Fixed #27935 -- Fixed crash with BrinIndex name > 30 characters.

2 files changed, 18 insertions, 6 deletions

diff --git a/django/contrib/postgres/indexes.py b/django/contrib/postgres/indexes.py
index 60578e6c16..feb7053ed8 100644
--- a/django/contrib/postgres/indexes.py
+++ b/django/contrib/postgres/indexes.py
@@ -1,4 +1,6 @@
+from django.db import connection
 from django.db.models import Index
+from django.utils.functional import cached_property
 
 __all__ = ['BrinIndex', 'GinIndex']
 
@@ -34,6 +36,14 @@ class BrinIndex(Index):
                 schema_editor.quote_value(self.pages_per_range)) + parameters['extra']
         return parameters
 
+    @cached_property
+    def max_name_length(self):
+        # Allow an index name longer than 30 characters since the suffix
+        # is 4 characters (usual limit is 3). Since this index can only be
+        # used on PostgreSQL, the 30 character limit for cross-database
+        # compatibility isn't applicable.
+        return connection.ops.max_name_length()
+
 
 class GinIndex(Index):
     suffix = 'gin'
diff --git a/django/db/models/indexes.py b/django/db/models/indexes.py
index 1370463beb..3bb73cf16a 100644
--- a/django/db/models/indexes.py
+++ b/django/db/models/indexes.py
@@ -4,12 +4,12 @@ from django.utils.encoding import force_bytes
 
 __all__ = ['Index']
 
-# The max length of the names of the indexes (restricted to 30 due to Oracle)
-MAX_NAME_LENGTH = 30
-
 
 class Index:
     suffix = 'idx'
+    # The max length of the name of the index (restricted to 30 for
+    # cross-database compatibility with Oracle)
+    max_name_length = 30
 
     def __init__(self, fields=[], name=None):
         if not isinstance(fields, list):
@@ -25,8 +25,8 @@ class Index:
         self.name = name or ''
         if self.name:
             errors = self.check_name()
-            if len(self.name) > MAX_NAME_LENGTH:
-                errors.append('Index names cannot be longer than %s characters.' % MAX_NAME_LENGTH)
+            if len(self.name) > self.max_name_length:
+                errors.append('Index names cannot be longer than %s characters.' % self.max_name_length)
             if errors:
                 raise ValueError(errors)
 
@@ -100,13 +100,15 @@ class Index:
             (('-%s' if order else '%s') % column_name)
             for column_name, (field_name, order) in zip(column_names, self.fields_orders)
         ]
+        # The length of the parts of the name is based on the default max
+        # length of 30 characters.
         hash_data = [table_name] + column_names_with_order + [self.suffix]
         self.name = '%s_%s_%s' % (
             table_name[:11],
             column_names[0][:7],
             '%s_%s' % (self._hash_generator(*hash_data), self.suffix),
         )
-        assert len(self.name) <= MAX_NAME_LENGTH, (
+        assert len(self.name) <= self.max_name_length, (
             'Index too long for multiple database support. Is self.suffix '
             'longer than 3 characters?'
         )