A controller should return data that is used as source for a D3.js line chart. In the controller, I've got a list of objects and I'm only interested in the property "Begin" and count(Begin). Begin is a datetime and what I want is to group all Objects where "Begin" is on the same day, and then count the number for each day.
I try to select this information and return it this way:
var results = from a in db.Questionaires
group a by a.Begin.Date into g
select new { Date = g.Key, Count = g.Count() };
return Json( results, JsonRequestBehavior.AllowGet);
Unfortunatly, I'm getting an error because the group by clause seems to be wrong ("The specified type member 'Date' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.").
How to select the information the right way? If anybody has some examples on D3.js and MVC I would appreciate that.
You should try this
var results = from a in db.Questionaires
group a by new { y = a.Begin.Year, m = a.Begin.Month, d = a.Begin.Day}
into g
select new { Day = g.Key.d, Year = g.Key.y,
Month = g.Key.m, Count = g.Count(),
Date = g.Select(d=>d.Begin).FirstOrDefault() };
Related
I am trying to convert the following sql query to LINQ statement
SELECT t.*
FROM (
SELECT Unique_Id, MAX(Version) mversion
FROM test
GROUP BY Unique_Id
) m INNER JOIN
test t ON m.Unique_Id = t.Unique_Id AND m.mversion = t.Version
LINQ statement
var testalt = (from altt in CS.test
group altt by altt.Unique_Id into g
join bp in CS.alerts on g.FirstOrDefault().Unique_Id equals bp.Unique_Id
select new ABCBE
{
ABCName= bp.Name,
number = bp.Number,
Unique_Id = g.Key,
Version = g.Max(x=>x.Version)
});
I am getting an error of where clause. Please help
SQL FIDDLE
This is not an easy straight forward conversion but you can accomplish the same thing using linq method syntax. The first query is executed to an expression tree, then you are joining that expression tree from the grouping against CS.alerts. This combines the expression tree from CS.test query into the expression tree of CS.alerts to join the two expression trees.
The expression tree is evaluated to build the query and execute said query upon enumeration. Enumeration in this case is the ToList() call but anything that gets a result from the enumeration will execute the query.
var query1 = CS.test.GroupBy(x => x.Unique_Id);
var joinResult = CS.alerts.Join(query1,
alert => new { ID = alert.Unique_Id, Version = alert.Version },
test => new { ID = test.Key, Version = test.Max(y => y.Version },
(alert, test) => new ABCBE {
ABCName = alert.Name,
number = alert.Number,
Unique_Id = test.Key,
Version = test.Max(y => y.Version)
}).ToList();
Because query1 is still an IQueryable and you are using CS.alerts (which I'm guessing CS is your data context) it should join and build the query to execute upon the ToList() enumeration.
There are 30 tables(categories) all with the same structure storing news items with a siteID field to filter on a particular client.
The client select which tables(categories) they show by setting the field visible(tinyint) field to 1 or 0.
I have the following test MYSQL which works okay. I am using Applicationcraft.com so the syntax is different than standard MYSQL but you can see the query.
function _getAllData(cObj,p){
var result = [];
console.log('started');
selectObj=cObj.select().from('schoolNews').order('newsIDDESC').where('siteID=?',p.siteID);
result[0] = cObj.exec(selectObj);
selectObj=cObj.select().from('schoolDocs').order('newsIDASC').where('siteID=?',p.siteID);
result[1] = cObj.exec(selectObj);
return result;
}
So I have an array with the results of each table in result[0] & result[1].
So I created the following to :
function _getAllData(cObj,p){
var result = [];
console.log('started');
selectObj=cObj.select().from('schoolNews').order('newsIDDESC').where('siteID=?',p.siteID).where('visible=?',1);
result[0] = cObj.exec(selectObj);
selectObj=cObj.select().from('schoolDocs').order('newsIDASC').where('siteID=?',p.siteID).where('visible=?',1);
result[1] = cObj.exec(selectObj);
selectObj=Obj.select().from('schoolNews_copy').order('newsIDDESC').where('siteID=?',p.siteID).where('visible=?',1);
result[2] = cObj.exec(selectObj);
selectObj=cObj.select().from('schoolNews_copy').order('newsIDDESC').where('siteID=?',p.siteID).where('visible=?',1);
result[3] = cObj.exec(selectObj);
selectObj=cObj.select().from('schoolNews_copy').order('newsIDDESC').where('siteID=?',p.siteID;
result[4] = cObj.exec(selectObj).where('visible=?', 1);
upto result[30].
I have populated schoolNews_copy with 1000 records and run the query from my app.
I am getting a timed out error.
Is this because.
query the same table causes the problem.
This is the wrong approach all together.
If not what is the best approach.
Is there a way to query every table in a single statement and populate the results into an array named results.
