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Nested ForEach loop to Linq
(4 answers)
Closed 2 months ago.
I am new to LINQ, help me convert this nested line of codes to LINQ.
foreach(var rule in rules)
{
foreach(var package in packages)
{
if(rule.KeyFrom == package.Key || rule.KeyTo == package.Key)
{
filteredRule.Add(new RuleModel{Package = new List<string>{rule.KeyTo, rule.KeyFrom}, Rule = rule.Rule});
}
}
}
Attempted query:
rules.SelectMany(r => packages.Select(p => p.Key == r.KeyFrom || p.Key == r.KeyTo))
.Select(new RuleModel {
Package = new List<string>{ r.Keyfrom, r.KeyTo},
Rule = r.Rule
}));
You are almost there. Your problem is that in the SelectMany you used Select for filtering insead of using Where:
rules.SelectMany(r => packages.Where(p => p.Key == r.KeyFrom || p.Key == r.KeyTo))
.Select(r => new RuleModel {
Package = new List<string>{ r.Keyfrom, r.KeyTo},
Rule = r.Rule
}));
Where - Filters a sequence of values based on a predicate
Select - Projects each element of a sequence into a new form
You have to use SelectMany.
The code will be like this:
var ruleModels = rules.SelectMany(r => r.packages).Where(rule.KeyFrom == package.Key || rule.KeyTo == package.Key).Select(r => new RuleModel{Package = new List<string>{r.KeyTo, r.KeyFrom}, Rule = r.Rule});
filteredRule.AddRange(ruleModels);
You may try the below code:
filteredRule.AddRange(rules.Where(b =>
packages.Any(a => b.KeyFrom == a.Key || b.KeyTo == a.Key)).select(
p=>new new RuleModel { Package = new List<string>
{ p.KeyTo, p.KeyFrom }, Rule = p.Rule }));
Related
I try to get a list of all innermost tables with AngleSharp. This tables doesn't contain any tables.
With HtmlAgilityPack I've realised it this way:
var wrapper = html.DocumentNode.SelectSingleNode(".//td[#class='wrapper']");
var innerMostTables = wrapper.SelectNodes(".//table [not(descendant::table)]");
With AngleSharp I've tried this, but it doesn't work:
var parser = new HtmlParser();
var document = parser.Parse(html);
var wrapper = document.All.Where(d => d.ClassName == "wrapper");
var innerMostTables = wrapper.Where(w => w.Descendents()
.Select(c => c.NodeName == "table").Count() == 0);
I could solve the problem:
foreach (IElement ch in wrapper.Descendents()
.Where(d => d.NodeName == "TABLE" && d.Descendents()
.Where(d2 => d2.NodeName == "TABLE").Count() == 0))
{
Console.WriteLine(ch.OuterHtml);
}
Have read other responses to similar issuebut I can not use PredicateBuilder, or copy its source. I'm trying what I've read here:
<https://blogs.msdn.microsoft.com/meek/2008/05/02/linq-to-entities-combining-predicates/
but as I'm newb, am having trouble with translating what I'm reading to what I'm applying. I have created a L2E query, and trying to append a series of OR clauses onto the WHERE:
So as simplified snippet (this one will be AND'd with the previously already defined WHERE clause):
if (firstParm == "realtor")
query = query.Where(x=> x.A == "realtor");
Now trying to OR:
if (secondParm == "clown")
// how to add this one as an OR to the above query:
query = query.OR(x=> x.fool == "clown");
I understand this can be done also with Union, but not clear on the syntax:
query = query.Union(x=> x.fool == "clown"); // ??
I've also referenced:
Combining two expressions (Expression<Func<T, bool>>)
Unable to create a compound Expression<Func<string, bool>> from a set of expressions
but again, I am new to LINQ and especially Expression Trees, so need more fillin.
There are two ways to generate expressions.
Use the compiler to do it.
Expression<Func<Person, bool>> = p => p.LastName.Contains("A");
Limitations: The only expressions that can be generated this way are instances of LambdaExpression. Also, it is rather complicated to extract parts of the expression and combine with other parts.
Use the static methods at System.Linq.Expressions.Expression.
