(pk=obj.pk, then=attr))
-                case_statement = Case(*when_statements, output_field=field)
-                if requires_casting:
-                    case_statement = Cast(case_statement, output_field=field)
-                update_kwargs[field.attname] = case_statement
-            updates.append(([obj.pk for obj in batch_objs], update_kwargs))
+
+                    if requires_casting_in_values:
+                        attr = Cast(attr, output_field=field)
+                    values.append(attr)
+
+                row_tuples.append(RowTuple(*values))
+            updates.append(
+                RowTupleValues(
+                    row_tuples, pk_field=self.model._meta.pk, field_list=fields
+                )
+            )
+
         rows_updated = 0
-        queryset = self.using(self.db)
         with transaction.atomic(using=self.db, savepoint=False):
-            for pks, update_kwargs in updates:
-                rows_updated += queryset.filter(pk__in=pks).update(**update_kwargs)
+            for row_tuples in updates:
+                if has_field_references or has_related_fields:
+                    rows_updated += self._bulk_update_slow(
+                        row_tuples, requires_casting=requires_casting
+                    )
+                else:
+                    query = sql.BulkUpdateQuery(self.model, row_tuples=row_tuples)
+                    rows_updated += query.get_compiler(using=self.db).execute_sql(
+                        result_type=CURSOR
+                    )
         return rows_updated
 
     bulk_update.alters_data = True
 
+    def _bulk_update_slow(self, row_tuples, requires_casting=False):
+        pks = [
+            row_tuple.source_expressions[0].value
+            for row_tuple in row_tuples.source_expressions
+        ]
+        update_kwargs = {}
+        # Skip the ID column
+        for field_idx, field in enumerate(row_tuples.field_list, start=1):
+            when_statements = []
+            for row_tuple in row_tuples.source_expressions:
+                row_tuple: RowTuple
+                id_expression = row_tuple.source_expressions[0]
+                attr_expression = row_tuple.source_expressions[field_idx]
+                when_statements.append(When(pk=id_expression, then=attr_expression))
+            case_statement = Case(*when_statements, output_field=field)
+            if requires_casting:
+                case_statement = Cast(case_statement, output_field=field)
+            update_kwargs[field.attname] = case_statement
+
+        return self.filter(pk__in=pks).update(**update_kwargs)
+
     async def abulk_update(self, objs, fields, batch_size=None):
         return await sync_to_async(self.bulk_update)(
             objs=objs,

django/db/models/sql/compiler.py

@@ -2090,6 +2090,62 @@ class SQLUpdateCompiler(SQLCompiler):
         self.query.reset_refcounts(refcounts_before)
 
 
+class SQLBulkUpdateCompiler(SQLCompiler):
+    def execute_sql(self, result_type):
+        cursor = super().execute_sql(result_type)
+        try:
+            rows = cursor.rowcount if cursor else 0
+        finally:
+            if cursor:
+                cursor.close()
+        return rows
+
+    def get_update_clause(self, values):
+        qn = self.quote_name_unless_alias
+        return "UPDATE %s " % qn(self.query.base_table), tuple()
+
+    def get_subquery_from_clause(self, values):
+        values_sql, value_params = self.compile(values)
+        return "FROM (%s) AS subquery" % values_sql, tuple(value_params)
+
+    def get_set_sql_clause(self, values):
+        qn = self.quote_name_unless_alias
+        set_sql = []
+        for idx, field in enumerate(values.field_list, 2):
+            name = field.column
+            set_sql.append(
+                "%s = %s.%s" % (qn(name), qn("subquery"), qn(f"column{idx}"))
+            )
+
+        return "SET %s" % ", ".join(set_sql), tuple()
+
+    def get_where_clause(self, values):
+        qn = self.quote_name_unless_alias
+        return (
+            f'WHERE {qn(values.pk_field.column)} = {qn("subquery")}.{qn("column1")}',
+            tuple(),
+        )
+
+    def as_sql(self, with_limits=True, with_col_aliases=False):
+        self.pre_sql_setup()
+
+        values = self.query.row_values.resolve_expression(
+            self.query, allow_joins=True, reuse=None
+        )
+
+        update_clause, update_params = self.get_update_clause(values)
+        set_clause, set_params = self.get_set_sql_clause(values)
+        from_clause, from_params = self.get_subquery_from_clause(values)
+        where_clause, where_params = self.get_where_clause(values)
+
+        result = [update_clause, set_clause]
+        if from_clause is not None:
+            result.append(from_clause)
+        result.append(where_clause)
+        params = update_params + set_params + from_params + where_params
+        return " ".join(result), tuple(params)
+
+
 class SQLAggregateCompiler(SQLCompiler):
     def as_sql(self):
         """

django/db/models/sql/subqueries.py

@@ -6,7 +6,13 @@ from django.core.exceptions import FieldError
 from django.db.models.sql.constants import CURSOR, GET_ITERATOR_CHUNK_SIZE, NO_RESULTS
 from django.db.models.sql.query import Query
 
-__all__ = ["DeleteQuery", "UpdateQuery", "InsertQuery", "AggregateQuery"]
+__all__ = [
+    "DeleteQuery",
+    "UpdateQuery",
+    "BulkUpdateQuery",
+    "InsertQuery",
+    "AggregateQuery",
+]
 
 
 class DeleteQuery(Query):
@@ -142,6 +148,23 @@ class UpdateQuery(Query):
         return result
 
 
+class BulkUpdateQuery(Query):
+    compiler = "SQLBulkUpdateCompiler"
+
+    def __init__(self, *args, row_tuples, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.row_values = row_tuples
+
+    def clone(self):
+        obj = super().clone()
+        if self.row_values is not None:
+            obj.related_updates = self.row_values.copy()
+        return obj
+
+    def add_row_values(self, row_values):
+        self.row_values = row_values
+
+
 class InsertQuery(Query):
     compiler = "SQLInsertCompiler"