I have a problem while comparing smalldatetime/datetime column value from DB(SQL Server 2008) with DateTime.Now in C#.
I know that datetime format in DB and on the server on which application is running are different, so I have done something like this to "cache" the results so date time comparison will be local and not be on server:
var inactiveAccounts = (from entry in ent.Accounts
where entry.Status == 0
select entry).ToArray();
var accountsFiltered = (from entry in inactiveAccounts
where entry.DeactivationDate < DateTime.Now
select entry).ToArray();
And at some pertiod of day I am not getting the right records.
I suspect it is due to where entry.DeactivationDate < DateTime.Now date comparison. And seems in EF it is tricky to work with datetime, please help me to identify the problem.
Don´t know if it solves your problem but i would create a local variable and set DateTime.Now on it. Then use the local variable in your linq query.
This is done, because DateTime.Now gets evaluated in your query each time the where clause is called. So for each entry in inactiveAccounts you are working against another DateTime.
Also if you want to compare Dates without the Time value, you should use DateTime.Today
var inactiveAccounts = (from entry in ent.Accounts
where entry.Status == 0
select entry).ToArray();
DateTime currentDateTime = DateTime.Now;
var accountsFiltered = (from entry in inactiveAccounts
where entry.DeactivationDate < currentDateTime
select entry).ToArray();
You can use this directly:
var inactiveAccounts = (from entry in ent.Accounts
where entry.Status == 0 && entry.DeactivationDate < DateTime.Now
select entry).ToArray();
Because DataTime.Now and DateTime.UtcNow are translated as canonical functions = they should not be evaluated on .NET side but translated toGETDATE() or GETUTCDATE() SQL function calls respectively.
The rest of your question is unanswerable because providing information like
And at some period of day I am not getting the right records.
You must put much bigger effort to analysis of the problem if you want to get answer including which periods cause problem, what timezones are used, etc. Generally we will not help you with that because we don't see your data. It is also not a problem of EF because in your case it happends completely in linq-to-object = plain .NET code.
Related
This is my LINQ for returning the matching record
var staffawards = await _context.StaffAwards.FirstOrDefaultAsync(c => c.StaffID == StaffAwards.StaffID && c.EmpID == StaffAwards.EmpID && c.AwardDate == StaffAwards.AwardDate);
The StaffAwards.AwardDate will be in this format "09/12/2020 12:00:00 AM"
whereas the AwardDate in my table will be like this "2020-12-09 17:16:00.000"
How can i convert the StaffAwards.AwardDate in Sql Server datetime?
AnyHelp would be appreciated.
If your code and your database use Date/DateTime types as they should be, and not strings then you need to understand a few things:
date datatypes don't have a format, only strings created from dates have a format. Whatever format you see in your code/sql query tool is the formatting it has applied when it showed you the date (it had to turn it to a string to display it)
a datetime with a time of midnight is a completely different datetime to one where the time is 17:16, just like a number 1.0 is a completely different number to 1.75352; you will never get a database to return you a record with a time of midnight if you use equals and pass a time of anything other than midnight, just like you will never succeed in getting a record where the age of the person is 1.0 by asking "where age = 1.75352"
Either fix up your parameter so it is midnight, like the db is, or use a parameter range (if the dates in the db will have times other than also)
//if the db date is always midnight
.Where(x => x.DateColumnInDb == datetimeParameter.Date);
//if the db might have times too
.Where(x => x.DateColumnInDb >= datetimeParameter.Date && x.DateColumnInDb < datetimeParameter.Date.AddDays(1));
By using a range, we do not risk asking the database to convert every datetime in the table, every time we want to query. Converting data in a where clause is typically a bad idea because it usually leads to significant performance loss because indexes cannot be used
Also, make sure your .net side datetime and your db time use the same timezone or they will actually be referring to different times
To use a Date with the Database-Format you can use the DbFunctions.
