I have a table named dbo.Question having two columns Id and Title. I want to write LINQ query to get all questions where the question Title begins with numbers.
The following is a sample of question search result where the "Title" starts with a number:
5 Useful Visual Studio shortcuts
7 Things to know about Hadoop.
10 Reasons You Should Be Thankful For Hackers
The SQL query is like:
SELECT Title FROM dbo.Question WHERE Title NOT LIKE '[a-z]%'
What will be the LINQ equivalent of the above SQL query?
var query = from x in dbcontext.Questions
where SqlFunctions.IsNumeric(EntityFunctions.Left(x.Title, 1)) == 1
select x;
Source:
http://msdn.microsoft.com/en-us/library/system.data.objects.sqlclient.sqlfunctions.isnumeric(v=vs.110).aspx
http://msdn.microsoft.com/en-us/library/dd383069(v=vs.110).aspx
Come to think of it, this isn't very efficient, given that it doesn't use indices. You can instead do this...
IEnumerable<string> digits = Enumerable.Range(0, 10) // 0-9
.Select(i => i.ToString());
//Create a query for starts with on each digit.
IEnumerable<IQueryable<Question>> questions = digits
.Select(i => dbcontext.Questions.Where(q => q.StartsWith(i))
IQueryable<Question> concatedTogether = .Aggregate(Queryable.Concat) //Union all each of them together
int count = concatedTogether.Count();
OR simply
int count = Enumerable.Range(0, 9)
.Select(int.ToString)
.Select(i => dbcontext.Questions.Where(q => q.StartsWith(i))
.Aggregate(Queryable.Concat)
.Count();
Related
I want to select records where any of the selected fields is a 1.
decimal myNumber = 1;
query = from q in query where myNumber.Contains(q.trial, q.score, q.id) select q;
in sql I would write
select trial, score, id
from query q
where 1 in (q.trial, q.score, q.id)
How do I duplicate the sql using linq?
You could use an array and use Contains method, for sample:
var query = from q in query
where new[]{q.trial, q.score, q.id}.Contains(myNumber)
select q;
The oposite, when you have many values and you need to compare with an single column, you could do something like this:
var myValues = new[] {1, 2, 3, 4, 5};
var query = from q in query
where myValues.Contains(q.trial)
select q;
Elaborating a bit more on #Felipe's post:
var found = from q in query
let arr = new []{ q.trial, q.score, q.id}
where arr.Contains(1)
select q;
EDIT: looks like #Felipe updated his post to use dynamically created arrays. I'm going to leave my post in to demonstrate the usage of variables within the LINQ query (let). This is useful to know for occasional cases.
How to change the following SQL query to Linq query and how to convert results to a list of strings?
select Name
from Categories
where ID in (select CID from CategoryLink where VID = 57)
Please, provide some extra context. From the fist sight the code should be something like this:
List<string> names = db.Categories
.Where(c => db.CategoryLink.Any(cl=>cl.VID == 57 && CID == c.ID))
.ToList();
I have used too much time (days) on this and I really hope someone can help me out.
I found a good article on describing my problem in a generic way so let's stick to it.
I am trying to build this query but NHibernate fails to build the correct sql and returns a sql query exception.
Column vSagsAendring.Id is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause. It could not execute the following query:
select
viewsagsae0_.Id as Id155_,
viewsagsae0_.SagId as SagId155_,
viewsagsae0_.JournalNr as JournalNr155_,
viewsagsae0_.LbfNr as LbfNr155_,
viewsagsae0_.OrgNr as OrgNr155_,
viewsagsae0_.OrgNavn as OrgNavn155_,
viewsagsae0_.AfdNavn as AfdNavn155_,
viewsagsae0_.SagsType as SagsType155_,
viewsagsae0_.Status as Status155_,
viewsagsae0_.SagsbehandlerInit as Sagsbeh10_155_,
viewsagsae0_.Dato as Dato155_,
viewsagsae0_.JournalAktionType as Journal12_155_,
viewsagsae0_.Beskrivelse as Beskriv13_155_,
viewsagsae0_.Ekstern as Ekstern155_
from vSagsAendring viewsagsae0_
group by viewsagsae0_.SagId
var query = from p in _session.Query<ViewSagsAendring>()
group p by p.SagId
into grp
select grp.OrderByDescending(g => g.Dato).First();
This is another version also took from the article:
var query = from p in _session.Query<ViewSagsAendring>()
group p by p.SagId
into grp
let maxDato = grp.Max(g => g.Dato)
from p in grp
where p.Dato == maxDato
select p;
It's have been a long journey, but now it's over. I hope that I can help someone else in the same situation by answering my own question.
