I have a table in Mongo. One of the fields is a DateTime. I would like to be able to get all of the records that are only for a single day (i.e. 9/3/2011).
If I do something like this:
var list = (from c in col
where c.PublishDate == DateTime.Now
select c).ToList();
Then it doesn't work because it is using the time in the comparison. Normally I would just compare the ToShortDateString() but NoRM does not allow me to use this.
Thoughts?
David
The best way to handle this is normally to calculate the start datetime and end datetime for the date in question and then query for values in that range.
var start = DateTime.Now.Date;
var end = start.AddDays(1);
...
But you'd also be well advised to switch to the official C# driver now. You should also use UTC datetimes in your database (but that gets more complicated).
Related
I have several records in my database, the table has a column named "weekday" where I store a weekday like "mon" or "fri". Now from the frontend when a user does search the parameters posted to the server are startday and endDay.
Now I would like to retrieve all records between startDay and endDay. We can assume startDay is "mon" and endDay is "sun". I do not currently know how to do this.
Create another table with the names of the days and their corresponding number. Then you'd just need to join up your current table with the days table by name, and then use the numbers in that table to do your queries.
Not exactly practical, but it is possible to convert sun,mon,tue to numbers using MySQL.
Setup a static year and week number like 201610 for the 10th week of this year, then use a combination of DATE_FORMAT with STR_TO_DATE:
DATE_FORMAT(STR_TO_DATE('201610 mon', '%X%V %a'), '%w')
DATE_FORMAT(STR_TO_DATE('201610 sun', '%X%V %a'), '%w')
DATE_FORMAT(STR_TO_DATE('201610 tue', '%X%V %a'), '%w')
These 3 statements will evaluate to 0,1,2 respectively.
The main thing this is doing is converting the %a format (Sun-Sat) to the %w format (0-6)
well i don't know the architecture of your application as i think storing and querying a week day string is not appropriate, but i can tell you a work around this.
make a helper function which return you an array of weekdays in the range i-e
function getWeekDaysArray($startWeekDay, $endWeekDay) {
returns $daysArray['mon','tue','wed'];
}
$daysRangeArray = getWeekDaysArray('mon', 'wed');
now with this array you can query in table
DB::table('TableName')->whereIn('week_day', $daysRangeArray)->get();
Hope this help
I need to be able to display data for all date range and for the same date range but only for Saturdays.
Data stored in sql server.
Table:
DateTime Vlaue
Is it possible to create linq to sql query which would do that?
Or just select all for particular range and than on server side find all Saturdays?
What is the better way to do that?
You should be able to do something like this:
var results = Entities.YourTable.Where(r => r.SomeDate.DayOfWeek == DayOfWeek.Saturday);
I'd be inclined to just query the database once, then use linq to objects on the result set for the saturday data...
var values = db.Values.ToList(); // assuming your table is called values
var satValues = values.Where( v => v.TheDate.DayOfWeek == DayOfWeek.Saturday);
Is there any easy way to compare dates, that ignores year, using Linq and the Entity Framework?
Say I have the following
var result = context.SomeEntity.Where(e => e.SomeDate > startDate);
This is assuming that SomeDate and startDate are .NET DateTime's.
What I would like to do is compare these dates without comparing year. SomeDate can be any year. Is there any easy way to do this? The only way I could think of would be to use the following:
var result = context.SomeEntity(e =>
e.SomeDate.Month > startDate.Month ||
(e.SomeDate.Month == startDate.Month && e.SomeDate.Day >= startDate));
This method quickly gets more complicated if I am looking to have an endDate as well, as I will have to do things like take account for when the start date is at the end of the year and the end date is at the beginning.
Is there any easy way to go about this?
Update:
I ended up just going about it the way I had initially thought in the post... a heck of a lot of code for something conceptually simple. Basically just had to find if a date fell within a range, ignoring year, and looping the calendar if startDate > endDate If anyone knows an easier way, please post as I am still interested.
If you really need to compare only dates (not times) then DateTime.DayOfYear property might help. But you should be careful regarding leap years in this case. Other of this I cannot imagine anything more simple than your approach with comparing months and days.
