由于 Where+ToDictionary,LINQ 查询变慢
Slow LINQ query because of Where+ToDictionary
我有这个查询需要 运行:
IEnumerable<MerchantWithParameters> merchants =
from i in (
from m in d.GetTable<Merchant>()
join mtp in d.GetTable<MerchantToParameters>() on m.Id equals mtp.MerchantId into mtps
from mtp in mtps.DefaultIfEmpty()
join cp in d.GetTable<ContextParameters>() on mtp.ContextParametersId equals cp.Id into cps
from cp in cps.DefaultIfEmpty()
select new {Merchant = m, ContextParameter = cp}
)
group i by new { i.Merchant.Id } into ig
select new MerchantWithParameters()
{
Id = ig.Key.Id,
Parameters = ig.Where(g => g.ContextParameter != null).ToDictionary(g => g.ContextParameter.Key, g => g.ContextParameter.Text)
};
由于某种原因,完成此查询需要很长时间。
我认为这与
有关
Parameters = ig.Where(g => g.ContextParameter != null).ToDictionary(g => g.ContextParameter.Key, g => g.ContextParameter.Text)
因为当我删除这一行时,查询开始执行得非常快。
你能告诉我我做错了什么吗?
更新:
我正在使用 ToList() 从数据库中提取数据。
已知 SQL 限制。您无法获取分组项目,只能获取分组键或聚合结果。由于你需要所有记录,我们可以在客户端进行分组,但之前最大限度地限制了检索数据。
var query =
from m in d.GetTable<Merchant>()
from mtp in d.GetTable<MerchantToParameters>().LeftJoin(mtp => m.Id == mtp.MerchantId)
from cp in d.GetTable<ContextParameters>().LeftJoin(cp => mtp.ContextParametersId == cp.Id)
select new
{
MerchantId = m.Id,
ContextParameterKey = (int?)cp.Key,
ContextParameterText = cp.Text
};
var result =
from q in query.AsEnumerable()
group q by q.MerchantId into g
select new MerchantWithParameters
{
Id = g.Key,
Parameters = g.Where(g => g.ContextParameterKey != null)
.ToDictionary(g => g.ContextParameterKey.Value, g => g.ContextParameterText)
};
var merchants = result.ToList();
我有这个查询需要 运行:
IEnumerable<MerchantWithParameters> merchants =
from i in (
from m in d.GetTable<Merchant>()
join mtp in d.GetTable<MerchantToParameters>() on m.Id equals mtp.MerchantId into mtps
from mtp in mtps.DefaultIfEmpty()
join cp in d.GetTable<ContextParameters>() on mtp.ContextParametersId equals cp.Id into cps
from cp in cps.DefaultIfEmpty()
select new {Merchant = m, ContextParameter = cp}
)
group i by new { i.Merchant.Id } into ig
select new MerchantWithParameters()
{
Id = ig.Key.Id,
Parameters = ig.Where(g => g.ContextParameter != null).ToDictionary(g => g.ContextParameter.Key, g => g.ContextParameter.Text)
};
由于某种原因,完成此查询需要很长时间。
我认为这与
有关Parameters = ig.Where(g => g.ContextParameter != null).ToDictionary(g => g.ContextParameter.Key, g => g.ContextParameter.Text)
因为当我删除这一行时,查询开始执行得非常快。
你能告诉我我做错了什么吗?
更新: 我正在使用 ToList() 从数据库中提取数据。
已知 SQL 限制。您无法获取分组项目,只能获取分组键或聚合结果。由于你需要所有记录,我们可以在客户端进行分组,但之前最大限度地限制了检索数据。
var query =
from m in d.GetTable<Merchant>()
from mtp in d.GetTable<MerchantToParameters>().LeftJoin(mtp => m.Id == mtp.MerchantId)
from cp in d.GetTable<ContextParameters>().LeftJoin(cp => mtp.ContextParametersId == cp.Id)
select new
{
MerchantId = m.Id,
ContextParameterKey = (int?)cp.Key,
ContextParameterText = cp.Text
};
var result =
from q in query.AsEnumerable()
group q by q.MerchantId into g
select new MerchantWithParameters
{
Id = g.Key,
Parameters = g.Where(g => g.ContextParameterKey != null)
.ToDictionary(g => g.ContextParameterKey.Value, g => g.ContextParameterText)
};
var merchants = result.ToList();