Develop Reference

C# LINQ value substitution

I have two tables with the following layout
username | displayname username| FirstName | surname
---------|------------ -----------------------------
foo test foo | andrew | blah
fa display
What I'm trying to do is display all of the displayname entries in the left hand table on my page. However, if there is a match on the username in the right hand table, I want the value test to be replaced by andrew.
Example out:
username | displayname
---------|------------
foo andrew
fa display
Everything is a string.
Below is my attempt at what I need but I've messed it up as its applying the firstname value to every entry in my first table.
_users = UserService.GetAll().ToList();
_updates = UserUpdateService.GetAll().ToList();
foreach (var user in _users)
{
foreach (var update in _updates)
if (user.FirstName != "" && user.UserName == update.UserName)
{
update.DisplayName = user.FirstName;
}
else
{
update.DisplayName = user.UserName;
}
}
Is there a way to do this with a single LINQ query?

As mentioned in the comment by #HimBromBeere which I also agree that --- LINQ is just syntactic sugar, it adds absoluetely no behaviour to your code.
As to write different style of writing you can use the below code which uses few Linq operators
_users = UserService.GetAll().ToList();
_updates = UserUpdateService.GetAll().ToList();
_updates.ForEach(u =>
{
var record == _users.FirstOrDefault(us => !string.IsNullOrEmpty(us.FirstName) && string.Equals(us.UserName, u.UserName));
u.DisplayName = record != null ? record.FirstName : u.DisplayName;
});

It won't be exactly as you posted, because we are going to be creating new instances instead of modifying existing ones, but you can do this query:
var table = _users
.Select(user => new {
user.UserName,
DisplayName = _updates.Any(update =>
user.FirstName != "" && user.UserName == update.UserName)
? user.FirstName
: user.UserName
})
);

This is ordinal LINQ query with LEFT JOIN, don't try to do that with lists.
var users = UserService.GetAll();
var updates = UserUpdateService.GetAll();
var query =
from update in updates
join user in users on user.UserName equals update.UserName into gj
from user in gj.DefaultIfEmpty()
select new
{
update.UserName,
DisplayName = !string.IsNullOrEmpty(user.FirstName) ? user.FirstName : update.DisplayName
};
var result = query.ToList();

LInq query return value specific field

I have 2 tables as follows :
CatTable
CatCode
CatName
DogTable
DogCode
CatCode
NameCode
So I would like to write down a query where return me the list of all data present in the table CatTable
PLUS if in the Table DogTable the value in the field “CatCode” is the same of CatTable.CatCode and the field “NameCode” is Empty then should return a value "false" in the field “DogTable.CatCode”
Example
var query = from c in CatTable
from d in DogTable
where c.CatCode == d.CatCode
select new { c.CatCode, c.CatName, d.CatCode }
Do you have any suggestion about that?

a simple version is to use the Any to return the boolean of the logic you want on that last field
var query = CatTable.Select(ct => new
{
CatCode = ct.CatCode,
CatName = ct.CatName,
DogCatCode = !DogTable.Any(dt => dt.CatCode == ct.CatCode && dt.NameCode == "")
});

Join table with object list

I have a table, lets say tblCar with all the related columns like Id, Make, Model, Color etc.
I have a search model for car containing two params Id and Model.
public class CarSearch
{
public int Id { get; set; }
public string Model { get; set; }
}
var carSearchObjets = new List<CarSearch>();
With list of primitive data (like Id list), to get cars with those Ids I could have done:
var idList = new List<int> { 1, 2, 3 };
var carsFromQuery = context.Cars.Where(x => idList.Contains(x.Id);
But if I have to fetch all the cars with Id and model from the list, how do I do it? Simple join cannot be done between in memory objects and tables.
I need something like,
from m in context.Cars
join n in carSearchObjets
on new { Id = n.Id, Model = n.Model } equals new { Id = m.Id, Model = m.Model }
select m;
This obviously won't work.
Please ignore any typos.And if you need more info or the question is not clear, let me know.

