Develop Reference

ASP.NET Core Linq query for lists

I have this query that was recently changed to allow searches using lists. However, the logic doesn't seem correct. My initial search logic was as follows:
data = data.where(u=>u.location.contains(FilterInput.RepositoryName)).ToList();
This worked for individual inputs and the logic made sense. In the data result, check if location field contains the Input variable
However in order to handle inputs that are lists, I had to change it to the bottom code which is in this Input list, check if the it contains the location field.
The database outputs data as follows:
Output = {arhde, brhje, ckio}
That means my list input is a small section of what the database contains.
FilterInput.RepositoryName = {a,b,c}
data = (from item in dbContext.Documents
join id in initialData
on item.Id equals id.DocumentId
select new DocumentsListViewModel
{
Id = item.Id,
Name = item.Name,
ApplicationName = item.ApplicationName,
ApplicationSecretKey = item.ApplicationSecretKey,
Link = item.Link,
Location = item.Location,
FileType = item.FileType,
CreatedOn = item.CreatedOn
}).ToList();
if (FilterInput.RepositoryName.Count>0)
{
data = data.Where(u => FilterInput.RepositoryName.Contains(u.Location)).ToList();
}
I don't know if its possible to change this logic to use the first one but accomodate lists as well?

Speeding up a linq query with 40,000 rows

In my service, first I generate 40,000 possible combinations of home and host countries, like so (clientLocations contains 200 records, so 200 x 200 is 40,000):
foreach (var homeLocation in clientLocations)
{
foreach (var hostLocation in clientLocations)
{
allLocationCombinations.Add(new AirShipmentRate
{
HomeCountryId = homeLocation.CountryId,
HomeCountry = homeLocation.CountryName,
HostCountryId = hostLocation.CountryId,
HostCountry = hostLocation.CountryName,
HomeLocationId = homeLocation.LocationId,
HomeLocation = homeLocation.LocationName,
HostLocationId = hostLocation.LocationId,
HostLocation = hostLocation.LocationName,
});
}
}
Then, I run the following query to find existing rates for the locations above, but also include empty the missing rates; resulting in a complete recordset of 40,000 rows.
var allLocationRates = (from l in allLocationCombinations
join r in Db.PaymentRates_AirShipment
on new { home = l.HomeLocationId, host = l.HostLocationId }
equals new { home = r.HomeLocationId, host = (Guid?)r.HostLocationId }
into matches
from rate in matches.DefaultIfEmpty(new PaymentRates_AirShipment
{
Id = Guid.NewGuid()
})
select new AirShipmentRate
{
Id = rate.Id,
HomeCountry = l.HomeCountry,
HomeCountryId = l.HomeCountryId,
HomeLocation = l.HomeLocation,
HomeLocationId = l.HomeLocationId,
HostCountry = l.HostCountry,
HostCountryId = l.HostCountryId,
HostLocation = l.HostLocation,
HostLocationId = l.HostLocationId,
AssigneeAirShipmentPlusInsurance = rate.AssigneeAirShipmentPlusInsurance,
DependentAirShipmentPlusInsurance = rate.DependentAirShipmentPlusInsurance,
SmallContainerPlusInsurance = rate.SmallContainerPlusInsurance,
LargeContainerPlusInsurance = rate.LargeContainerPlusInsurance,
CurrencyId = rate.RateCurrencyId
});
I have tried using .AsEnumerable() and .AsNoTracking() and that has sped things up quite a bit. The following code shaves several seconds off of my query:
var allLocationRates = (from l in allLocationCombinations.AsEnumerable()
join r in Db.PaymentRates_AirShipment.AsNoTracking()
But, I am wondering: How can I speed this up even more?
Edit: Can't replicate foreach functionality in linq.
allLocationCombinations = (from homeLocation in clientLocations
from hostLocation in clientLocations
select new AirShipmentRate
{
HomeCountryId = homeLocation.CountryId,
HomeCountry = homeLocation.CountryName,
HostCountryId = hostLocation.CountryId,
HostCountry = hostLocation.CountryName,
HomeLocationId = homeLocation.LocationId,
HomeLocation = homeLocation.LocationName,
HostLocationId = hostLocation.LocationId,
HostLocation = hostLocation.LocationName
});
I get an error on from hostLocation in clientLocations which says "cannot convert type IEnumerable to Generic.List."

The fastest way to query a database is to use the power of the database engine itself.
While Linq is a fantastic technology to use, it still generates a select statement out of the Linq query, and runs this query against the database.
Your best bet is to create a database View, or a stored procedure.
Views and stored procedures can easily be integrated into Linq.
Material Views ( in MS SQL ) can further speed up execution, and missing indexes are by far the most effective tool in speeding up database queries.

