I have a table (or entity) named Cases. There is another table CaseStatus_Lookup and the primary key of this table is a foreign key in the Cases table.
What I want to do is: For every status type I want the number of count of cases. For e.g. if status = in progress , I want to know how many cases are in that status.
one other thing: I also want to filter the Cases based on UserID.
I tried several ways in LINQ but could not get vary far. I was wondering if someone could help.
try Linq .GroupBy
am assuming your entity structure
suppose your Case Entity is like
public class Case
{
public int Id{get;set;}
public int CaseStatusId{get;set;}
public int UserId{get;set;}
//navigational fields
public virtual CaseStatus CaseStatus {get;set;}
}
and suppose your CaseStatus entity is like:
public class CaseStatus
{
public int Id{get;set;}
public string Name{get;set;}
//navigational fields..
public virtual ICollection<Case> Cases{get;set;}
}
then you can do this:
using (myDbContext db = new myDbContext())
{
var query = db.Cases.GroupBy(case => case.CaseStatus.Name)
.Select(group =>
new {
Name = group.Key,
Cases= group.OrderBy(x => x.Id),
Count= group.Count()
}
).ToList();
//query will give you count of cases grouped by CaseStatus.
}
similarly you can further filter your result based on userId.
Start to explore about Linq .GroupBy
You need a function that returns the sum and takes the status as parameter :- something like below.
MyCaseStatusEnum caseStatus; //Pass your required status
int caseCount = myCases
.Where(r => r.Status == caseStatus)
.GroupBy(p => p.Status)
.Select(q => q.Count()).FirstOrDefault<int>();
Related
Let's suppose I have a list of player scores that looks somewhat like this:
public class ScoreEntry
{
public int PlayerId {get; set;}
public int Score {get; set;}
public string SomeOtherValue {get;set;}
}
And there are multiple entries for a single player, so I want to group those score entries and sum up their score values, something like this:
var query =
from entry in scores
group entry by entry.PlayerId into scoreEntryGroup
select new ScoreEntry()
{
PlayerId = scoreEntryGroup.Key,
Amount = scoreEntryGroup.Sum(g => g.Score),
SomeOtherValue = scoreEntryGroup.FirstOrDefault().SomeOtherValue
};
It throws an exception and I know that the problem is that I can't use SingleOrDefault() and many other similar methods in a group in EF Core 3.1
Could you help me find another way to achieve this? Any help would be highly appreciated!
Try the following query. It uses CROSS APPLY for joining to aggregation result.
var aggregations =
from entry in scores
group entry by entry.PlayerId into scoreEntryGroup
select new
{
PlayerId = scoreEntryGroup.Key,
Amount = scoreEntryGroup.Sum(g => g.Score)
};
var query =
from a in aggregations
from entry in scores
.Where(entry => entry.PlayerId == a.PlayerId)
.Take(1)
select new ScoreEntry()
{
PlayerId = entry.PlayerId,
SomeOtherValue = entry.SomeOtherValue,
Amount = a.Amount
};
I'm using LINQ to execute a query on a List type variable with a large amount of data (over a million). For performance purposes I'm using IEnumerable to store the results but when I try to access it there is a slight delay.
Specifically I want to see if the query produced any results, but when I use the .Count() or .Any() functions the performance drops.
I read that for IEnumerable types the execution of the query happens at the time of need, hence the delay. Is there a way to see if the IEnumerable has elements inside it without having that much delay?
This is what I'm trying to run.
IEnumerable<Entity> matchingEntities = entities.Where(e => e.Names.Any(n => myEntity.Names.Any(entityName => entityName.CompareNameObjects(n))));
and here are my classes
public class Entity
{
public string EntityIdentifier { get; set; }
public List<Name> Names { get; set; }
}
public class Name
{
public string FullName { get; set; }
public string NameType { get; set; }
public bool CompareNameObjects(Name name2)
{
return FullName == name2.FullName &&
NameType == name2.NameType;
}
}
entities is a list of all my objects and I want to check if myEntity has any Names identical with another entity in the set.
