从带有Razor页面的Page方法和WebApi控制器中调用共享代码

Question

I'm using the new Razor Pages with core 2.0 and I'm trying to see if I can share the query code by putting the linq and db initialization into a Utility class in App_code folder but I'm having an issue with making this class to work.

Basically I'm querying the database with linq but I also have another asp-page-handler that will create a PDF.

Here is my page

public class IndexModel : PageModel
    {
        private readonly CrewLogContext _context;
        //initialize db
        public IndexModel(CrewLogContext context)
        {
            _context = context;
        }
        public IList<SelectionDailyReport> SelectionDailyReport { get; set; }
        public DateSearchRange DateSearchRange { get; set; }


 public async Task OnPostSelectionAsync(DateSearchRange DateSearchRange)
        {
            var result= await _context.TaskSelection.Where(x => x.WorkDate >= startDate && x.WorkDate <= endDate)
                .Include(t => t.Zone).OrderBy(x => x.AssocId).ToListAsync();

SelectionDailyReport = result;
}

OK. so this works fine. I also have a another button that calls a webApi controller that will basically query the same data and generates a PDF as well.

I wanted to create a utility class and call its method from the page or the webapi controller so I don't have to write the linq query twice.

I created an App_Folder and add a .cs file

in Utility.cS

   namespace WebCrewLog.App_Code
    {
        public class Utility
        {
            private CrewLogContext _context;

            //initiate db connection
            public Utility(CrewLogContext context)
            {
               _context = context;
            }

            public  IList<SelectionDailyReport> GetSelectionData (DateSearchRange DateSearchRange)
            {
                var myList =  _context.TaskSelection.Where(x => x.WorkDate >=DateSearchRange.StartDate && x.WorkDate <= DateSearchRange.EndDate)
                    .Include(t => t.Zone).OrderBy(x => x.AssocId).ToList();
         return  myList ;
       }

Then from my page or my webapi I wanted to call

SelectionDailyReport = Utility.GetSelectionData(DateSearchRange);

So the problem is that intellisense does not detect the GetSelectionData method. So I thought I should make the GetSelectionData method static.

so Change Utility Class

 public IList<SelectionDailyReport> GetSelectionData (DateSearchRange DateSearchRange)
        {
            var myList =  _context.TaskSelection.Where(x => x.WorkDate >=DateSearchRange.StartDate && x.WorkDate <= DateSearchRange.EndDate)
                .Include(t => t.Zone).OrderBy(x => x.AssocId).ToList();
....

 public  static IList<SelectionDailyReport> GetSelectionData (DateSearchRange DateSearchRange)
        {
            var myList =  _context.TaskSelection.Where(x => x.WorkDate >=DateSearchRange.StartDate && x.WorkDate <= DateSearchRange.EndDate)
                .Include(t => t.Zone).OrderBy(x => x.AssocId).ToList();
....

However, when I do that I'm getting a null exception on _context.TaskSelection and not sure why is that.

Answer 1

The problem is that when you changed the function to be static , now calling it does not initialize the class and the constructor public Utility(CrewLogContext context) is not called, so the _context field is not assigned to anything and stays null .

One way to solve this is to remove static and call the function after building the object and passing the context. So instead of:

SelectionDailyReport = Utility.GetSelectionData(DateSearchRange);

Try something like:

Utility u = new Utility(myContext); //Change myContext to the name of your context
SelectionDailyReport = u.GetSelectionData(DateSearchRange);

If you want it to be static , then you'll have to pass it the context:

public  static IList<SelectionDailyReport> GetSelectionData (DateSearchRange DateSearchRange, CrewLogContext context) {
    var myList =  context.TaskSelection.Where(x => x.WorkDate >=DateSearchRange.StartDate && x.WorkDate <= DateSearchRange.EndDate)
            .Include(t => t.Zone).OrderBy(x => x.AssocId).ToList();
     return  myList ;
   }

The above solutions may seem easier, but it's probably better to use the proper injection just like how it works in the controllers.