[SILO-1087] feat: Added IssueRelations external API

apps/api/plane/api/serializers/__init__.py

@@ -25,6 +25,10 @@
     IssueCommentCreateSerializer,
     IssueLinkCreateSerializer,
     IssueLinkUpdateSerializer,
+    IssueRelationCreateSerializer,
+    IssueRelationResponseSerializer,
+    IssueRelationSerializer,
+    RelatedIssueSerializer,
 )
 from .state import StateLiteSerializer, StateSerializer
 from .cycle import (

apps/api/plane/api/serializers/issue.py

@@ -20,6 +20,7 @@
     IssueComment,
     IssueLabel,
     IssueLink,
+    IssueRelation,
     Label,
     ProjectMember,
     State,
@@ -479,6 +480,184 @@ class Meta:
         ]
 
 
+class IssueRelationResponseSerializer(serializers.Serializer):
+    """
+    Serializer for issue relations response showing grouped relation types.
+
+    Returns issue IDs organized by relation type for efficient client-side processing.
+    """
+
+    blocking = serializers.ListField(
+        child=serializers.UUIDField(),
+        help_text="List of issue IDs that are blocking this issue",
+    )
+    blocked_by = serializers.ListField(
+        child=serializers.UUIDField(),
+        help_text="List of issue IDs that this issue is blocked by",
+    )
+    duplicate = serializers.ListField(
+        child=serializers.UUIDField(),
+        help_text="List of issue IDs that are duplicates of this issue",
+    )
+    relates_to = serializers.ListField(
+        child=serializers.UUIDField(),
+        help_text="List of issue IDs that relate to this issue",
+    )
+    start_after = serializers.ListField(
+        child=serializers.UUIDField(),
+        help_text="List of issue IDs that start after this issue",
+    )
+    start_before = serializers.ListField(
+        child=serializers.UUIDField(),
+        help_text="List of issue IDs that start before this issue",
+    )
+    finish_after = serializers.ListField(
+        child=serializers.UUIDField(),
+        help_text="List of issue IDs that finish after this issue",
+    )
+    finish_before = serializers.ListField(
+        child=serializers.UUIDField(),
+        help_text="List of issue IDs that finish before this issue",
+    )
+
+
+class IssueRelationCreateSerializer(serializers.Serializer):
+    """
+    Serializer for creating issue relations.
+
+    Creates issue relations with the specified relation type and issues.
+    Validates relation types and ensures proper issue ID format.
+    """
+
+    RELATION_TYPE_CHOICES = [
+        ("blocking", "Blocking"),
+        ("blocked_by", "Blocked By"),
+        ("duplicate", "Duplicate"),
+        ("relates_to", "Relates To"),
+        ("start_before", "Start Before"),
+        ("start_after", "Start After"),
+        ("finish_before", "Finish Before"),
+        ("finish_after", "Finish After"),
+    ]
+
+    relation_type = serializers.ChoiceField(
+        choices=RELATION_TYPE_CHOICES,
+        required=True,
+        help_text="Type of relationship between work items",
+    )
+    issues = serializers.ListField(
+        child=serializers.UUIDField(),
+        required=True,
+        min_length=1,
+        help_text="Array of work item IDs to create relations with",
+    )
+
+    def validate_issues(self, value):
+        """Validate that issues list is not empty and contains valid UUIDs."""
+        if not value:
+            raise serializers.ValidationError("At least one issue ID is required.")
+        return value
+
+
+class IssueRelationRemoveSerializer(serializers.Serializer):
+    """
+    Serializer for removing issue relations.
+
+    Removes existing relationships between work items by specifying
+    the related issue ID.
+    """
+
+    related_issue = serializers.UUIDField(
+        required=True, help_text="ID of the related work item to remove relation with"
+    )
+
+
+class IssueRelationSerializer(BaseSerializer):
+    """
+    Serializer for issue relationships showing related issue details.
