I have a Database with schools, and each school is in a City.
Now I want to create a dictionary that contains all the cities of each schoool. To achieve this I tried this approach:
var schoolCities = schoolsWithAddresses.Where(school => school.Address.City != null).ToDictionary(sc => sc.Address.City.Name.ToLower());
Now, the problem with this is that a City can have multiple schools. So, when I create my dictionary, I end up with an exception "Repeated Key".
I want to create a dicitonary because it will allow me to make a very quick lookup on the cities that have schools (that is why I am not using a List, for example).
How do I overcome this problem in a way rhat allows me to still make efficient lookups?
Use the ToLookUp extension method rather
var schoolCities = schoolsWithAddresses
.Where(school => school.Address.City != null)
.ToLookup(sc => sc.Address.City.Name.ToLower());
You should group the items first, so that you have unique cities.
schoolsWithAddresses.Where(school => school.Address.City != null)
.GroupBy(s => s.Address.City, (k, v) => new { City = k, Schools = v })
.ToDictionary(d => d.City, e => e.Schools)
;
Something like this:
Dictionary<string, List<School>> schoolCities = schoolsWithAddresses
.Where(school => school.Address.City != null)
.GroupBy(school => school.Address.City)
.ToDictionary(group => group.Key, group => group.ToList());
I think what you want is a Lookup:
Represents a collection of keys each mapped to one or more values.
Example usage:
Lookup<string, School> schoolCities = schoolsWithAddresses
.Where(school => school.Address.City != null)
.ToLookup(school => school.Address.City);
IEnumerable<School> schoolsInLondon = schoolCities["London"];
try this
var schoolCities = schoolsWithAddresses
.GroupBy(x => x.city!=null)
.ToDictionary(x => x.Key, x => x.ToList());
Related
I want to get all the Pre_Number where all Reconcile_Status related to that Pre_Number=null. In this case there should not be any item in list.If there would be some other Pre_number for eg. 7/2018 and it has two records and Reconcile_Status for those records is NULL then i should get one item in list that is 7/2018.
I tried
var NoNReconciled = context.tbl_prerelease_invoice
.Where(x => x.Reconcile_Status==null)
.Select(y => new { y.Pre_number }).Distinct().ToList();
But i got 6/2018
Well, your current attempt only checks that there is at least one record where Reconcile_Status is null, but it doesn't check that there are no records with the same Pre_number where Reconcile_Status is not null.
This should do the trick:
var NoNReconciled = context.tbl_prerelease_invoice
.Where(x => x.Reconcile_Status == null &&
!context.tbl_prerelease_invoice
.Any(y => y.Pre_number == x.Pre_number && y.Reconcile_Status != null)
).Select(y => new { y.Pre_number })
.Distinct().ToList();
No need to create anonymous object for Pre_Number. Try below code
var NoNReconciled = context.tbl_prerelease_invoice
.Where(x => x.Reconcile_Status==null)
.Select(y => y.Pre_number).Distinct().ToList();
Try this-
context.tbl_prerelease_invoice.GroupBy(r => r.Pre_number).Where(kv => kv.All(r => r.Reconcile_Status==null)).Select(kv => kv.Key).ToList();
I need to use equal instead of Contains.
I have an array of codes called selectedDeviceTypeIDs i assume it has two codes {1,2}
I need get result from the query if Devices ids are exactly {1,2} so i have replace selectedDeviceTypeIDs.Contains with selectedDeviceTypeIDs.equal or something like that ...
m => m.Devices.Any(w => selectedDeviceTypeIDs.Contains(w.DeviceTypeID)
if (DeviceTypeIDs != null)
{
Guid[] selectedDeviceTypeIDs = DeviceTypeIDs.Split(',').Select(Guid.Parse).ToArray();
query = query.Where(j => j.HospitalDepartments.Any(jj => jj.Units.Any(m => m.Devices.Any(w => selectedDeviceTypeIDs.Contains(w.DeviceTypeID)))));
}
Use !.Except().Any() to make sure m.Devices doesn't contains any DeviceTypeID not present in selectedDeviceTypeIDs
query = query.Where(j => j.HospitalDepartments.Any(jj => jj.Units
.Where(m => !m.Devices.Select(w => w.DeviceTypeID).Except(selectedDeviceTypeIDs).Any())));
Option 1:
If you care about the Order of the items, use SequenceEqual extension method. This will return false, even if the collection has the items but in different order
m => m.Devices.Any(w => selectedDeviceTypeIDs.SequenceEqual(w.DeviceTypeID)
Option 2:
If you don't care about the order , use All extension method. This will return true, if the items in both collections are same irrespective of the order.
m => m.Devices.Any(w => selectedDeviceTypeIDs.All(w.DeviceTypeID.Contains)
You need to check if the selectedDeviceTypeIDs contains every device, and that every device contains selectedDeviceTypeIDs. You could use this:
query = query
.Where(j =>
j.HospitalDepartments.Any(jj =>
jj.Units.Any(m =>
m.Devices.All(
w => selectedDeviceTypeIDs.Contains(w.DeviceTypeID))
&&
selectedDeviceTypeIDs.All(
g => m.Devices.Select(d => d.DeviceTypeID).Contains(g))
)
)
);
To get a performance gain, I am trying to replace the call to Distinct() below with GroupBy(...), however I am getting errors.
