Fixed #24938 -- Added PostgreSQL trigram support.

django/contrib/postgres/apps.py

@@ -3,7 +3,7 @@ from django.db.backends.signals import connection_created
 from django.db.models import CharField, TextField
 from django.utils.translation import ugettext_lazy as _
 
-from .lookups import SearchLookup, Unaccent
+from .lookups import SearchLookup, TrigramSimilar, Unaccent
 from .signals import register_hstore_handler
 
 
@@ -17,3 +17,5 @@ class PostgresConfig(AppConfig):
         TextField.register_lookup(Unaccent)
         CharField.register_lookup(SearchLookup)
         TextField.register_lookup(SearchLookup)
+        CharField.register_lookup(TrigramSimilar)
+        TextField.register_lookup(TrigramSimilar)

django/contrib/postgres/lookups.py

@@ -60,3 +60,8 @@ class SearchLookup(SearchVectorExact):
             self.lhs = SearchVector(self.lhs)
         lhs, lhs_params = super(SearchLookup, self).process_lhs(qn, connection)
         return lhs, lhs_params
+
+
+class TrigramSimilar(PostgresSimpleLookup):
+    lookup_name = 'trigram_similar'
+    operator = '%%'

django/contrib/postgres/operations.py

@@ -40,3 +40,9 @@ class UnaccentExtension(CreateExtension):
 
     def __init__(self):
         self.name = 'unaccent'
+
+
+class TrigramExtension(CreateExtension):
+
+    def __init__(self):
+        self.name = 'pg_trgm'

django/contrib/postgres/search.py

@@ -185,3 +185,19 @@ class SearchRank(Func):
 
 
 SearchVectorField.register_lookup(SearchVectorExact)
+
+
+class TrigramBase(Func):
+    def __init__(self, expression, string, **extra):
+        if not hasattr(string, 'resolve_expression'):
+            string = Value(string)
+        super(TrigramBase, self).__init__(expression, string, output_field=FloatField(), **extra)
+
+
+class TrigramSimilarity(TrigramBase):
+    function = 'SIMILARITY'
+
+
+class TrigramDistance(TrigramBase):
+    function = ''
+    arg_joiner = ' <-> '