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

problem ：

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. 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. however , If I offer x instead of aa[i] It can work .

Why? Why? ？

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Solution ：

Reference resources ： https://stackoom.com/en/question/Z3F6