I am wanting to group news articles by year in a repeater. The format would be:
2010
list of articles
2011
List of Articles
My access layer returns a flat list of news articles, specifically List. Therefore, I am grouping them and binding them to the Repeater as follows:
events = DAL.GetEvents();
var groupedNewsList = from e in events
group e by e.StoryDate.Year
into g
select new {
Year = g.Key
, Events = g
};
rptEvents.DataSource = groupedNewsList;
rptEvents.DataBind();
The problem is trying to get the List from within the ItemDataBound event. So far, I have the following:
var data = e.Item.DataItem;
System.Type type = data.GetType();
// getting the year works fine
string year = (string)type.GetProperty("Year").GetValue(data, null).ToString();
// this returns something, but I can't access any properties. I need to get
//access to the contained List<News>
var newsList = type.GetProperty("Events").GetValue(data, null);
Any ideas?
Thanks in advance!
You don't have a List<News> - you just have a grouping. If you want a List<News>, you'll need to change your query, e.g.
var groupedNewsList = from e in events
group e by e.StoryDate.Year into g
select new { Year = g.Key, Events = g.ToList() };
Note that if you're using C# 4 you could do reflection rather more easily using dynamic typing:
dynamic data = e.Item.DataItem;
string year = data.Year.ToString();
List<News> newsList = data.Events;
Alternatively, you could avoid using an anonymous type in the first place - create your own GroupedNewsList type with Year and Events properties, populate that in your query, and then cast to it in your event handler.
The "sender" object in the ItemDataBound event is the repeater -- use it to get to the data-source. If the data-source has been grouped before binding, you can compare the current value to the previous value & hide the year-field if they are equal. Like this:
MyObject item = (MyObject)item.DataItem;
Repeater repeater = (sender as Repeater);
List<MyObject> items = repeater.DataSource as List<MyObject>;
Label lblGrouping = (Label)item.FindControl("lblGrouping");
if (item.ItemIndex == 0 || item.DateField.Year != items[item.ItemIndex - 1].DateField.Year) {
lblGrouping.Text = item.DateField.Year.ToString();
}
This worked for me, as I used a table with each row being one item, and the left-most column contained the "lblGrouping" control.
Related
I have some errors using Linq on DataTable and I couldn't figure it out how to solve it. I have to admit that i am pretty new to Linq and I searched the forum and Internet and couldn't figure it out. hope you can help.
I have a DataTable called campaign with three columns: ID (int), Product (string), Channel (string). The DataTable is already filled with data. I am trying to select a subset of the campaign records which satisfied the conditions selected by the end user. For example, the user want to list only if the Product is either 'EWH' or 'HEC'. The selection criteria is dynaically determined by the end user.
I have the following C# code:
private void btnClick()
{
IEnumerable<DataRow> query =
from zz in campaign.AsEnumerable()
orderby zz.Field<string>("ID")
select zz;
string whereClause = "zz.Field<string>(\"Product\") in ('EWH','HEC')";
query = query.Where(whereClause);
DataTable sublist = query.CopyToDataTable<DataRow>();
}
But it gives me an error on line: query = query.Where(whereClause), saying
No property or field 'zz' exists in type 'DataRow'".
If I changed to:
string whereClause = "Product in ('EWH','HEC')"; it will say:
No property or field 'Product' exists in type 'DataRow'
Can anyone help me on how to solve this problem? I feel it could be a pretty simple syntax change, but I just don't know at this time.
First, this line has an error
orderby zz.Field<string>("ID")
because as you said, your ID column is of type int.
Second, you need to learn LINQ query syntax. Forget about strings, the same way you used from, orderby, select in the query, you can also use where and many other operators. Also you'll need to learn the equivalent LINQ constructs for SQL-ish things, like for instance IN (...) is mapped to Enumerable.Contains etc.
With all that being said, here is your query
var productFilter = new[] { "EWH", "HEC" };
var query =
from zz in campaign.AsEnumerable()
where productFilter.Contains(zz.Field<string>("Product"))
orderby zz.Field<int>("ID")
select zz;
Update As per your comment, if you want to make this dynamic, then you need to switch to lambda syntax. Multiple and criteria can be composed by chaining multiple Where clauses like this
List<string> productFilter = ...; // coming from outside
List<string> channelFilter = ...; // coming from outside
var query = campaign.AsEnumerable();
// Apply filters if needed
if (productFilter != null && productFilter.Count > 0)
query = query.Where(zz => productFilter.Contains(zz.Field<string>("Product")));
if (channelFilter != null && channelFilter.Count > 0)
query = query.Where(zz => channelFilter.Contains(zz.Field<string>("Channel")));
// Once finished with filtering, do the ordering
query = query.OrderBy(zz => zz.Field<int>("ID"));
I am attempting to get unique values in a list of similar value distinguished only by a one element in a pipe delimited string... I keep getting at least one object must implement Icomparable. I don't understand why I keep getting that. I am able to groupBy that value... Why can't I find the max... I guess it is looking for something to compare it with. If I get the integer version will it stop yelling at me? This is the last time I am going to try using LINQ...
