dotnetcore EF 动态查询指定列

普通情况下，可以通过select实现查询指定列，

    ctx.Students.Select(s => new {s.Id, s.Name});
    ctx.Students.Select(s => new object[] {s.Id, s.Name});

这里使用动态方式实现select查询指定列

    using (MyDbContext ctx = new MyDbContext())
    {
        var students = Query<Student>(ctx, "Id", "Name");

        foreach (object[] s in students)
        {
            Console.WriteLine(s[0] + "," + s[1]);
        }
    }

        static IEnumerable<object[]> Query<T>(MyDbContext ctx, params string[] propertyNames)
            where T : class
        {
            var p = Parameter(typeof(T));
            List<Expression> propExprList = new List<Expression>();
            foreach (string propertyName in propertyNames)
            {
                Expression propExpr = Convert(MakeMemberAccess(p, typeof(T).GetProperty(propertyName)), typeof(object));
                propExprList.Add(propExpr);
            }

            var newArrayExpr = NewArrayInit(typeof(object), propExprList.ToArray());
            var selectExpr = Lambda<Func<T, object[]>>(newArrayExpr, p);

            return ctx.Set<T>().Select(selectExpr);
        }