I have a database that keep track of books and borrowers. I want to answer this question with linq: what is the most borrowed books?(top 5 for example).
in the Book table we have : Id , Title and in the table loan We have : Id, Book Id
I use the code bellow but it return the key and I need the Title of books
var MostBorrowedBook = _context.Books.Join(_context.Loans,
y=> y.Id,
x=> x.BookId,
(y,x)=> y)
.GroupBy(q=> q.Id)
.OrderByDescending(q=>q.Count())
.Take(5)
.Select(q=>q.Key).ToList();
This works:
var mostBorrowedBook = _context.Books.Join(_context.Loans, y => y.Id, x => x.BookId, (y, x) => y)
.GroupBy(q => new{q.Id, q.Title})
.OrderByDescending(q => q.Count())
.Take(5)
.Select(g => g.Key.Title)
.ToList();
Related
trying to convert a query which has 2 levels of where in clauses to linq and getting some errors. Can anybody help me on this?
Original Query:
select id
from student
where suId
in (select suId
from subjects
where cid
in (select id
from chapters
where chapter='C203'))
LINQ query:
var query = (from s in dc.students
let subs = (from su in dc.subjects
where su.cid == Convert.ToInt32(from c in dc.Chapters
where c.chapter == 'Ç203'
select c.id) //Single chapter id will be returned
select su.suid)
where subs.Contains(s.sid)
select s.id).ToArray();
Am getting below 2 errors while compiling app
'System.Linq.IQueryable' does not contain a definition for 'Contains' and the best extension method overload 'System.Linq.ParallelEnumerable.Contains(System.Linq.ParallelQuery, TSource)' has some invalid arguments
Instance argument: cannot convert from 'System.Linq.IQueryable' to 'System.Linq.ParallelQuery'
Since Linq is lazy-loading everything you don't need to cram everything into a single statement; you can do something like this:
var chapterIds = dc.Chapters
.Where(c => c.Chapter == "C023")
.Select(c => c.Id);
var subjectIds = dc.Subjects
.Where(s => chapterIds.Contains(s.Cid))
.Select(s => s.Suid);
var students = dc.Students
.Where(s => subjectIds.Contains(s.Suid))
.Select(s => s.Sid)
.ToArray();
This way you can debug each subquery by looking at what it returns.
However, looking at your original select you can rewrite the whole thing as a Join and get rid of the bugging issue:
var students = dc.Chapters.Where(c => c.Chapter == "C023")
.Join(dc.Subjects,
c => c.Id,
s => s.Cid,
(chapter, subject) => subject)
.Join(dc.Students,
subj => subj.Suid,
student => student.Suid,
(subj, st) => st.Sid)
.ToArray();
I need to return all records (items) that has a part (X) so I can use that in a group or .GroupBy afterwards
Using this summary data:
ItemName PartName
1 A
1 B
2 A
3 C
So Item1 has two parts (A,B), etc...
I need a LINQ query that will
- find all items that have part A (i.e items 1 and 2)
- return all rows for all these items
1 A
1 B
2 A
Notice that the end result returned the row (1 B) because Item1 has PartA and so I need to get back all rows for Item1.
I was looking at something like:
let items = from data in summary where data.PartName == A select new { data.ItemName } // to get all the items I need
But then, now that I have that list I need to use it to get all the rows for all items listed, and I can't seem to figure it out ...
Actual Source Code (for reference):
NOTE:
Recipe = ITEM
Ingredient = PART
(I was just trying to make it simpler)
ViewFullRecipeGrouping = (
from data in ViewRecipeSummary
group data by data.RecipeName into recipeGroup
let fullIngredientGroups = recipeGroup.GroupBy(x => x.IngredientName)
select new ViewFullRecipe()
{
RecipeName = recipeGroup.Key,
RecipeIngredients = (
from ingredientGroup in fullIngredientGroups
select new GroupIngredient()
{
IngredientName = ingredientGroup.Key
}
).ToList(),
ViewGroupRecipes = (
from data in ViewRecipeSummary
// this is where I am looking to add the new logic to define something I can then use within the next select statement that has the right data based on the information I got earlier in this query.
let a = ViewRecipeSummary.GroupBy(x => x.RecipeName)
.Where(g => g.Any(x => x.IngredientName == recipeGroup.Key))
.Select(g => new ViewRecipe()
{
RecipeName = g.Key,
IngredientName = g.Select(x => x.IngredientName)
})
select new GroupRecipe()
{
// use the new stuff here
}).ToList(),
}).ToList();
Any help would be much appreciated.
