When converting month number to string error : Does not recognize the method 'System.String ToString(Int32)'

Question

trying to select disctinct months in number form from db where there is a record of that month on database.

        public IEnumerable<months> dropdownMonths(datafilter dataparams)
    {
        try
        {
            var _dbEntity = new VXI_GLOBALiTRACKEntities();
            var unique_months =
                _dbEntity
                    .TBL_REQUEST
                    .Select(s => new months
                    {
                        value = s.REQUEST_DATE_SUBMITTED.Value.Month,
                        yr = s.REQUEST_DATE_SUBMITTED.Value.Year,
                        month = Convert.ToString(s.REQUEST_DATE_SUBMITTED.Value.Month)

                    })
                    .Distinct()
                    .Where(s => s.yr == dataparams.year)
                    .ToList();

            return unique_months;
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }

now on month = Convert.ToString(s.REQUEST_DATE_SUBMITTED.Value.Month)

it gets the error

LINQ to Entities does not recognize the method 'System.String ToString(Int32)' method, and this method cannot be translated into a store expression.

how can i fix this or how can i convert the number of that month into month string eg {value: 1, month: JAN}

Answer 1

Check your RDBMS version and EF version,do they support DATEPART method

eg

sqlserver 2017 have a table like below

CREATE TABLE [Table1](
    [col_datetime] [datetime] NULL
);

insert into [Table1] 
select '2019/01/02 03:04:05'

then ef query

Table1s.Select(w => new { month = Convert.ToString(w.Col_datetime.Value.Month)})

it'll query below sql

SELECT CONVERT(NVarChar,DATEPART(Month, [t0].[col_datetime])) AS [month]
FROM [Table1] AS [t0]

if it not support then it'll get error LINQ to Entities does not recognize the method 'System.String ToString(Int32)' method, and this method cannot be translated into a store expression.

if you must to do it without support function,you can ToList() save data to memory first then select

Table1s.Where(w=>/*your filter logic*/).ToList().Select(w => new { month = Convert.ToString(w.Col_datetime.Value.Month)})

Answer 2

If REQUEST_DATE_SUBMITTED is of type DateTime in your entity then

month = s.REQUEST_DATE_SUBMITTED.ToString().Substring(0, 3).ToUpper()

month = "JAN"

If you are not getting the result then see if your column in the table is

datetime or smalldate

if it is not then change it to datetime