Sorting with Objects on Multiple Fields

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Introduction

This article demonstrates how to apply sorting on objects. It is useful when you need to apply sorting on objects e.g. Object Person(Name, Age) and you want to apply sorting on Person->Name, or you may wish to apply sorting on multiple fields i.e. Person->name DESC + person->age DESC.

It is very useful when you want to apply multiple column sorting on GridViews with ObjectDataSource.

Using the Code

Using Reflection, its very easy to sort objects. I had used Lists<T> to sort objects and ObjectComparer class is inherited from IComparer<ComparableObject>.

ObjectComparer supports single as well as multiple sorting.

//
//
//Test.cs 
//Created an array of Person object, for which i wish to apply sorting 

Person[] personArray = new Person[] { 
new Person("Ritesh", 26),
new Person("Arpan", 20),
new Person("Arpan", 23),
new Person("Hiren", 22),
new Person("Ankit", 22),
new Person("Dhaval", 23),
new Person("Gaurav", 25)
};

//Sort array on field Name in Ascending Order
Array.Sort(personArray, new ObjectComparer<Person>("Name"));

//Sort array on field Name Descending and Age Ascending
Array.Sort(personArray, new ObjectComparer<Person>("Name DESC, Age ASC",true));

ObjectComparer.cs

[Serializable]
public class ObjectComparer<ComparableObject> : IComparer<ComparableObject>
{
    #region Constructor
    public ObjectComparer()
    {
    }

    public ObjectComparer(string p_propertyName)
    {    
        //We must have a property name for this comparer to work
        this.PropertyName = p_propertyName;
    }

    public ObjectComparer(string p_propertyName, bool p_MultiColumn)
    {
        //We must have a property name for this comparer to work
        this.PropertyName = p_propertyName;
        this.MultiColumn = p_MultiColumn;
    }
    #endregion

    #region Property
    private bool _MultiColumn;
    public bool MultiColumn
    {
        get { return _MultiColumn; }
        set { _MultiColumn = value; }
    }

    private string _propertyName;
    public string PropertyName
    {
        get { return _propertyName; }
        set { _propertyName = value; }
    }
    #endregion 

    #region IComparer<ComparableObject> Members
    /// <summary>
    /// This comparer is used to sort the generic comparer
    /// The constructor sets the PropertyName that is used
    /// by reflection to access that property in the object to 
    /// object compare.
    /// </summary>
    /// <param name="x"></param>
    /// <param name="y"></param>
    /// <returns></returns>
    public int Compare(ComparableObject x, ComparableObject y)
    {
        Type t = x.GetType();
        if (_MultiColumn) // Multi Column Sorting
        {
            string[] sortExpressions = _propertyName.Trim().Split(',');
            for (int i = 0; i < sortExpressions.Length; i++)
            {
                string fieldName, direction = "ASC";
                if (sortExpressions[i].Trim().EndsWith(" DESC"))
                {fieldName = sortExpressions[i].Replace(" DESC", "").Trim();
                direction = "DESC";
            }
            else
            {
                fieldName = sortExpressions[i].Replace(" ASC", "").Trim();
            }

            //Get property by name
            PropertyInfo val = t.GetProperty(fieldName);
            if (val != null)
            {
                //Compare values, using IComparable interface of the property's type
                int iResult = Comparer.DefaultInvariant.Compare
				(val.GetValue(x, null), val.GetValue(y, null));
                if (iResult != 0)
                {
                    //Return if not equal
                    if (direction == "DESC")
                    {
                        //Invert order
                        return -iResult;
                    }
                    else
                    {
                        return iResult;
                    }
                }
            }
            else
            {
                throw new Exception(fieldName + " is not a valid property to sort on. 
			It doesn't exist in the Class.");
            }
        }
        //Objects have the same sort order
        return 0;
    }
    else
    {
        PropertyInfo val = t.GetProperty(this.PropertyName);
        if (val != null)
        {
            return Comparer.DefaultInvariant.Compare
		(val.GetValue(x, null), val.GetValue(y, null));
        }
        else
        {
            throw new Exception(this.PropertyName + " 
	      is not a valid property to sort on. It doesn't exist in the Class.");
        }
    }
}
#endregion

}

//

Points of Interest

• Sorting with objects
• Multicolumn sorting with objects