In order to generate dynamic expressions, you can either choose between different compiler-generated expressions:
// using Record and Records as a placeholder for the actual record type and DbSet property
Expression<Func<Record,bool>> expr;
if (firstParam == "realtor") {
if (secondParam == "clown") {
expr = x => x.A == "realtor" || x.fool == "clown";
} else {
expr = x => x.A == "realtor";
}
} else {
if (secondParam == "clown") {
expr = x => x.fool="clown";
} else {
expr = x => false;
}
}
var ctx = new MyDbContext();
var qry = ctx.Records.Where(expr).Select(x => new {x.A, x.fool});
Or, you can dynamically create the expression using the static methods:
(Add using System.Linq.Expressions; and using static System.Linq.Expressions.Expression; to the top of the file.)
Expression expr;
var parameter = Parameter(typeof(Record));
if (firstParam == "realtor") {
expr = Equals(
MakeMemberAccess(parameter, typeof(Record).GetProperty("A")),
Constant("realtor")
);
}
if (secondParam == "clown") {
var exprClown = Equals(
MakeMemberAccess(parameter, typeof(Record).GetProperty("fool")),
Constant("clown")
);
if (expr == null) {
expr = exprClown;
} else {
expr = Or(expr, exprClown);
}
}
var lambda = Lambda<Func<Record,bool>>(expr, new [] {parameter});
var ctx = new MyDbContext();
var qry = ctx.Records.Where(lambda).Select(x => new {x.A, x.fool});
Given a query with a type unknown at compile time, so any variable referring to it must be IQueryable only, and not IQueryable<T>:
IQueryable qry = ctx.GetQuery(); //dynamically built query here
var parameter = Parameter(qry.ElementType);
if (firstParam == "realtor") {
expr = Equals(
MakeMemberAccess(parameter, qry.ElementType.GetProperty("A")),
Constant("realtor")
);
}
if (secondParam == "clown") {
var exprClown = Equals(
MakeMemberAccess(parameter, qry.ElementType.GetProperty("fool")),
Constant("clown")
);
if (expr == null) {
expr = exprClown;
} else {
expr = Or(expr, exprClown);
}
}
var lambda = Lambda(expr, new [] {parameter});
//Since we don't have access to the TSource type to be used by the Where method, we have
//to invoke Where using reflection.
//There are two overloads of Queryable.Where; we need the one where the generic argument
//is Expression<Func<TSource,bool>>, not Expression<Func<TSource,int,bool>>
var miWhere = typeof(Queryable).GetMethods().Single(mi => {
mi.Name == "Where" &&
mi.GetParameters()[1].ParameterType.GetGenericArguments()[0].GetGenericArguments().Length == 2
});
qry = miWhere.Invoke(null, new [] {qry, lambda});
For Or you can try
if (secondParm == "clown")
{
query = query.Where(x=> x.fool == "clown" || x.fool==x.fool);
}
OR
if (secondParm == "clown")
{
query = query.Where(x=> x.fool == "clown" || true );
}
I have 3 tables,
Table Operation
Columns:
idOperation int cdLangPrimary char(2)
Table Languages
Columns:
cdLang char(2) nmLang nvarchar(10)
Table OperationLanguages
Columns: idOperation int cdLang char(2)
My code:
var jsonObject = dbContext.Operations
.Single(o => o.idOperation == idOperation)
.Languages
.Select(l => new { l.cdLang, l.nmLang });
What I was trying to do (with no success),
is Order the Languages by a-Z, but put the cdLangPrimary as the first.
I know it is possible if I create a List(or Dictionary) like so:
var languages = new List<Languages>();
var dLanguage = operation.Languages.Single(l => l.cdLang == operation.cdLangPRIMARY);
languages.Add(dLanguage);
languages.AddRange(operation.Languages.Where(l => l.cdLang != dLanguage.cdLang));
Just wondering if there is an option to the same with linq
or in a more effective way?
If I understand your question, the following should do it:
var result = dbContext.Languages
.Where(l => l.OperationId == idOperation)
.OrderByDescending(l => l.cdLang == l.Operation.cdLangPrimary)
.ThenBy(l => l.cdLang)
.Select(l => new { l.cdLang, l.nmLang });
If you don't have relationships set up in entity framework between an Operation and a Language then you can achieve the same result as follows:
var operation = dbContext.Operations
.SingleOrDefault(o => o.idOperation == idOperation);
if(operation != null)
{
var result = dbContext.Languages
.Where(l => l.OperationId == idOperation)
.OrderByDescending(l => l.cdLang == operation.cdLangPrimary)
.ThenBy(l => l.cdLang)
.Select(l => new { l.cdLang, l.nmLang });
}
I need to build a dynamic where clause in a Linq statement with multiple joins.
