I had the following query using normal linq and it was working great (using anonymous type),
var result = from s in Items
group s by s.StartTime into groupedItems
select new {groupedItems.Key, Items= groupedItems.OrderBy(x => x.Name) };
But using Dynamic Linq I cannot get it to order by within the groupby.
result = Items.GroupBy("StartTime", "it").OrderBy("Name");
It states the Name isn't available. It is worth noting that if I take my OrderBy off, everything works great but items inside each "Key" are not ordered.
This is a good question!
I simulated your situation by creating a class called Item.
public class Item
{
public DateTime StartTime { get; set; }
public string Name { get; set; }
}
and then created a basic list of items to do the groupby.
List<Item> Items = new List<Item>()
{
new Item() { StartTime = DateTime.Today, Name = "item2"},
new Item() { StartTime = DateTime.Today, Name = "item1"},
new Item() { StartTime = DateTime.Today.AddDays(-1), Name = "item3"},
};
Now the big difference in the 2 queries is where the order by is being performed. In the first query, when you perform groupedItems.OrderBy(x => x.Name) its being performed on a IGrouping<DateTime,Item> or a single entry as it iterates through all the groupings.
In the second query, the orderby is being performed after the fact. This means you're doing an orderby on a IEnumerable<IGrouping<DateTime,Item>> because the iterations have already happened.
Since Microsoft was nice they added something to help deal with this for expressions. This overload allows you to specify the item returned as it iterates through the collection. Here's an example of the code:
var expressionResult = Items.GroupBy(x => x.StartTime,
(key, grpItems) => new { key, Items = grpItems.OrderBy(y => y.Name) });
The second part of the GroupBy you can specify a lambda expression that takes a key and a grouping of items under that key and return an entry that you specify, which is the same as you're doing in the original query.
Hope this helps!
Related
I am just not understanding the LINQ non-query syntax for GroupBy.
I have a collection of objects that I want to group by a single property. In this case Name
{ Id="1", Name="Bob", Age="23" }
{ Id="2", Name="Sally", Age="41" }
{ Id="3", Name="Bob", Age="73" }
{ Id="4", Name="Bob", Age="34" }
I would like to end up with a collection of all the unique names
{ Name="Bob" }
{ Name="Sally" }
Based on some examples I looked at I thought this would be the way to do it
var uniqueNameCollection = Persons.GroupBy(x => x.Name).Select(y => y.Key).ToList();
But I ended up with a collection with one item. So I though maybe I was over complicating things with the projection. I tried this
var uniqueNameCollection = Persons.GroupBy(x => x.Name).ToList();
Same result. I ended up with a single item in the collection. What am I doing wrong here? I am just looking to GroupBy the Name property.
var names = Persons.Select(p => p.Name).Distinct().ToList()
If you just want names
LINQ's GroupBy doesn't work the same way that SQL's GROUP BY does.
GroupBy takes a sequence and a function to find the field to group by as parameters, and return a sequence of IGroupings that each have a Key that is the field value that was grouped by and sequence of elements in that group.
IEnumerable<IGrouping<TSource>> GroupBy<TSource, TKey>(
IEnumerable<TSource> sequence,
Func<TSource, TKey> keySelector)
{ ... }
So if you start with a list like this:
class Person
{
public string Name;
}
var people = new List<Person> {
new Person { Name = "Adam" },
new Person { Name = "Eve" }
}
Grouping by name will look like this
IEnumerable<IGrouping<Person>> groups = people.GroupBy(person => person.Name);
You could then select the key from each group like this:
IEnumerable<string> names = groups.Select(group => group.Key);
names will be distinct because if there were multiple people with the same name, they would have been in the same group and there would only be one group with that name.
For what you need, it would probably be more efficient to just select the names and then use Distinct
var names = people.Select(p => p.Name).Distinct();
var uniqueNameCollection = Persons.GroupBy(x => x.Name).Select(y => y.Key).ToList();
Appears valid to me. .net Fiddle showing proper expected outcome: https://dotnetfiddle.net/2hqOvt
Using your data I ran the following code statement
var uniqueNameCollection = people.GroupBy(x => x.Name).Select(y => y.Key).ToList();
The return results were List
Bob
Sally
With 2 items in the List
run the following statement and your count should be 2.
people.GroupBy(x => x.Name).Select(y => y.Key).ToList().Count();
Works for me, download a nugget MoreLinq
using MoreLinq
var distinctitems = list.DistinctBy( u => u.Name);
I have a cluttery piece of code that I would like to shorten using Linq. It's about the part in the foreach() loop that performs an additional grouping on the result set and builds a nested Dictionary.
