Question

I need to find the biggest size of each string column in a database as one of the informations to design another database. The only access I have to the source database is by a web service. I can just do it for each of the many columns to find the biggest size but I want it generic so I can use it later.

I wrote this very simplified version to make it simple to understand. Two of the last lines have invented syntax and it is where I need help.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public class myClass
    {
        private string s;
        public string S
        {
            get { return s; }
            set { s = value; }
        }
        private int i;
        public int I
        {
            get { return i; }
            set { i = value; }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Type myClassType = typeof(myClass);
            System.Reflection.PropertyInfo[] propertyInfo = myClassType.GetProperties();
            Dictionary<string, int> property = new Dictionary<string, int>();

            foreach (System.Reflection.PropertyInfo info in propertyInfo)
               if (info.PropertyType == typeof(System.String))
                    property.Add(info.Name, -1);

            myClass[] myPa = new myClass[2];
            myPa[0] = new myClass();
            myPa[0].S = "1";
            myPa[0].I = 0;
            myPa[1] = new myClass();
            myPa[1].S = "12";
            myPa[1].I = 1;

This is where I need help. I invented the c[pair.key]. How to have a reference to a property that I know the name of?

            foreach (myClass c in myPa)
                foreach (KeyValuePair<string, int> pair in property)
                    if (c[pair.Key].Length > pair.Value)
                        property[pair.Key] = c[pair.Key].Length;

            foreach (KeyValuePair<string, int> pair in property)
                Console.WriteLine("Property: {0}, Biggest Size: {1}", pair.Key, pair.Value);
        }
    }
}

Output shoud be:

Property: S Biggest Size: 2

Answer 1

The following should suffice:

static void Main()
{
    // Demo data
    myClass[] myPa = new myClass[2];
    myPa[0] = new myClass();
    myPa[0].S = "1";
    myPa[0].I = 0;
    myPa[1] = new myClass();
    myPa[1].S = "12";
    myPa[1].I = 1;

    PrintMaxLengthsOfStringProperties(myPa);
}

public static void PrintMaxLengthsOfStringProperties<T>(IEnumerable<T> items)
{
    var t = typeof(T);
    t.GetProperties().Where(p => p.PropertyType == typeof(string)) // TODO: Add other filters
                        .SelectMany(p => items.Select(o => (string)p.GetValue(o, null)).Select(v => new { Property = p, Value = v }))
                        .GroupBy(u => u.Property)
                        .Select(gu => new { Property = gu.Key, MaxLength = gu.Max(u => u.Value != null ? u.Value.Length : 0) })
                        .ToList()
                        .ForEach(u2 => Console.WriteLine("Property: {0}, Biggest Size: {1}", u2.Property.Name, u2.MaxLength))
                        ;
}

Though you might add some extra filters on the “GetProperties” result set (such as taking out static ones, or indexing properties, etc.

It makes use of a couple of Linq extension functions, namely, “Where”, “GroupBy”, “SelectMany”, “Select”, and “Max” as well using anonymous types.