ASP.NET Core WebApi Retrieve Last n Records

Question

I have put together a GET request that returns the last n (5) records on WebApi. Simply creating a call to get the entire list back async, then count the last five items, add them to a List of the custom type, that is Application in this case, then add then to a new list and return that.

Is there a more efficient way to run this query using Entity Framework core on .Net Core 6 webapi?

Here is my current code:

// GET: api/Application/last5
[HttpGet("last5")]
public async Task<ActionResult<IEnumerable<Application>>> Get5Applications()
{
    var list = await _context.Applications.ToListAsync();

    List<Application> returnedData = new List<Application>();

    for (int i = Math.Max(0, list.Count - 5); i < list.Count; ++i)
    {
        returnedData.Add(list[i]);
    }

    return returnedData;
}

Does this answer your question? [Using Linq to get the last N elements of a collection?](https://stackoverflow.com/questions/3453274/using-linq-to-get-the-last-n-elements-of-a-collection) — Yong Shun, May 26 '22 at 05:12

Ethan · Answer 1 · 2022-05-26T14:14:14.217

4

Try

_context.Applications.OrderByDescending(x => x.sortingproperty).Take(5);

System.Linq provides a Take function but it looks like you need to sort by decending order. You need to have some sort of property you're wanting to sort by. Replace sortingproperty with anything that fits your needs, normally an ID of some sort. I hope this helps. If you don't need the reversed order then you can use _context.Applications.Take(5)

edited May 26 '22 at 14:14

answered May 26 '22 at 05:24

Ethan

160
2
10

you need to add an orderbydesc before take 5, he need last 5 record not the first 5 record – Den May 26 '22 at 07:36
"You can also use TakeLast(n) if that better fits your needs." - I feel like that answers your point there. – Ethan May 26 '22 at 13:56
TakeLast can't be translated to SQL, then is better orderbydescending then use take. – Den May 26 '22 at 14:08
1

Ah okay. I'll update my answer. – Ethan May 26 '22 at 14:10

Yusif Karimov · Answer 2 · 2022-05-27T05:49:00.970

If you want to get Last insert items. You can try 2 ways. I mentioned both of them followed photos. In this example I have product entity and I saved some items in database, then tried both worked correctly. Also you can order by any column if you want. I ordered by id because it is auto increment

[Route("api/[controller]")]
[ApiController]
public class ProductController : ControllerBase
{
    private readonly AppDbContext _context;

    public ProductController(AppDbContext context)
    {
        _context = context;
    }

    [HttpGet("GetLastItems1/{take}")]
    public IEnumerable<Product> GetLastItems1(int take) => _context.Products
                                                                    .TakeLast(take)
                                                                    .ToList();

    [HttpGet("GetLastItems2/{take}")]
    public IEnumerable<Product> GetLastItems2(int take) => _context.Products
                                                                    .OrderByDescending(x => x.Id)
                                                                    .Take(take)
                                                                    .OrderBy(x => x.Id)
                                                                    .ToList();
}

ASP.NET Core WebApi Retrieve Last n Records

2 Answers2