class SomeObject
{
int Value { get; set; }
string ID { get; set; }
}
var TheList = List<SomeObject> { ... }
var groupedObjects = TheList.GroupBy(o => o.ID);
The return type is IEnumerable<IGrouping<SomeObject, string, SomeObject>>
In the Debug "Results View" the Items are grouped correctly.
How can I get List<List<SomeObject>> as return?
A simple ToList() does obviously not work.
You need two ToList()s:
TheList.GroupBy(o => o.ID, c => c)
.Select(g=>g.ToList())
.ToList();
Here's a similar question with good answers: How to get values from IGrouping
You could try
var groupedObjects = TheList.GroupBy(o => o.ID, c => c).SelectMany();
Related
Assume the following code:
var citizens = await _stateProvider.SelectWhere(whereParams);
var retDto = new PercentGroupBy()
{
Total = citizens.Count,
Elements = citizens.GroupBy(p => p.Content.Current.AggState.ToString()).ToDictionary(g => g.Key, g => g.Count())
};
return retDto;
citizens is a list of the following class:
public class Citizen {
public string ETag { get; set; }
public string Name{ get; set; }
public dynamic Content { get; set; }
}
What is the best option to test that "p.Content.Current.AggState" property exists?
SelectWhere might return a few citizens where Content.Current is null and therefore asking for AggState throws error.
Oops I found the answer while posting the question, so here it is to share the knowledge:
Add a fluid "Where" before "GroupBy"
var citizens = await _stateProvider.SelectWhere(whereParams);
var retDto = new PercentGroupBy()
{
Total = citizens.Count,
Elements = citizens
.Where(p => p.Content.Current != null)
.GroupBy(p => p.Content.Current.AggState.ToString())
.ToDictionary(g => g.Key, g => g.Count())
};
return retDto;
I am trying to write an OrderBy clause in a Linq to EntityFramework query. My problem is that the entity table I am looking at stores an ID, that relates to a table in a different database and I cannot adjust the database.
MainDatabase.EntityToOrder
ID
Name
OtherID
SecondDatabase.OtherEntity
ID
Name
My C# EntityToOrder Model looks like this, and I need to be able to order by "OtherName"
EntityToOrder.cs
public class EntityToOrder
{
[DataMember]
public long ID { get; set; }
[DataMember]
public string Name { get; set; }
[DataMember]
public long OtherId { get; set; }
public string OtherName { get; set; }
}
So, I would like to Order EntityToOrder by "OtherName" in the most efficient way possible. My existing query looks like this.
var entities = mainContext.EntityToOrder.OrderBy(e => e.Name).Skip(startIndex).Take(pageSize).ToList();
var otherIds = entities.Select(e => e.OtherID).ToList();
Dictionary<long, string> otherNames = secondContext.OtherEntity
.Where(oe => otherIds.Contains(oe.ID))
.Select(oe => new { ID = oe.ID, Name = oe.Name })
.ToDictionary(oe => oe.ID, oe => oe.Name);
entities.ForEach(e => OtherName = otherNames[e.OtherID]);
How can I write the most efficient query to order by "OtherName", preferably avoiding selecting the whole EntityToOrder table into memory.
Update
For clarity, here is some code that achieves the OrderBy, but needs to retrieve the entire EntityToOrder table into memory. I was hoping this could be achieved in a more efficient way. Also, the OtherEntity can belong to many EntityToOrder rows.
