如何通过 LINQ Join() 链接两个 IQueryable？

Question

我有两个 IQueryable：

成分：

IngId
Description

可用成分：

IngId

我已经有一个 IQueryable for Ingredient：

var ingQuery = from i in context.Ingredients
               select i;

我如何向他添加一个联接，以便它按

AvailableIngredient

进行过滤（即内部联接）？如果我必须一直加入，即从... join context.Available ... 等），我知道该怎么做，但加入是有条件的，所以我需要使用其他语法：

if (filterByAvailable)
{
   IQueryable<Available> availableQuery = GetAvailableIngredientQuery(context);
   ingQuery = ingQuery.Join(...); // Can I use this to join to the query?
}

这可能不是正确的方法，所以这就是我想做的：

• GetAvailableIngredientQuery 返回 可用成分查询，即 6000 中的 3000（但事实并非如此） 枚举结果，因为它是 从 EF 作为 IQueryable 返回）
• 将 availableQuery 连接到 ingQuery，这样两个查询之间就有一个 Inner Join

编辑：

这是我当前正在使用的代码（非常快），但这意味着重复的代码：

IQueryable<Ingredient> query;
if (filterByAvailable)
{
    IQueryable<Available> availableQuery = GetAvailableIngredientQuery(context);
    query = from item in context.Ingredients
               // Quite a few `where` clauses and stuff
            join t in availableQuery on item.IngId equals t.IngId
            select item;
}
else
{ 
    query = from item in context.Ingredients
               // The SAME `where` clauses and stuff as above
            select item;
}

Answer 1

使用第一个查询作为后续查询的来源。

IQueryable<Ingredient> query = from item in context.Ingredients
                             // Quite a few `where` clauses and stuff
                               select item;

if (filterByAvailable)
{
    IQueryable<Available> availableQuery = GetAvailableIngredientQuery(context);
    query = from item in query
            join t in availableQuery on item.IngId equals t.IngId
            select item;
}

Answer 2

我已经使用Where子句实现了分页逻辑，任何人都可以将其用于分页和其他目的。 ResponseDTO 响应 = 新 ResponseDTO();

        var requests =  (from r in _context.Requests.Where(x => x.IsActive && x.EmployeeId == search.EmployeeNumber && x.ServiceId == search.ServiceId)
                              join s in _context.Services
                              on r.ServiceId equals s.Id
                              join b in _context.RequestStatus
                              on r.RequestStatusId equals b.RequestStatusId
                              select new GetRequestHistoryDto
                              {
                                  Id = r.Id,
                                  ReferenceNumber = r.ReferenceNumber,
                                  ServiceId = r.ServiceId,
                                  ServiceNameEn = s.NameEn,
                                  ServiceNameAr = s.NameAr,
                                  RequesterId = r.RequesterId,
                                  RequestStatusId = r.RequestStatusId,
                                  RequestStatusName = b.RequestStatusEn,
                                  CreatedOn = r.CreatedOn
                              });
        if (requests != null)
        {
            if (!string.IsNullOrEmpty(search.SearchKey))
            {
                requests = requests.Where(x => x.ReferenceNumber.ToLower().Contains(search.SearchKey.ToLower())
                || x.ServiceId.ToString().Contains(search.SearchKey)
                || x.ServiceNameEn.ToString().ToLower().Contains(search.SearchKey.ToLower())
                || x.ServiceNameAr.ToString().ToLower().Contains(search.SearchKey.ToLower())
                || x.RequesterId.ToString().ToLower().Contains(search.SearchKey.ToLower())
                || x.RequestStatusName.ToString().ToLower().Contains(search.SearchKey.ToLower()));
            }
            if (search.IsSortDesc)
            {
                requests = requests.OrderByDescending(e => e.CreatedOn);
            }
            else
            {
                requests = requests.OrderBy(e => e.CreatedOn);
            }
        }

        response.TotalRecords = requests.Count();

        if (search.pageNumber > 0 && search.pageSize > 0)
        {
            requests = requests.Skip((search.pageNumber - 1) * search.pageSize).Take(search.pageSize);
        }
        requests = requests.OrderByDescending(x => x.CreatedOn);
        response.Data = await requests.ToListAsync();