Error accessing array indices inside a LINQ expression

Question

I am doing a query to search all weather with a certain date, but when executing occurs the following error:

An exception of type 'System.NotSupportedException' occurred in EntityFramework.SqlServer.dll but was not handled in user code

Additional information: The LINQ expression node type 'ArrayIndex' is not supported in LINQ to Entities.

Follow the code below:

var metereologias = from b in db.Metereologias.Where(b => b.data_de_leitura.Equals(tmp[i]))
                                   select new MetereologiaDTO()
                                   {
                                       metereologiaId = b.metereologiaId,
                                       data_de_leitura = b.data_de_leitura,
                                       hora_de_leitura = b.hora_de_leitura,
                                       temperatura = b.temp,
                                       vento = b.vento,
                                       pressão = b.pressao,
                                       NO = b.NO,
                                       NO2 = b.NO2,
                                       CO2 = b.CO2,
                                       Local = b.Local.Nome
                                   };
                List<MetereologiaDTO> tmpResult = new List<MetereologiaDTO>(metereologias);

Answer 1

To fix the problem use a temporary variable to store the value in the index i of the matrix tmp:

var tempValue = tmp[i];
var metereologias = db.Metereologias.Where(b => b.data_de_leitura.Equals(tempValue))
                                    .Select(new MetereologiaDTO
                                    {
                                       metereologiaId = b.metereologiaId,
                                       data_de_leitura = b.data_de_leitura,
                                       hora_de_leitura = b.hora_de_leitura,
                                       temperatura = b.temp,
                                       vento = b.vento,
                                       pressão = b.pressao,
                                       NO = b.NO,
                                       NO2 = b.NO2,
                                       CO2 = b.CO2,
                                       Local = b.Local.Nome
                                    }).ToList();

var result = new List<MetereologiaDTO>(metereologias);

If you use a matrix index tmp[i] within an Expression Tree, it will attempt to convert this into an expression as well, causing error.

UPDATED

I’ve updated the code by adopting a standard - doing all the commands through the fluent interface, but the way you wrote your code will work the same.