Like this:
var staffawards = await _context.StaffAwards.FirstOrDefaultAsync(c => c.StaffID == StaffAwards.StaffID && c.EmpID == StaffAwards.EmpID && DbFunctions.TruncateTime(DateTime.Parse(c.AwardDate)) == StaffAwards.AwardDate);
Important: For TruncateTime, you have to use a DateTime. You have to convert c.AwardDate to DateTime. DateTime.Parse(c.AwardDate)
Most likely, you have the SQL server installed on a separate machine, which may be due to a different date format.
But there is no need for this conversion, the entity framework will do it automatically for you.
If you just compare date, you can use this code :
var staffawards = await _context.StaffAwards.FirstOrDefaultAsync(c => c.StaffID == StaffAwards.StaffID && c.EmpID == StaffAwards.EmpID && c.AwardDate.Date == StaffAwards.AwardDate.Date);
My query looks like so:
using (var ctx = new PCLvsCompContext())
{
var brokerId = broker?.Id;
var symbolId = company?.Id;
var result = (from t in ctx.TradeHistoryJoineds
where t.TradeDate >= fromDate
&& t.TradeDate <= toDate
&& (brokerId == null || t.BrokerId == brokerId)
&& (symbolId == null || t.SymbolId == symbolId)
select t).OrderBy(x => x.TradeDate).ThenBy(x => x.BrokerName).ToList();
return result;
}
As an example, I run this query with dates like fromDate March-01-2017 toDate March-31-2017. I then captured the generated sql in SQL profiler that this query produces and ran it in SQL management studio. The output was as expected where for each weekday, each company has some trades. The query is based off of a view which casts all dates to "datetime" so that excel can parse them as dates correctly. However, when I put a breakpoint at "return result" and inspect the dates, all but 2 of the dates are March-1-2017. This is incorrect, the query result in SQL manager shows trades for almost every weekday in March (which is correct).
What is going on here? Why is Linq losing its mind?
Although based on the results I cannot see exactly how you would end up with those results, it is very common that you could be dealing with a DateTime timezone issue. I suspect that perhaps you saved your dates to the database using a DateTime object from say DateTime.Now instead of DateTime.UtcNow. So at that point in time and based on the machine it was called on it would be based on the timezone and datelight savings of that machine.
A DateTime object should not be used as it can relate to the region of the SQL database, the region of the server making this LINQ call and so the two regions could be on different timezones.
Instead you should always use DateTimeOffset.
If you cannot do that for some reason, then double-check your dates toDate and fromDate and do:
var utcToDate = toDate.ToUniversalTime().ToString("yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fff'Z'");
var utcFromDate = toDate.ToUniversalTime().ToString("yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fff'Z'");
Which gives something like this if it was run on 3rd April 2018 at 22:56.
2018-04-03T22:56:57.740Z
You would then also need to make sure when you save any date to the SQL backing store that you do ToUniversalTime() firstly. You can check your SQL tables directly with a normal SQL query and they should be stored in the database as the same UTC string format as above, and then the comparison should be obvious to whether it is valid.
However I would strongly recommend changing all your DateTime calls and gets to DateTimeOffset. The only time to use DateTime in majority of cases is for the final display to a user.
Thank you all for your suggestions. For those who are familiar with linq, EF and views this may seem like a stupid oversight, but I will post my shame for others in case this happens to them since the cause and the resulting behavior are not immediately obviously linked (as can be seen by all the suggestions, none of which actually point to the answer).
When you are querying a view using linq and Entity Framework, you apparently must have a column called 'Id', otherwise Entity Framework can't distinguish any of the rows from one another and simply makes some sort of duplication that I can't quite decipher (all the rows were unique based on their data even without an Id column, so I can't quite figure out why this is necessary).
So by adding an the TradeId with an 'Id' alias to the view, then Entity Framework seemed to return to sanity and map the data as expected.
I have a database field like this:
Timestamp varchar(19) utf8mb4_unicode_ci
containing a timestamp (string) like this
"2013-05-29 00:00:00"
I am using the entity framework and I would like to filter by time - meaning I would like to get all entries having a timestamp > (now-interval).
