Let's say that I have a table like:
Id Name Category CreatedDate
1 test test 10-10-2015
2 test1 test1 10-10-2015
...
Now, I would like to delete all rows and leave only the top 10 from all categories (by top 10 I mean the 10 newest according to createdDate).
Using raw SQL, it would be like:
DELETE FROM [Product]
WHERE id NOT IN
(
SELECT id FROM
(
SELECT id, RANK() OVER(PARTITION BY Category ORDER BY createdDate DESC) num
FROM [Product]
) X
WHERE num <= 10
How is this done when using the DbContext in Entity Framework?
// GET all products
var list = ctx.Products.ToList();
// GROUP by category, ORDER by date descending, SKIP 10 rows by category
var groupByListToRemove = list.GroupBy(x => x.Category)
.Select(x => x.OrderByDescending(y => y.CreatedDate)
.Skip(10).ToList());
// SELECT all data to remove
var listToRemove = groupByListToRemove.SelectMany(x => x);
// Have fun!
ctx.Products.RemoveRange(listToRemove);
Guessing it will take a whil if you have a lot of data but.
var oldItems = efContext.Products
.GroupBy(x => x.Category,
(c,p) => p.OrderByDescending(x => p.createdDate).Skip(10))
.SelectMany(p => p);
efContext.Products.RemoveRange(oldItems);
Will do the trick
(Written in notepad)
Related
I have a table with the following data
ID DateColumn Amount
1 2021-01-25 50
2 2021-01-24 10
1 2021-01-25 100
I need the following output,
ID DayCount TotalAmount
1 1 150
2 1 10
I'm trying to lambda expression that would generate the following SQL query,
select ID, Count(distinct DateColumn) as DayCount, Sum(Amount) as TotalAmount
from test
group by id
I've writte the following expression,
return await _context.Tests
.GroupBy(g => g.id)
.Select(s => new
{
Data = s.Key,
Count = s.Select(t => t.DateColumn).Distinct().Count()
}).ToListAsync();
and it throws the InValidOperation exception.
There seems to be an error in the resulting table for the first record, which should have a value of 2 for the DayCount.
The resting table construction looks like it could use some rearchitecting due to the Id column containing duplicates.
Regardless of structure, you can use an inner GROUP BY to achieve similar results:
return await _context.Tests
.GroupBy(g => g.id)
.Select(s => new
{
Data = s.Key,
Count = s.GroupBy(t => t.DateColumn).Select(g => g.key).Count()
})
.ToListAsync();
again, I'm struggeling with Linq or EF6.
I have a table with columns (DateTime)[BeginOfWork] and (DateTime)[EndOfWork].
Now, I need to substract the BeginOfWork-value from the EndOfWork-value. From this result, I need to build a total sum.
In SQL, it looks like this:
SELECT Timesheets.EmployeeId, Sum(DateDiff("h",[Timesheets].[BeginOfWork],[Timesheets].[EndOfWork])) AS HoursOfWork
FROM Timesheets
GROUP BY Timesheets.EmployeeId
HAVING (((Timesheets.EmployeeId)=1));
How do I do this in EF6?
Actually, not working some variations of that:
int employeeId = 1;
var timesheetSum = (from ts in db.Timesheets
where (ts.EmployeeId == employeeId)
select new
{
hoursOfWork = DbFunctions.DiffHours(ts.BeginOfWork, ts.EndOfWork)
}).Sum(ts => ts.hoursOfWork);
The above results in integer rounded hoursOfWork, that don't include minutes.
So I tried that:
var timesheetSum = (from ts in db.Timesheets
where (ts.EmployeeId == employeeId)
select new
{
hoursOfWork = DbFunctions.DiffMinutes(ts.BeginOfWork, ts.EndOfWork) / 60
}).Sum(ts => ts.hoursOfWork);
But here, hoursOfWork seems to be rounded (integer), so 2,5 hours will result in 2. Perhaps a conversion of the result would work but I don't get it run.
`(double)hoursOfWork` results in an error.
Perhaps someone has a link to a complete guide, how to convert SQL to Linq-queries.
SOLUTION
var timesheetSum = (from ts in db.Timesheets
where (ts.EmployeeId == employeeId && ts.TimesheetDate <= DateTime.Today)
select new
{
hoursOfWork = DbFunctions.DiffMinutes(ts.BeginOfWork, ts.EndOfWork)/60m
}).Sum(ts => ts.hoursOfWork);
decimal result = 0;
if(timesheetSum!=null)
result = (decimal)timesheetSum;
Thanks a lot
Carsten
How do I order this query by month not alphabetically? I have two columns in my db. One for the month name and one for month number.
