Allow attribute default/permitted values to be blank (#6454)

This is de facto already allowed when CVAT is accessed via the UI/API,
even though the model/serializer configuration seem to prohibit it.
That's because validation for attribute properties is effectively
disabled on the server due to a bug. However, the SDK checks the schema,
and thus doesn't allow such values.

I think blank default values make sense (particularly for "text" type
attributes), so I updated the code to allow them.

Blank permitted values don't make quite as much sense, but I had to
allow them too, because the UI always submits the default value as the
first permitted value (even for freeform text attributes). This will let
us fix the broken validation on the server side (which I'm planning to
do soon) without removing the ability to set blank default attribute
values via the UI.

(FWIW, I don't think that the UI should add a `values` property when
serializing freeform text attributes at all, but it would take a more
substantial change to fix that, which I don't have time for right now.)

CHANGELOG.md

@@ -19,7 +19,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - TDB
 
 ### Fixed
-- TDB
+- \[SDK\] Ability to create attributes with blank default values
+  (<https://github.com/opencv/cvat/pull/6454>)
 
 ### Security
 - TDB

cvat/apps/engine/migrations/0073_alter_attributespec_default_value_and_more.py

+# Generated by Django 4.2.1 on 2023-07-10 15:57
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("engine", "0072_alter_issue_updated_date"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="attributespec",
+            name="default_value",
+            field=models.CharField(blank=True, max_length=128),
+        ),
+        migrations.AlterField(
+            model_name="attributespec",
+            name="values",
+            field=models.CharField(blank=True, max_length=4096),
+        ),
+    ]

cvat/apps/engine/models.py

@@ -881,8 +881,8 @@ class AttributeSpec(models.Model):
     mutable = models.BooleanField()
     input_type = models.CharField(max_length=16,
         choices=AttributeType.choices())
-    default_value = models.CharField(max_length=128)
-    values = models.CharField(max_length=4096)
+    default_value = models.CharField(blank=True, max_length=128)
+    values = models.CharField(blank=True, max_length=4096)
 
     class Meta:
         default_permissions = ()

cvat/apps/engine/serializers.py

@@ -214,7 +214,7 @@ class UserSerializer(serializers.ModelSerializer):
 
 class AttributeSerializer(serializers.ModelSerializer):
     values = serializers.ListField(allow_empty=True,
-        child=serializers.CharField(max_length=200),
+        child=serializers.CharField(allow_blank=True, max_length=200),
     )
 
     class Meta:

cvat/schema.yml

@@ -5993,7 +5993,6 @@ components:
             type: string
             maxLength: 200
       required:
-      - default_value
       - input_type
       - mutable
       - name
@@ -6011,16 +6010,13 @@ components:
           $ref: '#/components/schemas/InputTypeEnum'
         default_value:
           type: string
-          minLength: 1
           maxLength: 128
         values:
           type: array
           items:
             type: string
-            minLength: 1
             maxLength: 200
       required:
-      - default_value
       - input_type
       - mutable
       - name

tests/python/sdk/test_projects.py

@@ -115,6 +115,30 @@ class TestProjectUsecases:
         assert project.id != 0
         assert project.name == "test project"
 
+    def test_can_create_project_with_attribute_with_blank_default(self):
+        project = self.client.projects.create(
+            spec=models.ProjectWriteRequest(
+                name="test project",
+                labels=[
+                    models.PatchedLabelRequest(
+                        name="text",
+                        attributes=[
+                            models.AttributeRequest(
+                                name="text",
+                                mutable=True,
+                                input_type=models.InputTypeEnum("text"),
+                                values=[],
+                                default_value="",
+                            )
+                        ],
+                    )
+                ],
+            )
+        )
+
+        labels = project.get_labels()
+        assert labels[0].attributes[0].default_value == ""
+
     def test_can_create_project_from_dataset(self, fxt_coco_dataset: Path):
         pbar_out = io.StringIO()
         pbar = make_pbar(file=pbar_out)