One (ugly-but-working) way to manage that is to use concatenation with a "never used" concat char.
I mean a char that should never appear in the datas. This is always dangerous, as... never is never sure, but you've got the idea.
For example, we'll say that our "never used" concat char will be ~
This is not good for perf, but at least working :
var carSearchObjectsConcatenated = carSearchObjets.Select(m => new { m.Id + "~" + m.Model});
then you can use Contains again (concatenating on the db too) : you'll need to use SqlFunctions.StringConvert if you wanna concatenate string and numbers on the db side.
var result = context.Cars.Where(m =>
carSearchObjectsConcatenated.Contains(SqlFunctions.StringConvert((double)m.Id) + "~" + m.Model);
EDIT
Another solution would be to use PredicateBuilder, as mentionned by Sorax, or to build your own Filter method if you don't want a third party lib (but PredicateBuilder is really fine).
Something like that in a static class :
public static IQueryable<Car> FilterCars(this IQueryable<Car> cars, IEnumerable<SearchCar> searchCars)
{
var parameter = Expression.Parameter(typeof (Car), "m");
var idExpression = Expression.Property(parameter, "Id");
var modelExpression = Expression.Property(parameter, "Model");
Expression body = null;
foreach (var search in searchCars)
{
var idConstant = Expression.Constant(search.Id);
var modelConstant = Expression.Constant(search.Model);
Expression innerExpression = Expression.AndAlso(Expression.Equal(idExpression, idConstant), Expression.Equal(modelExpression, modelConstant));
body = body == null
? innerExpression
: Expression.OrElse(body, innerExpression);
}
var lambda = Expression.Lambda<Func<Car, bool>>(body, new[] {parameter});
return cars.Where(lambda);
}
usage
var result = context.Cars.FilterCars(carSearchObjets);
this will generate an sql looking like
select ...
from Car
where
(Id = 1 And Model = "ax") or
(Id = 2 And Model = "az") or
(Id = 3 And Model = "ft")

'PredicateBuilder' might be helpful.
var predicate = PredicateBuilder.False<Car>();
carSearchObjects
.ForEach(a => predicate = predicate.Or(p => p.Id == a.Id && p.Model == a.Model));
var carsFromQuery = context.Cars.AsExpandable().Where(predicate);
Note the text in the link regarding EF:
If you're using Entity Framework, you'll need the complete LINQKit -
for the AsExpandable functionality. You can either reference
LINQKit.dll or copy LINQKit's source code into your application.

Old school solution..
//in case you have a
List<CarSearch> search_list; //already filled
List<Cars> cars_found = new List<Cars>();
foreach(CarSearch carSearch in search_list)
{
List<Cars> carsFromQuery = context.Cars.Where(x => x.Id == carSearch.Id && x.Model == carSearch.Model).ToList();
cars_found.AddRange(carsFromQuery);
}
Abd don't worry about the for loops.

I landed up passing in an xml list as a parameter to the sql query and joined to that:
var xml = new XElement("Cars", yourlist.Select(i => new XElement("Car", new XElement("Id", i.Id), new XElement("Model", i.Model))));
var results = Cars
.FromSql("SELECT cars.*"
+ "FROM #xml.nodes('/Cars/Car') Nodes(Node)"
+ "JOIN Cars cars on cars.Id = Nodes.Node.value('Id[1]', 'int') and cars.Model = Nodes.Node.value('Model[1]', 'varchar(100)')",
new SqlParameter("#xml", new SqlXml(xml.CreateReader())));
For entity-framework-core users I created a nuget package extension:
EntityFrameworkCore.SqlServer.Extensions.Contains

Using Intersect I'm getting a Local sequence cannot be used in LINQ to SQL implementations of query operators except the Contains operator

