From 3b31e6bb7d4f8e9678234ab6bce1a64f6dc4fa2b Mon Sep 17 00:00:00 2001
From: Twyco <twyco@icloud.com>
Date: Wed, 25 Mar 2026 08:35:17 +0100
Subject: [PATCH] Implement parent child ticket hierarchy

---
 app/Actions/Tickets/UpdateProjectTicket.php   |  13 ++
 .../Controllers/ProjectTicketController.php   |  53 +++++
 .../Requests/UpdateProjectTicketRequest.php   | 109 +++++++++-
 app/Models/Ticket.php                         |  12 ++
 database/factories/TicketFactory.php          |   1 +
 ..._add_parent_ticket_id_to_tickets_table.php |  32 +++
 resources/js/components/TicketTreeList.vue    |  51 +++++
 resources/js/pages/projects/Ticket.vue        | 145 +++++++++----
 resources/js/types/models/ticket-model.ts     |   1 +
 .../js/types/models/ticket-tree-node-model.ts |   7 +
 resources/js/types/page-props.ts              |   7 +
 tests/Feature/Models/TicketTest.php           |  40 ++++
 .../Projects/ProjectTicketControllerTest.php  | 192 ++++++++++++++++++
 13 files changed, 617 insertions(+), 46 deletions(-)
 create mode 100644 database/migrations/2026_03_25_072501_add_parent_ticket_id_to_tickets_table.php
 create mode 100644 resources/js/components/TicketTreeList.vue
 create mode 100644 resources/js/types/models/ticket-tree-node-model.ts

diff --git a/app/Actions/Tickets/UpdateProjectTicket.php b/app/Actions/Tickets/UpdateProjectTicket.php
index 5ae957c..5fd7f4e 100644
--- a/app/Actions/Tickets/UpdateProjectTicket.php
+++ b/app/Actions/Tickets/UpdateProjectTicket.php
@@ -39,6 +39,7 @@ class UpdateProjectTicket
             $ticket->loadMissing([
                 'fieldValues.ticketFieldDefinition',
                 'fieldValues.userValue',
+                'parentTicket',
                 'project',
                 'ticketPriority',
                 'ticketType',
@@ -104,6 +105,18 @@ class UpdateProjectTicket
                 $summaryLabels[] = 'priority';
             }
 
+            if ($ticket->parent_ticket_id !== $ticketAttributes['parent_ticket_id']) {
+                $newParentTicket = $ticketAttributes['parent_ticket_id'] === null
+                    ? null
+                    : Ticket::query()->find($ticketAttributes['parent_ticket_id']);
+
+                $changes['parent_ticket'] = [
+                    'from' => $ticket->parentTicket?->ticket_key,
+                    'to' => $newParentTicket?->ticket_key,
+                ];
+                $summaryLabels[] = 'parent ticket';
+            }
+
             $ticket->fill($ticketAttributes);
 
             if ($ticket->isDirty()) {
diff --git a/app/Http/Controllers/ProjectTicketController.php b/app/Http/Controllers/ProjectTicketController.php
index 2e0b79b..5848590 100644
--- a/app/Http/Controllers/ProjectTicketController.php
+++ b/app/Http/Controllers/ProjectTicketController.php
@@ -27,13 +27,28 @@ class ProjectTicketController extends Controller
             403,
         );
 