Is this possible using a shorter Linq syntax?
var q = from entity in this.Context.Entities
join text in this.Context.Texts on new { ObjectType = 1, ObjectId = entity.EntityId} equals new { ObjectType = text.ObjectType, ObjectId = text.ObjectId}
into texts
select new {entity, texts};
foreach (var result in q)
{
//Can this grouping be performed in the LINQ query above?
var grouped = from tx in result.texts
group tx by tx.Language
into langGroup
select new
{
langGroup.Key,
langGroup
};
//End grouping
var byLanguage = grouped.ToDictionary(x => x.Key, x => x.langGroup.ToDictionary(y => y.PropertyName, y => y.Text));
result.f.Apply(x => x.Texts = byLanguage);
}
return q.Select(x => x.entity);
Sideinfo:
What basically happens is that "texts" for every language and for every property for a certain objecttype (in this case hardcoded 1) are selected and grouped by language. A dictionary of dictionaries is created for every language and then for every property.
Entities have a property called Texts (the dictionary of dictionaries). Apply is a custom extension method which looks like this:
public static T Apply<T>(this T subject, Action<T> action)
{
action(subject);
return subject;
}
isn't this far simpler?
foreach(var entity in Context.Entities)
{
// Create the result dictionary.
entity.Texts = new Dictionary<Language,Dictionary<PropertyName,Text>>();
// loop through each text we want to classify
foreach(var text in Context.Texts.Where(t => t.ObjectType == 1
&& t.ObjectId == entity.ObjectId))
{
var language = text.Language;
var property = text.PropertyName;
// Create the sub-level dictionary, if required
if (!entity.Texts.ContainsKey(language))
entity.Texts[language] = new Dictionary<PropertyName,Text>();
entity.Texts[language][property] = text;
}
}
Sometimes good old foreach loops do the job much better.
Language, PropertyName and Text have no type in your code, so I named my types after the names...
I am trying to work with MvcContrib Grid control. But I cannot seem to get the sorting to work on complex objects that hold other objects.
I have setup my controller/classes/Views similar to the OP in this question.
Sorting with MVCContrib
I have tried to use the SortColumnName to my childobject.property but it gives me an error saying My main object does not have this property. This is my code snippet
//POCO class
class Issue {
public int ID {get; get; }
.....
public int priorityId {get; set;}
public virtual Priority priority {get; set;}
}
//Controller code
public ViewResult Index(int? pageNo, GridSortOptions sort)
{
var issues = db.issues.Include(i => i.priority);
ViewBag.sort = sort;
if (!string.IsNullOrEmpty(sort.Column))
{
issues = issues.OrderBy(sort.Column, sort.Direction);
}
return View(issues.ToList().AsPagination(pageNo ?? 1, 10));
}
//View code for the Grid
#Html.Grid(Model).Sort(ViewBag.sort as GridSortOptions).Columns(column => {
column.For(issue => Html.ActionLink(" ", "Edit", new { id = issue.ID, areas = "Issues", controller = "Main"}, new { #id="editBtn"})).Named("Edit");
column.For(issue => Html.ActionLink(issue.ID.ToString(), "Edit", new {id = issue.ID, areas = "Issues", controller = "Main"})).Named("ID").Sortable(true);
column.For(issue => issue.priority.codeDesc).Named("Priority").SortColumnName("priority.codeDesc").Sortable(true);
}).Empty("No data found")
When I try to sort on the priority string, it gives me an error saying 'priority.codeDesc is not a property of Issue'.
TIA
The issue here isn't actually related to the grid, but rather to the .OrderBy extension method provided as part of the MvcContrib sorting extensions. This extension is fairly simplistic and I only wrote it to cover simple cases where you want to sort on a direct property of the object, however in your case you're trying to order on a nested property ("priority.codeDesc") which isn't supported - you can't use dot notation with this extension.
