To get a performance gain, I am trying to replace the call to Distinct() below with GroupBy(...), however I am getting errors.
Any suggestions on how this query should be rewritten to use GroupBy(...)?
I am trying to use GroupBy() on the Description field itself.
var result=
GetResults()
.Select(x => new SelectList { Text = x.Description, Value = x.Description })
.Where(x => x.Text != null)
.Distinct()
.ToList();
You can't force the Entity Framework to use GroupBy instead of Distinct clause in generated SQL. Entity framework will determine the appropriate query and it will use that.
One thing that is apparent from your code is that you are only interested in List<string> based on unique Description values. I don't think you have to create a collection of SelectList.
You can do:
var result= GetResults()
.Where(x => x.Description != null)
.GroupBy(x => x.Description)
.Select(grp => grp.Key)
.ToList();
OR
var result= GetResults()
.Where(x => x.Description != null)
.Select(x => x.Description)
.Distinct()
.ToList();
Both of the above queries would produce a list of unique description values. Now what type of SQL will be generated against both of these depends on the Entity Framework.
Old Answer:
Use GroupBy to group on Description and then Select where Key is not null like:
var result= GetResults()
.Select(x => new SelectList { Text = x.Description, Value = x.Description })
.Where(x => x.Text != null)
.GroupBy(x => x.Value) //Here select Value for Description
.Select(grp => grp.Key)
.ToList();
This will not give you any performance gain, even if there is any, it would be negligible.
You can yry grouping by Description:
var result=GetResults()
.GroupBy(x => x.Description)
.Where(g => g.Key != null)
.Select(g => new SelectList { Text = g.Key, Value = g.Key })
.ToList();
But I'd be surprised if you got better performance that a Distinct.
Related
There is a way to prevent duplicates Id, but if id is null to let the list to be with duplicates null?
data = data
.OrderByDescending(x => x.DocVersionNumber)
.DistinctBy(x => x.RequireId)
.ToList();
in this way if I have few items with null on RequireId, only one will stay.
Thanks
you can do it like this
var temp = data.Where(x => x.RequireId == null).ToList();
data = data.Where(x => x.RequireId != null)
.OrderByDescending(x => x.DocVersionNumber)
.DistinctBy(x => x.RequireId)
.ToList();
data.AddRange(temp);
data = data
.Where(i => i.RequireId != null)
.OrderByDescending(x => x.DocVersionNumber)
.DistinctBy(x => x.RequireId)
.ToList();
I have the data in the source table.
And I want to get this kind of result in list using lambda expression and Entity Framework. I don't know how to do it. I need to get top 3 rows in for each CategoryId.
Probably using something like this:
context.GroupBy(x => x.CategoryId)
.Select(group => new {
CategoryId = group.Key,
NameId = group.Select(x => x.NameId),
group.OrderByDescending(e => e.Count).Take(3)
})
.ToListAsync()
var list = context
.GroupBy(x => x.CategoryId)
.SelectMany(group => group.OrderByDescending(e => e.Count).Take(3))
.OrderByDescending(e => e.Count)
.ToListAsync();
If you want an anonymous type:
var list = context
.GroupBy(x => x.CategoryId)
.SelectMany(group => group.OrderByDescending(e => e.Count).Take(3))
.Select(x => new
{
x.CategoryId,
x.NameId,
x.Count
})
.OrderByDescending(x => x.Count)
.ToListAsync();
I have 2 tables Outlet and Order with below schemas:
Outlet Order
------ -------------------
Id Id
Name Name
OrderCompletedTime
NextOrderDueTime
OutletIds
Earlier when I wanted to get the NextOrderDueTime for each outlet using entity framework core, I did:
return _dbAccessor.RequestContext.MyDbContext.Order
.Where(i => i.OutletId == _dbAccessor.RequestContext.OutletId &&
!i.IsRemoved && i.NextOrderDueTime.HasValue)
.GroupBy(i => i.OutletId)
.Select(g => new { OutletId = g.Key, NextOrderDueTime = g.Min(x => x.NextOrderDueTime) })
.ToDictionary(i => i.OutletId, i => i.NextOrderDueTime);
Now on the UI we need to make this due time as link and wants user to get navigated to that Order details page based on order id
How can I change the above query to also return OrderId along with time?
My thoughts:
Change return type of method from Dictionary<int, DateTimeOffset?> to Dictionary<int, Tuple<int,DateTimeOffset?>>
I tried changing the Linq query to :
return _dbAccessor.RequestContext.MyDbContext.Order
.Where(i => i.OutletId == _dbAccessor.RequestContext.OutletId &&
!i.IsRemoved && i.NextOrderDueTime.HasValue)
.GroupBy(i => i.OutletId)
.Select(g =>
new
{
OutletId = g.Key,
NextOrderDueTime = g.FirstOrDefault(x => x.NextOrderDueTime == g.Min(y => y.NextOrderDueTime)).NextOrderDueTime,
NextOrderId = g.FirstOrDefault(x => x.NextOrderDueTime == g.Min(y => y.NextOrderDueTime)).OrderId
})
.ToDictionary(i => i.OutletId, i => new Tuple<int, DateTimeOffset?>(i.NextOrderId, i.NextOrderDueTime));
But this throws exception at runtime?
Please help to let me know what I am doing wrong here.
You could just take the entire order along with the outletid when you return:
.Select(g => new {
OutletId = g.Key,
NextOrder = g.OrderBy(x => x.NextOrderDueTime).FirstOrDefault()
})
You could select on this to take multiple properties from the order:
.Select(g => new {
OutletId = g.Key,
NextOrder = g.OrderBy(x => x.NextOrderDueTime).FirstOrDefault()
})
.Select(s => new {
s.OutletId,
NextOrderId = NextOrder.Id,
NextOrder.NextOrderDueTime,
NextOrderName = NextOrder.Name
})
etc..
