Deprecate `where.not` working as NOR and will be changed to NAND in Rails 6.1

`where.not` with polymorphic association is partly fixed incidentally at
213796f (refer #33493, #26207, #17010, #16983, #14161), and I've added
test case e9ba12f to avoid lose that fix accidentally in the future.

In Rails 5.2, `where.not(polymorphic: object)` works as expected as
NAND, but `where.not(polymorphic_type: object.class.polymorphic_name,
polymorphic_id: object.id)` still unexpectedly works as NOR.

To will make `where.not` working desiredly as NAND in Rails 6.1, this
deprecates `where.not` working as NOR. If people want to continue NOR
conditions, we'd encourage to them to `where.not` each conditions
manually.

```ruby
all = [treasures(:diamond), treasures(:sapphire), cars(:honda), treasures(:sapphire)]
assert_equal all, PriceEstimate.all.map(&:estimate_of)
```

In Rails 6.0:

```ruby
sapphire = treasures(:sapphire)

nor = all.reject { |e|
  e.estimate_of_type == sapphire.class.polymorphic_name
}.reject { |e|
  e.estimate_of_id == sapphire.id
}
assert_equal [cars(:honda)], nor

without_sapphire = PriceEstimate.where.not(
  estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id
)
assert_equal nor, without_sapphire.map(&:estimate_of)
```

In Rails 6.1:

```ruby
sapphire = treasures(:sapphire)

nand = all - [sapphire]
assert_equal [treasures(:diamond), cars(:honda)], nand

without_sapphire = PriceEstimate.where.not(
  estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id
)
assert_equal nand, without_sapphire.map(&:estimate_of)
```

Resolves #31209.

1 files changed, 41 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 485547f036..adc7e754a4 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,44 @@
+*   Deprecate `where.not` working as NOR and will be changed to NAND in Rails 6.1.
+
+    ```ruby
+    all = [treasures(:diamond), treasures(:sapphire), cars(:honda), treasures(:sapphire)]
+    assert_equal all, PriceEstimate.all.map(&:estimate_of)
+    ```
+
+    In Rails 6.0:
+
+    ```ruby
+    sapphire = treasures(:sapphire)
+
+    nor = all.reject { |e|
+      e.estimate_of_type == sapphire.class.polymorphic_name
+    }.reject { |e|
+      e.estimate_of_id == sapphire.id
+    }
+    assert_equal [cars(:honda)], nor
+
+    without_sapphire = PriceEstimate.where.not(
+      estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id
+    )
+    assert_equal nor, without_sapphire.map(&:estimate_of)
+    ```
+
+    In Rails 6.1:
+
+    ```ruby
+    sapphire = treasures(:sapphire)
+
+    nand = all - [sapphire]
+    assert_equal [treasures(:diamond), cars(:honda)], nand
+
+    without_sapphire = PriceEstimate.where.not(
+      estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id
+    )
+    assert_equal nand, without_sapphire.map(&:estimate_of)
+    ```
+
+    *Ryuta Kamizono*
+
 *   Fix dirty tracking after rollback.
 
     Fixes #15018, #30167, #33868.