+        $excludedParentIds = [$ticket->id, ...$this->descendantIds($ticket)];
+
         return Inertia::render('projects/Ticket', [
             'canEditTicket' => $this->projectPermissionService->userHasPermission($request->user(), $project, 'edit'),
+            'childTicketTree' => $this->buildChildTicketTree($ticket),
+            'parentTicketOptions' => Ticket::query()
+                ->where('project_id', $project->id)
+                ->whereNotIn('id', $excludedParentIds)
+                ->whereHas('ticketType', fn ($query) => $query->where('system_key', 'parent'))
+                ->orderByDesc('sequence_number')
+                ->get()
+                ->map(fn (Ticket $parentTicket): array => [
+                    'id' => $parentTicket->id,
+                    'ticket_key' => $parentTicket->ticket_key,
+                    'title' => $parentTicket->title,
+                ]),
             'project' => $project,
             'status' => session('status'),
             'ticket' => $ticket->load([
                 'fieldValues.ticketFieldDefinition',
                 'fieldValues.userValue',
+                'parentTicket',
                 'ticketPriority',
                 'ticketType',
                 'worklogEntries.actor',
@@ -71,4 +86,42 @@ class ProjectTicketController extends Controller
         return to_route('projects.tickets.show', [$project, $ticket])
             ->with('status', $statusMessage);
     }
+
+    /**
+     * @return array<int, array{
+     *     children: array<int, mixed>,
+     *     id: int,
+     *     ticket_key: string,
+     *     ticket_type_name: string|null,
+     *     title: string
+     * }>
+     */
+    private function buildChildTicketTree(Ticket $ticket): array
+    {
+        return $ticket->childTickets()
+            ->with('ticketType')
+            ->get()
+            ->map(fn (Ticket $childTicket): array => [
+                'children' => $this->buildChildTicketTree($childTicket),
+                'id' => $childTicket->id,
+                'ticket_key' => $childTicket->ticket_key,
+                'ticket_type_name' => $childTicket->ticketType?->name,
+                'title' => $childTicket->title,
+            ])
+            ->all();
+    }
+
+    /**
+     * @return array<int, int>
+     */
+    private function descendantIds(Ticket $ticket): array
+    {
+        return $ticket->childTickets()
+            ->get()
+            ->flatMap(function (Ticket $childTicket): array {
+                return [$childTicket->id, ...$this->descendantIds($childTicket)];
+            })
+            ->values()
+            ->all();
+    }
 }
diff --git a/app/Http/Requests/UpdateProjectTicketRequest.php b/app/Http/Requests/UpdateProjectTicketRequest.php
index aed4581..1046b65 100644
--- a/app/Http/Requests/UpdateProjectTicketRequest.php
+++ b/app/Http/Requests/UpdateProjectTicketRequest.php
@@ -3,10 +3,13 @@
 namespace App\Http\Requests;
 
 use App\Models\Project;
+use App\Models\Ticket;
+use App\Models\TicketType;
 use Illuminate\Contracts\Validation\ValidationRule;
 use Illuminate\Foundation\Http\FormRequest;
 use Illuminate\Support\Arr;
 use Illuminate\Validation\Rule;
+use Illuminate\Validation\Validator;
 
 class UpdateProjectTicketRequest extends FormRequest
 {
@@ -40,6 +43,11 @@ class UpdateProjectTicketRequest extends FormRequest
             ],
             'field_values.*.value_number' => ['nullable', 'numeric'],
             'field_values.*.value_user_id' => ['nullable', 'integer', Rule::exists('users', 'id')],
+            'parent_ticket_id' => [
+                'nullable',
+                'integer',
+                Rule::exists('tickets', 'id')->where('project_id', $project->id),
+            ],
             'ticket_priority_id' => [
                 'required',
                 'integer',
@@ -54,10 +62,69 @@ class UpdateProjectTicketRequest extends FormRequest
         ];
     }
 
