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C# linq Contains method with List

I need help with Linq Contains method. Here's the code below.
This code does work but outputs an empty sets.
var query = _context.RegistrationCodes.Select(x => x);
if (request.OperatorId != null && request.OperatorId != Guid.Empty)
{
var checkOperator = _context.Operators.Include(a => a.OperatorLevel).Include(a => a.City).Include("City.StateRegion.Country").FirstOrDefault(a => a.Id == request.OperatorId);
List<String> Cities = new List<String>();
if (checkOperator.OperatorLevel.Name == "City")
{
Cities = await _context.Cities
.Where(a => (checkOperator.CityId) == (a.Id))
.Select(a => a.Code)
.ToListAsync();
}
else if (checkOperator.OperatorLevel.Name == "Regional")
{
Cities = await _context.Cities
.Where(a => checkOperator.City.StateRegionId == a.StateRegionId)
.Select(a => a.Code)
.ToListAsync();
}
else if (checkOperator.OperatorLevel.Name == "National")
{
List<Guid> StateRegion = await _context.StateRegions
.Where(a => checkOperator.City.StateRegion.CountryId == a.CountryId)
.Select(a => a.Id)
.ToListAsync();
Cities = await _context.Cities
.Where(a => StateRegion.Contains(a.StateRegionId))
.Select(a => a.Code)
.ToListAsync();
}
var nullableStrings = Cities.Cast<String?>().ToList();
query = query.Where(a => nullableStrings.Contains(a.Code));
}
I need to compare nullableStrings to a.Code which is something like this, but does not work.
query = query.Where(a => a.Code.Contains(nullableStrings));
Error : Argument 1: cannot convert from 'System.Collections.Generic.List' to 'char'
I need a method that would replace
query = query.Where(a => nullableStrings.Contains(a.Code));
A help would be appreciated. Thanks.

Looking at the code, my guess is the requirement is to get a list of operators depending on the current (check) operator's level. I suspect the issue you are encountering is that some cities may not have a code. You then want to apply all found codes to another query that you are building up.
My guess is that the crux of the problem is that some cities might not have a code, hence the concern for null-able strings, while others might have multiple codes hacked into a single-code intended field. The solution there would typically be to remove any null values
Firstly, this line:
var checkOperator = _context.Operators.Include(a => a.OperatorLevel).Include(a => a.City).Include("City.StateRegion.Country").FirstOrDefault(a => a.Id == request.OperatorId);
can be simplified to:
var checkOperator = _context.Operators
.Select(a => new
{
Level = a.OperatorLevel.Name,
CityId = a.City.Id,
CityCode = a.City.Code,
StateRegionId = a.City.StateRegion.Id,
CountryId = a.City.StateRegion.Country.Id
}).FirstOrDefault(a => a.Id == request.OperatorId);
This builds a faster query, rather than fetching an entire operator object graph, just select the fields from the object graph that we need.
Now to handle the operator level. Here I don't recommend trying to force every scenario into a single pattern. The goal is just to apply a filter to the built query, so have the scenarios do just that:
select (checkOperator.Level)
{
case "City":
query = query.Where(a => a.Code == checkOperator.CityCode);
break;
case "Regional":
var cityCodes = await _context.Cities
.Where(a => a.Code != null && a.StateRegion.Id == checkOperator.StateRegionId)
.Select(a => a.Code)
.ToListAsync();
query = query.Where(a => cityCodes.Contains(a.Code));
break;
case "Country":
var cityCodes = await _context.Cities
.Where(a => a.Code != null && a.StateRegion.Country.Id == checkOperator.CountryId)
.Select(a => a.Code)
.ToListAsync();
query = query.Where(a => cityCodes.Contains(a.Code));
break;
}
Now based on the comments it sounds like your data with cities and codes is breaking proper normalization where Code was intended as a 1-to-1 but later hacked to handle one city having multiple codes, so multiple values were concatenated with hyphens. (I.e. ABC-DEF) If this represents 2 Codes for the city then you will need to handle this..
private List<string> splitCityCodes(List<string> cityCodes)
{
if (cityCodes == null) throw NullReferenceException(nameof(cityCodes));
if (!cityCodes.Any()) throw new ArgumentException("At least one city code is expected.");
var multiCodes = cityCodes.Where(x => x.Contains("-")).ToList();
if (!multiCodes.Any())
return cityCodes;
var results = new List<string>(cityCodes);
results.RemoveRange(multiCodes);
foreach(var multiCode in multiCodes)
{
var codes = multiCode.Split("-");
results.AddRange(codes);
}
return results.Distinct();
}
That can probably be optimized, but the gist is to take the city codes, look for hyphenated values and split them up, then return a distinct list to remove any duplicates.
List<string> cityCodes = new List<string>();
select (checkOperator.Level)
{
case "City":
cityCodes = splitCityCodes(new []{checkOperator.CityCode}.ToList());
if(cityCodes.Count == 1)
query = query.Where(a => a.Code == cityCodes[0]);
else
query = query.Where(a => cityCodes.Contains(a.Code));
break;
case "Regional":
cityCodes = await _context.Cities
.Where(a => a.Code != null && a.StateRegion.Id == checkOperator.StateRegionId)
.Select(a => a.Code)
.ToListAsync();
cityCodes = splitCityCodes(cityCodes);
query = query.Where(a => cityCodes.Contains(a.Code));
break;
case "Country":
cityCodes = await _context.Cities
.Where(a => a.Code != null && a.StateRegion.Country.Id == checkOperator.CountryId)
.Select(a => a.Code)
.ToListAsync();
cityCodes = splitCityCodes(cityCodes);
query = query.Where(a => cityCodes.Contains(a.Code));
break;
}
... and I suspect that would about do it for handling the possibility of a city code containing multiple values.

