Overview
The Problem model represents a programming problem with test cases, judging configuration, and metadata. Problems can be attached to assignments or used for practice.
Fillable Fields
Unique identifier for the problem
Display name of the problem
Command used to compare output (e.g., ‘diff’, ‘diff -w’, custom script)
Additional arguments passed to the diff command
Whether students can practice this problem outside of assignmentsCast: boolean
Internal notes visible only to administrators and problem owner
Difficulty level (e.g., ‘easy’, ‘medium’, ‘hard’)
ID of the user who created/owns this problem
Whether other instructors can use this problem in their assignmentsCast: boolean
Original author or source of the problem
Editorial/solution explanation (HTML supported)
Whether students can download test case input filesCast: boolean
Whether students can download test case output filesCast: boolean
Casts
protected $casts = [
'allow_practice' => 'boolean',
'sharable' => 'boolean',
'allow_input_download' => 'boolean',
'allow_output_download' => 'boolean',
];
Relationships
user() / owner()
The user who created this problem (both user() and owner() return the same relationship)
$problem->user // Returns User model
$problem->owner // Same as user()
languages()
Programming languages allowed for this problemPivot fields:
time_limit - Execution time limit in seconds for this languagememory_limit - Memory limit in KB for this language
Timestamps: Yes $problem->languages()->withPivot('time_limit', 'memory_limit')
assignments()
assignments
BelongsToMany<Assignment>
Assignments that include this problem
$problem->assignments // Returns collection of Assignment models
submissions()
All submissions made to this problem
Tags for categorizing this problem (e.g., ‘dynamic-programming’, ‘graphs’)
$problem->tags // Returns collection of Tag models
Public Methods
get_directory_path()
Returns the filesystem path where problem files are stored.
public function get_directory_path()
string - Absolute path to problem directory
Example:
$path = $problem->get_directory_path();
// Returns: '/var/www/assignments/problems/123/'
problems/{id}/
├── desc.html # Problem description
├── problem.pdf # Optional PDF version
├── template.cpp # Code template (private)
├── template.public.cpp # Public code template
├── in/ # Test input files
│ ├── input1.txt
│ └── input2.txt
└── out/ # Test output files
├── output1.txt
└── output2.txt
can_practice()
Checks if a user has permission to practice this problem.
public function can_practice(User $user)
$user (User) - User requesting access
Returns: boolean
Permission logic:
- Admin users: Always
true
- Problem owner: Always
true
- If
allow_practice is true: Returns true
- If
sharable is true AND user is head_instructor/instructor: Returns true
- Otherwise: Returns
false
Example:
if ($problem->can_practice($user)) {
// Show practice interface
} else {
abort(403, 'You don\'t have permission to practice this problem');
}
can_edit()
Checks if a user has permission to edit this problem.
public function can_edit(User $user)
$user (User) - User requesting edit access
Returns: boolean
Permission logic:
- Admin users: Can edit any problem
- Problem owner: Can edit their own problems
- Others: Cannot edit
delete()
Deletes the problem and all associated data.
Actions performed:
- Starts database transaction
- Deletes all submissions for this problem
- Detaches all languages
- Detaches from all assignments
- Detaches all tags
- Deletes the model
- Commits transaction
- Deletes problem directory from filesystem using
rm -rf
Example:
$problem->delete();
// Deletes database records and /var/www/assignments/problems/123/
The delete operation is destructive and removes all test cases and submissions. Use with caution.
pdf()
Serves the problem’s PDF file for download.
Returns: File response with PDF
Throws: 404 if PDF not found
Example:
Route::get('/problems/{problem}/pdf', function(Problem $problem) {
return $problem->pdf();
});
template_path()
Returns the path to the code template file for a specific language.
public function template_path($language_extension = 'cpp')
$language_extension (string) - File extension (e.g., ‘cpp’, ‘java’, ‘py’)
Returns: array - Array of matching file paths (or empty array)
Priority:
- Checks for
template.public.{extension} first
- Falls back to
template.{extension}
Example:
$template_path = $problem->template_path('cpp');
// Returns: ['/var/www/assignments/problems/123/template.public.cpp']
template_content()
Returns the content of the code template for a specific language.
public function template_content($language_id)
$language_id (integer) - Language ID
Returns: string|null - Template file content or null if not found
Example:
$template = $problem->template_content(1);
echo $template;
// Outputs: #include <iostream>...
description()
Returns the problem description and metadata.
public function description()
array with keys:
description (string) - HTML description or default messagehas_pdf (boolean) - Whether PDF file existshas_template (boolean) - Whether C++ template exists
Example:
$desc = $problem->description();
if ($desc['has_pdf']) {
echo '<a href="/problems/{$problem->id}/pdf">Download PDF</a>';
}
echo $desc['description'];
available()
Static query scope for problems available to a user.
public static function available($user_id)
$user_id (integer) - User ID
Returns: Builder - Query builder instance
Query logic: Returns problems where:
user_id matches the given user, ORsharable is true
Example:
$problems = Problem::available(auth()->id())->get();
// Returns all problems owned by user or marked as sharable
Example Usage
// Create a new problem
$problem = Problem::create([
'name' => 'Two Sum',
'diff_cmd' => 'diff',
'diff_arg' => '-w -B',
'allow_practice' => true,
'difficult' => 'easy',
'user_id' => auth()->id(),
'sharable' => true,
'author' => 'LeetCode',
'allow_input_download' => false,
'allow_output_download' => false,
]);
// Attach languages with limits
$problem->languages()->attach(1, [
'time_limit' => 1.0, // 1 second
'memory_limit' => 65536 // 64 MB
]);
// Add tags
$problem->tags()->attach([1, 5, 8]); // array, hash-table, two-pointers
// Check permissions
if ($problem->can_edit($user)) {
// Show edit button
}
// Get template for user's selected language
$template = $problem->template_content($languageId);
// Use in query
$myProblems = Problem::available(auth()->id())
->where('difficult', 'medium')
->with('tags')
->get();
File System Integration
Problems require a specific directory structure in the filesystem:
# Problem directory
assignments_root=/var/www/assignments
problem_id=123
# Structure
/var/www/assignments/problems/123/
desc.html # Problem description (HTML)
problem.pdf # Optional PDF version
template.cpp # Private template (for reference solutions)
template.public.cpp # Public template (shown to students)
template.java
template.public.java
in/ # Test inputs
01.txt
02.txt
out/ # Expected outputs
01.txt
02.txt
