[6.0.x] Refs #33647 -- Fixed silent data truncation in bulk_create on Postgres.

Regression in a16eedcf9c69d8a11d94cac1811018c5b996d491.

The UNNEST strategy is affected by the same problem bulk_update has wrt/
to silent data truncation due to its usage of db_type which always returns
a parametrized subtype.

Backport of d6ae2ed868e43671afc4d433c3d8f4d27f7eb555 from main.

1 files changed, 3 insertions, 1 deletions

diff --git a/django/db/backends/postgresql/compiler.py b/django/db/backends/postgresql/compiler.py
index 08d78e333a..81d291cf36 100644
--- a/django/db/backends/postgresql/compiler.py
+++ b/django/db/backends/postgresql/compiler.py
@@ -62,7 +62,9 @@ class SQLInsertCompiler(BaseSQLInsertCompiler):
             or any(any(hasattr(value, "as_sql") for value in row) for row in value_rows)
         ):
             return super().assemble_as_sql(fields, value_rows)
-        db_types = [field.db_type(self.connection) for field in fields]
+        # Manually remove parameters from `db_type` to ensure no data
+        # truncation takes place (e.g. varchar[] instead of varchar(50)[]).
+        db_types = [field.db_type(self.connection).split("(")[0] for field in fields]
         return InsertUnnest(["(%%s)::%s[]" % db_type for db_type in db_types]), [
             list(map(list, zip(*value_rows)))
         ]