+    /**
+     * @return array<int, callable(Validator): void>
+     */
+    public function after(): array
+    {
+        return [
+            function (Validator $validator): void {
+                /** @var Project $project */
+                $project = $this->route('project');
+
+                /** @var Ticket $ticket */
+                $ticket = $this->route('ticket');
+
+                $parentTicketId = $this->input('parent_ticket_id');
+                $parentTicketId = is_numeric($parentTicketId) ? (int) $parentTicketId : null;
+
+                if ($parentTicketId !== null) {
+                    if ($parentTicketId === $ticket->id) {
+                        $validator->errors()->add('parent_ticket_id', 'A ticket cannot be its own parent.');
+
+                        return;
+                    }
+
+                    $parentTicket = Ticket::query()
+                        ->where('project_id', $project->id)
+                        ->with('ticketType')
+                        ->find($parentTicketId);
+
+                    if ($parentTicket !== null && $parentTicket->ticketType?->system_key !== 'parent') {
+                        $validator->errors()->add('parent_ticket_id', 'Only tickets of type Parent can be selected as a parent.');
+
+                        return;
+                    }
+
+                    if ($parentTicket !== null && $this->createsCycle($ticket, $parentTicket)) {
+                        $validator->errors()->add('parent_ticket_id', 'A ticket cannot be assigned to one of its descendants.');
+
+                        return;
+                    }
+                }
+
+                $requestedTicketTypeId = $this->input('ticket_type_id');
+                $requestedTicketType = is_numeric($requestedTicketTypeId)
+                    ? TicketType::query()
+                        ->where('project_id', $project->id)
+                        ->find((int) $requestedTicketTypeId)
+                    : null;
+
+                if (
+                    $requestedTicketType?->system_key !== 'parent'
+                    && $ticket->childTickets()->exists()
+                ) {
+                    $validator->errors()->add('ticket_type_id', 'Tickets with child tickets must keep a Parent type.');
+                }
+            },
+        ];
+    }
+
     /**
      * @return array{
      *     acceptance_criteria: string|null,
      *     description: string|null,
+     *     parent_ticket_id: int|null,
      *     ticket_priority_id: int,
      *     ticket_type_id: int,
      *     title: string
@@ -68,18 +135,27 @@ class UpdateProjectTicketRequest extends FormRequest
         /** @var array{
          *     acceptance_criteria: string|null,
          *     description: string|null,
+         *     parent_ticket_id: int|null,
          *     ticket_priority_id: int,
          *     ticket_type_id: int,
          *     title: string
          * } $attributes
          */
-        $attributes = Arr::only($this->validated(), [
-            'acceptance_criteria',
-            'description',
-            'ticket_priority_id',
-            'ticket_type_id',
-            'title',
-        ]);
+        $attributes = array_merge(
+            [
+                'acceptance_criteria' => null,
+                'description' => null,
+                'parent_ticket_id' => null,
+            ],
+            Arr::only($this->validated(), [
+                'acceptance_criteria',
+                'description',
+                'parent_ticket_id',
+                'ticket_priority_id',
+                'ticket_type_id',
+                'title',
+            ]),
+        );
 
         return $attributes;
     }
@@ -103,4 +179,23 @@ class UpdateProjectTicketRequest extends FormRequest
 
         return $fieldValues;
     }
+
+    private function createsCycle(Ticket $ticket, Ticket $candidateParent): bool
+    {
+        $currentParent = $candidateParent;
+
+        while ($currentParent !== null) {
+            if ($currentParent->id === $ticket->id) {
+                return true;
+            }
+
+            if ($currentParent->parent_ticket_id === null) {
+                return false;
+            }
+
+            $currentParent = Ticket::query()->find($currentParent->parent_ticket_id);
+        }
+
+        return false;
+    }
 }
diff --git a/app/Models/Ticket.php b/app/Models/Ticket.php
index f986fab..f98f36e 100644
--- a/app/Models/Ticket.php
+++ b/app/Models/Ticket.php
@@ -13,6 +13,7 @@ use Illuminate\Database\Eloquent\Relations\HasMany;
     'acceptance_criteria',
     'board_column_id',
     'description',
+    'parent_ticket_id',
     'project_id',
     'sequence_number',
     'ticket_key',
@@ -30,12 +31,23 @@ class Ticket extends Model
         return $this->belongsTo(BoardColumn::class);
     }
 
+    public function childTickets(): HasMany
+    {
+        return $this->hasMany(Ticket::class, 'parent_ticket_id')
+            ->orderBy('sequence_number');
+    }
+
     public function fieldValues(): HasMany
     {
         return $this->hasMany(TicketFieldValue::class)
             ->orderBy('ticket_field_definition_id');
     }
 