If your search argument is in the form "ABC-DEF" and you want that to match "ABC" OR "DEF" then it can be done, but it is not clear from your data setup how that scenario comes about.
Lets assume these codes are airport codes, and that a city that has multiple airports has the City.Code as a hyphenated list of the Airport codes, then if the checkOperator is in Australia, and their OperatorLevel is "National" then this might build the following nullableStrings:
var Cities = new List<string> {
"PER",
"ADE",
"DRW",
"MEL-AVV",
"SYD",
"BNE",
"OOL",
"HBA"
};
If then your query is a listing of AirPorts and you want to search the airports by these codes, specifically to match both "MEL" and "AVV" then you can use syntax like this
var nullableStrings = Cities.Cast<String?>().ToList();
query = query.Where(ap => nullableStrings.Any(n => n.Contains(ap.Code)));
But if you intend this to be translated to SQL via LINQ to Entities (so be executed server-side) then we can make this query more efficient buy normalizing the search args so we can do an exact match lookup:
var nullableStrings = Cities.Where(x => !String.IsNullOrWhiteSpace (x))
.SelectMany(x => x.Split('-'))
.Cast<String?>()
.ToList();
query = query.Where(ap => nullableStrings.Contains(ap.Code));
As this routine is called as part of a larger set and your checkOperator goes out of scope, you should try to reduce the fields that you retrieve from the database to the specific set that this query needs through a projection
Using .Select() to project out specific fields can help improve the overall efficiency of the database, not just each individual query. If the additional fields are minimal or natural surrogate keys, and your projections are common to other query scenarios then they can make good candidates for specific index optimizations.
Instead of loading SELECT * from all these table in this include list:
var checkOperator = _context.Operators.Include(a => a.OperatorLevel)
.Include(a => a.City.StateRegion.Country)
.FirstOrDefault(a => a.Id == request.OperatorId);
So instead of all the fields from OperatorLevel, City, StateRegion, Country we can load just the fields that our logic needs:
var checkOperator = _context.Operators.Where(o => o.Id == request.OperatorId)
.Select(o => new {
OperatorLevelName = o.OperatorLevel.Name,
o.CityId,
o.City.StateRegionId,
o.City.StateRegion.CountryId
})
.FirstOrDefault();
So many of the EF has poor performance opinions out there stem from a lot of poorly defined examples that proliferate the web. Eagerly loading is the same as executing SELECT * FROM ... for simple tables it's only a bandwidth and memory waste, but for complex tables that have computed columns or custom expressions there can be significant server CPU costs.
It cannot be overstated the improvements that you can experience if you use projections to expose only the specific sub-set of the data that you need, especially if you will not be attempting to modify the results of the query.
Be a good corporate citizen, only take what you need!
So lets put this back into your logic:
if (request.OperatorId != null && request.OperatorId != Guid.Empty)
{
var checkOperator = _context.Operators.Where(o => o.Id == request.OperatorId)
.Select(o => new {
OperatorLevelName = o.OperatorLevel.Name,
o.CityId,
o.City.StateRegionId,
o.City.StateRegion.CountryId
})
.FirstOrDefault();
IQueryable<City> cityQuery = null;
if (checkOperator.OperatorLevelName == "City")
cityQuery = _context.Cities
.Where(a => checkOperator.CityId == a.Id);
else if (checkOperator.OperatorLevelName == "Regional")
cityQuery = _context. Cities
.Where(a => checkOperator.StateRegionId == a.StateRegionId);
else if (checkOperator.OperatorLevelName == "National")
cityQuery = _context. Cities
.Where(c => c.StateRegion.CountryId == checkOperator.CountryId);
// TODO: is there any default filter when operator level is something else?
if (cityQuery != null)
{
var nullableStrings = cityQuery.Select(a => a.Code)
.ToList()
.Where(x => !String.IsNullOrWhiteSpace(x))
.SelectMany(x => x.Split('-'))
.Cast<String?>()
.ToList();
query = query.Where(ap => nullableStrings.Contains(ap.Code));
}
}
If you don't want or need to normalize the strings, then you can defer this whole expression without realizing the city query at all:
// No nullable string, but we can still remove missing Codes
cityQuery = cityQuery.Where(c => c.Code != null);
query = query.Where(ap => cityQuery.Any(c => c.Code.Contains(ap.Code)));

