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The Locker Management system includes built-in employee tracking to ensure each employee is assigned to only one locker and to maintain accurate occupancy status across the system.

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Employee Assignments

Employee assignments are managed through the EmployeeNumber field in the locker model. This field links a locker to a specific employee.

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Data Model

The employee number is stored as an optional field in both the frontend and backend: 
export interface Locker {
    lockerNo: string;
    employeeNumber: string | null;    
    size: number;
    location: string;
    isEmpty: boolean;
}
The EmployeeNumber field is nullable, allowing lockers to exist without an assigned employee.

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Assigning Employees

Employees are assigned to lockers through the management form:
app.component.html:21-24
<div class="form-group">
  <label for="">Employee No</label>
  <input type="text" name="empNo" [(ngModel)]="locker.employeeNumber">
</div>
When a locker is created or updated with an employee number, the assignment is processed and validated by the backend.

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One Locker Per Employee Rule

The system enforces a strict rule: each employee can only be assigned to one locker at a time. This prevents double-booking and ensures accurate tracking.

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Validation Logic

During locker creation, the system checks if the employee number already exists:
LockersController.cs:45-47
var empNumberExist = await lockersDbContext.Lockers
                    .Where(x => x.EmployeeNumber == locker.EmployeeNumber && !x.EmployeeNumber.Equals(string.Empty))
                    .Select(x => x.EmployeeNumber).ToListAsync();
The validation excludes empty employee numbers, so multiple unassigned lockers are allowed.

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Rejection of Duplicate Assignments

If an employee is already assigned to another locker, the creation fails:
LockersController.cs:53-58
if (empNumberExist.Any())
{
    var message = new Exception($"Employee number {locker.EmployeeNumber} already exists");

    return BadRequest(message);
}
Attempting to assign an employee who already has a locker will result in a 400 Bad Request response with an error message.

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Complete Validation Flow

The complete validation process checks both locker numbers and employee numbers:
LockersController.cs:42-76
[HttpPost]
public async Task<IActionResult> AddLocker([FromBody] LockerInfo locker)
{
    var empNumberExist = await lockersDbContext.Lockers
                        .Where(x => x.EmployeeNumber == locker.EmployeeNumber && !x.EmployeeNumber.Equals(string.Empty))
                        .Select(x => x.EmployeeNumber).ToListAsync();

    var lockerNumberExist = await lockersDbContext.Lockers
                        .Where(x => x.LockerNo == locker.LockerNo)
                        .Select(x => x.EmployeeNumber).ToListAsync();

    if (empNumberExist.Any())
    {
        var message = new Exception($"Employee number {locker.EmployeeNumber} already exists");

        return BadRequest(message);
    }
    else if (lockerNumberExist.Any())
    {
        var message = new Exception($"Locker number {locker.LockerNo} already exists");

        return BadRequest(message);
    }
    else
    {
        // if the input of employee number is not null, then the value isEmpty is false
        locker.IsEmpty = locker.EmployeeNumber != string.Empty ? false : true;

        await lockersDbContext.Lockers.AddAsync(locker);
        await lockersDbContext.SaveChangesAsync();

        return CreatedAtAction(nameof(GetLocker), new { locker.IsEmpty }, locker);
    }
    
}

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Tracking Locker Occupancy Status

The system automatically tracks whether a locker is empty or occupied based on employee assignments using the IsEmpty field.

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Automatic Status Calculation

The IsEmpty status is calculated automatically and never set manually: During Locker Creation:
LockersController.cs:68
locker.IsEmpty = locker.EmployeeNumber != string.Empty ? false : true;
During Locker Updates:
LockersController.cs:92
existingLocker.IsEmpty = locker.EmployeeNumber != string.Empty ? false : true;

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Status Logic

The calculation follows this simple rule:
1

Check Employee Number

Evaluate whether the EmployeeNumber field contains a value
2

Set IsEmpty to false

If an employee number exists and is not empty, set IsEmpty = false (locker is occupied)
3

Set IsEmpty to true

If the employee number is empty or null, set IsEmpty = true (locker is available)

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Visual Representation

The occupancy status is visually represented in the dashboard with color coding:
app.component.html:33
[ngStyle]="{ 'background-color': locker.isEmpty ? '#92f08d' : '#8db0f0' }"
  • Green (#92f08d): Empty locker (isEmpty = true)
  • Blue (#8db0f0): Occupied locker (isEmpty = false)

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Display in Dashboard

The employee number is displayed on occupied locker cards:
app.component.html:36
<span>Emp ID: {{ locker.employeeNumber }}</span>

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Employee Number Validation

The system validates employee numbers to ensure data integrity and enforce business rules.

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Uniqueness Validation

The primary validation ensures each employee number is unique across all occupied lockers:
LockersController.cs:45-47
var empNumberExist = await lockersDbContext.Lockers
                    .Where(x => x.EmployeeNumber == locker.EmployeeNumber && !x.EmployeeNumber.Equals(string.Empty))
                    .Select(x => x.EmployeeNumber).ToListAsync();
The query uses two conditions:
  1. Match the employee number
  2. Exclude empty strings to allow multiple unassigned lockers

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Empty Employee Numbers

Empty employee numbers are explicitly allowed and excluded from uniqueness validation: 
&& !x.EmployeeNumber.Equals(string.Empty)
This allows the system to have multiple available (unassigned) lockers without triggering validation errors.

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Update Validation

When updating a locker, the system recalculates the occupancy status:
LockersController.cs:82-100
[HttpPut]
[Route("{lockerNo}")]
public async Task<IActionResult> UpdateLocker([FromRoute] string lockerNo, [FromBody] LockerInfo locker)
{
    var existingLocker = await lockersDbContext.Lockers.FirstOrDefaultAsync(x => x.LockerNo == lockerNo);

    if (existingLocker != null)
    {
        existingLocker.EmployeeNumber = locker.EmployeeNumber;
        existingLocker.LockerNo = locker.LockerNo;
        existingLocker.Size = locker.Size;
        existingLocker.Location = locker.Location;
        existingLocker.IsEmpty = locker.EmployeeNumber != string.Empty ? false : true;

        await lockersDbContext.SaveChangesAsync();

        return Ok(existingLocker);
    }

    return NotFound("Locker not found");
}
The update logic recalculates IsEmpty based on the new employee number, ensuring status accuracy after modifications.

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Business Logic Summary

The employee tracking system implements several key business rules:

One-to-One Relationship

Each employee can have maximum one locker assigned

Automatic Status

Occupancy status is calculated automatically from employee assignments

Unique Validation

Employee numbers must be unique across all occupied lockers

Optional Assignment

Lockers can exist without employee assignments

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Assignment Flow

1

User enters employee number

The employee number is captured in the form field
2

Backend validates uniqueness

The system checks if the employee already has a locker
3

Calculate occupancy status

IsEmpty is set based on whether an employee number exists
4

Save to database

The locker is created/updated with the validated assignment
5

Visual update

The dashboard refreshes to show the new occupancy status

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Unassigning Employees

To unassign an employee from a locker, simply clear the employee number field when updating:
  1. Click on the locker number to populate the form
  2. Clear the “Employee No” field (leave it empty)
  3. Submit the form
The backend will automatically:
  • Set IsEmpty = true
  • Update the locker’s occupancy status
  • Change the visual indicator to green
LockersController.cs:92
existingLocker.IsEmpty = locker.EmployeeNumber != string.Empty ? false : true;
Clearing an employee assignment frees up that employee to be assigned to a different locker.

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