Any suggestions on how this query should be rewritten to use GroupBy(...)?
I am trying to use GroupBy() on the Description field itself.
var result=
GetResults()
.Select(x => new SelectList { Text = x.Description, Value = x.Description })
.Where(x => x.Text != null)
.Distinct()
.ToList();
You can't force the Entity Framework to use GroupBy instead of Distinct clause in generated SQL. Entity framework will determine the appropriate query and it will use that.
One thing that is apparent from your code is that you are only interested in List<string> based on unique Description values. I don't think you have to create a collection of SelectList.
You can do:
var result= GetResults()
.Where(x => x.Description != null)
.GroupBy(x => x.Description)
.Select(grp => grp.Key)
.ToList();
OR
var result= GetResults()
.Where(x => x.Description != null)
.Select(x => x.Description)
.Distinct()
.ToList();
Both of the above queries would produce a list of unique description values. Now what type of SQL will be generated against both of these depends on the Entity Framework.
Old Answer:
Use GroupBy to group on Description and then Select where Key is not null like:
var result= GetResults()
.Select(x => new SelectList { Text = x.Description, Value = x.Description })
.Where(x => x.Text != null)
.GroupBy(x => x.Value) //Here select Value for Description
.Select(grp => grp.Key)
.ToList();
This will not give you any performance gain, even if there is any, it would be negligible.
You can yry grouping by Description:
var result=GetResults()
.GroupBy(x => x.Description)
.Where(g => g.Key != null)
.Select(g => new SelectList { Text = g.Key, Value = g.Key })
.ToList();
But I'd be surprised if you got better performance that a Distinct.
If I have a set of entities with 3 properties (Id, Type, Size) all of which are strings.
Is there a way using Linq to Entities where I can do a group query which gives me the Size + Type as the key and then a list of the related Id's for that Size + Type?
Example below of getting the count:
Items.GroupBy(x => new { x.Size, x.Type})
.Select(x => new { Key = x.Key, Count = x.Count() })
but I am looking to get a list of the Ids for each grouping?
I am looking to see if it is possible using Linq-to-EF before I decide to iterate through this in code and build up the result instead.
If you want to get List of Ids for each group then you have to select x.Select(r => r.Id) like:
var result = Items.GroupBy(x => new { x.Size, x.Type })
.Select(x => new
{
Key = x.Key,
Ids = x.Select(r => r.Id)
});
Another way to build up a Dictionary<string, IEnumerable<string?>> in dotnet 6.0 according to the docs;
where we have the dictionary Key as {Size, Type} and Value the list of Ids, you can write:
Dictionary<string, IEnumerable<string?>> result = Items.GroupBy(item => new { item.Size, item.Type }
item => item.Id),
(itemKey, itemIds) =>
{
Key = itemKey,
Ids = itemIds
})
.ToDictionary(x => x.Key, x=> x.Ids);
In my MVC app I am using 2 dictionaries to populate SelectList for DropDownList. Those dictionaries will be supplied with dates as string and datetime values.
I have this chunk of code for the first dictionary that works just fine:
if (m_DictDateOrder.Count == 0)
{
m_DictDateOrder = new Dictionary<string, DateTime>();
m_DictDateOrder =
m_OrderManager.ListOrders()
.OrderBy(x => x.m_OrderDate)
.Distinct()
.ToDictionary(x => x.m_OrderDate.ToString(), x => x.m_OrderDate);
}
But when I get to the second dictionary:
if (m_DictDateShipped.Count == 0)
{
m_DictDateShipped = new Dictionary<string, DateTime>();
m_DictDateShipped =
m_OrderManager.ListOrders()
.OrderBy(x => x.m_ShippedDate)
.Distinct()
.ToDictionary(x => x.m_ShippedDate.ToString(), x => x.m_ShippedDate);
}
I get a runtime error on the LINQ request for the second dictionary:
An item with the same key has already been added.
I first though that I add to instantiate a new dictionary (that's the reason for the "new" presence), but nope. What did I do wrong?
Thanks a lot!
You are Distinct'ing the rows, not the dates.
Do this instead:
if (m_DictDateShipped.Count == 0)
{
m_DictDateShipped = m_OrderManager.ListOrders()
//make the subject of the query into the thing we want Distinct'd.
.Select(x => x.m_ShippedDate)
.Distinct()
.ToDictionary(d => d.ToString(), d => d);
}
Don't bother sorting. Dictionary is unordered.
My standard pattern for this (since I have disdain for Distinct) is:
dictionary = source
.GroupBy(row => row.KeyProperty)
.ToDictionary(g => g.Key, g => g.First()); //choose an element of the group as the value.
You applied the Distinct to the order, not to the date. Try
m_OrderManager.ListOrders()
.OrderBy(x => x.m_ShippedDate)
.Select(x =>x.m_ShippedDate)
.Distinct()
.ToDictionary(x => x.ToString(), x => x);