Is there a way to simplify these linq statements using an .Include()?

Currently I am doing a keyword search on the Plates table (Name column) but also have a Search (searching on SearchTerm column) table which contains Plat Id's that I also want to search and return the corresponding platforms.
The code below works but I'd like to simplify the logic using an .Include statement if possible although I'm not quite sure how. Any help would be greatly appreciated.
if (!string.IsNullOrEmpty(request.Keyword))
{
var searchTermPlateIds = await _db.Search
.Where(x=> x.SearchTerm.ToLower().Contains(request.Keyword.Trim().ToLower()))
.Select(x => x.PlatformId)
.ToListAsync(ct);
var plateFromPlateIds = await _db.Plate
.OrderBy(x => x.Name)
.Where(x => searchTermPlateIds.Contains(x.Id) && x.Status != PlateStatus.Disabled)
.ToListAsync(ct);
plates = await _db.Plates
.OrderBy(x => x.Name)
.Where(x => !string.IsNullOrEmpty(request.Keyword.Trim()) && x.Name.ToLower().Contains(request.Keyword.Trim().ToLower()) && x.Status != PlateStatus.Disabled)
.ToListAsync(ct);
plates = plates.Union(platesFromPlateIds).ToList();
}

Remember simple thing, Include ONLY for loading related data, not for filtering.
What we can do here - optimize query, to make only one request to database, instead of three.
var query = _db.Plates
.Where(x => x.Status != PlateStatus.Disabled);
if (!string.IsNullOrEmpty(request.Keyword))
{
// do not materialize Ids
var searchTermPlateIds = _db.Search
.Where(x => x.SearchTerm.ToLower().Contains(request.Keyword.Trim().ToLower()))
.Select(x => x.PlatformId);
// queryable will be combined into one query
query = query
.Where(x => searchTermPlateIds.Contains(x.Id);
}
// final materialization, here you can add Includes if needed.
var plates = await query
.OrderBy(x => x.Name)
.ToListAsync(ct);

Include datatable in existing linq query

I have the below piece of code which gives my time zones as per each country
var zones = TzdbDateTimeZoneSource.Default
.ZoneLocations
.Where(x => x.CountryCode == countryCode)
.Select(x => x.ZoneId);
Now i need to include datatable within the above linq query to check if that datatable have the zone locations in database already as explained in below code. How do i do that ?
var zones = TzdbDateTimeZoneSource.Default
.ZoneLocations
.Where(x => x.CountryCode == countryCode &&
oratznamesoratznames.Select().ToList()
.Exists(row => row["TZNAME"].ToString().ToUpper() == x.ZoneId))
.Select(x => x.ZoneId);

