DataViewModel.cs

using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using ProjectPatronBackoffice.Models;
using ProjectPatronBackoffice.Repositories;
using GalaSoft.MvvmLight.Command;

namespace ProjectPatronBackoffice.ViewModels
{
    public class DepartmentViewModel : INotifyPropertyChanged
    {
        private ObservableCollection<Department> _departmentList;

        public event PropertyChangedEventHandler PropertyChanged;

        public ObservableCollection<Department> DepartmentList
        {
            get { return _departmentList; }
            set { _departmentList = value; }
        }


        // Constructor
        public DepartmentViewModel()
        {
            Department d = new Department {DepartmentId = 0, DepartmentName = "Test", DepartmentNumber = 4};
            this.FetchDepartmentCommand = new RelayCommand(FetchDepartments);
        }

        public RelayCommand FetchDepartmentCommand { get; set; }

        // Actual command
        public void FetchDepartments()
        {
            DepartmentList = DepartmentRepository.GetAllDepartments();            
        }

        private void OnPropertyChanged([CallerMemberName] string caller = null)
        {
            var handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(caller));
            }
        }
        protected bool SetField<T>(ref T field, T value, string propertyName)
        {
            if (EqualityComparer<T>.Default.Equals(field, value)) return false;
            field = value;
            OnPropertyChanged(propertyName);
            return true;
        }

        // props
        private string name;
        public string Name
        {
            get { return name; }
            set { SetField(ref name, value, "DepartmentList"); }
        }
    }

}