So I've got this query:
var query = from r in context.Cars
let h = context.CarHistories
.Where(u => r.ID == u.CarID)
.Where(u => u.EventID == intEventID)
.OrderByDescending(u => u.CreatedDate)
.FirstOrDefault()
select new RefundListItem()
{
ID = r.ID,
VendorID = r.VendorID,
RecipientName = r.RecipientName,
MostRecentSubmittedName = h.CreatedName,
CreatedDate = h.CreatedDate,
};
Later on, I add this to the query because I only want the rows that were created today:
DateTime today = DateTime.Today;
query.Where(u => Convert.ToDateTime(u.CreatedDate) >= today);
For some reason, this where statement does not affect the query at all. The query still returns items created from previous days instead of limiting them to just the rows created today.
I have also tried this but it does not work either:
DateTime today = DateTime.Today.Date;
query.Where(u => Convert.ToDateTime(u.CreatedDate.Date) >= today.Date);
I'm using Linq-to-Entities (MVC 4, EF 4).
Where does not modify query instance, it returns new one with additional condition added. Assign it back to query to make it work:
query = query.Where(u => Convert.ToDateTime(u.CreatedDate.Date) >= today.Date);
Related
Given a date, what is the most efficient way to query the last record before that date, any record that equals that date, and the next one after that date.
It should be functionally equivalent to a query like this:
from asset in Assets
where asset.Id == assetId
select new {
Previous = (from a in a.Orders where a.Date < myDate orderby a.Date descending select a).FirstOrDefault(),
Current = (from a in a.Orders where a.Date == myDate select a).SingleOrDefault(),
Next = (from a in a.Orders where a.Date > myDate orderby a.Date select a).FirstOrDefault()
}
As is, this query runs three queries, and presumably has to sort the dataset by myDate three times to do it.
Some similar questions:
How do I get 5 records before AND after a record with a specific ID? (just uses two queries)
How do I get records before and after given one? Not in Linq, and therefore hard for me to take advantage of (my team will get annoyed).
To provide the "most efficient" query depends on what you mean by efficient.
If you want a single query to the database, a single sort of orders by date and finally fast look-ups by date then I suggest the following might be the most efficient. :-)
var orders =
(from a in Assets
where a.Id == assetId
from o in a.Orders
orderby o.Date
select o).ToArray();
var previous = orders.LastOrDefault(o => o.Date < myDate);
var current = orders.SingleOrDefault(o => o.Date == myDate);
var next = orders.FirstOrDefault(o => o.Date > myDate);
This should query the database once for the orders associated with the required asset Id, sort them by date, and return them as an array in memory. Since this is in memory it is now blindingly fast to look for the current, previous & next records for the specified date.
Does your Orders table have a sequential ID field? If so, you might be able to do it with:
from asset in Assets
where asset.Id == assetID
let current = asset.Orders.Where(x => x.Date == myDate).FirstOrDefault()
where current != null
let previous = asset.Orders.Where(x => x.id == current.id - 1).FirstOrDefault()
let next = asset.Orders.Where(x => x.id == current.id + 1).FirstOrDefault()
select new {
Previous = previous,
Current = current,
Next = next
};
If it doesn't, then it'd be a bit more code:
from asset in Assets
where asset.Id == assetID
let current = asset.Orders.Where(x => x.Date == myDate).FirstOrDefault()
where current != null
let previous = asset.Orders.Where(x => x.Date < current.Date).OrderByDescending(x => x.Date).FirstOrDefault()
let next = asset.Orders.Where(x => x.Date > current.Date).OrderBy(x => x.Date).FirstOrDefault()
select new {
Previous = previous,
Current = current,
Next = next
};
That should get compiled into a single SQL query that utilizes sub-queries. IE: the database server will execute multiple queries, but your client program is only submitting one.
