Add curriculum read models

core/models.py

@@ -1,3 +1,61 @@
 from django.db import models
 
-# Create your models here.
+
+class Concept(models.Model):
+    slug = models.TextField(primary_key=True)
+
+    class Meta:
+        managed = False
+        db_table = "concept"
+
+    def __str__(self) -> str:
+        return self.slug
+
+
+class RelationType(models.Model):
+    slug = models.TextField(primary_key=True)
+
+    class Meta:
+        managed = False
+        db_table = "relation_type"
+
+    def __str__(self) -> str:
+        return self.slug
+
+
+class Relation(models.Model):
+    id = models.UUIDField(primary_key=True)
+
+    source = models.ForeignKey(
+        Concept,
+        on_delete=models.CASCADE,
+        db_column="source",
+        related_name="outgoing_relations",
+    )
+
+    type = models.ForeignKey(
+        RelationType,
+        on_delete=models.RESTRICT,
+        db_column="type",
+        related_name="relations",
+    )
+
+    target = models.ForeignKey(
+        Concept,
+        on_delete=models.CASCADE,
+        db_column="target",
+        related_name="incoming_relations",
+    )
+
+    class Meta:
+        managed = False
+        db_table = "relation"
+        constraints = [
+            models.UniqueConstraint(
+                fields=("source", "type", "target"),
+                name="unique_typed_relation",
+            ),
+        ]
+
+    def __str__(self) -> str:
+        return f"{self.source_id} —{self.type_id}→ {self.target_id}"

tests/test_curriculum_models.py

@@ -0,0 +1,77 @@
+import uuid
+
+from django.db.models.deletion import CASCADE, RESTRICT
+
+from core.models import Concept, Relation, RelationType
+
+
+def test_concept_uses_slug_as_primary_key():
+    primary_key = Concept._meta.pk
+
+    assert primary_key.name == "slug"
+    assert primary_key.column == "slug"
+
+
+def test_relation_type_uses_slug_as_primary_key():
+    primary_key = RelationType._meta.pk
+
+    assert primary_key.name == "slug"
+    assert primary_key.column == "slug"
+
+
+def test_relation_maps_expected_database_columns():
+    assert Relation._meta.pk.name == "id"
+    assert Relation._meta.get_field("source").column == "source"
+    assert Relation._meta.get_field("type").column == "type"
+    assert Relation._meta.get_field("target").column == "target"
+
+
+def test_relation_foreign_keys_reference_expected_models():
+    source = Relation._meta.get_field("source")
+    relation_type = Relation._meta.get_field("type")
+    target = Relation._meta.get_field("target")
+
+    assert source.remote_field.model is Concept
+    assert relation_type.remote_field.model is RelationType
+    assert target.remote_field.model is Concept
+
+
+def test_relation_reverse_names_are_explicit():
+    source = Relation._meta.get_field("source")
+    relation_type = Relation._meta.get_field("type")
+    target = Relation._meta.get_field("target")
+
+    assert source.remote_field.related_name == "outgoing_relations"
+    assert relation_type.remote_field.related_name == "relations"
+    assert target.remote_field.related_name == "incoming_relations"
+
+
+def test_relation_deletion_behaviour_matches_database_schema():
+    source = Relation._meta.get_field("source")
+    relation_type = Relation._meta.get_field("type")
+    target = Relation._meta.get_field("target")
+
+    assert source.remote_field.on_delete is CASCADE
+    assert relation_type.remote_field.on_delete is RESTRICT
+    assert target.remote_field.on_delete is CASCADE
+
+
+def test_relation_declares_semantic_unique_constraint():
+    constraint = next(
+        constraint
+        for constraint in Relation._meta.constraints
+        if constraint.name == "unique_typed_relation"
+    )
+
+    assert tuple(constraint.fields) == ("source", "type", "target")
+
+
+def test_relation_string_representation_uses_semantic_identity():
+    relation = Relation(
+        id=uuid.uuid4(),
+        source_id="matrix",
+        type_id="subtype_of",
+        target_id="data-structure",
+    )
+
+    assert str(relation) == "matrix —subtype_of→ data-structure"