+    public function parentTicket(): BelongsTo
+    {
+        return $this->belongsTo(Ticket::class, 'parent_ticket_id');
+    }
+
     public function project(): BelongsTo
     {
         return $this->belongsTo(Project::class);
diff --git a/database/factories/TicketFactory.php b/database/factories/TicketFactory.php
index 8d8789a..c34570f 100644
--- a/database/factories/TicketFactory.php
+++ b/database/factories/TicketFactory.php
@@ -24,6 +24,7 @@ class TicketFactory extends Factory
             'acceptance_criteria' => fake()->paragraph(),
             'board_column_id' => null,
             'description' => fake()->paragraphs(2, true),
+            'parent_ticket_id' => null,
             'sequence_number' => 1,
             'ticket_key' => 'TEST-1',
             'title' => fake()->sentence(4),
diff --git a/database/migrations/2026_03_25_072501_add_parent_ticket_id_to_tickets_table.php b/database/migrations/2026_03_25_072501_add_parent_ticket_id_to_tickets_table.php
new file mode 100644
index 0000000..f04dfe8
--- /dev/null
+++ b/database/migrations/2026_03_25_072501_add_parent_ticket_id_to_tickets_table.php
@@ -0,0 +1,32 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('tickets', function (Blueprint $table) {
+            $table->foreignId('parent_ticket_id')
+                ->nullable()
+                ->after('board_column_id')
+                ->constrained('tickets')
+                ->nullOnDelete();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('tickets', function (Blueprint $table) {
+            $table->dropConstrainedForeignId('parent_ticket_id');
+        });
+    }
+};
diff --git a/resources/js/components/TicketTreeList.vue b/resources/js/components/TicketTreeList.vue
new file mode 100644
index 0000000..c252a21
--- /dev/null
+++ b/resources/js/components/TicketTreeList.vue
@@ -0,0 +1,51 @@
+<script setup lang="ts">
+import { Link } from '@inertiajs/vue3';
+import { Badge } from '@/components/ui/badge';
+import { show as showTicket } from '@/routes/projects/tickets';
+import type { TicketTreeNodeModel } from '@/types/models/ticket-tree-node-model';
+
+defineProps<{
+    nodes: TicketTreeNodeModel[];
+    projectId: number;
+}>();
+</script>
+
+<template>
+    <ul class="space-y-3">
+        <li v-for="node in nodes" :key="node.id">
+            <div class="rounded-xl border border-border px-4 py-4">
+                <div class="flex flex-wrap items-center gap-2">
+                    <Link
+                        :href="
+                            showTicket({
+                                project: projectId,
+                                ticket: node.id,
+                            })
+                        "
+                        class="font-medium text-foreground transition hover:text-primary"
+                    >
+                        {{ node.ticket_key }}
+                    </Link>
+
+                    <Badge v-if="node.ticket_type_name" variant="secondary">
+                        {{ node.ticket_type_name }}
+                    </Badge>
+                </div>
+
+                <div class="mt-2 text-sm text-foreground">
+                    {{ node.title }}
+                </div>
+            </div>
+
+            <div
+                v-if="node.children.length > 0"
+                class="mt-3 border-l border-border pl-4"
+            >
+                <TicketTreeList
+                    :nodes="node.children"
+                    :project-id="projectId"
+                />
+            </div>
+        </li>
+    </ul>
+</template>
diff --git a/resources/js/pages/projects/Ticket.vue b/resources/js/pages/projects/Ticket.vue
index c3fbe32..9d1450e 100644
--- a/resources/js/pages/projects/Ticket.vue
+++ b/resources/js/pages/projects/Ticket.vue
@@ -3,6 +3,7 @@ import { useForm, Head, Link } from '@inertiajs/vue3';
 import ProjectTicketController from '@/actions/App/Http/Controllers/ProjectTicketController';
 import Heading from '@/components/Heading.vue';
 import InputError from '@/components/InputError.vue';
+import TicketTreeList from '@/components/TicketTreeList.vue';
 import { Badge } from '@/components/ui/badge';
 import { Button } from '@/components/ui/button';
 import {
@@ -57,6 +58,7 @@ const form = useForm({
             value_user_id: currentFieldValue?.value_user_id ?? '',
         };
     }),
+    parent_ticket_id: props.ticket.parent_ticket_id ?? '',
     ticket_priority_id: props.ticket.ticket_priority_id,
     ticket_type_id: props.ticket.ticket_type_id,
     title: props.ticket.title,
@@ -220,6 +222,34 @@ const formatDateTime = (value: string): string => {
                                 </div>
                             </div>
 
