Select 使用 LINQ 与 db 不同的列名

Question

I have a table that has several columns including CarMake, CarModel, CarModelLoading etc. I want to select distinct CarMake and return them as list. I have tried the following:

public IEnumerable<EbimaCarMakesAndModel> GetAll()
        {
            //var list<ebima>
            return (IEnumerable<EbimaCarMakesAndModel>)context.EbimaCarMakesAndModels.Select(l => new { l.CarMake }).Distinct().ToList();
            //var data = (from dbo in context.EbimaCarMakesAndModels where dbo.Listed == "Y" select dbo.CarMake).Distinct().OrderBy(name => name).ToList();

            //return (IEnumerable<EbimaCarMakesAndModel>)data;
}

but whenever run the app, I get the error:

An unhandled exception occurred while processing the request. InvalidCastException: Unable to cast object of type 'System.Collections.Generic.List 1[<>f__AnonymousType31 1[System.String]]' to type 'System.Collections.Generic.IEnumerable`1[motor_backend.Models.EbimaCarMakesAndModel]'. I have also tried the following but to no avail:

public IEnumerable<EbimaCarMakesAndModel> GetAll()
    {
        var res = context.EbimaCarMakesAndModels.GroupBy(x => new { x.CarMake }).
            Select(x => x.FirstOrDefault()).Where(v => v.Listed == "Y").ToList();
        return res;
     }

It gives me the error below:

FirstOrDefault()' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.

all the solutions given here haven't answered my query so far

Answer 1

Either declare your method to return an IE of string:

public IEnumerable<string> GetAllMakes()

And your query to not make an anonymous type but simply select the make:

return context.EbimaCarMakesAndModels.Select(l => l.CarMake).Distinct().ToList();

Or group by make and return some nominal entry from the group list (but that doesn't really make sense to me)

return context.EbimaCarMakesAndModels.GroupBy(x => x.CarMake)
       .Select(x => x.FirstOrDefault()).ToList();

Your last query introduced some additional unmentioned constraint .Where(v => v.Listed == "Y") - perhaps consider doing this on EbimaCarMakesAndModels before you group