Edit One other idea that would work if your Order table had sequential IDs:
var sample = (from asset in Assets
where asset.Id == assetID
let current = asset.Orders.Where(x => x.Date == myDate).FirstOrDefault()
where current != null
from order in asset.Orders
where order.Id == current.id - 1
select order)
.Take(3)
.ToArray();
var Previous = sample[0];
var Current = sample[1];
var Next = sample[2];
Other Answers, for example, SkipWhile etc. very very slow. Good luck ^^
//Current Record
var query
= (from item in db.Employee
where item.UserName.Equals(_username)
select item).SingleOrDefault();
//Next Record
var query
= (from item in db.Employee
where item.UserName.CompareTo(_username) > 0
select item).FirstOrDefault();
//Previous Record
var query
= (from item in db.Employee
where item.UserName.CompareTo(_username) < 0
orderby item.UserName Descending
select item).FirstOrDefault();
Almost the same, but the SQL query plan might be different.
var q =
from asset in Assets
where asset.Id == assetID
select new
{
Previous = asset.Orders.where(a => a.Date == asset.Orders.Where(x => x.Date < myDate).Max(x => x.Date)).FirstOrDefault(),
Current = asset.Orders.Where(x => x.Date == myDate).FirstOrDefault(),
Next = asset.Orders.where(a => a.Date == asset.Orders.Where(x => x.Date > myDate).Min(x => x.Date)).FirstOrDefault()
};
I've got a class like the following:
public class Invoice
{
public int InvoiceId {get;set;}
public int VersionId {get;set;}
}
Each time an Invoice is modified, the VersionId gets incremented, but the InvoiceId remains the same. So given an IEnumerable<Invoice> which has the following results:
InvoiceId VersionId
1 1
1 2
1 3
2 1
2 2
How can I get just the results:
InvoiceId VersionId
1 3
2 2
I.e. I want just the Invoices from the results which have the latest VersionId. I can easily do this in T-SQL, but cannot for the life of me work out the correct LINQ syntax. I'm using Entity Framework 4 Code First.
Order by the VersionId, group them by InvoiceId, then take the first result of each group. Try this:
var query = list.OrderByDescending(i => i.VersionId)
.GroupBy(i => i.InvoiceId)
.Select(g => g.First());
EDIT: how about this approach using Max?
var query = list.GroupBy(i => i.InvoiceId)
.Select(g => g.Single(i => i.VersionId == g.Max(o => o.VersionId)));
Try using FirstOrDefault or SingleOrDefault in place of Single as well... it would give the same result although Single shows the intention better.
EDIT: I've tested both these queries with LINQ to Entities. They seem to work, so perhaps the issue is something else?
Option 1:
var latestInvoices = invoices.GroupBy(i => i.InvoiceId)
.Select(group => group.OrderByDescending(i => i.VersionId)
.FirstOrDefault());
EDIT: Changed 'Last' to 'FirstOrDefault', LINQ to Entities has issues with the 'Last' query operator.
Option 2:
var invoices = from invoice in dc.Invoices
group invoice by invoice.InvoiceId into invoiceGroup
let maxVersion = invoiceGroup.Max(i => i.VersionId)
from candidate in invoiceGroup
where candidate.VersionId == maxVersion
select candidate;
My version:
var h = from i in Invoices
group i.VersionId by i.InvoiceId into grouping
select new {InvoiceId = grouping.Key, VersionId = grouping.Max()};
Update
As was mentioned by Ahmad in the comments, the above query will return a projection. The version below will return a IQueryable<Invoice>. I use composition to build the query because I think it is more clear.
var maxVersions = from i in Invoices
group i.VersionId by i.InvoiceId into grouping
select new {InvoiceId = grouping.Key,
VersionId = grouping.Max()};
var latestInvoices = from i in Invoices
join m in maxVersions
on new {i.InvoiceId, i.VersionId} equals
new {m.InvoiceId, m.VersionId}
select i;
I ended up with this horrible code below, I can't get a better result now.
What is a better way of doing that?
