使用Sieve包实现WebApi分页时的问题及求解

我正在开发一个采用CQRS和MediatR模式的小型WebApi作为求职作品集，目前用Sieve.net做结果过滤、排序和分页时遇到了分页相关问题。

期望返回格式 #

{
    "currentPage": 1,
    "pageSize": 5,
    "pageCount": 1,
    "rowCount": 5,
    "data": [
      {
          "id": 1,
          "name": "name",
          "description": "description"
       }
     ]
}  

现有基础代码 #

PagedRequestHandler基类 #

public abstract class PagedRequestHandler<TRequest, TResponse> : IRequestHandler<TRequest, TResponse>
       where TRequest : IRequest<TResponse>
{
    public abstract Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken);
}

PagedResponseExtension扩展类 #

public static class PagedResponseExtension
{
    public static async Task<PagedResponse<TResponse>> ToPagedAsync<TEntity, TResponse>
           (this IQueryable<TEntity> query, IMapper mapper, ISieveProcessor sieve, SieveModel model = null,
           CancellationToken cancellationToken = default) where TResponse : ResponseBase<TResponse>
    {
        var page = model?.Page ?? 1;
        var pageSize = model?.PageSize ?? 50;

        if (model != null)
            query = sieve.Apply(model, query, applyPagination: false);

        var rowCount = await query.CountAsync(cancellationToken);
        var pageCount = (int)Math.Ceiling((double)rowCount / pageSize);

        var skip = (page - 1) * pageSize;
        var pagedQuery = query.Skip(skip).Take(pageSize);

        var response = new PagedResponse<TResponse>
            {
                CurrentPage = page,
                PageSize = pageSize,
                PageCount = pageCount,
                RowCount = rowCount
            };

        response.Results = await pagedQuery.ProjectTo<TResponse>(mapper.ConfigurationProvider)
                                           .ToListAsync(cancellationToken);

        return response;
    }
}

PagedResponse类 #

public class PagedResponse<TResponse> where TResponse : class
{
    public int CurrentPage { get; set; }
    public int PageSize { get; set; }
    public int PageCount { get; set; }
    public long RowCount { get; set; }

    public IList<TResponse> Results { get; set; } = new List<TResponse>();

    public ErrorModel Error { get; internal set; }
}

GetProductsQuery查询类 #

public class GetProductsQuery : QueryBaseWithSieve<List<Product>>
{
    public SieveModel SieveModel { get; init; }

    public async override Task<List<Product>> Execute(FlowerShopStorageContext context, ISieveProcessor sieveProcessor)
    {
        var query = sieveProcessor.Apply(SieveModel, context.Products.AsNoTracking());
            
        return await query.ToListAsync();
    }
}

当前的GetProductsHandler处理类 #

public class GetProductsHandler : IRequestHandler<GetProductsRequest, GetProductsResponse>
{
    private readonly IMapper mapper;
    private readonly IQueryExecutor queryExecutor;

    public GetProductsHandler(IMapper mapper, IQueryExecutor queryExecutor)
    {
        this.mapper = mapper;
        this.queryExecutor = queryExecutor;
    }

    public async Task<GetProductsResponse> Handle(GetProductsRequest request, CancellationToken cancellationToken)
    {
        var query = new GetProductsQuery()
            {
                SieveModel = request.SieveModel
            };

        var products = await this.queryExecutor.ExecuteWithSieve(query);

        if (products == null)
        {
            return new GetProductsResponse()
                {
                    Error = new ErrorModel(ErrorType.NotFound)
                };
        }

        var mappedProducts = this.mapper.Map<List<Domain.Models.ProductDTO>>(products);

        var response = new GetProductsResponse()
            {
                Data = mappedProducts
            };

        return response;
    }
}

尝试修改后的错误 #

我修改了GetProductsHandler，但遇到编译错误：

public class GetProductsHandler : PagedRequestHandler<GetProductsRequest, PagedResponse<GetProductsResponse>>
{
    private readonly IMapper mapper;
    private readonly IQueryExecutor queryExecutor;
    private readonly SieveProcessor sieveProcessor;

    public GetProductsHandler(IMapper mapper, IQueryExecutor queryExecutor, SieveProcessor sieveProcessor)
    {
        this.mapper = mapper;
        this.queryExecutor = queryExecutor;
        this.sieveProcessor = sieveProcessor;
    }

    public override async Task<PagedResponse<GetProductsResponse>> Handle(GetProductsRequest request, CancellationToken cancellationToken)
    {
        var query = new GetProductsQuery()
            {
                SieveModel = request.SieveModel
            };

        var products = await this.queryExecutor.ExecuteWithSieve(query);

        if (products == null)
        {
            return new PagedResponse<GetProductsResponse>()
                {
                    Error = new ErrorModel(ErrorType.NotFound)
                };
        }

        products.AsQueryable();
        // var mappedProducts = this.mapper.Map<List<Domain.Models.ProductDTO>>(products);
            
        var response = new PagedResponse<GetProductsResponse>()
            {
                //Results = products
                // Data = mappedProducts
                //Results = (IList<GetProductsResponse>)products  //mappedProducts   
                //products.ToList()
            };

    // 错误    CS1929  'PagedResponse<GetProductsResponse>' 不包含 'ToPagedAsync' 的定义，最佳扩展方法重载
    // 'PagedResponseExtension.ToPagedAsync<GetProductsRequest, GetProductsResponse>(IQueryable<GetProductsRequest>, IMapper, ISieveProcessor, SieveModel, CancellationToken)' 
    // 需要接收类型 'IQueryable<GetProductsRequest>' 
         
        return await response.ToPagedAsync<GetProductsRequest, GetProductsResponse>(query, mapper, sieveProcessor, request.SieveModel);  

        //return response.ToPagedAsync<GetProductsRequest, GetProductsResponse>();         
    }
}

控制器中的错误 #

同时在ProductsController里也遇到了错误：

类型'Shop.ApplicationServices.API.Domain.Product.GetProductsRequest'无法用作泛型类型或方法'ApiControllerBase.HandleRequest<TRequest, TResponse>(TRequest)'的类型参数'TRequest'。不存在从'Shop.ApplicationServices.API.Domain.Product.GetProductsRequest'到'MediatR.IRequest<Shop.ApplicationServices.API.Domain.Product.GetProductsResponse>'的隐式引用转换。

控制器代码：

[HttpGet]
[Route("")]
public async Task<IActionResult> GetAllProducts([FromQuery] SieveModel sieveModel)
{            
    GetProductsRequest request = new GetProductsRequest { SieveModel = sieveModel };

    return await this.HandleRequest<GetProductsRequest, GetProductsResponse>(request);
}  

提问 #

请问我当前的解决思路是否正确？

内容的提问来源于stack exchange，提问作者luca88