Add lenght validator

Author: WaVEV

django_mongodb_backend/fields/array.py

@@ -41,6 +41,11 @@ def __init__(self, base_field, max_size=None, size=None, **kwargs):
                 *self.default_validators,
                 LengthValidator(self.size),
             ]
+        if self.fixed_size:
+            self.default_validators = [
+                *self.default_validators,
+                LengthValidator(self.fixed_size),
+            ]
         # For performance, only add a from_db_value() method if the base field
         # implements it.
         if hasattr(self.base_field, "from_db_value"):

django_mongodb_backend/fields/validators.py

@@ -0,0 +1,19 @@
+from django.core.validators import BaseValidator
+from django.utils.deconstruct import deconstructible
+from django.utils.translation import ngettext_lazy
+
+
+@deconstructible
+class LengthValidator(BaseValidator):
+    message = ngettext_lazy(
+        "List contains %(show_value)d item, it should contain %(limit_value)d.",
+        "List contains %(show_value)d items, it should contain %(limit_value)d.",
+        "show_value",
+    )
+    code = "length"
+
+    def compare(self, a, b):
+        return a == b
+
+    def clean(self, x):
+        return len(x)