Code would look something like this
var query = from r in db.route
where
r.timestamp > (now-interval);
select r;
How can I do this?
My first suggestion would be to fix the database so the date values are stored as the correct date type. That would solve many issues as well as increase search performance. However, in the (unlikely) situation that you are unable to do that, and that the format of the values in that column all match exactly as you specified in the question, you could convert your local time stamp variable to a string and compare it directly. As the format you have shown has an alphanumeric ordering that is identical to the date order, it should work:
//It's important that this is done here and not inline with the Linq query
var nowInterval = timeStamp.ToString("yyyy-MM-dd HH:mm:ss");
var query = from r in db.route
where string.Compare(r.timestamp, nowInterval, StringComparison.Ordinal) > 0
select r;
I have a Solution table in the database and I want to display any solutions that is less than a day old as of now(DateTime.Now) Thank you
IQueryable<Solution> Solutions=
from x in db.Solutions
where x.Created_at == DateTime.Now -1
select x;
Use DateTime.AddDays to get target date. Then use >= comparison to filter solutions which are less old than target date (or equal to it):
IQueryable<Solution> Solutions =
from s in db.Solutions
where s.Created_at >= DateTime.Now.AddDays(-1)
select s;
NOTE: That will give you entities withing 24 hours from now. If you want to get entities from beginning of yesterday, then use DateTime.Today instead of DateTime.Now.
I have a database with a ValidDate field - it's a string(we made a mistake, it should be a datetime, but we can't modify the database now.)
and now I want to compare this filed with a parameter(validDateStart) from the website:
priceList = priceList.Where(p => Convert.ToDateTime(p.ValidDate) >= Convert.ToDateTime(validDateStart));
var list = initPriceList.ToList();
But I get an error: The method ToDateTime is not implemented.
Can anybody give me some help? Thanks!
This is not supported in Linq to Entities (nor Linq to SQL to my knowledge). Remember that your query is executed on the database - where there is simply no equivalent for Convert.ToDateTime.
Any string parsing in your query would really just be a workaround - as a real solution make those columns not strings but datetime in the database and you would not have this problem in the first place.
A hacky workaround would be materializing all rows (you can use AsEnumerable() for that), then doing the parsing - this will have bad performance though but might work good enough if there are few rows:
var startDate = DateTime.Parse(validDateStart);
var list = priceList.AsEnumerable()
.Where(p => DateTime.Parse(p.ValidDate) >= startDate);
.ToList();
Edit:
With your example update it looks like you can just do string comparisons to do what you wanted - granted it's still a hack but would perform much better than materializing all rows. This is possible because your date format puts the most significant numbers first, then the less significant parts - it's year, then month, then day (should this not be the case and the day comes before the month in your example this solution will not work).
Assuming your input string validDateStart is in the same format as well you can just do:
var list = priceList.Where(p => p.ValidDate.CompareTo(validDateStart) >=0);
.ToList();
string comparison with String.CompareTo seems to be support both in Linq to Sql as well as Linq to Entities.
If all the records in your database always start with year, month and day (for example: the date format is yyyy-MM-dd HH:mm:ss or yyyy/MM/dd or yyyyMMdd) no matter if it has separators or not. The thing is that the values should has a format where it starts with year, month and day.
You can do the following:
1: Convert your filter value (website) to the same format as you have in your database:
// DateTime format in database: yyyy-MM-dd HH:mm:ss:ffffff
var from = filtro.CreationDateFrom?.ToString("yyyy-MM-dd");
var to = filtro.CreationDateTo?.AddDays(1).ToString("yyyy-MM-dd");
2: And write your query like this (using CompareTo method):
var query = (from x in ctx.TskTaskQueues
where x.CreationDatetime.CompareTo(from) >= 0
&& x.CreationDatetime.CompareTo(to) <= 0
select x);
It worked for me!
I'm not using LinqToEntities but I'm using LinqConnect (for Oracle) that is similar to LinqEntities.
If you use a format like this dd-MM-yyyy, it probably will not work.