If all you care about is that this method will become more complicated after introducing second comparison then simple method extraction should help.
Another approach might be creating an extension method which will return a number applicable for your comparison. For example let's call this method GetYearIgnoringOrdinal():
public static int GetYearIgnoringOrdinal(this DateTime date)
{
return date.Month*100 + date.Day;
}
And then use it like this:
var result = context.SomeEntity.Where(e => e.SomeDate.GetYearIgnoringOrdinal() > startDate.GetYearIgnoringOrdinal());
Slightly simpler looking way
var result = context.SomeEntity(e =>
e.SomeDate.Month * 100 + e.SomeDate.Day > startDate.Month * 100 + startDate.Day
);
You could also create a user defined function (assuming SQL server is used) and that function can be used in the query.
I have a table with many anniversaries : Date + Name.
I want to display the next anniversary and the one after with Linq.
How can i build the query ?
I use EF
Thanks
John
Just order by date and then use the .Take(n) functionality
Example with a list of some objects assuming you want to order by Date then Name:
List<Anniversaries> annivDates = GetAnnivDates();
List<Anniversaries> recentAnniv = annivDates.OrderBy(d => d.Date).ThenBy(d => d.Name).Take(2).ToList();
If the anniversaries are stored in regular DateTime structs, they may have the 'wrong' year set (i.e. wedding or birth year). I suggest writing a function which calculates the next date for an anniversary (based on the current day) like:
static DateTime CalcNext(DateTime anniversary) {
DateTime newDate = new DateTime(DateTime.Now.Year, anniversary.Month, anniversary.Day);
if (newDate < DateTime.Now.Date)
newDate = newDate.AddYear(1);
return newDate;
}
Then you proceed with sorting the dates and taking the first two values like described in the other postings:
(from e in anniversaries orderby CalcNext(e.Date) select e).Take(2)
I am ran into the following issue.
Take a look at the following where clause.
Where(x => x.CreateTS <= dateParameters.CreationDate.ToDateValue &&
x.CreateTS >= dateParameters.CreationDate.FromDateValue)
CreateTS is a Timestamp column in the table. so when my dateparameters are todate = 01/28/2010 12:00A.M" fromdate= "01/26/2010 12.00A.M" (c# DateTime types) my query doesnot retrivies the table records whose CreateTS look like 01/28/2010 1:45A.M and above just differeing in the timestamps.
I just wanted to do comparison and dont want to compare the timestamps. any help would be appreciated.
Just look at the .Date portion of the DateTime:
Where(x => x.CreateTS.Date <= dateParameters.CreationDate.ToDateValue && x.CreateTS.Date >= dateParameters.CreationDate.FromDateValue)
As a side note:
Personally, I would put from first, since it's a bit easier to follow from a readability standpoint:
Where(x => x.CreateTS.Date >= dateParameters.CreationDate.FromDateValue && x.CreateTS.Date <= dateParameters.CreationDate.ToDateValue)
(I find it easier to think of being between two values as being >low and
Edit: You didn't specify that you were using the EF LINQ providers, which do not allow you to do Date. You can, I believe, handle this by looking forward one day, and using < instead of <= for your "to" comparison:
Where(x => x.CreateTS >= dateParameters.CreationDate.FromDateValue && x.CreateTS.Date < dateParameters.CreationDate.AddDays(1).ToDateValue)
#SARAVAN, AFAIK timestamp columns cannot be used in comparisons like that. A timestamp columns are mapped as byte[] (byte array) in EF. If comparisons like that are needed, I suggest to change the timestamp column in database to a datetime one.
only to quote from MSDN:
The SQL Server timestamp data type has nothing to do with times or dates. SQL Server timestamps are binary numbers that indicate the relative sequence in which data modifications took place in a database.
Interesting moment here is that
01/28/2010 12:00A.M actually in 24 hour format is 00:00 while 01/28/2010 1:45A.M is 01:45 and that seems to be the reason why those records are not returned. The midday will be 01/28/2010 12:00P.M