var entities = mainContext.EntityToOrder.ToList();
var otherIds = entities.Select(e => e.OtherID).ToList();
Dictionary<long, string> otherNames = secondContext.OtherEntity
.Where(oe => otherIds.Contains(oe.ID))
.Select(oe => new { ID = oe.ID, Name = oe.Name })
.ToDictionary(oe => oe.ID, oe => oe.Name);
entities.ForEach(e => OtherName = otherNames[e.OtherID]);
return entities.OrderBy(e => e.OtherName).Skip(startIndex).Take(pageSize).ToList();
Quite challenging task. I was thinking initially just to switch the roles and perform pagination (OrderBy/Skip/Take) on OtherEntity table, but unfortunately that doesn't work due to one to many relationship. So I ended up with doing some pre pagination in memory on OtherEntity. However, in order to do that I needed counts of the matching items in EnityToOrder, so this is retrieved with additional db query, which makes the solution involving 3 db queries and some memory processing. Here it is
var countByOtherId = db.EntityToOrder
.GroupBy(e => e.OtherId)
.Select(g => new { ID = g.Key, Count = g.Count() })
.ToDictionary(e => e.ID, e => e.Count);
var other = new Dictionary<long, string>();
int skipCount = startIndex, useCount = 0;
foreach (var e in db.OtherEntity.OrderBy(e => e.Name))
{
int count;
if (!countByOtherId.TryGetValue(e.ID, out count)) continue;
if (skipCount > 0 && other.Count == 0)
{
if (skipCount >= count) { skipCount -= count; continue; }
count -= skipCount;
}
other.Add(e.ID, e.Name);
if ((useCount += count) >= pageSize) break;
}
var entities = db.EntityToOrder
.Where(e => other.Keys.Contains(e.OtherId))
.AsEnumerable()
.Select(e => new EntityToOrder { ID = e.ID, Name = e.Name,
OtherId = e.OtherId, OtherName = other[e.OtherId] })
.OrderBy(e => e.OtherName).ThenBy(e => e.Name)
.Skip(skipCount).Take(pageSize)
.ToList();
Now, I'm not quite sure if that's better to what are you doing currently, but it's worth trying.
If you can change the model, then you might try the following:
public class EntityToOrder
{
[DataMember]
public long ID { get; set; }
[DataMember]
public string Name { get; set; }
[DataMember]
public long OtherId { get; set; }
[ForeignKey("OtherId")]
public OtherEntity OtherEntity{ get; set; }
}
Then, you should be able to perform this query:
using System.Data.Entity;
var entities = mainContext
.EntityToOrder
.Include(x => x.OtherEntity)
.OrderBy(e => e.OtherEntity.Name)
.Skip(startIndex)
.Take(pageSize)
.ToList();
Edit :
Sorry, I missed the point that you had 2 databases....
I found an alternative which I thought I would post in case it is useful to anyone. I used a .Join() to merge the dictionary of OtherEntity into my query. This still selects into an IEnumerable so I don't think it is more efficient.
var entities = mainContext.EntityToOrder;
var otherIds = entities.Select(e => e.OtherID).ToList();
Dictionary<long, string> otherNames = secondContext.OtherEntity
.Where(oe => otherIds.Contains(oe.ID))
.Select(oe => new { ID = oe.ID, Name = oe.Name })
.ToDictionary(oe => oe.ID, oe => oe.Name);
Func<EntityToOrder, KeyValuePair<long, string>, EntityToOrder> joinFunc = ((a, b) => {
a.OtherName= b.Value;
return a;
});
return entities.Join(otherNames, e => e.OtherID, oe => oe.Key, joinFunc)
.OrderBy(e => e.OtherName)
.Skip(startIndex)
.Take(pageSize)
.ToList();
Note on Includes
When applying Join you select into an IEnumerable and therefore lose the ability to access properties from a linked table. To counter this you would need to add a .Include() for any linked table you need to access before applying the .Join(). E.g.
var entities = mainContext.EntityToOrder
.Include("LinkedEntity");
return entities.Join(otherNames, e => e.OtherID, oe => oe.Key, joinFunc)
.OrderBy(e => e.OtherName)
.ThenBy(e => e.LinkedEntity.Name) //reference to linked table
.ToList();
I have this query
[HttpGet]
public List<AttachedPhotosModel> GetReportAttachedPhotos(int reportId)
{
var photos = new ReportsRepository().GetInjuryPhotos(reportId);
return photos.Select(x => new AttachedPhotosModel()
{
Id = x.Id,
Type = x.InjuryType,
Photos = photos.Where(y => y.InjuryType == x.InjuryType).Select(z => z.ServicePhotoUrl).ToList()
}).ToList();
}
I need to GroupBy InjuryType, how to do this?
