I have one LINQ query with foreach loop. Everything is fine. But it takes more time to get the value. So anybody suggest me how can i do this in LINQ query itself.
Code
NormValue = "";
c = 0;
var NormValuelist = db.BCont.Where(x => x.BId == BId && x.TNo == Tag).ToList();
foreach (var item in NormValuelist)
{
if (c == 0)
NormValue = item.NormValue;
else
NormValue += " " + item.NormValue;
c = 1;
}
Thanks
You can rewrite this query with string.Join to avoid creating multiple string objects in a loop, like this:
string NormValue = string.Join(" ", db.BCont.Where(x => x.BId == BId && x.TNo == Tag));
The number of round-trips to DB will remain the same, but the creation of List<string> and the partially concatenated string objects will be optimized out.
In addition to using String.Join, you could also use Enumerable.Aggregate:
var NormValueList =
db.BCont.Where(x => x.Bid == BId && x.TNo == Tag)
.Select(x => x.NormValue)
.Aggregate((s, x) => s + " " + x);
If you are having large items in "NormValuelist" then it would be better to use StringBuilder instead of string(NormValue)
Related
I made a method on the back-end side to handle the filter of my datatable.
On the other hand, this one does not manage the accents of the French language, so if I have "école" and I write "ecole" it cannot find it.
I found this method on another question on stackoverflow
public static String RemoveDiacritics(this String s)
{
String normalizedString = s.Normalize(NormalizationForm.FormD);
StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i < normalizedString.Length; i++)
{
Char c = normalizedString[i];
if (CharUnicodeInfo.GetUnicodeCategory(c) != UnicodeCategory.NonSpacingMark)
{
stringBuilder.Append(c);
}
}
return stringBuilder.ToString().Normalize(NormalizationForm.FormC);
}
and it works, but only for part of my problem. It works on the letter or the word that is written in the search, but I am not able to apply it in my linq query, so with the .RemoveDiacritics() method my "école" becomes "ecole", but I don't am not able to apply it in the column of my table and it always looks for "école".
Here the code for the search:
if (search != null)
{
int n;
search = search.Trim();
var isNumeric = int.TryParse(search, out n);
if (isNumeric)
{
IdFilter = n;
query = query.Where(x => x.UsagerId == IdFilter || x.Niveau == IdFilter);
}
else if (search != "")
{
// this line work
textFilter = search.ToLower().RemoveDiacritics();
// This is the full line, but absolutely takes the accents out to get the right information out
// query = query.Where(x => x.Nom.ToLower().Contains(textFilter) || x.Prenom.ToLower().Contains(textFilter) || x.Username.ToLower().Contains(textFilter) || x.Email.ToLower().Contains(textFilter) || x.EtabNom.ToLower().Contains(textFilter) || x.ActifStatut.ToLower().Contains(textFilter));
// This is the line that will replace the line above, which I try and it doesn't work ( this part: x.Prenom.ToLower().RemoveDiacritics())
query = query.Where(x => x.Prenom.ToLower().RemoveDiacritics().Contains(textFilter));
}
}
This is the basic query:
IQueryable<ListeUsagers> query = (from u in db.USAGERs
join e in db.ETABLISSEMENTs on u.USAGER_INST equals e.ETAB_CODE
where u.USAGER_INST == instId && u.USAGER_NIVEAU > 3 && u.USAGER_NIVEAU < 5 //&& u.USAGER_ACTIF == 1
select new ListeUsagers()
{
UsagerId = u.USAGER_id,
Nom = u.USAGER_NOM,
Prenom = u.USAGER_PRENOM,
EtabCode = e.ETAB_CODE,
EtabNom = e.ETAB_NOM_COURT,
EtabType = e.ETAB_TYPE,
Niveau = u.USAGER_NIVEAU,
Username = u.USAGER_USERNAME,
UserPassword = u.USAGER_MP,
DateCreation = u.USAGER_DATE_INSC,
Sexe = u.USAGER_SEXE,
Lang = u.USAGER_LANGUE,
Telephone = u.USAGER_TELEPHONE,
Email = u.USAGER_EMAIL,
FonctionTravail = u.USAGER_FONCTION,
LieuTravail = u.USAGER_LIEUTRAVAIL,
Note = u.USAGER_NOTE,
Actif = u.USAGER_ACTIF,
ActifStatut = u.USAGER_ACTIF == 0 ? "Inactif" : "Actif"
});
This is the error:
LINQ to Entities does not recognize the method 'System.String RemoveDiacritics(System.String)' method, and this method cannot be translated into a store expression.
