Question

I need help using a UDF in a LINQ which calculates a users position from a fixed point.

int pointX = 567, int pointY = 534; // random points on a square grid
var q = from n in _context.Users 
join m in _context.GetUserDistance(n.posY, n.posY, pointX, pointY, n.UserId) on n.UserId equals m.UserId
select new User() {
  PosX = n.PosX,
  PosY = n.PosY,
  Distance = m.Distance,        
  Name = n.Name,
  UserId = n.UserId
};

The GetUserDistance is just a UDF that returns a single row in a TVP with that users distance from the points deisgnated in pointX and pointY variables, and the designer generates the following for it:

[global::System.Data.Linq.Mapping.FunctionAttribute(Name="dbo.GetUserDistance", IsComposable=true)]
public IQueryable<GetUserDistanceResult> GetUserDistance([global::System.Data.Linq.Mapping.ParameterAttribute(Name="X1", DbType="Int")] System.Nullable<int> x1, [global::System.Data.Linq.Mapping.ParameterAttribute(Name="X2", DbType="Int")] System.Nullable<int> x2, [global::System.Data.Linq.Mapping.ParameterAttribute(Name="Y1", DbType="Int")] System.Nullable<int> y1, [global::System.Data.Linq.Mapping.ParameterAttribute(Name="Y2", DbType="Int")] System.Nullable<int> y2, [global::System.Data.Linq.Mapping.ParameterAttribute(Name="UserId", DbType="Int")] System.Nullable<int> userId)
{
    return this.CreateMethodCallQuery<GetUserDistanceResult>(this, ((MethodInfo)(MethodInfo.GetCurrentMethod())), x1, x2, y1, y2, userId);
}

when i try to compile i get

The name 'n' does not exist in the current context

Answer 1

This isn’t really a UDF problem – it’s a LINQ problem. You can’t use an existing range variable in the source part of a join clause, so this would be equally wrong:

string[] files = ...;
var query = from file in files
            join line in File.ReadAllLines(file) on file equals line
            ...

I suspect you’ll need to write it as multiple from clauses instead:

var q = from n in _context.Users 
        from m in _context.GetUserDistance(n.posY, n.posY, pointX, pointY, n.UserId)
        where n.UserId == m.UserId
        ...

Although it seems slightly odd to need a join at all, when I’d expect the results of GetUserDistance to only be for that user anyway, right? This might be clearer with:

var q = from n in _context.Users 
        let m = _context.GetUserDistance(n.posY, n.posY, pointX, pointY, n.UserId)
                        .Single()
        ...