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How to shorten the LINQ query to calculate the sum for parent table from child tables


By : psriram
Date : September 13 2020, 09:00 AM
This might help you Currently I have this LINQ query which calculate the totalcount of a parent table (CafeTables) from child tables (CafeTableDetails). These code works. But somehow, I believe these code can the shorten. , I think you can try to use linq JOIN and GroupBy to make it.
code :
var result = db.CafeTables.Where(c => c.TableNo == userName)
                         .Join(db.CafeTableDetails.GroupBy(x=>x.CafeTableId)
                         .Select(g => new { CafeTableId = g.Key, cnt = g.Count() }), 
st => st.Id,
cd => cd.CafeTableId,
(st,cd) => new  
{
    st.Id,
    cd.cnt
    //..... your expect property
});


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Load parent and child table in one query linq to entitiy


By : Jennifer Anderson
Date : March 29 2020, 07:55 AM
it fixes the issue I have a following tables/classes structure in Linq to entities.
code :
(from b in books
select new { BookId = b.BookId,
             Title = b.Title,
             Tags = bookTag.Where(bt => bt.BookId == b.BookId).Select(bt => tags.Single(t => t.TagId == bt.TagId).TagTitle)
           }).ToList().Select( t => new 
           { BookId = b.BookId,
             Title = b.Title,
             Tags = string.Join(", ", t.Tags.ToArray())
           }

LINQ to SQL join two tables to select parent table twice based on two different columns from child table


By : user2239435
Date : March 29 2020, 07:55 AM
Hope this helps I'd like to get suggestion in both C# and VB.NET , This should do it in C#:
code :
var query = from log in db.CafeLogs
            join emp in db.Employees on log.EmployeeId equals emp.EmployeeId
            join cas in db.Employees on log.CashierId  equals cas.EmployeeId
            select new
            {
                log.LogId,
                Employee  = emp.FirstName + " " + emp.LastName,
                ChargedBy = cas.FirstName + " " + cas.LastName,
                log.Value
            };
Dim query = From log In db.CafeLogs                                          _
            Join emp In db.Employees On log.EmployeeId Equals emp.EmployeeId _
            Join cas In db.Employees On log.CashierId  Equals cas.EmployeeId _
            Select                                                           _
                log.LogId,                                                   _
                Employee  = emp.FirstName & " " & emp.LastName,              _
                ChargedBy = cas.FirstName & " " & cas.LastName,              _
                log.Value

LINQ Query for outerjoining Parent and child (nested) tables


By : Θοδωρής Παλτόγλου
Date : March 29 2020, 07:55 AM
I hope this helps you . I have three levels of tables "Directors", "Managers" and "Leaders" with one to many relationship between them. ,
It feels like a small tweak
code :
var query =
db.Directors.GroupJoin(db.Managers, director => director.DirectorId, manager => manager.DirectorId, (director, managerGroup) => new
{
    Id = director.DirectorID,
    Name = director.DirectorName,
    Managers = managerGroup.GroupJoin(db.Leaders, manager => manager.ManagerId, leader => leader.ManagerID, (manager, leaderGroup) => new
    {
        Id = manager.ManagerID,
        Name = manager.ManagerName,
        Leaders = leaderGroup.Select(leader => new
        {
            Id = leader.LeaderID,
            Name = leader.LeaderName
        })
    })
})
.SelectMany(director =>  
    new[] { new
    {
        DirID = director.Id, DirectorName = director.Name,
        MgrID = (int?)null, ManagerName = (string)null,
        LdrID = (int?)null, LeaderName = (string)null
    } }
    .Concat(director.Managers.SelectMany(manager => 
        new[] { new
        {
            DirID = director.Id, DirectorName = director.Name,
            MgrID = (int?)manager.Id, ManagerName = manager.Name,
            LdrID = (int?)null, LeaderName = (string)null
        } }
        .Concat(manager.Leaders.Select(leader => new
        {
            DirID = director.Id, DirectorName = director.Name,
            MgrID = (int?)manager.Id, ManagerName = manager.Name,
            LdrID = (int?)leader.Id, LeaderName = leader.Name
        }))
    ))
);

Linq get parent and child in one table and calculate their values in another table


By : Rebb Dellah
Date : March 29 2020, 07:55 AM
it helps some times I have 2 tables: , Assuming the table names acc.
code :
var parentRecords = records.Select(x => 
        new Record { RecordID = parents.FirstOrDefault(y => y.ChildID == x.RecordID || y.ParentID == x.RecordID).ParentID, Quantity = x.Quantity});

    var result = parentRecords.GroupBy(z => z.RecordID,
        (key, value) => new { RecordID= key, TotalQuantity= value.Sum(a => a.Quantity) });

Filter parent/child table (one to many association) in linq query based on entities in child table?


By : user3896224
Date : March 29 2020, 07:55 AM
Does that help I have a table (Projects) which is linked to projectVersions on projectID , If I understand correctly, the issue is in
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