var queryResults = PatientList.GroupBy(x => x.Value.Split('|')[1]).Select(x => x.Max());
I know I can get the unique values some other way. I am just having a hard time figuring it out. In that List I know that the string with the highest value amongst its similar brethren is the one that I want to add to the list. How can I do that? I am totally drawing a blank because I have been trying to get this to work in linq for the last few days with no luck...
foreach (XmlNode node in nodeList)
{
XmlDocument xDoc = new XmlDocument();
xDoc.LoadXml(node.OuterXml);
string popPatInfo = xDoc.SelectSingleNode("./template/elements/element[#name=\"FirstName\"]").Attributes["value"].Value + ", " + xDoc.SelectSingleNode("./template/elements/element[#name=\"LastName\"]").Attributes["value"].Value + " | " + DateTime.Parse(xDoc.SelectSingleNode("./template/elements/element[#name=\"DateOfBirth\"]").Attributes["value"].Value.Split('T')[0]).ToString("dd-MMM-yyyy");
string patientInfo = xDoc.SelectSingleNode("./template/elements/element[#name=\"PatientId\"]").Attributes["value"].Value + "|" + xDoc.SelectSingleNode("./template/elements/element[#name=\"PopulationPatientID\"]").Attributes["enc"].Value;// +"|" + xDoc.SelectSingleNode("./template/elements/element[#name=\"AdminDate\"]").Attributes["value"].Value;
int enc = Int32.Parse(patientInfo.Split('|')[1]);
if (enc > temp)
{
lastEncounter.Add(enc, patientInfo);
temp = enc;
}
//lastEncounter.Add(Int32.Parse(patientInfo.Split('|')[1]));
PatientList.Add( new SelectListItem { Text = popPatInfo, Value = patientInfo });
}
I was thinking about using some kind of temp variable to find out what is the highest value and then add that string to the List. I am totally drawing a blank however...
Here I get the IDs in an anonymous type to make it readable.
var patientEncounters= from patient in PatientList
let PatientID=Int32.Parse(patient.Value.Split('|')[0])
let EncounterID=Int32.Parse(patient.Value.Split('|')[1])
select new { PatientID, EncounterID };
Then we group by UserID and get the last encounter
var lastEncounterForEachUser=from pe in patientEncounters
group pe by pe.PatientID into grouped
select new
{
PatientID=grouped.Key,
LastEncounterID=grouped.Max(g=>g.EncounterID)
};
Linq doesn't know how to compare 2 Patient objects, so it can't determine which one is the "greatest". You need to make the Patient class implement IComparable<Patient>, to define how Patient objects are compared.
// Compare objets by Id value
public int CompareTo(Patient other)
{
return this.Id.CompareTo(other.Id);
}
Another option is to use the MaxBy extension method available in Jon Skeet's MoreLinq project:
var queryResults = PatientList.GroupBy(x => x.Value.Split('|')[1])
.Select(x => x.MaxBy(p => p.Id));
EDIT: I assumed there was a Patient class, but reading your code again, I realize it's not the case. PatientList is actually a collection of SelectListItem, so you need to implement IComparable in that class.
This is very confusing, I use AsDataView to bind query result to a dgv and it works fine with the following:
var query = from c in myDatabaseDataSet.Diamond where c.p_Id == p_Id select c;
dataGridView1.DataSource = query.AsDataView();
However, this one results in an Error:
var query = from item in myDatabaseDataSet.Items
where item.p_Id == p_Id
join diamond in myDatabaseDataSet.Diamond
on item.p_Id equals diamond.p_Id
join category in myDatabaseDataSet.DiamondCategory
on diamond.dc_Id equals category.dc_Id
select new
{
Product = item.p_Name,
Weight = diamond.d_Weight,
Category = category.dc_Name
};
dataGridView1.DataSource = query.AsDataView();
Error:
Instance argument: cannot convert from
'System.Collections.Generic.IEnumerable<AnonymousType#1>' to
'System.Data.DataTable'
AsDataView doesn't show up in query.(List). Why is this happen? How to bind the query above to the dgv then?.
The signature of the AsDataView is as follows:
public static DataView AsDataView(
this DataTable table
)
The only parameter is the DataTable.
The query you have is returning an IEnumerable of an anonymous type which doesn't have an implicit conversion to a DataTable (or a sequence of DataRow instances, in which case you could use that to help you create a DataTable).
You need to get the results back into a DataTable or something you can convert into a DataTable and then it will work.
