【发布时间】：2019-07-30 12:31:28
【问题描述】：
我正在使用带有 .NET Core 的 EF 6。我编写了以下查询以将一些数据选择到自定义对象中。目前主查询返回超过 25000 条记录。然后应用过滤器。此查询运行非常缓慢。我只是想找出我是否在这里犯了任何错误。为什么它会这么慢，并且过滤发生在内存而不是数据库端？
public IQueryable<TicketViewModel> GetTickets(int companyId, string locale, TicketFilterViewModel filters, Guid customerRef, int? take, int currentUser)
{
IQueryable<TicketViewModel> tickets = (from to in _context.Ticket
join co in _context.Company on to.CompanyId equals co.CompanyId
join con in _context.Contact on to.ContactId equals con.ContactId
join site in _context.Site on to.SiteId equals site.SiteId
join country in _context.Country on site.CountryId equals country.CountryId
join cus in _context.Customer on con.CustomerId equals cus.CustomerId
join tic_type in _context.TicketType on to.TicketTypeId equals tic_type.TicketTypeId
join ts in _context.TicketStatus on to.TicketStatusId equals ts.TicketStatusId
join sb in _context.ServiceBoard on to.ServiceBoardId equals sb.ServiceBoardId into ob1
from a in ob1.DefaultIfEmpty()
join u in _context.User on to.TechnitianId equals u.Id into ob2
from b in ob2.DefaultIfEmpty()
join pr in _context.Priority on to.PriorityId equals pr.PriorityId into ob3
from c in ob3.DefaultIfEmpty()
where to.CompanyId == companyId && (customerRef == Guid.Empty || cus.RefNo == customerRef)
&& to.MergedIntoTicketId == null
select new TicketViewModel
{
CreatedOn = Helpers.Custom.UtcToStandardTime(locale, to.AddedOnUtc).ToString("dd/MM/yyyy hh:mm tt"),
CustomerName = cus.CustomerName,
TicketNumber = to.TicketNumber,
TicketTitle = to.TicketTitle,
RefNo = to.RefNo,
CompanyName = co.CompanyName,
ContactName = string.Concat(con.FirstName, " ", con.LastName),
SiteAddress = String.Concat(site.AddressLine1, ", ", site.AddressLine2, ", ", site.Suburb, ", ", site.State, ", ", site.PostCode, ", ", country.Name),
ServiceBoardName = a.BoardName,
TechnicianName = string.Concat(b.FirstName, " ", b.LastName),
PriorityName = c.PriorityName,
TicketStatus = ts.StatusName, //d.StatusName,
ServiceBoardId = to.ServiceBoardId,
TicketStatusId = to.TicketStatusId,
CustomerId = cus.CustomerId,
PriorityId = to.PriorityId,
ContractId = site.ContractId,
TechnitianId = to.TechnitianId,
TicketId = to.TicketId,
StatusCategoryId = ts.CategoryId,//,//d.CategoryId,
DueOnUtc = to.DueOnUtc,
DefaultStatusId = ts.DefaultId,//d.DefaultId,
ClosedOnUtc = to.ClosedOnUtc,
ResolvedOnUtc = to.ResolvedOnUtc,
InitialResponseMade = to.InitialResponseMade,
TicketTypeId = to.TicketTypeId,
TicketTypeName = tic_type.TicketTypeName
}).OrderByDescending(o => o.TicketNumber);
bool isFiltersHit = false;
if (filters != null)
{
if (tickets != null && tickets.Count() > 0 && filters.serviceboard_selectedItems != null && filters.serviceboard_selectedItems.Count > 0)
{
isFiltersHit = true;
tickets = tickets.Where(x => x.ServiceBoardId != null && filters.serviceboard_selectedItems.Select(o => o.serviceBoardId).Contains(x.ServiceBoardId.Value));
}
if (tickets != null && tickets.Count() > 0 && filters.status_selectedItems != null && filters.status_selectedItems.Count > 0)
{
isFiltersHit = true;
tickets = tickets.Where(x => x.TicketStatusId != null && filters.status_selectedItems.Select(o => o.ticketStatusId).Contains(x.TicketStatusId.Value));
}
if (tickets != null && tickets.Count() > 0 && filters.type_selectedItems != null && filters.type_selectedItems.Count > 0)
{
isFiltersHit = true;
tickets = tickets.Where(x => filters.type_selectedItems.Select(o => o.ticketTypeId).Contains(x.TicketTypeId));
}
if (tickets != null && tickets.Count() > 0 && filters.technician_selectedItems != null && filters.technician_selectedItems.Count > 0)
{
isFiltersHit = true;
tickets = tickets.Where(x => x.TechnitianId != null && filters.technician_selectedItems.Select(o => o.id).Contains(x.TechnitianId.Value));
}
if (tickets != null && tickets.Count() > 0 && filters.customer_selectedItems != null && filters.customer_selectedItems.Count > 0)
{
isFiltersHit = true;
tickets = tickets.Where(x => x.CustomerId != 0 && filters.customer_selectedItems.Select(o => o.customerId).Contains(x.CustomerId));
}
if (tickets != null && tickets.Count() > 0 && filters.priority_selectedItems != null && filters.priority_selectedItems.Count > 0)
{
isFiltersHit = true;
tickets = tickets.Where(x => x.PriorityId != null && filters.priority_selectedItems.Select(o => o.priorityId).Contains(x.PriorityId.Value));
}
if (tickets != null && tickets.Count() > 0 && filters.contract_selectedItems != null && filters.contract_selectedItems.Count > 0)
{
isFiltersHit = true;
tickets = tickets.Where(x => x.ContractId != null && filters.contract_selectedItems.Select(o => o.contractId).Contains(x.ContractId.Value));
}
if (tickets != null && tickets.Count() > 0 && filters.source_selectedItems != null && filters.source_selectedItems.Count > 0)
{
isFiltersHit = true;
tickets = tickets.Where(x => x.SourceId != 0 && filters.source_selectedItems.Select(o => o.item_id).Contains(x.SourceId));
}
}
if (take.HasValue)
return tickets.Take(take.Value);
return tickets;
}
【问题讨论】：
-
你有没有试过看看生成的sql是什么样子的？
-
是翻译后的 sql-query 还是你的代码执行速度慢？
-
这不会改善查询，但尽可能使用导航属性将使代码更易于阅读。
-
一个问题是当您执行
Count时，您会在那些if语句中一遍又一遍地运行该查询。如果您没有任何结果，那么添加更多过滤器不会受到伤害。 -
过滤器部分既不需要“tickets != null”也不需要“tickets.Count() > 0”（tickets 永远不会为空，你不在乎是否有任何结果因为当您尝试同时评估已完成的查询和过滤器时，惰性评估将构建实际的查询）。尝试将生成的查询字符串输入数据库查询优化器以查找是否缺少所需的索引。
标签： c# entity-framework linq .net-core