var aendring = from sagsAendring in _session.Query<ViewSagsAendring>()
where sagsAendring.Dato ==
(
from innersagsAendring in _session.Query<ViewSagsAendring>()
where innersagsAendring.SagId == sagsAendring.SagId
select innersagsAendring.Dato
).Max()
select sagsAendring;
var result = aendring.ToList();
And because you can chain linq statements you can build a linq filter like this
if(Filters.VisInterneAendringer == false)
query = query.Where(x => x.Ekstern == true);
if (Filters.VisKunNyesteAendringer)
{
query = query.Where(sagsAendring => sagsAendring.Dato ==
(
from innerSagsAendring in Session.Query<ViewSagsAendring>() where innerSagsAendring.SagId == sagsAendring.SagId
select innerSagsAendring.Dato
).Max());
}
return query;
Your queries seem legit for LINQ in EntityFramework.
I'm not sure about hibernate, you might try to use QueryOver API instead of Query
http://nhibernate.info/blog/2009/12/17/queryover-in-nh-3-0.html
I need help to convert following ql query to Linq to Sql query.
select Name, Address
from Entity
group by Name, Address
having count(distinct LinkedTo) = 1
Idea is to find all unique Name, Address pairs who only have 1 distinct LinkedTo value. Remember that there are other columns in the table as well.
I would try something like this:
Entity.GroupBy(e => new { e.Name, e.Address})
.Where(g => g.Select(e => e.LinkedTo).Distinct().Count() == 1)
.Select(g => g.Key);
You should put a breakpoint after that line and check the SQL that is generated to find what is really going to the database.
You could use:
from ent in Entities
group ent by new { ent.Name, ent.Address } into grouped
where grouped.Select(g => g.LinkedTo).Distinct().Count() == 1
select new { grouped.Key.Name, grouped.Key.Address }
The generated SQL does not use a having clause. I'm not sure LINQ can generate that.
Customer.text is a field in an T-SQL DB (that I do not control and thus may not alter) of type "text".
I'd like to do something like this:
List<string> compare = new List<string>();
compare.Add("one");
compare.Add("two");
var q = from t in customer
where t.text.Contains( compare.First())
select t;
this will work.
But now I'd like to do something like: (!NOT WORKING!)
var q = from t in customer
where compare.Contains( t.text )
select t;
How can I achieve this? Is it even possible?
EDIT: The problem is obviously not exactly clear: A text column in SQL cannot be queried using "=" but only with LIKE. Thus the compare.Contains( t.text ) will result in an error, as it is converted into a query using "=".
What I did not tell - I thought it is irrelevant - is, that I use LINQ-to-ORM (LLBLGen in this case).
What I tried instead:
var q = from t in customer
where compare.Any( x => t.text.Contains(x) )
select t;
Now this did not work also. Currently I'm not at work, but the exception was something with a ConstantExpression not being convertable into a SetExpression.
I hope this gave some clarification.
EDIT2:
Joseph pointed this out to me: PredicateBuilder. It creates an Expression on a given ObjectType.
Now my problem is, that my type is an anonymous type out of multiple joins.
Is there an easy or elegant way to handle this?
Now I might be missing something, but your code looks like it should work. Did you include the namespaces at the top of the file?
using System.Linq;
using System.Linq.Expressions;
You could also rewrite it without the Linq2Sql syntax, like:
var q = customer.Where(c => compare.Contains(c.text));
You could build your query using LinqKit's free predicate builder class. Here is a blog post which describes its use and has a link to the download site.
http://thecodeslinger.wordpress.com/2008/10/28/linqkit-predicatebuildert-goodness/
Below is a code sample from the post
//First get a list of keywords that match the description entered.
string[] parts = txtInclude.Text.Split(new[] {‘ ‘});
string[] noparts = null;
if(txtButNot.Text.Trim().Length > 0)
noparts = txtExclude.Text.Trim().Split(new[] {‘ ‘});
var pred = PredicateBuilder.True<Pet>();
//here is where you would loop through your compare object
parts.ForEach(p => pred = pred.And(pl => pl.description.Contains(p)));
if(noparts != null)
noparts.ForEach(p => pred = pred.And(pl => !pl.description.Contains(p)));
var pets = from s in db.Pets.Where(pred)
select s;
You have to convert the text field to string
var query = from t in dataContext.table
where compare.Contains(t.textField.ToString())
select t;