It's about this part of my database:
EDIT
A Patient has a Subscription to multiple MonitoringObjects. Target records refer to these Subscriptions. I want to retrieve the target records with the newest date per Subscription for a given Patient and a Category of MonitoringObjects. These target records may have different max dates, as Targets can be added for Subscriptions to MonitoringsObjects independently.
var subs = db.Subscriptions.Where(p => p.PatientID == patID).Where(p => p.MonitoringObject.Category.Name == "Medication");
var targets1 = from t in db.Targets
where subs.Contains(t.Subscription)
select t;
var maxTa = from t in db.Targets
group t by t.SubscriptionID
into g
select new
{
Ky = g.Key,
Date = g.Max(p => p.Date)
};
var targets2 = from t in targets1
where maxTa.Select(p => p.Ky).Contains( t.SubscriptionID ) &&
maxTa.Select(p => p.Date).Contains( t.Date )
select t;
I am not exactly sure what this is trying to achieve, or what your datamodel looks like, but something like this?
var subs = db.Subscriptions.Where(p => p.PatientID == patID).Where(p => p.MonitoringObject.Category.Name == "Medication");
var targets = subs
.SelectMany(s => s.Targets)
.Where(t => t.Date == t.Subscription.Targets.Max(_t => _t.Date))
I have a LINQ Query that creates a new type that contains a days of week and a sum of hours worked.
My current (incorrect query) looks like this:
var resultSet = (from a in events
group a by a.Start.DayOfWeek into g
select new DaySummary
{
day = g.Key.ToString(),
hoursWorked = g.Any(p => p.Title == "Lunch") ? 0 :
Math.Round((g.Sum(
p => (Decimal.Parse((p.End - p.Start).TotalMinutes.ToString()))) / 60), 2)
}).ToList();
Hopefully you can see what Im trying to do. The Any method is not having the effect I'd like however. Basically I want to to sum up the hours worked, but if the title was "lunch" I want it to add 0.
The logic of this is just a little beyond me at the moment.
UPDATE
Ok, Im an idiot. Changes the query to this and it now works. Sorry.
var resultSet = (from a in events
group a by a.Start.DayOfWeek into g
select new DaySummary
{
day = g.Key.ToString(),
hoursWorked = Math.Round((g.Where(p => p.Title !="Lunch").
Sum(p => (Decimal.Parse((p.End - p.Start).TotalMinutes.ToString()))) / 60), 2)
}).ToList();
It seems each group is a sequence of 'periods' and you just want to ignore any 'lunch' periods in each calculation. In that case you just need to remove these from the sum using Where.
var hours = events
.GroupBy(e => e.Start.DayOfWeek)
.Select(g => new DaySummary {
day = g.Key.ToString(),
hoursWorked = Math.Round(
g.Where(p => p.Title != "Lunch")
.Sum(pd => (Decimal.Parse((pd.End - pd.Start).TotalMinutes.ToString())) / 60), 2)
}).ToList();
I have to work out how to write the following SQL query usingLINQ query or method syntax. (Edit: This is to return a list of latest AgentActivities for all Agents).
SELECT
a.[AgentActivityId],
a.[AgentId],
a.[ActivityId],
a.[StartedAt],
a.[EndedAt],
a.[Version]
FROM
[dbo].[AgentActivity] a
INNER JOIN
(
SELECT
[AgentId],
MAX([StartedAt])[StartedAt]
FROM
[dbo].[AgentActivity]
WHERE
([StartedAt] > '2010/01/24 23:59:59')
AND ([StartedAt] < '2010/10/25')
GROUP BY
AgentId
)grouped
ON (a.[AgentId] = grouped.[AgentId]
AND a.[StartedAt] = grouped.[StartedAt])
Just to recap, here's how I interpret the question:
What you want is a list with the most recently started activity for an agent, with the added requirement that the activity must be started within a given date interval.
This is one way to do it:
// the given date interval
DateTime startDate = new DateTime(2010, 1, 24);
DateTime endDate = new DateTime(2010, 10, 25);
IEnumerable<AgentActivity> agentActivities =
... original list of AgentActivities ...
IEnumerable<AgentActivity> latestAgentActivitiesByAgent = agentActivities
.Where(a => a.StartedAt >= startDate && a.StartedAt < endDate)
.GroupBy(a => a.AgentId)
.Select(g => g
.OrderByDescending(a => a.StartedAt)
.First());
(If the question involves LINQ to SQL, there may be some gotchas. I haven't tried that.)