The LINQ expression node type 'ArrayIndex' is not supported in LINQ to Entities

Question

public List<string> GetpathsById(List<long> id)
{
    long[] aa = id.ToArray();
        long x;
    List<string> paths = new List<string>();
    for (int i = 0; i < id.Count; i++)
    {
        x = id[i];
        Presentation press = context.Presentations.Where(m => m.PresId == aa[i]).FirstOrDefault();
        paths.Add(press.FilePath);
    }
    return paths;
}

This code throws the following exception: The LINQ expression node type 'ArrayIndex' is not supported in LINQ to Entities.

However, if I supply x instead of aa[i] it works.

Why?

Is this the same question as this: http://stackoverflow.com/questions/8353947/linq-to-entities-doesnt-recognize-array-index ? — kmp, Dec 02 '11 at 09:09

score 101 · Accepted Answer · edited Jan 12 '16 at 11:45

101

To fix this use a temporary variable:

var tmp = aa[i];
...
m => m.PresId == tmp

In your where clause you have

m => m.PresId == aa[i]

which is a way of expressing a lambda expression. When that is converted to an expression, then converted into a query on your database it finds the aa[i], which is an index into an array. i.e. it doesn't treat it as a constant. Since a translation of an indexer to your database language is impossible it gives the error.

edited Jan 12 '16 at 11:45

Ashkan Mobayen Khiabani

33,575
33
102
171

answered Dec 02 '11 at 09:10

George Duckett

31,770
9
95
162

It works in linq-to-sql, so why is it impossible in linq-to-entities? – tomsv Mar 18 '13 at 18:36
1

Basically because "it's not supported in linq to entities". The designers must've decided there wasn't an appropriate translation from an index into an array to the database L2E targets. Possibly they did in L2SQL as it doesn't have to support as much as L2E and so is easier to handle the translation. – George Duckett Mar 18 '13 at 19:35
because they screwed up, in other words :) – drogon Jun 11 '13 at 14:57
4

@drogon: Because it's more complex than it seems is more likely. :) – George Duckett Jun 11 '13 at 14:59

score 16 · Answer 2 · edited Dec 02 '11 at 09:15

16

Apparently, if you use an array index (aa[i]) inside an expression tree, it tries to convert that into an expression as well.

Just work around it by using a separate variable:

int presId = aa[i];
Presentation press = context.Presentations.Where(m => m.PresId == presId).FirstOrDefault();

edited Dec 02 '11 at 09:15

Glory Raj

17,397
27
100
203

answered Dec 02 '11 at 09:11

Trax72

958
5
12

score 5 · Answer 3 · answered Dec 02 '11 at 09:14

 public List<string> GetpathsById(List<long> id)
{
long[] aa = id.ToArray();
    long x;
List<string> paths = new List<string>();
for (int i = 0; i < id.Count; i++)
{
    x = id[i];
    int temp = aa[i];
    Presentation press = context.Presentations.Where(m => m.PresId == temp).FirstOrDefault();
    paths.Add(press.FilePath);
}
return paths;
}

try this

score 2 · Answer 4 · answered Dec 02 '11 at 09:07

It cannot be mapped to an SQL type or function.

You are aware you are mixing your list and array with each other. Everything you want doing in this code can be done simply using the list.

The following bit of code will do everything you need it to.

public List<string> GetpathsById(List<long> id) 
{ 
        long x; 
    List<string> paths = new List<string>(); 
    foreach(long aa in id) 
    { 
        Presentation press = context.Presentations.Where(m => m.PresId == aa).FirstOrDefault(); 
        paths.Add(press.FilePath); 
    } 
    return paths; 
}

score 1 · Answer 5 · answered May 08 '13 at 09:16

public List<string> GetpathsById(List<long> id) 
{ 
        long x; 
    List<string> paths = new List<string>(); 
    foreach(long aa in id) 
    { 
        Presentation press = context.Presentations.Where(m => m.PresId == aa).FirstOrDefault(); 
        paths.Add(press.FilePath); 
    } 
    return paths; 
}

to

public IEnumerable<String> GetpathsById(List<long> id) 
{ 
    foreach(long item in id) 
        yield return = (context.Presentations.Where(m => m.PresId == item).FirstOrDefault()).FilePath
}

"Short style", but not recomended if you write a lot of other function.

score 0 · Answer 6 · answered Aug 03 '18 at 14:16

0

Can be simplified to avoid the error:

public List<string> GetpathsById(List<long> id)
{
    return context.Presentations.Where(x => id.Contains(x.PresId)).Select(x => x.FilePath).ToList();
}

answered Aug 03 '18 at 14:16

2b77bee6-5445-4c77-b1eb-4df3e5

937
16
29

The LINQ expression node type 'ArrayIndex' is not supported in LINQ to Entities

6 Answers6

Linked

Related