What is the best way to implement filtering in ASP.NET Core Web API?

Question

I have a JobsController that has a GetJobs method as follows:

[HttpGet]
... Task<IActionResult> GetJobs([FromQuery] Pagination urlQuery)
... return await _dbContext.Jobs
              .AsNoTracking
              .Where(x => x.BankId == user.BankId)
              .Skip(urlQuery.Limit *(urlQuery.Offset -1))
              .Take(urlQuery.Limit)
              .ToListAsync()

I have successfully implemented paging functionality: .../jobs?limit=25&offset=1

I tried creating a filter class

...
public int BankId {get; set;}
public bool Archived {get; set;}
...
public bool HaveFilter => !string.IsNullOrEmpty(BankId.ToString()) ||
                          !string.IsNullOrEmpty(Archived.ToString())

But then it gets messy when trying to use this alongside Pagination.

What would be the best way to implement server-side filtering so that I can use something like .../jobs?limit=25&offset=1&bankId=3&archived=true ?

Jason Roner · Accepted Answer · 2018-06-20 23:05:26Z

2

You don't have to chain all the filters in the same statement. Since they all return IQueryable, and not actually performing the database call until ToListAsync is called, you can easily use If statements to chain what you need.

var dataToReturn = _dbContext.Jobs
          .AsNoTracking;

if(BankId > 0)
     dataToReturn = dataToReturn
          .Where(x => x.BankId == user.BankId);

if(Archived)
     dataToReturn = dataToReturn
          .Where(x => x.Archived);  

return dataToReturn
          .Skip(urlQuery.Limit *(urlQuery.Offset -1))
          .Take(urlQuery.Limit);
          .ToListAsync();

answered Jun 20, 2018 at 23:05

Jason Roner

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3 Comments

Joe Over a year ago

Thanks for answer! After getting myself familiar with IQueryable this made sense.

Jason Roner Over a year ago

No problem. There are other ways too, like building expression trees but that is a lot more complicated.

ssmith Over a year ago

Combine this with the Specification pattern if you want to name and avoid duplicating these different components. More here: deviq.com/specification-pattern and in the design pattern library on Pluralsight.

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