Entity Framework join query with int array - sql

Question

i have got 3 tables on my database.
---Student---
id - name
---Language---
id - lang
---StudentLanguage---(Common Table)
id - studentId - langId
Students can have more languages. i want to search students with an int[] array values. But not with IN() - Contains(), it must be with and - && operator and this operator take int[] values.
in sql =
`select t1.id, t1.name from Student t1 join StudentLanguage t2
ON(t1.id=t2.studentId) where (t2.langId=1 and t2.langId=3 and t2.langId=5);`
so how can i do this query with Entity Framework? (...where new int[] { 1,3,5 })

Answer 1

This code generate some clumsy sql query...
int[] ids = new[] { 1, 3, 5 };
var acc = from st in db.Students select st;
foreach (var id in ids)
{
int id1 = id;
var res =
from st in db.Students
from lng in st.Language
where lng.Id == id1
select st;
acc =
from a in acc
join st in res on a.Id equals st.Id
select a;
}
acc.ToList();
... sql query :
SELECT
[Extent1].[Id] AS [Id],
[Extent1].[Name] AS [Name]
FROM [dbo].[Student] AS [Extent1]
INNER JOIN [dbo].[StudentLanguage] AS [Extent2] ON [Extent1].[Id] = [Extent2].[Student_Id]
INNER JOIN [dbo].[StudentLanguage] AS [Extent3] ON [Extent1].[Id] = [Extent3].[Student_Id]
INNER JOIN [dbo].[StudentLanguage] AS [Extent4] ON [Extent1].[Id] = [Extent4].[Student_Id]
WHERE ([Extent2].[Language_Id] = #p__linq__0)
AND ([Extent3].[Language_Id] = #p__linq__1)
AND ([Extent4].[Language_Id] = #p__linq__2)

Answer 2

List<int> langIds = new int[] { 1, 3, 5 }.ToList();
var c = langIds.Count;
var res2 = _context.Students
.Where(x => x.StudentLanguages
.Where(l => langIds.Contains(l.langId)).Select(y => y.langId).Distinct().Count() >= c);
result SQL:
SELECT [t0].[id], [t0].[name]
FROM [dbo].[Student] AS [t0]
WHERE ((
SELECT COUNT(*)
FROM (
SELECT DISTINCT [t1].[langId]
FROM [dbo].[StudentLanguage] AS [t1]
WHERE ([t1].[langId] IN (1, 3, 5)) AND ([t1].[studentId] = [t0].[id])
) AS [t2]
)) >= 3
Use Distinct if StudentLanguages theoretically may have several overlapping bundles StudentId - LangId.

Answer 3

Try something like this...
resultArr = [];
For(int i = 0; i<arr.length; i++) {
var result = db.Student.Where(s=>s.StudentLanguage.langId == arr[i]);
resultArr.append(result);
}

Answer 4

var db = new MyDbContext();
var langIds = new[] { 1, 3, 5 };
IEnumerable<Student> student = from st in db.student select st;
foreach (var item in langIds)
{
student = student.Join(db.StudentLanguage.Where(w => w.langId == item),
st => st.studentId,
stMap => stMap.id,
(st, stMap) => new { Student= stMap, StudentLanguage = st})
.Select(x => x.Student).Distinct();
}
i can do this like that. Maybe foreach can be turn linq and this code can be only one line and a little short.

Answer 5

I try to search how to do it and here is what i come out with:
int[] langIds = new int[] { 1, 3, 5 };
var lang = _context.Languages.Where(x => langIds.Contains(x.id));
var result = _context.Students.Where(x => !lang
.Except(x.StudentLanguages
.Select(y => y.Language)
.Intersect(lang)).Any());
Here i use Except and Intersect linqToSQL extension methods.
It produces this SQL statement:
SELECT [t0].[id], [t0].[name]
FROM [dbo].[Student] AS [t0]
WHERE NOT (EXISTS(
SELECT NULL AS [EMPTY]
FROM (
SELECT DISTINCT [t1].[id], [t1].[name]
FROM [dbo].[Language] AS [t1]
WHERE (NOT (EXISTS(
SELECT NULL AS [EMPTY]
FROM (
SELECT DISTINCT [t3].[id], [t3].[name]
FROM [dbo].[StudentLanguage] AS [t2]
INNER JOIN [dbo].[Language] AS [t3] ON [t3].[id] = [t2].[langId]
WHERE (EXISTS(
SELECT NULL AS [EMPTY]
FROM [dbo].[Language] AS [t4]
WHERE ([t3].[id] = [t4].[id]) AND ([t4].[id] IN (#p0, #p1, #p2))
)) AND ([t2].[studentId] = [t0].[id])
) AS [t5]
WHERE [t1].[id] = [t5].[id]
))) AND ([t1].[id] IN (#p3, #p4, #p5))
) AS [t6]
))
Note that i populate languages from database. Unfortunatly you can not use local collections in your query since LinqToSQL don't know how to translate them into SQL. If you do the same thing with local int array or any other collection you will get this exception:
LINQ To SQL exception: Local sequence cannot be used in LINQ to SQL
implementation of query operators except the Contains operator