How can I speed this up even more?
Optimizing is a bitch.
Your code looks fine to me. Make sure to set the index on your DB schema where it's appropriate. And as already mentioned: Run your Linq against SQL to get a better idea of the performance.
Well, but how to improve performance anyway?
You may want to have a glance at the following link:
10 tips to improve LINQ to SQL Performance
To me, probably the most important points listed (in the link above):
Retrieve Only the Number of Records You Need
Turn off ObjectTrackingEnabled Property of Data Context If Not
Necessary
Filter Data Down to What You Need Using DataLoadOptions.AssociateWith
Use compiled queries when it's needed (please be careful with that one...)

Linq-to-Entities return list along with average of ratings infor each item

I am returning a list of restaurants that pulls information from the RESTAURANT, CUISINE, CITY, and STARRATING tables. I want to get a list of each restaurant with its associated city and cuisine along with the average rating in the STARRATING table. This is what I have, so far ... Thanks in advance.
RestaurantsEntities db = new RestaurantsEntities();
public List<RESTAURANT> getRestaurantsWRating(string cuisineName, string cityName, string priceName, string ratingName)
{
var cuisineID = db.CUISINEs.First(s => s.CUISINE_NAME == cuisineName).CUISINE_ID;
List<RESTAURANT> result = (from RESTAURANT in db.RESTAURANTs.Include("CITY").Include("CUISINE").Include("STARRATING")
where RESTAURANT.CUISINE_ID == cuisineID
orderby RESTAURANT.REST_NAME ascending
select RESTAURANT).ToList();
return result;
}

From what you have it looks like Restaurant has a STARRATING collection. If so, this is what you can do:
from r in db.Restaurants
where r.CUISINE_ID == cuisineID
orderby r.REST_NAME ascending
select new {
Restaurant = r,
City = r.CITY,
Cuisine = r.CUISINE,
AvgRating = r.STARRATING.Average(rt => rt.Rating)
}
You'd need to give more informations about your classes and associations (preferably a class diagram) if this is not right.
(BTW using capitals for class and property names is not conventional).

First I would wrap your whole code block above in a using statement:
using(RestaurantEntities db = new RestaurantEntities())
{
...
}
This will help with cleanup for the EF context.
The way I would typically do this is if you have control of your database, I would create a view in the database that does this work, add the view to your entity model and query the view. This simplifies the whole process and offloads the work of the aggregation to the database.
If you don't have control over the database or don't prefer the view technique then I would query using the include technique as you have done and then add a partial class to RESTAURANT (if using model-first) in order to add an AverageRating property and then manually calculate the average for each related STARRATING set of related rows and apply the resultant value to the added property. You could do this through linq to objects once you have all the data back. This technique would not scale very well as more data is accumulated unless you are confident you never return but one or a few RESTAURANT instances. You could use something like:
//query data as you have done above...
foreach(RESTAURANT r in result)
{
if(r.STARRATING.Count() > 0)
{
r.AverageRating = r.STARRATING.Average(rating => rating.Value); //.Value is your field name
}
else
{
r.AverageRating = 0; // or whatever default you prefer...
}
}
Hope this helps.

Error from use of C# Linq SQL CONCAT

I have the following three tables, and need to bring in information from two dissimilar tables.
Table baTable has fields OrderNumber and Position.
Table accessTable has fields OrderNumber and ProcessSequence (among others)
Table historyTable has fields OrderNumber and Time (among others).
.
var progress = from ba in baTable
from ac in accessTable
where ac.OrderNumber == ba.OrderNumber
select new {
Position = ba.Position.ToString(),
Time = "",
Seq = ac.ProcessSequence.ToString()
};
progress = progress.Concat(from ba in baTable
from hs in historyTable
where hs.OrderNumber == ba.OrderNumber
select new {
Position = ba.Position.ToString(),
Time = String.Format("{0:hh:mm:ss}", hs.Time),
Seq = ""
});
int searchRecs = progress.Count();
The query compiles successfully, but when the SQL executes during the call to Count(), I get an error
All queries combined using a UNION, INTERSECT or EXCEPT operator must have an equal number of expressions in their target lists.
Clearly the two lists each have three items, one of which is a constant. Other help boards suggested that the Visual Studio 2010 C# compiler was optimizing out the constants, and I have experimented with alternatives to the constants.
The most surprising thing is that, if the Time= entry within the select new {...} is commented out in both of the sub-queries, no error occurs when the SQL executes.