There's built-in functionality to do this in entityframework: https://learn.microsoft.com/en-us/ef/core/miscellaneous/collations-and-case-sensitivity if you're using EF 5+
You'll want an accent insensitive collation ("AI", not "AS" in the examples on that page.)
I have a need to verify that all the rows in a given set exist in the database and the current user has access to all the rows. I'd like to do this in a single query to the database, something like a .All() query but I can't quite come up with the right syntax (maybe it's not possible).
The iterative version of the code would look like:
bool canAccess;
foreach(var taskId in taskIds)
{
canAccess = await DataContext.WorkTasks.AnyAsync(wt => wt.DealerId == dealerId && wt.Id == taskId);
if(!canAccess) break;
}
I was thinking about something like:
var canAccess = await DataContext.WorkTasks.AllAsync(wt => wt.DealerId == dealerId && taskIds.Contains(wt.Id));
But I don't think that's what I want. Can this be done using LINQ?
Something like this:
var dbCount = await DataContext.WorkTasks.Where(wt => wt.DealerId == dealerId && taskIds.Contains(wt.Id)).Count();
Will send all your IDs to the server and count the matching rows.
To combine into a single query:
var q = DataContext.WorkTasks.Take(0); // setup q to right type
foreach (var taskId in taskIds)
q = q.Concat(DataContext.WorkTasks.Where(wt => wt.Id == taskId && wt.DealerId == dealerId));
var canAccess = (taskIds.Count() == q.Count());
I am doing a asp.net-mvc with entity-framework App.
I have a select instruction, where I need to have a dymanic where condition.
It is a common case where you have a filter composed by a string like "aaaa bbbb cccc". I need to bring all data that contains all the filter string or part of it.
I doing part ot it witt Split function, but it is difficult to get all posible combinations.
I Would rather use a Store Procedure. But the porpose of it, is to use Entity Framework.
As far I did this.
public IEnumerable<UploadSearch> GetUploadsBySearch(string search)
{
IEnumerable<UploadSearch> viewModel = (from uploads in _db.Uploads
.Where(p => p.ProcessState_id == Security.APPROVED && p.Finder.Contains(search))
.OrderByDescending(p => p.UploadDate)
select new UploadSearch
{
User_id = uploads.User_id,
UserName = uploads.Users.Name,
UserLastName = uploads.Users.LastName,
});
And I Add a for instruction to loop throu the string,
string[] param = search.Replace(" "," ").Split(' ');
string _param = "";
int large = param.Length;
for (int i=0;i<large-1;i++)
{
_param +=param[i] ' ' + param[i + 1];
IEnumerable<UploadSearch> _viewModel = (from uploads in _db.Uploads
.Where(p => p.ProcessState_id == Security.APPROVED && p.Finder.Contains(_param))
.OrderByDescending(p => p.UploadDate)
select new UploadSearch
{
User_id = uploads.User_id,
UserName = uploads.Users.Name,
UserLastName = uploads.Users.LastName,
});
viewModel = viewModel.Union(_viewModel);
}
And I use a Union clause.
But There has to be another way to do it.
Any Ideas?
You should use LinqKit, it has a PredicateBuilder class that allows you to dynamically build queries
https://github.com/scottksmith95/LINQKit#predicatebuilder
IQueryable<Product> SearchProducts (params string[] keywords)
{
var predicate = PredicateBuilder.New<Product>();
foreach (string keyword in keywords)
{
string temp = keyword;
predicate = predicate.Or (p => p.Description.Contains (temp));
}
return dataContext.Products.Where (predicate);
}
This is driving me nuts. What am I missing here. I'm using EF and if I have code like the following:
using (LexiconEntities ctx = new LexiconEntities())
{
var query = from w in ctx.Words
select new WordEntryDataModel
{
Word = w.Anagram,
NumOfAnagrams = w.NumAnagrams.Value,
Length = w.Length.Value,
...