In your particular case, it seems that you were (or are) using typed DataSets. If that is the case, then you should be able to take the values that were selected and then create new typed DataRow instances (there should be factory methods for you) which can then be put into a typed DataTable, which AsDataView can be called on.
just simply convert the result to a list and bind it to your grid.
var query = from item in myDatabaseDataSet.Items
where item.p_Id == p_Id
join diamond in myDatabaseDataSet.Diamond
on item.p_Id equals diamond.p_Id
join category in myDatabaseDataSet.DiamondCategory
on diamond.dc_Id equals category.dc_Id
select new
{
Product = item.p_Name,
Weight = diamond.d_Weight,
Category = category.dc_Name
}.ToList();
dataGridView1.DataSource = query;
I have a single table and I need to build a bunch of nested objects based on the single table.
Data:
PointA PointB Month Time Price
1 2 11 11:00 10.99
1 2 12 11:00 9.99
Objects are
POINTS {PointA, PointB, Details}
Details {Month, ExtraDetails}
ExtraDetails {Time, Price}
I want to avoid having loads of loops and if statements, so should be able to use linq to do this. but its beyond my linq experience.
edit: These need grouping aswell
any help would be great.
Thanks
Just tried out a solution:
var nestedObjects = from row in data
select new {row.PointA, row.PointB, Details = new {
row.Month, ExtraDetails = new {
row.Time, row.Price
}
}};
This is assuming that you have already got your data into data.
Group by
If you want to group the Points together, you need 'Group By':
var nestedObjects = from row in data
group row by new { row.PointA, row.PointB } into Points
select new {
Points = Points.Key,
Details = from details in Points
select new { row.Month, ExtraDetails = new {
row.Time, row.Price
}}
};
A little more complicated - of course you might want to group by month as well, in which case, you need to follow the same pattern as for the Points bit. Note, this will not create tables, because the group by doesn't quite do that, but it at least creates the structure for you.
Assuming you got your classes defined for the objects you mentioned, and you have a constructor or properties so you can propery create the object in one line you could have a LINQ query returning a list of a POINTS.
If would go something lik this :
var res =
from item in table.AsEnumerable()
select new Points(){PointA = item["PointA"];
PointB = item["PointB"];
Details = from item2 in table.AsEnumberable()
where item["PointA"] = item2["PointA"] and item["PointB"] = item2["PointB"]
select new Details(){
month=item2["month"],
extraDetails = from item3 in table.AsEnumerable()...
}
};
At the end res will be a IEnumerable of Points
I am sorry for the code, I am not at a computer with .NET 3.5 so I cannot write a proper testable query
I have a combo box in Silverlight. It has a collection of values built out of the properties of one of my LINQ-to-SQL objects (ie Name, Address, Age, etc...). I would like to filter my results based off the value selected in a combo box.
Example: Say I want everyone with a last name "Smith". I'd select 'Last Name' from the drop down list and enter smith into a textbox control. Normally I would write a LINQ query similar to...
var query = from p in collection where p.LastName == textbox.Text select p;
Is it possible to decide the property dynamically, maybe using Reflection? Something like
var query = from p in collection where p.(DropDownValue) == textbox.Text select p;
Assuming:
public class Person
{
public string LastName { get; set; }
}
IQueryable<Person> collection;
your query:
var query =
from p in collection
where p.LastName == textBox.Text
select p;
means the same as:
var query = collection.Where(p => p.LastName == textBox.Text);
which the compiler translates from an extension method to:
var query = Queryable.Where(collection, p => p.LastName == textBox.Text);
The second parameter of Queryable.Where is an Expression<Func<Person, bool>>. The compiler understands the Expression<> type and generates code to build an expression tree representing the lambda:
using System.Linq.Expressions;
var query = Queryable.Where(
collection,
Expression.Lambda<Func<Person, bool>>(
Expression.Equal(
Expression.MakeMemberAccess(
Expression.Parameter(typeof(Person), "p"),
typeof(Person).GetProperty("LastName")),
Expression.MakeMemberAccess(
Expression.Constant(textBox),
typeof(TextBox).GetProperty("Text"))),
Expression.Parameter(typeof(Person), "p"));
That is what the query syntax means.
You are free to call these methods yourself. To change the compared property, replace this:
typeof(Person).GetProperty("LastName")
with:
typeof(Person).GetProperty(dropDown.SelectedValue);
Scott Guthrie has a short series on dyamically built LINQ to SQL queries:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
That's the easy way...then there's another way that's a bit more involved:
http://www.albahari.com/nutshell/predicatebuilder.aspx
You can also use the library I created: http://tomasp.net/blog/dynamic-linq-queries.aspx. You would store the properties in ComboBox as lambda expressions and then just write:
var f = (Expression<Func<Product, string>>)comboBox.SelectedValue;
var query =
from p in collection
where f.Expand(textBox.Text)
select p;