Refs #28643 -- Added Ord, Chr, Left, and Right database functions.

django/db/models/functions/text.py

@@ -1,7 +1,23 @@
-from django.db.models import Func, Transform, Value, fields
+from django.db.models import Func, IntegerField, Transform, Value, fields
 from django.db.models.functions import Coalesce
 
 
+class Chr(Transform):
+    function = 'CHR'
+    lookup_name = 'chr'
+
+    def as_mysql(self, compiler, connection):
+        return super().as_sql(
+            compiler, connection, function='CHAR', template='%(function)s(%(expressions)s USING utf16)'
+        )
+
+    def as_oracle(self, compiler, connection):
+        return super().as_sql(compiler, connection, template='%(function)s(%(expressions)s USING NCHAR_CS)')
+
+    def as_sqlite(self, compiler, connection, **extra_context):
+        return super().as_sql(compiler, connection, function='CHAR', **extra_context)
+
+
 class ConcatPair(Func):
     """
     Concatenate two arguments together. This is used by `Concat` because not
@@ -55,6 +71,30 @@ class Concat(Func):
         return ConcatPair(expressions[0], self._paired(expressions[1:]))
 
 
+class Left(Func):
+    function = 'LEFT'
+    arity = 2
+
+    def __init__(self, expression, length, **extra):
+        """
+        expression: the name of a field, or an expression returning a string
+        length: the number of characters to return from the start of the string
+        """
+        if not hasattr(length, 'resolve_expression'):
+            if length < 1:
+                raise ValueError("'length' must be greater than 0.")
+        super().__init__(expression, length, **extra)
+
+    def get_substr(self):
+        return Substr(self.source_expressions[0], Value(1), self.source_expressions[1])
+
+    def use_substr(self, compiler, connection, **extra_context):
+        return self.get_substr().as_oracle(compiler, connection, **extra_context)
+
+    as_oracle = use_substr
+    as_sqlite = use_substr
+
+
 class Length(Transform):
     """Return the number of characters in the expression."""
     function = 'LENGTH'
@@ -70,6 +110,18 @@ class Lower(Transform):
     lookup_name = 'lower'
 
 
+class Ord(Transform):
+    function = 'ASCII'
+    lookup_name = 'ord'
+    output_field = IntegerField()
+
+    def as_mysql(self, compiler, connection, **extra_context):
+        return super().as_sql(compiler, connection, function='ORD', **extra_context)
+
+    def as_sqlite(self, compiler, connection, **extra_context):
+        return super().as_sql(compiler, connection, function='UNICODE', **extra_context)
+
+
 class Replace(Func):
     function = 'REPLACE'
 
@@ -77,6 +129,13 @@ class Replace(Func):
         super().__init__(expression, text, replacement, **extra)
 
 
+class Right(Left):
+    function = 'RIGHT'
+
+    def get_substr(self):
+        return Substr(self.source_expressions[0], self.source_expressions[1] * Value(-1))
+
+
 class StrIndex(Func):
     """
     Return a positive integer corresponding to the 1-indexed position of the