I'm using a Linq to SQL query to provide a list of search term matches against a database field. The search terms are an in memory string array. Specifically, I'm using an "intersect" within the Linq query, comparing the search terms with a database field "Description". In the below code, the description field is iss.description. The description field is separated into an array within the Linq query and the intersect is used to compare the search terms and description term to keep all of the comparing and conditions within the Linq query so that the database is not taxed. In my research, trying o overcome the problem, I have found that the use of an in-memory, or "local" sequence is not supported. I have also tried a few suggestions during my research, like using "AsEnumerable" or "AsQueryable" without success.
searchText = searchText.ToUpper();
var searchTerms = searchText.Split(' ');
var issuesList1 = (
from iss in DatabaseConnection.CustomerIssues
let desc = iss.Description.ToUpper().Split(' ')
let count = desc.Intersect(searchTerms).Count()
where desc.Intersect(searchTerms).Count() > 0
join stoi in DatabaseConnection.SolutionToIssues on iss.IssueID equals stoi.IssueID into stoiToiss
from stTois in stoiToiss.DefaultIfEmpty()
join solJoin in DatabaseConnection.Solutions on stTois.SolutionID equals solJoin.SolutionID into solutionJoin
from solution in solutionJoin.DefaultIfEmpty()
select new IssuesAndSolutions
{
IssueID = iss.IssueID,
IssueDesc = iss.Description,
SearchHits = count,
SolutionDesc = (solution.Description == null)? "No Solutions":solution.Description,
SolutionID = (solution.SolutionID == null) ? 0 : solution.SolutionID,
SolutionToIssueID = (stTois.SolutionToIssueID == null) ? 0 : stTois.SolutionToIssueID,
Successful = (stTois.Successful == null)? false : stTois.Successful
}).ToList();
...
The only way I have been successful is to create two queries and calling a method as shown below, but this requires the Linq Query to return all of the matching results (with the number of hits for search terms in the description) including the non-matched records and provide an in-memory List<> and then use another Linq Query to filter out the non-matched records.
public static int CountHits(string[] searchTerms, string Description)
{
int hits = 0;
foreach (string item in searchTerms)
{
if (Description.ToUpper().Contains(item.Trim().ToUpper())) hits++;
}
return hits;
}
public static List<IssuesAndSolutions> SearchIssuesAndSolutions(string searchText)
{
using (BYCNCDatabaseDataContext DatabaseConnection = new BYCNCDatabaseDataContext())
{
searchText = searchText.ToUpper();
var searchTerms = searchText.Split(' ');
var issuesList1 = (
from iss in DatabaseConnection.CustomerIssues
join stoi in DatabaseConnection.SolutionToIssues on iss.IssueID equals stoi.IssueID into stoiToiss
from stTois in stoiToiss.DefaultIfEmpty()
join solJoin in DatabaseConnection.Solutions on stTois.SolutionID equals solJoin.SolutionID into solutionJoin
from solution in solutionJoin.DefaultIfEmpty()
select new IssuesAndSolutions
{
IssueID = iss.IssueID,
IssueDesc = iss.Description,
SearchHits = CountHits(searchTerms, iss.Description),
SolutionDesc = (solution.Description == null)? "No Solutions":solution.Description,
SolutionID = (solution.SolutionID == null) ? 0 : solution.SolutionID,
SolutionToIssueID = (stTois.SolutionToIssueID == null) ? 0 : stTois.SolutionToIssueID,
Successful = (stTois.Successful == null)? false : stTois.Successful
}).ToList();
var issuesList = (
from iss in issuesList1
where iss.SearchHits > 0
select iss).ToList();
...
I would be comfortable with two Linq Queries, but with the first Linq Query only returning the matched records and then maybe using a second, maybe lambda expression to order them, but my trials have not been successful.
Any help would be most appreciated.

Ok, so after more searching more techniques, and trying user1010609's technique, I managed to get it working after an almost complete rewrite. The following code first provides a flat record query with all of the information I am searching, then a new list is formed with the filtered information compared against the search terms (counting the hits of each search term for ordering by relevance). I was careful not to return a list of the flat file so there would be some efficiency in the final database retrieval (during the formation of the filtered List<>). I am positive this is not even close to being an efficient method, but it works. I am eager to see more and unique techniques to solving this type of problem. Thanks!
searchText = searchText.ToUpper();
List<string> searchTerms = searchText.Split(' ').ToList();
var allIssues =
from iss in DatabaseConnection.CustomerIssues
join stoi in DatabaseConnection.SolutionToIssues on iss.IssueID equals stoi.IssueID into stoiToiss
from stTois in stoiToiss.DefaultIfEmpty()
join solJoin in DatabaseConnection.Solutions on stTois.SolutionID equals solJoin.SolutionID into solutionJoin
from solution in solutionJoin.DefaultIfEmpty()
select new IssuesAndSolutions
{
IssueID = iss.IssueID,
IssueDesc = iss.Description,
SolutionDesc = (solution.Description == null) ? "No Solutions" : solution.Description,
SolutionID = (solution.SolutionID == null) ? 0 : solution.SolutionID,
SolutionToIssueID = (stTois.SolutionToIssueID == null) ? 0 : stTois.SolutionToIssueID,
Successful = (stTois.Successful == null) ? false : stTois.Successful
};
List<IssuesAndSolutions> filteredIssues = new List<IssuesAndSolutions>();
foreach (var issue in allIssues)
{
int hits = 0;
foreach (var term in searchTerms)
{
if (issue.IssueDesc.ToUpper().Contains(term.Trim())) hits++;
}
if (hits > 0)
{
IssuesAndSolutions matchedIssue = new IssuesAndSolutions();
matchedIssue.IssueID = issue.IssueID;
matchedIssue.IssueDesc = issue.IssueDesc;
matchedIssue.SearchHits = hits;
matchedIssue.CustomerID = issue.CustomerID;
matchedIssue.AssemblyID = issue.AssemblyID;
matchedIssue.DateOfIssue = issue.DateOfIssue;
matchedIssue.DateOfResolution = issue.DateOfResolution;
matchedIssue.CostOFIssue = issue.CostOFIssue;
matchedIssue.ProductID = issue.ProductID;
filteredIssues.Add(matchedIssue);
}
}