Id I understand your question correcty, you could use .Any(). It returns a boolean indicating where any of the elements of the collection matches the predicate.
Also, note that there is no need to use && in this case.
var zones = TzdbDateTimeZoneSource.Default
.ZoneLocations
.Where(x => x.CountryCode == countryCode)
.Select(x => x.ZoneId)
.Where(x => oratznamesoratznames
.Any(r => r["TZNAME"].ToString().ToUpper() == x))

If/else selected count from sql database

What I'm doing now is getting my SQL database table: IsAcross varchar(45) into my if/else statement. My IsAcross table only consist of YES and NO.
So now I want to take out only select YES statement from SQL Server, so therefore I have put the thingy in the whole list first. Then I use if/else statement to extract out the YES but how am I supposed to do that?
Example: I have a total of 7 items in a list, 4 yes 3 no. I want to take out the all the 4 yes only. Something like that:
ViewModels.WordSearchVM wsvm = new ViewModels.WordSearchVM();
wsvm.ActivityID = id;
var results = db.CrossPuzzles.Where(m => m.ActivityID == id)
.Select(m => m.IsAcross)
.AsEnumerable()
.ToList();
if (results = "yes")
{
else
}

As far as I understand your problem, you can forget your if statement and simply extend the .Where part:
.Where(m => m.ActivityID == id && m.results=="yes")

var results = db.CrossPuzzles.Where(m => m.ActivityID == id)
.Where(m => m.IsAcross)
.AsEnumerable()
.ToList();
//OR
var results = db.CrossPuzzles.Where(m => m.ActivityID == id)
.Where(m => m.IsAcross == "YES")
.AsEnumerable()
.ToList();

var results = db.CrossPuzzles
.Where(m => m.ActivityID == id)
.Select(m => m.IsAcross)
.Where(x => x == "YES") // filter to "YES"
.ToList();
if (results.Count > 0)
// YES
else
// NO
This what you're looking for?

syntax in LINQ IEnumerable<string>

This is my code that works great:
IPRepository rep = new IPRepository();
var Q = rep.GetIp()
.Where(x => x.CITY == CITY)
.GroupBy(y => o.Fam)
.Select(z => new IpDTO
{
IId = z.Key.Id,
IP = z.Select(x => x.IP).Distinct()
});
IP is IEnumerable<string>
I need to add to this code above a call to a function PAINTIP(ip).
I need to send each one of the elements that will be inside IP to a function PAINTIP(ip).
therefore i need to use some kind of foreach function but i cannot figure out how.

rep.GetIp()
.Where(x => x.CITY == CITY)
.GroupBy(y => o.Fam)
.Select(z => new IpDTO
{
IId = z.Key.Id,
IP = z.Select(x => x.IP).Distinct()
})
.SelectMany(item => item.IP)
.ToList()
.ForEach(PAINTIP)

You can do something like this :
var result = from item in collection
.Where(i => i.condition == value)
.Select(i => new{ Name = i.name, Description = i.Description })
.ToList().ForEach(i => Function(i));
Hope this help !

Very similiar to the answer of this question
LINQ equivalent of foreach for IEnumerable<T>
There is no For Each for an IEnumerable but there is for List
items.ToList().ForEach(i => i.DoStuff());
Edit
I'm not sure you can do it in the way you want to other than this:
ep.GetIp()
.Where(x => x.CITY == CITY)
.GroupBy(y => o.Fam)
.Select(z => new IpDTO
{
IId = z.Key.Id,
IP = z.Select(x => x.IP).Distinct()
})
.ToList().ForEach(IpObj => IpObj.IP.ToList().ForEach(ip => PAINTIP(ip));
This way you get your list of IpDTO objects out first. Then Enumerate over each and then in turn over each IpDTO objects IP IEnumerable. I haven't seen a way to do it where you can Enumerate inside the creation of your IpDTO object. If someone has an example of how to do so I'd like to see to learn myself.