.Net 3.5
Linq-To-Sql
I have these incoming parameters for the Linq statement, only the "UID" is required.
int uid = 23702; // <-- Only one Required
string courseNumber = "";
string title = "";
int? categoryId = null;
int? typeId = null;
I've been testing this out in LinqPad and while I've gotten the query to work with all Where clauses in place, the Nullable int parameters end up returning incorrect results.
Here's my Linq statement:
var ci = course_instances;
var query = courses.Join(ci,
c => c.course_id,
i => i.course_id,
(c, i) => new
{
c = c,
i = i
}).Join(user_courses,
temp => temp.i.instance_id,
uc => uc.instance_id,
(temp, uc) => new
{
temp = temp,
uc = uc
})
.Where (temp1 => (temp1.uc.uid == uid))
.Where (temp1 => (temp1.temp.c.course_number.Contains(courseNumber)))
.Where (temp1 => (temp1.temp.c.title.Contains(title)))
//.Where (temp1 => (temp1.temp.c.course_type_id == typeId))
//.Where (temp1 => (temp1.temp.c.course_category_id == categoryId))
.Select (temp1 => new CourseSearchMyCourses
{
// snipped the many properties
});
I've tried using PredicateBuilder, but it returns the error:
The type arguments for method 'System.Linq.Queryable.Where(System.Linq.IQueryable, System.Linq.Expressions.Expression>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.
Here's my PredicateBuilder Linq attempt:
var conditions = PredicateBuilder.True<user_course>();
conditions = conditions.And(c => c.uid == uid);
var ci = course_instances;
var query = courses.Join(ci,
c => c.course_id,
i => i.course_id,
(c, i) => new
{
c = c,
i = i
}).Join(user_courses,
temp => temp.i.instance_id,
uc => uc.instance_id,
(temp, uc) => new
{
temp = temp,
uc = uc
})
.Where (conditions)
.Select (temp1 => new CourseSearchMyCourses
{
// snipped the many properties
});
BTW, I also tried using "System.Linq.Dynamic" using string queries, and got the error the " and " isn't recognized.
Any help is appreciated.
Thanks.
Linq predicates with nullable type variables get translated into a SQL predicate = NULL. But that is totally different than what it should be: IS NULL.
You expect to get the rows where course_type_id is empty, but the = comparison returns no results because NULL is not a value and the comparison returns UNKNOWN. I think that is the cause of your "incorrect results".
If this is your problem, a fix can be found here.
I'm trying to implement a T-SQL equivalent of a where in (select ...) code in LINQ.
This is what I have now:
int contactID = GetContactID();
IEnumerable<string> threadList = (from s in pdc.Messages
where s.ContactID == contactID
group 1 by new { s.ThreadID } into d
select new { ThreadID = d.Key.ThreadID}).ToList<string>();
var result = from s in pdc.Messages
where threadList.Contains(s.ThreadID)
group new { s } by new { s.ThreadID } into d
let maxMsgID = d.Where(x => x.s.ContactID != contactID).Max(x => x.s.MessageID)
select new {
LastMessage = d.Where(x => x.s.MessageID == maxMsgID).SingleOrDefault().s
};
However, my code won't compile due to this error for the ToList():
cannot convert from
'System.Linq.IQueryable<AnonymousType#1>'
to
'System.Collections.Generic.IEnumerable<string>'
Anyone have any suggestions on how to implement this? Or any suggestions on how to simplify this code?
Your query returns a set of anonymous types; you cannot implicitly convert it to a List<string>.
Instead, you should select the string itself. You don't need any anonymous types.
Change it to
var threadList = pdc.Messages.Where(s => s.ContactID == contactID)
.Select(s => s.ThreadID)
.Distinct()
.ToList();
var result = from s in pdc.Messages
where threadList.Contains(s.ThreadID)
group s by s.ThreadID into d
let maxMsgID = d.Where(x => x.ContactID != contactID).Max(x => x.MessageID)
select new {
LastMessage = d.Where(x => x.MessageID == maxMsgID).SingleOrDefault()
};