+                            <div class="grid gap-2">
+                                <Label for="parent_ticket_id">
+                                    Parent ticket
+                                </Label>
+                                <select
+                                    id="parent_ticket_id"
+                                    v-model="form.parent_ticket_id"
+                                    :disabled="
+                                        !canEditTicket || form.processing
+                                    "
+                                    class="rounded-md border border-input bg-background px-3 py-2 text-sm shadow-xs transition-[color,box-shadow] outline-none focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50 disabled:cursor-not-allowed disabled:opacity-60"
+                                >
+                                    <option value="">No parent ticket</option>
+                                    <option
+                                        v-for="parentTicketOption in parentTicketOptions"
+                                        :key="parentTicketOption.id"
+                                        :value="parentTicketOption.id"
+                                    >
+                                        {{
+                                            `${parentTicketOption.ticket_key} - ${parentTicketOption.title}`
+                                        }}
+                                    </option>
+                                </select>
+                                <InputError
+                                    :message="form.errors.parent_ticket_id"
+                                />
+                            </div>
+
                             <div class="grid gap-2">
                                 <Label for="description">Description</Label>
                                 <textarea
@@ -357,53 +387,90 @@ const formatDateTime = (value: string): string => {
                     </CardContent>
                 </Card>
 
-                <Card class="h-fit">
-                    <CardHeader>
-                        <CardTitle>Worklog</CardTitle>
-                        <CardDescription>
-                            Every tracked ticket change is recorded with actor
-                            and timestamp.
-                        </CardDescription>
-                    </CardHeader>
+                <div class="space-y-6">
+                    <Card class="h-fit">
+                        <CardHeader>
+                            <CardTitle>Child tickets</CardTitle>
+                            <CardDescription>
+                                Parent tickets expose their full child tree
+                                here, including nested parent chains.
+                            </CardDescription>
+                        </CardHeader>
 
-                    <CardContent class="space-y-4">
-                        <div
-                            v-if="(ticket.worklog_entries?.length ?? 0) === 0"
-                            class="rounded-xl border border-dashed border-border px-4 py-6 text-sm text-muted-foreground"
-                        >
-                            No worklog entries exist for this ticket yet.
-                        </div>
-
-                        <div v-else class="flex flex-col gap-4">
+                        <CardContent>
                             <div
-                                v-for="worklogEntry in ticket.worklog_entries"
-                                :key="worklogEntry.id"
-                                class="rounded-xl border border-border px-4 py-4"
+                                v-if="childTicketTree.length === 0"
+                                class="rounded-xl border border-dashed border-border px-4 py-6 text-sm text-muted-foreground"
                             >
-                                <div class="flex flex-wrap items-center gap-2">
-                                    <Badge variant="outline">
-                                        {{ worklogEntry.entry_type }}
-                                    </Badge>
-                                    <span
-                                        class="text-sm font-medium text-foreground"
+                                No child tickets are assigned to this ticket
+                                yet.
+                            </div>
+
+                            <TicketTreeList
+                                v-else
+                                :nodes="childTicketTree"
+                                :project-id="project.id"
+                            />
+                        </CardContent>
+                    </Card>
+
+                    <Card class="h-fit">
+                        <CardHeader>
+                            <CardTitle>Worklog</CardTitle>
+                            <CardDescription>
+                                Every tracked ticket change is recorded with
+                                actor and timestamp.
