Refs #14030 -- Added repr methods to all expressions

3 files changed, 111 insertions, 6 deletions

diff --git a/django/db/models/aggregates.py b/django/db/models/aggregates.py
index 668f79f622..c1ddc75d4c 100644
--- a/django/db/models/aggregates.py
+++ b/django/db/models/aggregates.py
@@ -94,6 +94,13 @@ class Count(Aggregate):
         super(Count, self).__init__(
             expression, distinct='DISTINCT ' if distinct else '', output_field=IntegerField(), **extra)
 
+    def __repr__(self):
+        return "{}({}, distinct={})".format(
+            self.__class__.__name__,
+            self.arg_joiner.join(str(arg) for arg in self.source_expressions),
+            'False' if self.extra['distinct'] == '' else 'True',
+        )
+
     def convert_value(self, value, connection, context):
         if value is None:
             return 0
@@ -117,6 +124,13 @@ class StdDev(Aggregate):
         self.function = 'STDDEV_SAMP' if sample else 'STDDEV_POP'
         super(StdDev, self).__init__(expression, output_field=FloatField(), **extra)
 
+    def __repr__(self):
+        return "{}({}, sample={})".format(
+            self.__class__.__name__,
+            self.arg_joiner.join(str(arg) for arg in self.source_expressions),
+            'False' if self.function == 'STDDEV_POP' else 'True',
+        )
+
     def convert_value(self, value, connection, context):
         if value is None:
             return value
@@ -135,6 +149,13 @@ class Variance(Aggregate):
         self.function = 'VAR_SAMP' if sample else 'VAR_POP'
         super(Variance, self).__init__(expression, output_field=FloatField(), **extra)
 
+    def __repr__(self):
+        return "{}({}, sample={})".format(
+            self.__class__.__name__,
+            self.arg_joiner.join(str(arg) for arg in self.source_expressions),
+            'False' if self.function == 'VAR_POP' else 'True',
+        )
+
     def convert_value(self, value, connection, context):
         if value is None:
             return value
diff --git a/django/db/models/expressions.py b/django/db/models/expressions.py
index fb094fd4ef..9caa5dace4 100644
--- a/django/db/models/expressions.py
+++ b/django/db/models/expressions.py
@@ -340,6 +340,12 @@ class Expression(ExpressionNode):
         self.lhs = lhs
         self.rhs = rhs
 
+    def __repr__(self):
+        return "<{}: {}>".format(self.__class__.__name__, self)
+
+    def __str__(self):
+        return "{} {} {}".format(self.lhs, self.connector, self.rhs)
+
     def get_source_expressions(self):
         return [self.lhs, self.rhs]
 
@@ -408,7 +414,7 @@ class DurationExpression(Expression):
         return expression_wrapper % sql, expression_params
 
 
-class F(CombinableMixin):
+class F(Combinable):
     """
     An object capable of resolving references to existing query objects.
     """
@@ -419,6 +425,9 @@ class F(CombinableMixin):
         """
         self.name = name
 
+    def __repr__(self):
+        return "{}({})".format(self.__class__.__name__, self.name)
+
     def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
         return query.resolve_ref(self.name, allow_joins, reuse, summarize)
 
@@ -446,6 +455,13 @@ class Func(ExpressionNode):
         self.source_expressions = self._parse_expressions(*expressions)
         self.extra = extra
 
+    def __repr__(self):
+        args = self.arg_joiner.join(str(arg) for arg in self.source_expressions)
+        extra = ', '.join(str(key) + '=' + str(val) for key, val in self.extra.items())
+        if extra:
+            return "{}({}, {})".format(self.__class__.__name__, args, extra)
+        return "{}({})".format(self.__class__.__name__, args)
+
     def get_source_expressions(self):
         return self.source_expressions
 
@@ -504,6 +520,9 @@ class Value(ExpressionNode):
         super(Value, self).__init__(output_field=output_field)
         self.value = value
 
+    def __repr__(self):
+        return "{}({})".format(self.__class__.__name__, self.value)
+
     def as_sql(self, compiler, connection):
         connection.ops.check_expression_support(self)
         val = self.value
@@ -545,6 +564,9 @@ class RawSQL(ExpressionNode):
         self.sql, self.params = sql, params
         super(RawSQL, self).__init__(output_field=output_field)
 
+    def __repr__(self):
+        return "{}({}, {})".format(self.__class__.__name__, self.sql, self.params)
+
     def as_sql(self, compiler, connection):
         return '(%s)' % self.sql, self.params
 
@@ -556,6 +578,9 @@ class Random(ExpressionNode):
     def __init__(self):
         super(Random, self).__init__(output_field=fields.FloatField())
 
+    def __repr__(self):
+        return "Random()"
+
     def as_sql(self, compiler, connection):
         return connection.ops.random_function_sql(), []
 
@@ -567,6 +592,10 @@ class Col(ExpressionNode):
         super(Col, self).__init__(output_field=source)
         self.alias, self.target = alias, target
 
+    def __repr__(self):
+        return "{}({}, {})".format(
+            self.__class__.__name__, self.alias, self.target)
+
     def as_sql(self, compiler, connection):
         qn = compiler.quote_name_unless_alias
         return "%s.%s" % (qn(self.alias), qn(self.target.column)), []
@@ -588,8 +617,10 @@ class Ref(ExpressionNode):
     """
     def __init__(self, refs, source):
         super(Ref, self).__init__()
-        self.source = source
-        self.refs = refs
+        self.refs, self.source = refs, source
+
+    def __repr__(self):
+        return "{}({}, {})".format(self.__class__.__name__, self.refs, self.source)
 
     def get_source_expressions(self):
         return [self.source]
@@ -743,6 +774,9 @@ class Date(ExpressionNode):
         self.col = None
         self.lookup_type = lookup_type
 