};
SearchCriterion c1 = new SearchCriterion();
SearchCriterion c2 = new SearchCriterion();
c1.MinValue = 3;
c1.MaxValue = 3;
c2.MinValue = 4;
c2.MaxValue = 4;
query = query.Where(w => w.Length >= c1.MinValue && w.Length <= c1.MaxValue);
query = query.Where(w => w.NumOfAnagrams >= c2.MinValue && w.NumOfAnagrams <= c2.MaxValue);
...
}
And when I debug the query, I get the proper results (8 records). This also works as expected in Linqpad (which frickin' rocks).
But if I construct the search criteria as a List of criterion objects, and I dynamically add on Where() clauses by iterating over the search criteria as follows:
foreach (SearchCriterion c in criteria.SearchCriteria)
{
switch (c.Type)
{
case SearchCriterionType.WordLength:
query = query.Where(w => w.Length >= c.MinValue && w.Length <= c.MaxValue);
break;
case SearchCriterionType.NumberOfAnagrams:
query = query.Where(w => w.NumOfAnagrams >= c.MinValue && w.NumOfAnagrams <= c.MaxValue);
break;
...
case SearchCriterionType.NumberOfVowels:
query = query.Where(w => w.NumOfVowels >= c.MinValue && w.NumOfVowels <= c.MaxValue);
break;
}
}
...
I get the totally different (and incorrect) results. I've debugged the switch statement and my search criteria has two properly constructed criterion objects set to correct values. There's something about the conditionally added where clauses that my query doesn't like.
What am I doing wrong?
Closure. Assign c to a local variable within the loop. Also see my SO answer here
I have a query as follows:
var query = from x in context.Employees
where (x.Salary > 0 && x.DeptId == 5) || x.DeptId == 2
order by x.Surname
select x;
The above is the original query and returns let's say 1000 employee entities.
I would now like to use the first query to deconstruct it and recreate a new query that would look like this:
var query = from x in context.Employees
where ((x.Salary > 0 && x.DeptId == 5) || x.DeptId == 2) && (x,i) i % 10 == 0
order by x.Surname
select x.Surname;
This query would return 100 surnames.
The syntax is probably incorrect, but what I need to do is attach an additional where clause and modify the select to a single field.
I've been looking into the ExpressionVisitor but I'm not entirely sure how to create a new query based on an existing query.
Any guidance would be appreciated. Thanks you.
In an expression visitor you would override the method call. Check if the method is Queryable.Where, and if so, the methods second parameter is a quoted expression of type lambda expression. Fish it out and you can screw with it.
static void Main()
{
IQueryable<int> queryable = new List<int>(Enumerable.Range(0, 10)).AsQueryable();
IQueryable<string> queryable2 = queryable
.Where(integer => integer % 2 == 0)
.OrderBy(x => x)
.Select(x => x.ToString());
var expression = Rewrite(queryable2.Expression);
}
private static Expression Rewrite(Expression expression)
{
var visitor = new AddToWhere();
return visitor.Visit(expression);
}
class AddToWhere : ExpressionVisitor
{
protected override Expression VisitMethodCall(MethodCallExpression node)
{
ParameterExpression parameter;
LambdaExpression lambdaExpression;
if (node.Method.DeclaringType != typeof(Queryable) ||
node.Method.Name != "Where" ||
(lambdaExpression = ((UnaryExpression)node.Arguments[1]).Operand as LambdaExpression).Parameters.Count != 1 ||
(parameter = lambdaExpression.Parameters[0]).Type != typeof(int))
{
return base.VisitMethodCall(node);
}
return Expression.Call(
node.Object,
node.Method,
this.Visit(node.Arguments[0]),
Expression.Quote(
Expression.Lambda(
lambdaExpression.Type,
Expression.AndAlso(
lambdaExpression.Body,
Expression.Equal(
Expression.Modulo(
parameter,
Expression.Constant(
4
)
),
Expression.Constant(
0
)
)
),
lambdaExpression.Parameters
)
)
);
}
}
}