find property value from List<Postavke>() with linq

I have class "Postavke" and then i store it into
List<Postavke> postavke = new List<Postavke>();
Now i want to find some elemnt (property) from this List. I know "Name", "Surname" and i want to get "Address".
How to get "Adress" if i know "Name" and "Surname". All this are properties in "Postavke" class
whole class
public class Postavke
{
#region Properties
public string Name { get; set; }
public string Surname { get; set; }
public string Address { get; set; }
#endregion
#region Methods
public Postavke(string name, string surname, string address, string oznakaLokacije, string oznakaZapore)
{
Name = ean;
Surname = surname;
Address = address;
}
#endregion
}

You can query postavke for all results that contain the name and surname and put the results into a list. Putting the results into a list I find makes things easier to validate and handle unforseen items as from the looks of it it is possible that duplicate items could appear.
if the results must have all data within the list item then:
List<Postavke> results = new List<Postavke>();
var query1 = from a in postavke
where a.Name == searchName
&& a.Surname == searchSurname
select a;
results.AddRange(query1);
this list will have all the results that contain the exact name and surname.
If you just want the address then you can use:
List<string> results = new List<string>();
var query1 = from a in postavke
where a.Name == searchName
&& a.Surname == searchSurname
select a.Address;
results.AddRange(query1);
this will produce a list of addresses. From here you can then validate the list if you want by doing such things as checking to see how many items in the list there are so you know how you want to handle it etc.
If you want to use just either the name or the surname then you can remove the line that asks for one or the other.
If you end up with duplicates but the results are the same then you can change the line
results.AddRange(query1);
to
results.AddRange(query1.Distinct());
by using the Distinct() method it will sort the query and remove duplicates so the list will not be in the same order as it would if you didn't use it.
If you only wanted one result then it's worth validating it by checking how many items are in the list by using
results.Count
you could if it equals 1 carry on, otherwise throw up a message or some other way you may want to handle it. Other pieces of validation that are good is to set values ToLower() and Trim() during the search as to avoid actually changing the original text.
So taking the last query as an example:
List<string> results = new List<string>();
var query1 = from a in postavke
where a.Name.ToLower().Trim() == searchName.ToLower().Trim()
&& a.Surname.ToLower().Trim() == searchSurname.ToLower().Trim()
select a.Address;
results.AddRange(query1);
you can also filter the query with the where clause after you make the query by doing:
List<string> results = new List<string>();
var query1 = from a in postavke
select a.Address;
query1 = query1.Where(h => h.Name == searchName);
query1 = query1.Where(h => h.Surname == searchSurname);
results.AddRange(query1);
The 2 where clauses were split to show you can perform where clause at different points so you could have where clauses within if statements. you can combine the 2 into:
query1 = query1.Where(h => h.Name == searchName && h.Surname == searchSurname);
Hopefully this helps

This will work if you can be sure there's exactly one match
var address = poatavke.Where(p=>p.Name == name && p.Surname == surname).Single().Address;
If you don't know if there's no matches or exactly one you can do:
var posta = poatavke.Where(p=>p.Name == name && p.Surname == surname).SingleOrDefault()
var address = posta == null ? string.Empty : posta.Address;
if you don't know how many matches there's going to be but always want the first (or are using ET which doesn't understand Single())
var posta = poatavke.Where(p=>p.Name == name && p.Surname == surname).FirstOrDefault()
var address = posta == null ? string.Empty : posta.Address;