You'd either need to switch to using a different mechanism to perform the actual sorting, or if this is a one-off situation then you could hard-code the sorting logic for this particular column (not ideal, but if it's a one off then it's simpler than writing a new sorting mechanism), eg:
if (!string.IsNullOrEmpty(sort.Column))
{
if(sort.Column == "priority.codeDesc")
{
issues = issues.OrderBy(x => x.priority.codeDesc);
}
else
{
issues = issues.OrderBy(sort.Column, sort.Direction);
}
}
OMG! Dots!
I was in the same boat but thanks God I found a brilliant solution posted by our fellow developer Jarrett Meyer. I found it after maybe 3 hours Googling in the past and just now when I decided to boost my pagination and sorting with MvcContrib Grid.
You can find the full post here:
Server-Side Sorting With Dynamic LINQ
His code saved me... :D The use of LINQ's Aggregate function was AWESOME! Kudozzz to him.
I had to change Jarretts' original code a little bit to fit it to my needs. Here's the code after I modified it:
public static IQueryable<T> OrderBy<T>(this IQueryable<T> collection, GridSortOptions sortOptions)
{
if (string.IsNullOrEmpty(sortOptions.Column))
{
return collection;
}
Type collectionType = typeof(T);
ParameterExpression parameterExpression = Expression.Parameter(collectionType, "p");
Expression seedExpression = parameterExpression;
Expression aggregateExpression = sortOptions.Column.Split('.').Aggregate(seedExpression, Expression.Property);
MemberExpression memberExpression = aggregateExpression as MemberExpression;
if (memberExpression == null)
{
throw new NullReferenceException(string.Format("Unable to cast Member Expression for given path: {0}.", sortOptions.Column));
}
LambdaExpression orderByExp = Expression.Lambda(memberExpression, parameterExpression);
const string orderBy = "OrderBy";
const string orderByDesc = "OrderByDescending";
Type childPropertyType = ((PropertyInfo)(memberExpression.Member)).PropertyType;
string methodToInvoke = sortOptions.Direction == MvcContrib.Sorting.SortDirection.Ascending ? orderBy : orderByDesc;
var orderByCall = Expression.Call(typeof(Queryable), methodToInvoke, new[] { collectionType, childPropertyType }, collection.Expression, Expression.Quote(orderByExp));
return collection.Provider.CreateQuery<T>(orderByCall);
}
Now you can call this extension method like this in your controller method:
var users = Database.Memberships.OrderBy(sort);
where sort is GridSortOptions that lives in MvcContrib.UI.Grid.
sort.ColumnName can contain strings like these ones now:
User.UserName
User.MyRelatedEntity.RelatedEntityProperty
User.MyRelatedEntity.RelatedEntityProperty.AndSoON
Note that when you create your Grid columns you can specify
.SortColumnName("User.UserName")
This has been ruining my life for a few days now, time to ask...
I am using Entity Framework 4.0 for my app.
A Location (such as a house or office) has one or more facilities (like a bathroom, bedroom, snooker table etc..)
I want to display a checkbox list on the location page, with a checkbox list of facilities, with the ones checked that the location currently has.
My View Model for the facilities goes like this...
public class FacilityViewItem
{
public int Id { get; set; }
public string Name { get; set; }
public bool Checked { get; set; }
}
So when im passing the Location View Model to the UI, i want to pass a List<T> of facilities where T is of type FacilityViewItem.
To get the facilities that the location already has is simple - i make a query using Location.Facilities which returns an EntityCollection where T is of type Facility. This is because Facilities is a navigation property....
var facs = from f in location.Facilities
select new FacilityViewItem()
{
Id = f.FacilityId,
Name = f.Name,
Checked = true
};
So here is where my problem lies - i want the rest of the facilities, the ones that the Location does not have.
I have tried using Except() and Any() and Contains() but i get the same error.
Examples of queries that do not work...
var restOfFacilities = from f in ctx.Facilities
where !hasFacilities.Contains(f)
select new FacilityViewItem()
{
Id = f.FacilityId,
Name = f.Name
};
var restOfFacilities = ctx.Facilities.Except(facilitiesThatLocationHas);
var notFacs = from e in ctx.Facilities
where !hasFacilities.Any(m => m.FacilityId == e.FacilityId)
select new FacilityViewItem()
{
Id = e.FacilityId,
Name = e.Name
};
And the error i get with every implementation...
