Linq OrderBy 计算属性

Question

我使用表达式生成器对表数据进行排序和过滤。但是，当属性中有计算时，查询不会执行。

我在这里阅读了类似的帖子，但找不到答案！

例如如果我尝试按“到期”对下面的查询进行排序，则会失败并出现以下错误。

System.InvalidOperationException：LINQ 表达式 'DbSet() .Where(i => i.OrganisationId == __organisationId_0) .OrderBy(i => (Nullable)(DateTime.Now - i.PaymentDueDate).TotalDays)' 无法翻译。以可翻译的形式重写查询，或通过插入对“AsEnumerable”、“AsAsyncEnumerable”、“ToList”或“ToListAsync”的调用显式切换到客户端评估。请参阅https://go.microsoft.com/fwlink/?linkid=2101038 了解更多信息。

我该如何应对这种情况，或者我在这里做错了什么？ 谢谢，非常感谢！

方法：

public async Task<PaginatedList<GetInvoiceListDto>> Handle(GetInvoiceListQuery request, CancellationToken cancellationToken)
    {
        var organisationId = _tenantService.GetOrganisationId();
        return await _context.Invoices
            .Include(i => i.InvoiceSaleItems)
            .Where(w => w.OrganisationId == organisationId)
            .Select(y => new GetInvoiceListDto
            {
                Status = y.PaymentDueDate < DateTime.Now ? "Overdue" : "Sent",
                Due = (DateTime.Now - y.PaymentDueDate).TotalDays,
                InvoiceDate = y.InvoiceDate,
                InvoiceNumber = y.InvoiceNumber,
                CustomerName = y.Customer.CustomerName,
                AmountDue = y.InvoiceSaleItems.Sum(yx => yx.Amount) + y.InvoiceSaleItems.SelectMany(ss => ss.InvoiceSaleItemTaxes).Sum(sg => sg.Amount),
            }).PaginatedListAsync(request.PageNumber, request.PageSize, request.SortColumn, request.SortOrder, request.q);

    }

扩展名：

public static Task<PaginatedList<TDestination>> PaginatedListAsync<TDestination>(this IQueryable<TDestination> queryable, int pageNumber, int pageSize, string sortColumn, string sortOrder, string filter)
        => PaginatedList<TDestination>.CreateAsync(queryable, pageNumber, pageSize, sortColumn, sortOrder, filter);


public static async Task<PaginatedList<T>> CreateAsync(IQueryable<T> source, int pageIndex, int pageSize, string sortColumn, string sortOrder, string filter)
    {
        var query = source;
        // query = query.Filter<T>(filter); // commented for simplicity.
        query = query.OrderBy<T>(sortColumn, sortOrder);
        var count = query.Count(); // <= The error is thrown at this line.
        var items = await Task.FromResult (query.Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList());

        return new PaginatedList<T>(items, count, pageIndex, pageSize);
    }

public static IQueryable<T> OrderBy<T>(this IQueryable<T> query, string sortColumn, string direction)
    {
        var methodNameFirst = string.Format("OrderBy{0}", direction.ToLower() == "asc" ? "" : "descending");
        var methodNameContinue = string.Format("ThenBy{0}", direction.ToLower() == "asc" ? "" : "descending");
        ParameterExpression parameter = Expression.Parameter(query.ElementType, "p");
        Expression result = query.Expression;
        var methodName = methodNameFirst;
        foreach (var fields in sortColumn.Split(','))
        {
            Expression memberAccess = null;
            foreach (var property in fields.Split('.'))
            {
                if (string.IsNullOrEmpty(property.Trim()) == false)
                {
                    var newProp = "";
                    if (property.IndexOf(" asc") == -1)
                    {
                        newProp = property.Trim();
                    }
                    else
                    {
                        newProp = property.Substring(0, property.IndexOf(" asc")).Trim();
                    }
                    try
                    {
                        memberAccess = MemberExpression.Property(memberAccess ?? (parameter as Expression), newProp);
                    }
                    catch (Exception e)
                    {
                    }
                }
            }
            LambdaExpression orderByLambda = Expression.Lambda(memberAccess, parameter);
            result = Expression.Call(
                typeof(Queryable),
                methodName,
                new[] { query.ElementType, memberAccess.Type },
                result,
                Expression.Quote(orderByLambda));
            methodName = methodNameContinue;
        }
        return query.Provider.CreateQuery<T>(result);
    }

Answer 1

不要使用(DateTime.Now - y.PaymentDueDate).TotalDays，而是尝试用 EF Core 可以转换为 SQL 的东西替换：

return await _context.Invoices
    .Where(w => w.OrganisationId == organisationId)
    .Select(y => new GetInvoiceListDto
    {
        Status = y.PaymentDueDate < DateTime.Now ? "Overdue" : "Sent",
        Due = EF.Functions.DateDiffDay(DateTime.Now, y.PaymentDueDate),
        InvoiceDate = y.InvoiceDate,
        InvoiceNumber = y.InvoiceNumber,
        CustomerName = y.Customer.CustomerName,
        AmountDue = y.InvoiceSaleItems.Sum(yx => yx.Amount) + y.InvoiceSaleItems.SelectMany(ss => ss.InvoiceSaleItemTaxes).Sum(sg => sg.Amount),
    }).PaginatedListAsync(request.PageNumber, request.PageSize, request.SortColumn, request.SortOrder, request.q);

请注意，我已删除 Include，如果您有 Select，则不需要。