The main thing to appreciate is that grouping gives you an object that has a key, but itself is a list of all things that have that key, so if you order the list by something like the DUeDat and take the first thing then you have an entire object with the lowest duedate from which you can take various things
The .GroupBy(...).Select(...).ToDictionary(...); cannot be converted to SQL since EF Core 3.0.
Due to the breaking change in EF Core 3.0. https://learn.microsoft.com/en-us/ef/core/what-is-new/ef-core-3.0/breaking-changes , EF Core 3.0 will throw exception to make sure you know that all records in Order will be fetched from database before grouping and map to Dictionary.
I was able to get my query working as below:
return _dbAccessor.RequestContext.MyDbContext.Order
.Where(i => i.OutletId == _dbAccessor.RequestContext.OutletId &&
!i.IsRemoved && i.NextOrderDueTime.HasValue).AsEnumerable()
.GroupBy(i => i.OutletId)
.Select(g =>
new
{
OutletId = g.Key,
NextOrderDueTime = g.FirstOrDefault(x => x.NextOrderDueTime == g.Min(y => y.NextOrderDueTime)).NextOrderDueTime,
NextOrderId = g.FirstOrDefault(x => x.NextOrderDueTime == g.Min(y => y.NextOrderDueTime)).OrderId
})
.ToDictionary(i => i.OutletId, i => new Tuple<int, DateTimeOffset?>(i.NextOrderId, i.NextOrderDueTime));
The same can be done as shown in another answer by just adding AsEnumerable() before GroupBy:
_dbAccessor.RequestContext.MyDbContext.Order
.Where(i => i.OutletId == _dbAccessor.RequestContext.OutletId &&
!i.IsRemoved && i.NextOrderDueTime.HasValue).AsEnumerable()
.GroupBy(i => i.OutletId)
.Select(g => new {
OutletId = g.Key,
NextOrder = g.OrderBy(x => x.NextOrderDueTime).FirstOrDefault()
})
.Select(s => new {
s.OutletId,
NextOrderId = NextOrder.Id,
NextOrder.NextOrderDueTime,
NextOrderName = NextOrder.Name
})`enter code here`;
I want to get all the Pre_Number where all Reconcile_Status related to that Pre_Number=null. In this case there should not be any item in list.If there would be some other Pre_number for eg. 7/2018 and it has two records and Reconcile_Status for those records is NULL then i should get one item in list that is 7/2018.
I tried
var NoNReconciled = context.tbl_prerelease_invoice
.Where(x => x.Reconcile_Status==null)
.Select(y => new { y.Pre_number }).Distinct().ToList();
But i got 6/2018
Well, your current attempt only checks that there is at least one record where Reconcile_Status is null, but it doesn't check that there are no records with the same Pre_number where Reconcile_Status is not null.
This should do the trick:
var NoNReconciled = context.tbl_prerelease_invoice
.Where(x => x.Reconcile_Status == null &&
!context.tbl_prerelease_invoice
.Any(y => y.Pre_number == x.Pre_number && y.Reconcile_Status != null)
).Select(y => new { y.Pre_number })
.Distinct().ToList();
No need to create anonymous object for Pre_Number. Try below code
var NoNReconciled = context.tbl_prerelease_invoice
.Where(x => x.Reconcile_Status==null)
.Select(y => y.Pre_number).Distinct().ToList();
Try this-
context.tbl_prerelease_invoice.GroupBy(r => r.Pre_number).Where(kv => kv.All(r => r.Reconcile_Status==null)).Select(kv => kv.Key).ToList();
I'm doing a query over two different tables.
In the first query, i get some Ids that I then have to check in another table.
Then I do the first query again with the result of the second query.
This can't be the best way to do this.
But I haven't found a good way to solve it. So some help would be appreciated.
IntOrderInvoiceCostOut y = null;
var list = session.QueryOver<IntOrderInvoiceCostOut>(() => y)
.Where(x => x.IntegrationHandleDate == null)
.Select(Projections.Distinct(Projections.Property(() => y.Externalid)))
.List<string>();
var nonPreliminaryOrders = session.QueryOver<RefImplOrderEntity>()
.WhereRestrictionOn(x => x.ExternalId).IsIn(list.ToList())
.Where(x => x.StatusTypeId != 95)
.Select(x => x.ExternalId)
.List<string>();
var finalList = session.QueryOver<IntOrderInvoiceCostOut>()
.WhereRestrictionOn(x => x.Externalid).IsIn(nonPreliminaryOrders.ToList())
.Where(x => x.IntegrationHandleDate == null)
.OrderBy(x => x.IntegrationCreateDate)
.Asc
.List();
The code works...but i't really ugly.
you could use detacheCriteria for this. I have omitted couple of conditions and you might have to twick a bit as per your requirement.
for example
IntOrderInvoiceCostOut y = null;
var list = QueryOver.Of<IntOrderInvoiceCostOut>(() => y)
.Where(x => x.IntegrationHandleDate == null)
.Select(Projections.Distinct(Projections.Property(() => y.Externalid)))
.DetachedCriteria;
var nonPreliminaryOrders = QueryOver.Of<RefImplOrderEntity>()
.Where(Subqueries.PropertyIn(nameof(RefImplOrderEntity.ExternalId), list));
.Select(x => x.ExternalId)
.DetachedCriteria
var finalList = session.QueryOver<IntOrderInvoiceCostOut>()
.Where(Subqueries.PropertyIn(nameof(IntOrderInvoiceCostOut.ExternalId), nonPreliminaryOrders));
.List();