Efficient Pagination in .NET: Best Practices and Tools for Returning Paged Collections
Published: 2023-04-12 09:52:11




## INTRO
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Pagination is an essential aspect of designing RESTful APIs that return collections of resources. It allows clients to retrieve data in smaller, more manageable chunks, reducing the load on the server and the client. In this blog post, we’ll explore how to implement pagination in .NET, using generic services and libraries to provide an efficient and easy-to-use solution.

## The Problem with Large Collections
When working with large collections of resources in a RESTful API, returning all the resources in a single response can cause performance issues and overload the client. This is where pagination comes in. By dividing the collection into smaller subsets, or pages, and returning only a specific subset in each response, pagination allows clients to retrieve data in smaller chunks.

However, implementing pagination in .NET can be a challenge, especially if you’re working with generic services that need to support different types of resources. In addition, you need to provide metadata about the current page, the total number of items, and the total number of pages in the response to make it easier for clients to navigate the collection.

Fortunately, there are several libraries and tools available in .NET that can help simplify the process of implementing pagination.

## Using Generic Services
One way to implement pagination in .NET is by using generic services. These are services that can work with different types of resources and provide common functionality, like pagination.

Here’s an example of a generic service for pagination in .NET:
`
public class GenericPagedService<T> where T : class
{
    private readonly DbContext _context;

    public GenericPagedService(DbContext context)
    {
        _context = context;
    }

    public async Task<PagedResult<T>> GetPagedAsync(Expression<Func<T, bool>> predicate, int pageNumber, int pageSize)
    {
        var pagedResult = new PagedResult<T>();
        pagedResult.PageNumber = pageNumber;
        pagedResult.PageSize = pageSize;
        pagedResult.RowCount = await _context.Set<T>().Where(predicate).CountAsync();

        var pageCount = (double)pagedResult.RowCount / pageSize;
        pagedResult.PageCount = (int)Math.Ceiling(pageCount);

        var skip = (pageNumber - 1) * pageSize;
        var take = pageSize;

        pagedResult.Results = await _context.Set<T>()
            .Where(predicate)
            .Skip(skip)
            .Take(take)
            .ToListAsync();

        return pagedResult;
    }
}

public class PagedResult<T>
{
    public int PageNumber { get; set; }
    public int PageSize { get; set; }
    public int RowCount { get; set; }
    public int PageCount { get; set; }
    public List<T> Results { get; set; }
}
`

In this example, the GenericPagedService class provides a generic method for returning a paged collection of resources. The method takes an Expression<Func<T, bool>> predicate to filter the collection, as well as the current page number and page size. The method calculates the total row count, page count, and applies pagination to the collection before returning a PagedResult<T> object containing the paged collection and metadata.

## Using Libraries
Another way to simplify pagination in .NET is by using libraries that provide pagination functionality out of the box. One such library is PagedList, which provides an easy-to-use API for working with paged collections.

Here’s an example of how to use PagedList in a .NET controller:
`
[HttpGet]
public async Task<IActionResult> Get(int page = 1, int pageSize = 10)
{
    var resources = await _repository.GetResourcesAsync();

    if(resources == null || !resources.Any())
    {
      return NotFound();
    }
  
    var pagedResources = await resources.ToPagedListAsync(page, pageSize);

    return Ok(pagedResources);
}
`

In this example, the `Get` method retrieves all the resources from the repository and applies pagination using the `ToPagedListAsync` method from `PagedList`. The method returns an `IActionResult` object containing the paged collection and the appropriate HTTP status code.

Using `PagedList` makes it easy to work with paged collections in .NET, as it provides a simple API and handles the pagination logic for you.

## Conclusion
Pagination is an essential aspect of designing RESTful APIs that return collections of resources. By dividing the collection into smaller subsets and returning only a specific subset in each response, you can reduce the load on the server and the client and provide a better experience for your clients.

In this blog post, we’ve explored two ways to implement pagination in .NET: using generic services and using libraries like `PagedList`. Both approaches provide an efficient and easy-to-use solution for working with paged collections in .NET.

By following these best practices and leveraging the available tools and libraries, you can design a RESTful API that efficiently handles pagination and provides a good developer experience.