+                            </CardDescription>
+                        </CardHeader>
+
+                        <CardContent class="space-y-4">
+                            <div
+                                v-if="
+                                    (ticket.worklog_entries?.length ?? 0) === 0
+                                "
+                                class="rounded-xl border border-dashed border-border px-4 py-6 text-sm text-muted-foreground"
+                            >
+                                No worklog entries exist for this ticket yet.
+                            </div>
+
+                            <div v-else class="flex flex-col gap-4">
+                                <div
+                                    v-for="worklogEntry in ticket.worklog_entries"
+                                    :key="worklogEntry.id"
+                                    class="rounded-xl border border-border px-4 py-4"
+                                >
+                                    <div
+                                        class="flex flex-wrap items-center gap-2"
+                                    >
+                                        <Badge variant="outline">
+                                            {{ worklogEntry.entry_type }}
+                                        </Badge>
+                                        <span
+                                            class="text-sm font-medium text-foreground"
+                                        >
+                                            {{
+                                                worklogEntry.actor?.name ??
+                                                'System'
+                                            }}
+                                        </span>
+                                    </div>
+                                    <p class="mt-3 text-sm text-foreground">
+                                        {{ worklogEntry.summary }}
+                                    </p>
+                                    <p
+                                        class="mt-2 text-xs text-muted-foreground"
                                     >
                                         {{
-                                            worklogEntry.actor?.name ?? 'System'
+                                            formatDateTime(
+                                                worklogEntry.created_at,
+                                            )
                                         }}
-                                    </span>
+                                    </p>
                                 </div>
-                                <p class="mt-3 text-sm text-foreground">
-                                    {{ worklogEntry.summary }}
-                                </p>
-                                <p class="mt-2 text-xs text-muted-foreground">
-                                    {{
-                                        formatDateTime(worklogEntry.created_at)
-                                    }}
-                                </p>
                             </div>
-                        </div>
-                    </CardContent>
-                </Card>
+                        </CardContent>
+                    </Card>
+                </div>
             </div>
         </div>
     </AppLayout>
diff --git a/resources/js/types/models/ticket-model.ts b/resources/js/types/models/ticket-model.ts
index 65921ad..075576d 100644
--- a/resources/js/types/models/ticket-model.ts
+++ b/resources/js/types/models/ticket-model.ts
@@ -9,6 +9,7 @@ export type TicketModel = {
     board_column_id: number | null;
     description: string | null;
     field_values?: TicketFieldValueModel[];
+    parent_ticket_id: number | null;
     project_id: number;
     sequence_number: number;
     ticket_key: string;
diff --git a/resources/js/types/models/ticket-tree-node-model.ts b/resources/js/types/models/ticket-tree-node-model.ts
new file mode 100644
index 0000000..9a803d8
--- /dev/null
+++ b/resources/js/types/models/ticket-tree-node-model.ts
@@ -0,0 +1,7 @@
+export type TicketTreeNodeModel = {
+    children: TicketTreeNodeModel[];
+    id: number;
+    ticket_key: string;
+    ticket_type_name: string | null;
+    title: string;
+};
diff --git a/resources/js/types/page-props.ts b/resources/js/types/page-props.ts
index a0492f7..6f70603 100644
--- a/resources/js/types/page-props.ts
+++ b/resources/js/types/page-props.ts
@@ -4,6 +4,7 @@ import type { TeamModel } from '@/types/models/team-model';
 import type { TicketFieldDefinitionModel } from '@/types/models/ticket-field-definition-model';
 import type { TicketModel } from '@/types/models/ticket-model';
 import type { TicketPriorityModel } from '@/types/models/ticket-priority-model';
+import type { TicketTreeNodeModel } from '@/types/models/ticket-tree-node-model';
 import type { TicketTypeModel } from '@/types/models/ticket-type-model';
 import type { UserModel } from '@/types/models/user-model';
 