Right now it orders months alphabetically.
var querythpmsick = (from r in db.SickLeaveRequestForms
where r.EmployeeID == id
group r by r.MonthOfHoliday into g
select new { Value = g.Key, Count1 = g.Sum(h => h.SickLeaveTaken) }
).OrderBy(e => e.Value);
If you have both the month name and the month number in your DB, then just group by the number instead of the month name:
var querythpmsick = (from r in db.SickLeaveRequestForms where r.EmployeeID == 2
group r by r.MonthOfHolidayInt into g
select new { Value = g.Key, Count1 = g.Sum(h => h.SickLeaveTaken), MonthName = g.Select(d => d.MonthOfHoliday) })
.OrderBy(e => e.Value);
Here is a DotNetFiddle with the example: https://dotnetfiddle.net/6vE4lo
I have tables with articles and users, both have many-to-many mapping to third table - reads.
What I am trying to do here is to get all unread articles for particular user ( user_id not present in table reads ).
My query is getting all articles but those read are marked, which if fine as I can filter them out (user_id field contains id of user in question).
I have an SQL query like this:
SELECT articles.id, reads.user_id
FROM articles
LEFT JOIN
reads
ON articles.id = reads.article_id AND reads.user_id = 9
ORDER BY articles.last_update DESC LIMIT 5;
Which yields following:
articles.id | reads.user_id
-------------------+-----------------
57125839 | 9
57065456 |
56945065 |
56945066 |
56763090 |
(5 rows)
This is fine. This is what I want.
I'd like to get same result in Catalyst using my article model, but I cannot find any option to add conditions to a JOIN clause.
Do you know any way how to add AND X = Y to DBIx JOIN?
I know this can be done with custom resoult source and virtual view, but I have some other queries that could benefit from it and I'd like to avoid creating virtual view for each of them.
Thanks,
Canto
I don't even know what Catalyst is but I can hack the SQL query:
select articles.id, reads.user_id
from
articles
left join
(
select *
from reads
where user_id = 9
) reads on articles.id = reads.article_id
order by articles.last_update desc
limit 5;
I got an solution.
It's not straight forward, but it's better than virtual view.
http://search.cpan.org/dist/DBIx-Class/lib/DBIx/Class/Relationship/Base.pm#condition
Above describes how to use conditions in JOIN clause.
However, my case needs an variable in those conditions, which is not available by default in model.
So getting around a bit of model concept and introducing variable to it, we have the following.
In model file
our $USER_ID;
__PACKAGE__->has_many(
pindols => "My::MyDB::Result::Read",
sub {
my $args = shift;
die "no user_id specified!" unless $USER_ID;
return ({
"$args->{self_alias}.id" => { -ident => "$args->{foreign_alias}.article_id" },
"$args->{foreign_alias}.user_id" => { -ident => $USER_ID },
});
}
);
in controller
$My::MyDB::Result::Article::USER_ID = $c->user->id;
$articles = $channel->search(
{ "pindols.user_id" => undef } ,
{
page => int($page),
rows => 20,
order_by => 'last_update DESC',
prefetch => "pindols"
}
);
Will fetch all unread articles and yield following SQL.
SELECT me.id, me.url, me.title, me.content, me.last_update, me.author, me.thumbnail, pindols.article_id, pindols.user_id FROM (SELECT me.id, me.url, me.title, me.content, me.last_update, me.author, me.thumbnail FROM articles me LEFT JOIN reads pindols ON ( me.id = pindols.article_id AND pindols.user_id = 9 ) WHERE ( pindols.user_id IS NULL ) GROUP BY me.id, me.url, me.title, me.content, me.last_update, me.author, me.thumbnail ORDER BY last_update DESC LIMIT ?) me LEFT JOIN reads pindols ON ( me.id = pindols.article_id AND pindols.user_id = 9 ) WHERE ( pindols.user_id IS NULL ) ORDER BY last_update DESC: '20'
Of course you can skip the paging but I had it in my code so I included it here.
Special thanks goes to deg from #dbix-class on irc.perl.org and https://blog.afoolishmanifesto.com/posts/dbix-class-parameterized-relationships/.
Thanks,
Canto
Table1 :
userid name address
1 venkat srinagr
2 venkatesh sainagar
Table2:
id userid lat lon
1 1 14.000 15.000
2 2 14.3526 15.3698
by passing "venkat" as parameter then need to pull all matching records and his userid,name,lat,lon.
in above table1 "venkat" contains in both rows then need to pull 2 records.how to get userid,name,lat,lon for all matching rows..
for sigle record i am able to get.but there are multiple rows how to get please tell me....
var result = from p in cxt.Table2
where p.Table1.Name.Contains(name)
select new
{
p.Users.User_Id,p.Users.Name,p.Latitude,p.Longitude
};
Im sure someone will say this is not the most effective way but this is how i would do it.
string InputString = "venkat";
var tab =(from a in db.tablea
from b in db.tableb
where a.userid == b.userid && a.name == InputString
select new
{
UserID = a.userid,
Username = a.name,
Latitude = b.lat,
Longditude = b.lon
}).FirstOrDefault();
FirstOrDefault() is only if you want to force only one output or null,
if you want a collection of some sort, then just remove it.