+
+    Provides comprehensive information about related issues including
+    project context, sequence ID, and relationship type.
+    """
+
+    id = serializers.UUIDField(source="related_issue.id", read_only=True)
+    project_id = serializers.UUIDField(source="related_issue.project_id", read_only=True)
+    sequence_id = serializers.IntegerField(source="related_issue.sequence_id", read_only=True)
+    name = serializers.CharField(source="related_issue.name", read_only=True)
+    relation_type = serializers.CharField(read_only=True)
+    state_id = serializers.UUIDField(source="related_issue.state.id", read_only=True)
+    priority = serializers.CharField(source="related_issue.priority", read_only=True)
+
+    class Meta:
+        model = IssueRelation
+        fields = [
+            "id",
+            "project_id",
+            "sequence_id",
+            "relation_type",
+            "name",
+            "state_id",
+            "priority",
+            "created_by",
+            "created_at",
+            "updated_at",
+            "updated_by",
+        ]
+        read_only_fields = [
+            "workspace",
+            "project",
+            "created_by",
+            "created_at",
+            "updated_by",
+            "updated_at",
+        ]
+
+
+class RelatedIssueSerializer(BaseSerializer):
+    """
+    Serializer for reverse issue relationships showing issue details.
+
+    Provides comprehensive information about the source issue in a relationship
+    including project context, sequence ID, and relationship type.
+    """
+
+    id = serializers.UUIDField(source="issue.id", read_only=True)
+    project_id = serializers.PrimaryKeyRelatedField(source="issue.project_id", read_only=True)
+    sequence_id = serializers.IntegerField(source="issue.sequence_id", read_only=True)
+    name = serializers.CharField(source="issue.name", read_only=True)
+    type_id = serializers.UUIDField(source="issue.type.id", read_only=True)
+    relation_type = serializers.CharField(read_only=True)
+    is_epic = serializers.BooleanField(source="issue.type.is_epic", read_only=True)
+    state_id = serializers.UUIDField(source="issue.state.id", read_only=True)
+    priority = serializers.CharField(source="issue.priority", read_only=True)
+
+    class Meta:
+        model = IssueRelation
+        fields = [
+            "id",
+            "project_id",
+            "sequence_id",
+            "relation_type",
+            "name",
+            "type_id",
+            "is_epic",
+            "state_id",
+            "priority",
+            "created_by",
+            "created_at",
+            "updated_by",
+            "updated_at",
+        ]
+        read_only_fields = [
+            "workspace",
+            "project",
+            "created_by",
+            "created_at",
+            "updated_by",
+            "updated_at",
+        ]
+
+
 class IssueAttachmentSerializer(BaseSerializer):
     """
     Serializer for work item file attachments.

apps/api/plane/api/urls/work_item.py

@@ -17,6 +17,7 @@
     IssueAttachmentDetailAPIEndpoint,
     WorkspaceIssueAPIEndpoint,
     IssueSearchEndpoint,
+    IssueRelationListCreateAPIEndpoint,
 )
 
 # Deprecated url patterns
@@ -145,6 +146,11 @@
         IssueAttachmentDetailAPIEndpoint.as_view(http_method_names=["get", "patch", "delete"]),
         name="work-item-attachment-detail",
     ),
+    path(
+        "workspaces/<str:slug>/projects/<uuid:project_id>/work-items/<uuid:issue_id>/relations/",
+        IssueRelationListCreateAPIEndpoint.as_view(http_method_names=["get", "post"]),
+        name="work-item-relation-list",
+    ),
 ]
 
 urlpatterns = old_url_patterns + new_url_patterns

apps/api/plane/api/views/__init__.py

@@ -29,6 +29,7 @@
     IssueAttachmentListCreateAPIEndpoint,
     IssueAttachmentDetailAPIEndpoint,
     IssueSearchEndpoint,
+    IssueRelationListCreateAPIEndpoint,
 )
 
 from .cycle import (