@@ -82,6 +83,12 @@ export type ProjectBacklogPageProps = {
 
 export type ProjectTicketPageProps = {
     canEditTicket: boolean;
+    childTicketTree: TicketTreeNodeModel[];
+    parentTicketOptions: Array<{
+        id: number;
+        ticket_key: string;
+        title: string;
+    }>;
     project: ProjectModel;
     status?: string | null;
     ticket: TicketModel;
diff --git a/tests/Feature/Models/TicketTest.php b/tests/Feature/Models/TicketTest.php
index 875fc08..9b3080b 100644
--- a/tests/Feature/Models/TicketTest.php
+++ b/tests/Feature/Models/TicketTest.php
@@ -125,4 +125,44 @@ class TicketTest extends TestCase
             $ticket->fresh()->fieldValues->modelKeys(),
         );
     }
+
+    /**
+     * Ensure tickets expose parent and child relationships for hierarchy rendering.
+     */
+    public function test_ticket_parent_and_child_relationships_are_available(): void
+    {
+        $project = Project::factory()->create([
+            'key' => 'CORE',
+        ]);
+
+        app(InitializeProjectTicketMetadata::class)->handle($project);
+
+        $priority = TicketPriority::factory()->for($project)->create([
+            'name' => 'Medium',
+            'position' => 1,
+        ]);
+
+        $taskType = $project->ticketTypes()->where('system_key', 'task')->firstOrFail();
+        $parentType = $project->ticketTypes()->where('system_key', 'parent')->firstOrFail();
+
+        $parentTicket = Ticket::factory()->create([
+            'project_id' => $project->id,
+            'sequence_number' => 1,
+            'ticket_key' => 'CORE-1',
+            'ticket_priority_id' => $priority->id,
+            'ticket_type_id' => $parentType->id,
+        ]);
+
+        $childTicket = Ticket::factory()->create([
+            'parent_ticket_id' => $parentTicket->id,
+            'project_id' => $project->id,
+            'sequence_number' => 2,
+            'ticket_key' => 'CORE-2',
+            'ticket_priority_id' => $priority->id,
+            'ticket_type_id' => $taskType->id,
+        ]);
+
+        $this->assertSame($parentTicket->id, $childTicket->fresh()->parentTicket?->id);
+        $this->assertSame([$childTicket->id], $parentTicket->fresh()->childTickets->modelKeys());
+    }
 }
diff --git a/tests/Feature/Projects/ProjectTicketControllerTest.php b/tests/Feature/Projects/ProjectTicketControllerTest.php
index 6822c27..b8bec17 100644
--- a/tests/Feature/Projects/ProjectTicketControllerTest.php
+++ b/tests/Feature/Projects/ProjectTicketControllerTest.php
@@ -230,4 +230,196 @@ class ProjectTicketControllerTest extends TestCase
             'summary' => 'Updated title, description, acceptance criteria, type, priority, Assignee field, and Story Points field.',
         ]);
     }
+
+    /**
+     * Ensure non-parent tickets cannot be assigned as a parent target.
+     */
+    public function test_assigning_a_non_parent_ticket_as_parent_is_rejected(): void
+    {
+        $editor = User::factory()->create();
+        $project = Project::factory()->create([
+            'key' => 'CORE',
+        ]);
+
+        app(InitializeProjectTicketMetadata::class)->handle($project);
+
+        $priority = TicketPriority::factory()->for($project)->create([
+            'name' => 'Medium',
+            'position' => 1,
+        ]);
+
+        $taskType = $project->ticketTypes()->where('system_key', 'task')->firstOrFail();
+
+        $candidateParent = Ticket::factory()->create([
+            'project_id' => $project->id,
+            'sequence_number' => 1,
+            'ticket_key' => 'CORE-1',
+            'ticket_priority_id' => $priority->id,
+            'ticket_type_id' => $taskType->id,
+            'title' => 'Task ticket',
+        ]);
+
+        $childTicket = Ticket::factory()->create([
+            'project_id' => $project->id,
+            'sequence_number' => 2,
+            'ticket_key' => 'CORE-2',
+            'ticket_priority_id' => $priority->id,
+            'ticket_type_id' => $taskType->id,
+            'title' => 'Child ticket',
+        ]);
+
+        app(ProjectPermissionService::class)->syncUserPermissions($project, $editor, ['edit', 'view']);
+
+        $this->actingAs($editor)
+            ->from(route('projects.tickets.show', [$project, $childTicket]))
+            ->patch(route('projects.tickets.update', [$project, $childTicket]), [
+                'title' => $childTicket->title,
+                'description' => $childTicket->description,
+                'acceptance_criteria' => $childTicket->acceptance_criteria,
+                'parent_ticket_id' => $candidateParent->id,
+                'ticket_type_id' => $childTicket->ticket_type_id,
+                'ticket_priority_id' => $childTicket->ticket_priority_id,
+                'field_values' => [],
+            ])
+            ->assertRedirect(route('projects.tickets.show', [$project, $childTicket]))
+            ->assertSessionHasErrors('parent_ticket_id');
+    }
+
+    /**
+     * Ensure parent relationships can be assigned and are written to the worklog.
+     */
+    public function test_users_with_edit_permission_can_assign_parent_tickets(): void
+    {
+        $editor = User::factory()->create();
