Fixed #27834 -- Added StrIndex database function.

2 files changed, 25 insertions, 2 deletions

diff --git a/django/db/models/functions/__init__.py b/django/db/models/functions/__init__.py
index eeafc1dc48..b8bb89b171 100644
--- a/django/db/models/functions/__init__.py
+++ b/django/db/models/functions/__init__.py
@@ -1,6 +1,6 @@
 from .base import (
     Cast, Coalesce, Concat, ConcatPair, Greatest, Least, Length, Lower, Now,
-    Substr, Upper,
+    StrIndex, Substr, Upper,
 )
 from .datetime import (
     Extract, ExtractDay, ExtractHour, ExtractMinute, ExtractMonth,
@@ -12,7 +12,7 @@ from .datetime import (
 __all__ = [
     # base
     'Cast', 'Coalesce', 'Concat', 'ConcatPair', 'Greatest', 'Least', 'Length',
-    'Lower', 'Now', 'Substr', 'Upper',
+    'Lower', 'Now', 'StrIndex', 'Substr', 'Upper',
     # datetime
     'Extract', 'ExtractDay', 'ExtractHour', 'ExtractMinute', 'ExtractMonth',
     'ExtractSecond', 'ExtractWeek', 'ExtractWeekDay', 'ExtractYear',
diff --git a/django/db/models/functions/base.py b/django/db/models/functions/base.py
index beac2e2d72..bb4354ac87 100644
--- a/django/db/models/functions/base.py
+++ b/django/db/models/functions/base.py
@@ -187,6 +187,29 @@ class Now(Func):
         return self.as_sql(compiler, connection, template='STATEMENT_TIMESTAMP()')
 
 
+class StrIndex(Func):
+    """
+    Return a positive integer corresponding to the 1-indexed position of the
+    first occurrence of a substring inside another string, or 0 if the
+    substring is not found.
+    """
+    function = 'INSTR'
+    arity = 2
+
+    def __init__(self, expression, substring, **extra):
+        """
+        expression: the name of a field, or an expression returning a string
+        substring: a string to find inside expression
+        """
+        if not hasattr(substring, 'resolve_expression'):
+            substring = Value(substring)
+        expressions = [expression, substring]
+        super().__init__(*expressions, output_field=fields.IntegerField(), **extra)
+
+    def as_postgresql(self, compiler, connection):
+        return super().as_sql(compiler, connection, function='STRPOS')
+
+
 class Substr(Func):
     function = 'SUBSTRING'