LINQ to Entities无法识别方法'Int32 ToInt32（System.Object）'方法

Question

I wrote this SQL query

select 
    acc.DepartmentID,
    dept.DepartmentName,
    dept.DepartmentDivision,
    county.CountyName,
    sp.StateProvinceID
from [AccountDepartmentXREF] acc
inner join [Department] dept on dept.DepartmentID = acc.DepartmentID
left join [DepartmentStateCountyXREF] dscx on dscx.DepartmentID = acc.DepartmentID
left join [StateCounty] county on county.StateCountyID = dscx.StateCountyID
inner join [StateProvince] sp on sp.StateProvinceID = dept.StateProvinceID
where acc.AccountID = 1

and want to rewrite it using LINQ, but I always get confused when writing left joins in LINQ, so I decided to use a convertor and went with Linqer and this is what it produced

from acc in db.AccountDepartmentXREF
join dscx in db.DepartmentStateCountyXREF on acc.DepartmentID equals dscx.DepartmentID into dscx_join
from dscx in dscx_join.DefaultIfEmpty()
join county in db.StateCounty on new { StateCountyID = Convert.ToInt32(dscx.StateCountyID) } equals new { StateCountyID = county.StateCountyID } into county_join
from county in county_join.DefaultIfEmpty()
join sp in db.StateProvince on acc.Department.StateProvinceID equals sp.StateProvinceID
where
acc.AccountID == 1
select new {
acc.DepartmentID,
acc.Department.DepartmentName,
acc.Department.DepartmentDivision,
CountyName = county.CountyName,
sp.StateProvinceID
}

so when I put everything together in code

public List<DepartmentList> GetDepartmentsByAccountID(string email)
    {
        HWC = new HWCEntities();
        List<DepartmentList> result = new List<DepartmentList>();

        int id = CurrentUserID(email);

        List<AccountDepartmentXREF> adx = HWC.AccountDepartmentXREFs.Where(w => w.AccountID == id).ToList();

        foreach(var a in adx)
        {
            var query = from acc in HWC.AccountDepartmentXREFs
                        join dscx in HWC.DepartmentStateCountyXREFs on acc.DepartmentID equals dscx.DepartmentID into dscx_join
                        from dscx in dscx_join.DefaultIfEmpty()                                
                        join county in HWC.StateCounties on new { StateCountyID = Convert.ToInt32(dscx.StateCountyID) } equals new { StateCountyID = county.StateCountyID } into county_join
                        from county in county_join.DefaultIfEmpty()
                        join sp in HWC.StateProvinces on acc.Department.StateProvinceID equals sp.StateProvinceID
                        where
                          acc.AccountID == a.AccountID
                        select new
                        {
                            acc.DepartmentID,
                            acc.Department.DepartmentName,
                            acc.Department.DepartmentDivision,
                            CountyName = county.CountyName,
                            sp.StateProvinceID
                        };

            foreach(var b in query)
            {
                result.Add(new DepartmentList
                {
                    DepartmentID = b.DepartmentID,
                    DepartmentName = b.DepartmentName,
                    StateProvinceID = b.StateProvinceID,
                    DivisionName = b.DepartmentDivision,
                    CountyName = b.CountyName
                });
            }
        }

        return result;
    }

I get the error

LINQ to Entities does not recognize the method 'Int32 ToInt32(System.Object)' method, and this method cannot be translated into a store expression.

at the

foreach(var b in query)

Any idea's on how to fix this? I have looked around but other solutions I found aren't dealing with joins

Answer 1

Linq doesn't support the Convert.ToInt32(dscx.StateCountyID) method inside the query because this will need to be converted to sql for execution on the db.

I am not sure what datatype StateCountyID is in both tables but you will need to use some sql compatible conversion method like SqlFunctions.StringConvert() to get them to the same datatype.

Answer 2

Convert them to Strings

from acc in HWC.AccountDepartmentXREFs
                        join dscx in HWC.DepartmentStateCountyXREFs on acc.DepartmentID equals dscx.DepartmentID into dscx_join
                        from dscx in dscx_join.DefaultIfEmpty()                                
                        join county in HWC.StateCounties on new { StateCountyID = dscx.StateCountyID.ToString() } equals new { StateCountyID = county.StateCountyID.ToString() } 

or use the below:

dscx.StateCountyID equals SqlFunctions.Convert(county.StateCountyID)

Answer 3

I figured out why I was getting that error. It was because I had StateCountyID as nullable in my DepartmentStateCountyXREF table. Once I changed the StateCountyID column from a nullable and then removed the Convert.ToInt32, everything worked.