So the result I need is an example array :
result[0] has data visible set to 1
result[1] has data visible set to 1
result[2] has data visible set to 0
I have now restructured the table as you said. And using joins can get all the info I need in one query.
SELECT * FROM categories INNER JOIN allNews on allNews.catID = categories.catID WHERE categories.visible = 1 AND categories.siteID = '+p.siteID;
MrWarby.
I have a history table for Students in SQL Server 2008.
StudentHistoryId, StudentId, Grade, CreatedAt, ModifiedAt, ModifiedBy, Active
I am new to LINQ.
How do I write a LINQ query to get the latest modified row for all the active students and also the equivalent sql query for the same ?
Something like (Assuming LINQ-SQL):
using (YourDataContext db = new YourDataContext())
{
var data = from s in db.Students
select new
{
StudentId = s.StudentId,
LastHistory = s.Histories
.OrderByDescending(s => s.ModifiedAt)
.Where(s => s.Active)
.FirstOrDefault()
};
}
This is assuming that you want all students, regardless of whether they actually have any history. If don't want this, you can start with the History table and group by Student ID.
To view the SQL, you can hover the variable in debugging to see the SQL produced. I'm too lazy to convert the LINQ ;-)
var q =
from h in history
where h.Active
group h by new { h.StudentId, h.Grade } into g
select new
{
StudentId = g.Key.StudentId,
Grade = g.Key.Grade,
LatestModified = g.Max (x => x.ModifiedAt)
}
LINQ
var tempresult = (from student in Students
where Active == true).OrderByDesc(ModifiedAt)
List<Student> results = new List<Student>();
foreach(var result in tempResult)
{
if((results.Where(r => r.StudentId == result.StudentId).FirstOrDefault()) == null)
{
results.Add(result);
}
}
SQL
Select [Rows]
From Students S
Where S.Active = 1
And S.ModifiedAt = (Select Max(ModifiedAt)
From Student S1
Where S1.StudentId = S.StudentId)
The Linq is hacky (and I'm sure there's a better way, but I can't remember it) and I'm only sort-of confident about the SQL syntax (though that should point you in the right direction even if it's not exactly right), but either of those should get: The maximum ModifiedAt for every student that is currently active.
.FirstOrDefault() [LINQ] or Top 1 would only select the single row (only one student) with the most recent ModifiedAt.
I've written a simple linq query as follows:
var query = from c in context.ViewDeliveryClientActualStatus
join b in context.Booking on c.Booking equals b.Id
join bg in context.BookingGoods on c.Booking equals bg.BookingId
select new { c, b, bg };
I have filtered the previous query with a number of premises and then needed to group by a set of fields and get the sum of some of them, as so:
var rows = from a in query
group a by new {h = a.c.BookingRefex, b = a.c.ClientRefex, c = a.b.PickupCity, d = a.b.PickupPostalCode} into g
select new
{
Booking_refex = g.Key.h,
Client_refex = g.Key.b,
//Local = g.
Sum_Quan = g.Sum(p => p.bg.Quantity),
};
I'd like to get a few values from a which I haven't included in the group by clause. How can I get those values? They're not accessible through g.
The g in your LINQ expression is an IEnumerable containing a's with an extra property Key. If you want to access fields of a that are not part of Key you will have to perform some sort of aggregation or selection. If you know that a particular field is the same for all elements in the group you can pick the value of the field from the first element in the group. In this example I assume that c has a field named Value:
var rows = from a in query
group a by new {
h = a.c.BookingRefex,
b = a.c.ClientRefex,
c = a.b.PickupCity,
d = a.b.PickupPostalCode
} into g
select new {
BookingRefex = g.Key.h,
ClientRefex = g.Key.b,
SumQuantity = g.Sum(p => p.bg.Quantity),
Value = g.First().c.Value
};
However, if c.Value is the same within a group you might as well include it in the grouping and access it using g.Key.cValue.
Just add those field in the
new {h = a.c.BookingRefex, b = a.c.ClientRefex, c = a.b.PickupCity, d = a.b.PickupPostalCode}
they will be accessible in g then.
I have been playing with the Linq to Sql and I was wondering if it was possible to get a single result out? For example, I have the following:
using(DataClassContext context = new DataClassContext())
{
var customer = from c in context.table
where c.ID = textboxvalue
select c;
}
And with this I need to do a foreach around the var customer but i know that this will be a single value! Anyone know how I could do a textbox.text = c.name; or something along that line?
Yes, it's possible.
using(DataClassContext context = new DataClassContext())
{
var customer = (from c in context.table
where c.ID = textboxvalue
select c).SingleOrDefault();
}
This way you get 1 result or null if there isn't any result.
You can also use Single(), which throws an exception when there isn't a result.
First() will give you only the first result found, where Last() will give you only the last result, if any.
Here's an Overview of all Enumerable methods.
var customer = context.table.SingleOrDefault(c => c.ID == textboxvalue);