I actually think the problem is that Sql won't recognize your String.Format(..) method.
Change your second query to:
progress = progress.Concat(from ba in baTable
from hs in historyTable
where hs.OrderNumber == ba.OrderNumber
select new {
Position = ba.Position.ToString(),
Time = hs.Time.ToString(),
Seq = ""
});
After that you could always loop trough the progress and format the Time to your needs.

Efficient Way To Query Nested Data

I have need to select a number of 'master' rows from a table, also returning for each result a number of detail rows from another table. What is a good way of achieving this without multiple queries (one for the master rows and one per result to get the detail rows).
For example, with a database structure like below:
MasterTable:
- MasterId BIGINT
- Name NVARCHAR(100)
DetailTable:
- DetailId BIGINT
- MasterId BIGINT
- Amount MONEY
How would I most efficiently populate the data object below?
IList<MasterDetail> data;
public class Master
{
private readonly List<Detail> _details = new List<Detail>();
public long MasterId
{
get; set;
}
public string Name
{
get; set;
}
public IList<Detail> Details
{
get
{
return _details;
}
}
}
public class Detail
{
public long DetailId
{
get; set;
}
public decimal Amount
{
get; set;
}
}

Normally, I'd go for the two grids approach - however, you might also want to look at FOR XML - it is fairly easy (in SQL Server 2005 and above) to shape the parent/child data as xml, and load it from there.
SELECT parent.*,
(SELECT * FROM child
WHERE child.parentid = parent.id FOR XML PATH('child'), TYPE)
FROM parent
FOR XML PATH('parent')
Also - LINQ-to-SQL supports this type of model, but you need to tell it which data you want ahead of time. Via DataLoadOptions.LoadWith:
// sample from MSDN
Northwnd db = new Northwnd(#"c:\northwnd.mdf");
DataLoadOptions dlo = new DataLoadOptions();
dlo.LoadWith<Customer>(c => c.Orders);
db.LoadOptions = dlo;
var londonCustomers =
from cust in db.Customers
where cust.City == "London"
select cust;
foreach (var custObj in londonCustomers)
{
Console.WriteLine(custObj.CustomerID);
}
If you don't use LoadWith, you will get n+1 queries - one master, and one child list per master row.

It can be done with a single query like this:
select MasterTable.MasterId,
MasterTable.Name,
DetailTable.DetailId,
DetailTable.Amount
from MasterTable
inner join
DetailTable
on MasterTable.MasterId = DetailTable.MasterId
order by MasterTable.MasterId
Then in psuedo code
foreach(row in result)
{
if (row.MasterId != currentMaster.MasterId)
{
list.Add(currentMaster);
currentMaster = new Master { MasterId = row.MasterId, Name = row.Name };
}
currentMaster.Details.Add(new Detail { DetailId = row.DetailId, Amount = row.Amount});
}
list.Add(currentMaster);
There's a few edges to knock off that but it should give you the general idea.

select < columns > from master
select < columns > from master M join Child C on M.Id = C.MasterID

You can do it with two queries and one pass on each result set:
Query for all masters ordered by MasterId then query for all Details also ordered by MasterId. Then, with two nested loops, iterate the master data and create a new Master object foreach row in the main loop, and iterate the details while they have the same MasterId as the current Master object and populate its _details collection in the nested loop.

Depending on the size of your dataset you can pull all of the data into your application in memory with two queries (one for all masters and one for all nested data) and then use that to programatically create your sublists for each of your objects giving something like:
List<Master> allMasters = GetAllMasters();
List<Detail> allDetail = getAllDetail();
foreach (Master m in allMasters)
m.Details.Add(allDetail.FindAll(delegate (Detail d) { return d.MasterId==m.MasterId });
You're essentially trading memory footprint for speed with this approach. You can easily adapt this so that GetAllMasters and GetAllDetail only return the master and detail items you're interested in. Also note for this to be effective you need to add the MasterId to the detail class

This is an alternative you might consider. It does cost $150 per developer, but time is money too...
We use an object persistence layer called Entity Spaces that generates the code for you to do exactly what you want, and you can regenerate whenever your schema changes. Populating the objects with data is transparent. Using the objects you described above would look like this (excuse my VB, but it works in C# too):
Dim master as New BusinessObjects.Master
master.LoadByPrimaryKey(43)
Console.PrintLine(master.Name)
For Each detail as BusinessObjects.Detail in master.DetailCollectionByMasterId
Console.PrintLine(detail.Amount)
detail.Amount *= 1.15
End For
With master.DetailCollectionByMasterId.AddNew
.Amount = 13
End With
master.Save()