Thanks,
I believe this does what you want:
var data = /* enumerable containing rows in your table */;
var part = "X";
var items = new HashSet<int>(data
.Where(x => x.PartName == part)
.Select(x => x.ItemName));
var query = data.Where(x => items.Contains(x.ItemName));
If I understand your comment at the end, I believe this also does what you want:
var query = data
.GroupBy(x => x.ItemName)
.Where(g => g.Any(x => x.PartName == part))
.Select(g => new
{
ItemName = g.Key,
PartNames = g.Select(x => x.PartName)
});
I have a requirement to sort a list by 1) the number of times a distinct item appears and then 2) if the count of two distinct rows is the same, the most recently used date of that group.
My group by function and sorting by count is working without the date:
(from x in data
group x by new { x.Col1, x.Col2, x.Col3}
into g
let count = g.Count()
select new
{
g.Key.Col1,
g.Key.Col2,
g.Key.Col3,
count
}).OrderByDescending(x => x.count)
However, I have been unable to successfully add the date sort. I was trying to add the date column as an aggregate in the group by expression, but that doesn't work.
(from x in data
group x by new { x.Col1, x.Col2, x.Col3, MaxDate = x.CreatedDateTime.Max()}
into g
let count = g.Count()
select new
{
g.Key.Col1,
g.Key.Col2,
g.Key.Col3,
count,
g.Key.MaxDate
}).OrderByDescending(x => x.count).ThenByDescending(x => x.MaxDate)
I get why it doesn't work, I just can't think of another route to add the secondary sort. Any ideas are appreciated!
This is what you're looking for (I think)
from x in data
group x by new { x.Col1, x.Col2, x.Col3}
into g
let count = g.Count()
select new
{
g.Key.Col1,
g.Key.Col2,
g.Key.Col3,
MaxDate = g.Select(x => x.CreatedDateTime)
.OrderByDescending(d => d).FirstOrDefault(),
count
}).OrderByDescending(x => x.count).ThenByDescending(x => x.MaxDate)
How about:
var ordered = Elev8SnaTowelTables
.GroupBy(x => new { x.Col1, x.Col2, x.Col3 })
.OrderByDescending(g => g.Count())
.ThenByDescending(g => g.Max(x => x.CreatedDateTime));
I have this DB diagram and want to make a query to find all UserLists in a given region. RegionId is supplied.
So I can get all the departments by this code (may not be the best way..):
var region = context.Regions.Find(regionId);
IEnumerable<Department> departments = region.Areas
.SelectMany(a => a.Workplaces)
.SelectMany(w => w.Departments);
The Account can have many UserLists, and an Account can be linked to many Departments. Can someone formulate a queryto achieve this please?
for completeness the final code was:
List<UserList> query2 = context.Regions.Where(r => r.RegionId == regionId)
.SelectMany(r => r.Areas)
.SelectMany(a => a.Workplaces)
.SelectMany(w => w.Departments)
.SelectMany(d => d.AccountsAllowedToPost)
.Distinct()
.SelectMany(da => da.Lists).ToList();
You can use the let syntax (or the .Select method) to navigate the ManyToOne relationship.
var query =
from r in context.Regions
where r.RegionId == regionId
from a in r.Areas
from w in a.Workplaces
from d in w.Departments
from da in d.DepartmentAccounts
let acc = da.Account
from u in acc.UserLists
select u;
var query2 = context.Regions.Where(r => r.RegionId == regionId)
.SelectMany(r => r.Areas)
.SelectMany(a => a.Workplaces)
.SelectMany(w => w.Departments)
.SelectMany(d => d.DepartmentAccounts)
.Select(da => da.Account)
.SelectMany(acc => acc.UserLists);
I ended up with this horrible code below, I can't get a better result now.
What is a better way of doing that?
It's about this part of my database:
EDIT
A Patient has a Subscription to multiple MonitoringObjects. Target records refer to these Subscriptions. I want to retrieve the target records with the newest date per Subscription for a given Patient and a Category of MonitoringObjects. These target records may have different max dates, as Targets can be added for Subscriptions to MonitoringsObjects independently.
var subs = db.Subscriptions.Where(p => p.PatientID == patID).Where(p => p.MonitoringObject.Category.Name == "Medication");
var targets1 = from t in db.Targets
where subs.Contains(t.Subscription)
select t;
var maxTa = from t in db.Targets
group t by t.SubscriptionID
into g
select new
{
Ky = g.Key,
Date = g.Max(p => p.Date)
};
var targets2 = from t in targets1
where maxTa.Select(p => p.Ky).Contains( t.SubscriptionID ) &&
maxTa.Select(p => p.Date).Contains( t.Date )
select t;
I am not exactly sure what this is trying to achieve, or what your datamodel looks like, but something like this?
var subs = db.Subscriptions.Where(p => p.PatientID == patID).Where(p => p.MonitoringObject.Category.Name == "Medication");
var targets = subs
.SelectMany(s => s.Targets)
.Where(t => t.Date == t.Subscription.Targets.Max(_t => _t.Date))