I added return photos.GroupBy(k => k.InjuryType).Select(x => new AttachedPhotosModel() but how to select model, x have new value key and I don't know how to select my data
This code should work. Assuming photos is collection of objects with InjuryType property and PhotoUrl property and AttachedPhotosModel has an InjuryType and Photos properties like this.
public class AttachedPhotosModel
{
public string InjuryType { set; get; }
public List<string> Photos { set; get; }
}
Code for grouping by InjurType.
var grouped = photos
.GroupBy(s => s.InjuryType,d => d.PhotoUrl, (k, g) => new
AttachedPhotosModel
{
InjuryType = k,
Photos = g.ToList()
}).ToList();
static void Main(){
List<Foo> t = new List<Foo>{
new Foo(){Id=1,Name="A",Value=1},
new Foo(){Id=2,Name="B",Value=1},
new Foo(){Id=3,Name="C",Value=1},
new Foo(){Id=3,Name="D",Value=1}};
var x = t.GroupBy(gp => gp.Id).Select(sel => new Foo { Id = ,Name=,Value= });
}
public class Foo{
public string Name { get; set; }
public int Id { get; set; }
public int Value { get; set; }
}
In the var x I want to group all the Foo objects by their ID and get the SUM in the Value field.
The problem is that it seems I cannot access the members/fields of the class in the select method.
Thanks
After GroupBy you don't select an IEnumerable<Foo> but groups of them. You probably want:
var x = t.GroupBy(f => f.Id)
.Select(grp => new Foo {
Id = grp.Key,
Name = String.Join(",", grp.Select(f => f.Name)),
Value = grp.Sum(f => f.Value)
});
I'm using String.Join to concenate all names of each ID-group, the values are summed.
Try this way
var x = t.GroupBy(gp => gp.Name).OrderBy(group => group.Key).Select(group => Tuple.Create(group.Key, group.Count()));
I have the following entities:
public class Parent
{
int Id { get; set; }
string ParentName { get; set; }
List<Child> Children { get; set; }
}
public class Child
{
int Id { get; set; }
string ChildName { get; set; }
}
and the following dto:
public class ParentDTO
{
int Id { get; set; }
List<string> ChildrenNames { get; set; }
}
using QueryOver code below I can get the Parent values
ParentDTO result = null;
Parent parentAlias = null;
Child childAlias = null;
var query = session.QueryOver(() => parentAlias)
.JoinAlias(() => parentAlias.Children, () => childAlias, JoinType.LeftOuterJoin)
.SelectList(list => list.Select(c => c.Id).WithAlias(() => result.Id)
.Select(c => c.ParentName).WithAlias(() => result.Name)
//this part does not work
.Select(c => c.Children .Select(v => v.ChildName)).WithAlias(() => result.ChildrenNames)
//
)
.TransformUsing(Transformers.AliasToBean<ParentDTO>());
return query.List<ParentDTO>();
However I cant seem to be able to project the list of childName values into my ChildrenNames collection.
Any ideas?
As some guys said in comments, you need to do two queries. Using linq, you could try something like this:
// get the parent Ids
var parentIds = session.Query<Parent>().Select(c => c.Id).ToList();
// get the childNames
var childNames = session.Query<Child>()
.Where(x => parentIds.Contains(x.ParentId)) // get on the child from parents query
.Select(x => new {x.Name, x.ParentId}) // get only the properties you need
.ToList(); // list of anon objects
// loop in memory between parentIds filling the corresponding childNames
var result = parentIds.Select(parentId => new ParentDTO()
{
Id = parentId,
ChildrenNames = childNames.Where(x => x.ParentId == parentId).ToList()
}).ToList();
I am not sure if it works, but you could try this in a single query:
var query = from p in session.Query<Parent>()
let names = p.Children.Select(c => c.ChildName).ToList()
select new ParentDTO()
{
Id = o.Id,
ChildrenNames = names
};
return query.Tolist();
Obs: I did not test it.