+    def __repr__(self):
+        return "{}({}, {})".format(self.__class__.__name__, self.lookup, self.lookup_type)
+
     def get_source_expressions(self):
         return [self.col]
 
@@ -792,6 +826,10 @@ class DateTime(ExpressionNode):
             self.tzname = timezone._get_timezone_name(tzinfo)
         self.tzinfo = tzinfo
 
+    def __repr__(self):
+        return "{}({}, {}, {})".format(
+            self.__class__.__name__, self.lookup, self.lookup_type, self.tzinfo)
+
     def get_source_expressions(self):
         return [self.col]
 
@@ -833,8 +871,6 @@ class DateTime(ExpressionNode):
 
 class OrderBy(BaseExpression):
     template = '%(expression)s %(ordering)s'
-    descending_template = 'DESC'
-    ascending_template = 'ASC'
 
     def __init__(self, expression, descending=False):
         self.descending = descending
@@ -842,6 +878,10 @@ class OrderBy(BaseExpression):
             raise ValueError('expression must be an expression type')
         self.expression = expression
 
+    def __repr__(self):
+        return "{}({}, descending={})".format(
+            self.__class__.__name__, self.expression, self.descending)
+
     def set_source_expressions(self, exprs):
         self.expression = exprs[0]
 
diff --git a/tests/expressions/tests.py b/tests/expressions/tests.py
index 3c508b8520..f7e8cae856 100644
--- a/tests/expressions/tests.py
+++ b/tests/expressions/tests.py
@@ -6,10 +6,17 @@ import uuid
 
 from django.core.exceptions import FieldError
 from django.db import connection, transaction, DatabaseError
-from django.db.models import F, Value, TimeField, UUIDField
+from django.db.models import TimeField, UUIDField
+from django.db.models.aggregates import Avg, Count, Max, Min, StdDev, Sum, Variance
+from django.db.models.expressions import (
+    Case, Col, Date, DateTime, F, Func, OrderBy,
+    Random, RawSQL, Ref, Value, When
+)
+from django.db.models.functions import Coalesce, Concat, Length, Lower, Substr, Upper
 from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
 from django.test.utils import Approximate
 from django.utils import six
+from django.utils.timezone import utc
 
 from .models import Company, Employee, Number, Experiment, Time, UUID
 
@@ -812,3 +819,40 @@ class ValueTests(TestCase):
         UUID.objects.create()
         UUID.objects.update(uuid=Value(uuid.UUID('12345678901234567890123456789012'), output_field=UUIDField()))
         self.assertEqual(UUID.objects.get().uuid, uuid.UUID('12345678901234567890123456789012'))
+
+
+class ReprTests(TestCase):
+
+    def test_expressions(self):
+        self.assertEqual(
+            repr(Case(When(a=1))),
+            "<Case: CASE WHEN <Q: (AND: ('a', 1))> THEN Value(None), ELSE Value(None)>"
+        )
+        self.assertEqual(repr(Col('alias', 'field')), "Col(alias, field)")
+        self.assertEqual(repr(Date('published', 'exact')), "Date(published, exact)")
+        self.assertEqual(repr(DateTime('published', 'exact', utc)), "DateTime(published, exact, UTC)")
+        self.assertEqual(repr(F('published')), "F(published)")
+        self.assertEqual(repr(F('cost') + F('tax')), "<Expression: F(cost) + F(tax)>")
+        self.assertEqual(repr(Func('published', function='TO_CHAR')), "Func(F(published), function=TO_CHAR)")
+        self.assertEqual(repr(OrderBy(Value(1))), 'OrderBy(Value(1), descending=False)')
+        self.assertEqual(repr(Random()), "Random()")
+        self.assertEqual(repr(RawSQL('table.col', [])), "RawSQL(table.col, [])")
+        self.assertEqual(repr(Ref('sum_cost', Sum('cost'))), "Ref(sum_cost, Sum(F(cost)))")
+        self.assertEqual(repr(Value(1)), "Value(1)")
+
+    def test_functions(self):
+        self.assertEqual(repr(Coalesce('a', 'b')), "Coalesce(F(a), F(b))")
+        self.assertEqual(repr(Concat('a', 'b')), "Concat(ConcatPair(F(a), F(b)))")
+        self.assertEqual(repr(Length('a')), "Length(F(a))")
+        self.assertEqual(repr(Lower('a')), "Lower(F(a))")
+        self.assertEqual(repr(Substr('a', 1, 3)), "Substr(F(a), Value(1), Value(3))")
+        self.assertEqual(repr(Upper('a')), "Upper(F(a))")
+
+    def test_aggregates(self):
+        self.assertEqual(repr(Avg('a')), "Avg(F(a))")
+        self.assertEqual(repr(Count('a')), "Count(F(a), distinct=False)")
+        self.assertEqual(repr(Max('a')), "Max(F(a))")
+        self.assertEqual(repr(Min('a')), "Min(F(a))")
+        self.assertEqual(repr(StdDev('a')), "StdDev(F(a), sample=False)")
+        self.assertEqual(repr(Sum('a')), "Sum(F(a))")
+        self.assertEqual(repr(Variance('a', sample=True)), "Variance(F(a), sample=True)")