System.NotSupportedException was unhandled
Message=Unable to create a constant value of type 'Chapter2ConsoleApp.Facility'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.
What am i overlooking here?
ironically enough i solved it in a matter of hours after i posted the question on here, after days of suffering.
The error is basically saying 'i dont know how to calculate what items are not included by comparing strongly typed objects. Give me a list of Ints or some simple types, and i can take care of it'.
So, first you need to get a list of the primary keys, then use that in the contains clause...
//get the primary key ids...
var hasFacilityIds = from f in hasFacilities
select f.FacilityId;
//now use them in the contains clause...
var restOfFacilities = from f in ctx.Facilities
where !hasFacilityIds.Contains(f.FacilityId)
select new FacilityViewItem()
{
Id = f.FacilityId,
Name = f.Name
};
The first query seems fine, but you need to compare the Ids:
var restOfFacilities = from f in ctx.Facilities
where !facs.Select(fac => fac.Id).Contains(f.Id)
select f;
I wanna see what's hasFacilities, anyway, as L2E shows, "Only primitive types ('such as Int32, String, and Guid') are supported in this context", so I suppose you must retrieve first the data and put into a collection of FacilityViewItem.
var restOfFacilities = ctx
.Facilities
.Where(f => !hasFacilities.Contains(f))
.Select(f => new { f.FacilityId, f.Name })
.ToList()
.Select(f => new FacilityViewItem {
Id = f.FacilityId,
Name = f.Name
});
var notFacs = ctx
.Facilities
.Where(e => !hasFacilities.Any(m => m.FacilityId == e.FacilityId))
.Select(e => new { e.FacilityId, e.Name })
.ToList()
.Select(e => new FacilityViewItem {
Id = e.FacilityId,
Name = e.Name
});
hope it helps
I have the following collection
public IQueryable<myObjectType > GetWorkCellLoadGraphDataByIdDummy()
{
IList<myObjectType> workCellLoadGraphDataCollection = new List<myObject>()
{
new myObjectType(DateTime.Today.AddHours(8).AddMinutes(30), 1),
new myObjectType(DateTime.Today.AddHours(10).AddMinutes( 10 ), 6 ),
new myObjectType(DateTime.Today.AddHours(13).AddMinutes( 30 ),8 ),
new myObjectType(DateTime.Today.AddDays(1).AddHours(8).AddMinutes(30), 1),
new myObjectType(DateTime.Today.AddDays(1).AddHours( 10 ).AddMinutes( 10 ), 5 ),
new myObjectType(DateTime.Today.AddDays(1).AddHours( 13 ).AddMinutes( 30 ), 2 )
};
// Write some LINQ code to group data according to first parameter
// Perform sum of last parameter
// Shape the data to be in the form of myObjectType
// return result;
}
and what I want to do is to group items by the first parameter of the myObjectType class.
Then for each grouping, I'd like to do the sum of all the last parameters.
Finally the result should be returned in the form of "myObjectType"
I know how to do it the old fashioned way i.e. looping through all the items and doing the sums. However, I'd like to learn how to do it in LINQ which is something I've just started.
Can anyone point me in the right direction so that I can translate my requirements into LINQ?
In effect, the result should be a collection containing two objects of type myObjectType as follows:
First object in collection is (DateTime.Today, 15 )
Second object in collection is (DateTime.Today.AddDays(1), 8)
TIA,
David
Given a class with this basic design
class MyObjectType
{
public MyObjectType(DateTime date, int count)
{
this.MyDate = date;
this.MyCount = count;
}
public DateTime MyDate { get; set; }
public int MyCount { get; set; }
}
You could fulfill your requirement using LINQ in the manner below. The first example produces IEnumerable<MyObjectType> using fluent extension method syntax.
var query = collection.GroupBy(obj => obj.MyDate.Date)
.Select(grp =>
new MyObjectType(grp.Key, grp.Sum(obj => obj.MyCount))
);
The second version achieves the same result but uses the more SQL-esque query expression syntax.
var query = from obj in collection
group obj by obj.MyDate.Date into grp
let mySum = grp.Sum(item => item.MyCount)
select new MyObjectType(grp.Key, mySum);
From there, you utilize the extension methods AsQueryable to yield an IQueryable result, or ToList() / ToArray() to yield concrete collections.