+        $project = Project::factory()->create([
+            'key' => 'CORE',
+        ]);
+
+        app(InitializeProjectTicketMetadata::class)->handle($project);
+
+        $priority = TicketPriority::factory()->for($project)->create([
+            'name' => 'Medium',
+            'position' => 1,
+        ]);
+
+        $taskType = $project->ticketTypes()->where('system_key', 'task')->firstOrFail();
+        $parentType = $project->ticketTypes()->where('system_key', 'parent')->firstOrFail();
+
+        $parentTicket = Ticket::factory()->create([
+            'project_id' => $project->id,
+            'sequence_number' => 1,
+            'ticket_key' => 'CORE-1',
+            'ticket_priority_id' => $priority->id,
+            'ticket_type_id' => $parentType->id,
+            'title' => 'Parent ticket',
+        ]);
+
+        $childTicket = Ticket::factory()->create([
+            'project_id' => $project->id,
+            'sequence_number' => 2,
+            'ticket_key' => 'CORE-2',
+            'ticket_priority_id' => $priority->id,
+            'ticket_type_id' => $taskType->id,
+            'title' => 'Child ticket',
+        ]);
+
+        app(ProjectPermissionService::class)->syncUserPermissions($project, $editor, ['edit', 'view']);
+
+        $this->actingAs($editor)
+            ->patch(route('projects.tickets.update', [$project, $childTicket]), [
+                'title' => $childTicket->title,
+                'description' => $childTicket->description,
+                'acceptance_criteria' => $childTicket->acceptance_criteria,
+                'parent_ticket_id' => $parentTicket->id,
+                'ticket_type_id' => $childTicket->ticket_type_id,
+                'ticket_priority_id' => $childTicket->ticket_priority_id,
+                'field_values' => [],
+            ])
+            ->assertRedirect(route('projects.tickets.show', [$project, $childTicket]))
+            ->assertSessionHas('status', 'CORE-2 was updated.');
+
+        $this->assertDatabaseHas('tickets', [
+            'id' => $childTicket->id,
+            'parent_ticket_id' => $parentTicket->id,
+        ]);
+
+        $this->assertDatabaseHas('ticket_worklog_entries', [
+            'ticket_id' => $childTicket->id,
+            'actor_id' => $editor->id,
+            'entry_type' => 'updated',
+            'summary' => 'Updated parent ticket.',
+        ]);
+    }
+
+    /**
+     * Ensure parent ticket detail pages show nested child trees.
+     */
+    public function test_parent_ticket_detail_pages_show_nested_child_trees(): void
+    {
+        $viewer = User::factory()->create();
+        $project = Project::factory()->create([
+            'key' => 'CORE',
+        ]);
+
+        app(InitializeProjectTicketMetadata::class)->handle($project);
+
+        $priority = TicketPriority::factory()->for($project)->create([
+            'name' => 'Medium',
+            'position' => 1,
+        ]);
+
+        $taskType = $project->ticketTypes()->where('system_key', 'task')->firstOrFail();
+        $parentType = $project->ticketTypes()->where('system_key', 'parent')->firstOrFail();
+
+        $rootParent = Ticket::factory()->create([
+            'project_id' => $project->id,
+            'sequence_number' => 1,
+            'ticket_key' => 'CORE-1',
+            'ticket_priority_id' => $priority->id,
+            'ticket_type_id' => $parentType->id,
+            'title' => 'Root parent',
+        ]);
+
+        $nestedParent = Ticket::factory()->create([
+            'parent_ticket_id' => $rootParent->id,
+            'project_id' => $project->id,
+            'sequence_number' => 2,
+            'ticket_key' => 'CORE-2',
+            'ticket_priority_id' => $priority->id,
+            'ticket_type_id' => $parentType->id,
+            'title' => 'Nested parent',
+        ]);
+
+        $directTask = Ticket::factory()->create([
+            'parent_ticket_id' => $rootParent->id,
+            'project_id' => $project->id,
+            'sequence_number' => 3,
+            'ticket_key' => 'CORE-3',
+            'ticket_priority_id' => $priority->id,
+            'ticket_type_id' => $taskType->id,
+            'title' => 'Direct task',
+        ]);
+
+        $nestedTask = Ticket::factory()->create([
+            'parent_ticket_id' => $nestedParent->id,
+            'project_id' => $project->id,
+            'sequence_number' => 4,
+            'ticket_key' => 'CORE-4',
+            'ticket_priority_id' => $priority->id,
+            'ticket_type_id' => $taskType->id,
+            'title' => 'Nested task',
+        ]);
+
+        app(ProjectPermissionService::class)->syncUserPermissions($project, $viewer, ['view']);
+
+        $this->actingAs($viewer)
+            ->get(route('projects.tickets.show', [$project, $rootParent]))
+            ->assertOk()
+            ->assertInertia(fn (Assert $page) => $page
+                ->component('projects/Ticket')
+                ->where('childTicketTree.0.ticket_key', $nestedParent->ticket_key)
+                ->where('childTicketTree.0.children.0.ticket_key', $nestedTask->ticket_key)
+                ->where('childTicketTree.1.ticket_key', $directTask->ticket_key),
+            );
+    }
 }
-- 
2.54.0