在WHERE子句中具有动态列名称的MVC Linq查询

Question

I have a number of calls for the same query but with slightly different WHERE clause, does anyone know if it's possible to pass a variable as the column name as I can't seem to acheive it.

I know the below isn't correct but just to give you an idea of what i'm trying to acheive.

public EmailUserListViewModel EmailUserListData(int CaseId, string ColumnName)
{
    CaseId = CaseId,
    EmailUserList = (from u in efContext.PgsUsers
                        where ColumnName == true
                        orderby u.FirstName, u.LastName
                        select new EmailUserListModel
                        {
                            UserId = u.Id,
                            Name = ((u.FirstName == null) ? "" : u.FirstName) 
                                   + ((u.LastName == null) ? "" : " " + u.LastName),
                            Email = u.Email,
                            Checked = false

                        }).ToList()
    };
}

Answer 1

I suppose you could use Reflection to dynamically retrieve the value of the property

from u in efContext.PgsUsers where (typeof(PgsUser).GetProperty(ColumnName).GetValue(u) as bool) == true

or

from u in efContext.PgsUsers where (u.GetType().GetProperty(ColumnName).GetValue(u) as bool) == true

Answer 2

You could write such method:

public Expression<Func<T, bool>> getExpression<T>(string columnName)
{
    var param = Expression.Parameter(typeof(T));
    var equal = Expression.Equal(Expression.Property(param, columnName), Expression.Constant(true));
    return (Expression<Func<T, bool>>)Expression.Lambda(equal, param);
}

and use it in where:

where getExpression<YourType>("ColumnName")