EDITED:
The data structure is similar to the 2 classes (Entity and Name). The entities are created by selecting all the entities, along with their names, from the database in XML format and then I convert the XML to a List as such:
List<Entity> entities = new List<Entity>();
using (SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["myCS"].ConnectionString))
{
conn.Open();
SqlCommand cmd = new SqlCommand("GetAllEntities", conn);
cmd.CommandType = CommandType.StoredProcedure;
string entitiesXml = "";
using (SqlDataReader rdr = cmd.ExecuteReader())
{
while (rdr.Read())
{
entitiesXml += rdr["XmlString"].ToString();
}
}
using (TextReader reader = new StringReader(entitiesXml))
entities = (Entity)xmlSerializer.Deserialize(reader);
conn.Close();
}
GetAllEntities (Stored Procedure):
declare #xmlString nvarchar(max) =(
select e.EntityIdentifier,
(
select n.[Full Name] as 'FullName',
n.[Name Type] as 'NameType'
from tblNames n
where e.EntityID=n.[Entity_ID]
for xml path('Name'), type
)
from tblEntities e
order by e.EntityID
for xml path('Entity')
)
select #xmlString as XmlString
Basically, you should avoid getting all data from your database then filter it with C# code. It consumes a lot of effort.
However, for quick solution, you can improve performance by preparing your conditions in a Dictionary form firstly.
// Let's say you have myEntity here
var myEntity = new Entity();
var entities = new List<Entity>();
// You should prepare the list of name that you wanna to find before you do it so that you don't have to make it repeatedly for every iteration
var names = myEntity.Names.Select(p=> p.FullName + p.NameType ).ToDictionary(p=>p, p=>p);
IEnumerable<Entity> matchingEntities = entities.Where(e => e.Names.Any(n => names.ContainsKey(n.FullName + n.NameType)));
This is just an example that may give you more idea. You can improve much more. I hope it can help you
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!
The big picture:
I'm working on a search form where the user can choose one or more criteria to filter the search results. One of the criteria is related to a child relationship.
I'm trying to create an extention method to Iqueryable<Parent> so I can use as part of my "chaining".
The method signature (as of now) is:
public static IQueryable<Parent> ContainsChild(this IQueryable<Parent> qry, int[] childrenIDs)
The parent table and a child table:
Parent
ParentID
Name
Description
Child
ParentID (FK)
AnotherID (from a lookup table)
Selection criteria:
int[] ids = new int[3] {1,2,3};
Usage would be something like this:
var parents = repository.All() //returns Iqueryable<Parent>
public IQueryable<Parent> Search(Search seach){
if (search.Criteria1 != null){
parents = parents.FilterByFirstCriteria(search.Criteria1);
}
if (search.ChildrenIDs != null){ //ChildrenIDs is an int[] with values 1,2,3
parents = parents.ContainsChild(search.ChildrenIDs)
}
}
What I'm trying to figure out is how to create the ContainsChild method that returns an IQueryable<Parent> where the parents have at least one child with the AnotherID in the ids array.
(I'm trying to use EF4 to accomplish this)
Any help fully appreciated.
Perhaps this:
public static IQueryable<Parent> ContainsChild(this IQueryable<Parent> qry,
int[] childrenIDs)
{
return qry.Where(p => p.Children.Any(c => childrenIDs.Contains(c.AnotherID)));
}
Edit
Just for fun another way which should give the same result:
public static IQueryable<Parent> ContainsChild(this IQueryable<Parent> qry,
int[] childrenIDs)
{
return qry.Where(p => p.Children.Select(c => c.AnotherID)
.Intersect(childrenIDs).Any());
}
The generated SQL for the first version looks more friendly though, so I'd probably prefer the first version.
Given the classes A and B where
class A
{
string Name;
Ilist<B> BList;
}
class B
{
string Name;
}
With FluentNH mapping, relationship is many-to-many which is HasManyToMany(x => x.B) for A. B has no reference to A. NH version is 2.1.2.4000.
What should be the linq query to select the collection where each row contains B.Name and count of A's containing that B? Result must be the List of anonymous type who has 2 fields: Name and Count. Result also should include all B's, hence it should be outer join.
My intend is to get the result with minimum round-trips to database, possibly in one go.
If you want to do it in Linq in one hit in code, you could do this...
var result = Session.Linq<A>()
.SelectMany(a => a.BList, (a, b) => new { b.Name, A = a.Id })
.ToList()
.GroupBy(x => x.Name)
.Select(x => new { Name = x.Key, Count = x.Count() })
.ToList();
NHibernate.Linq (2.1.2.4000) can't handle a GroupBy after a SelectMany it seems, so the first ToList pulls all the data into memory. This is inefficient -- a SQL count would be better.
Alternatively, you could add a lazy loaded collection to your B class that goes back to A. If you're using a many-to-many table in the middle, that should be easy.
public class B
{
public virtual string Name { get; set; }
public virtual IList<A> AList { get; private set; }
}
Your query simply becomes...
var result = Session.Linq<B>()
.Where(b => b.AList.Count > 0)
.Select(b => new { b.Name, b.AList.Count }
.ToList();
Which produces very efficient SQL from Linq (using a count) and gives the same result.