Sunday, November 22, 2009

.NET C# Extension Methods - Reflection

Other extension methods:

---------------------------

I was wondering how to get the name of a property via reflection. So I searched the Internet and I found this on Google code. The code was not good enough though. I was not able to get a string name from level 3 (i.e: User.Name.First). I did a small modifications and ended with this class that works perfect.

    /// <summary>
/// An extentension method on an actual object to get its member names
/// </summary>
public static class ReflectionExtensions
{
public static string MemberName<T, R>( this T obj, Expression<Func<T, R>> expr )
{
var node = expr.Body as MemberExpression;
if( object.ReferenceEquals( null, node ) )
throw new InvalidOperationException( "Expression must be of member access" );
return node.Member.Name;
}
}

/// <summary>
/// If we don't have an actual object we can still refer to its type with this generic static class
/// </summary>
public static class MembersOf<T>
{
public static string GetName<R>( Expression<Func<T, R>> expr )
{
var node = expr.Body as MemberExpression;
if( object.ReferenceEquals( null, node ) )
throw new InvalidOperationException( "Expression must be of member access" );

string result = BuildName( node, sb );

sb.Remove( 0, sb.Length );
temp.Remove( 0, temp.Length );

return result.Remove( result.Length-1 );
}

private static StringBuilder sb = new StringBuilder();
private static StringBuilder temp = new StringBuilder();
private static string BuildName( MemberExpression expr, StringBuilder sb )
{
if( expr.IsNotNull() )
{
temp.Append( expr.Member.Name );
temp.Append(".");

sb.Insert( 0, temp.ToString() );
temp.Remove( 0, temp.Length );

BuildName( expr.Expression as MemberExpression, sb );
}

return sb.ToString();
}
}

Now the question is where this code can be handy? I use this when I want to build NHibernate Criteria or DetachedCriteria. When you create a Criteria you use a code like this one:


ICriteria crit = session.CreateCriteria(typeof(Customer));
crit.Add(Expression.Eq("Customer.Name.First", someValue));

Here the Name property is a NHibernate component. The problem is that if you change the property Name to FirstName you will not get a compile error but you will get runtime error when the query is executed against the database. Also you can use some refactoring tool like RefactorPro! and the changes in the component will be applied also in the criteria. Nice, ahh?!? And the code above will be:


ICriteria crit = session.CreateCriteria(typeof(Customer));
crit.Add(Expression.Eq(MembersOf<Customer>.GetName(x=>x.Name.First), someValue));


Thursday, November 19, 2009

.NET C# Extension Methods - IDictionary

Other extension methods:

---------------------------

Extension method for IDictionary. Returns the values associated with the key specified by parameter key.

        /// <summary>
/// Gets the value of an element within a dictionary object.
/// </summary>
/// <typeparam name="TValue">The type of the value.</typeparam>
/// <param name="bag">The actual dictionary.</param>
/// <param name="key">The key that will be searched for within the dictionary object.</param>
/// <param name="defaultValue">Returns default value if the specified key was not found.</param>
/// <returns>Specific value within dictionary object.</returns>
public static TValue GetValue<TValue>( this IDictionary bag, string key, TValue defaultValue )
{
object value = bag[ key ];

if( value == null )
{
value = defaultValue;
}

return defaultValue;
}

Extension method for IDictionary. Adds a key-value pair.

        /// <summary>
/// Adds a (key,value) pair in a dictionary object.
/// </summary>
/// <typeparam name="TKey">The type of keys in the dictionary.</typeparam>
/// <typeparam name="TValue">The type of values in the dictionary.</typeparam>
/// <param name="bag">The actual dictionary.</param>
/// <param name="key">The name of the key used for easy navigation in a dictionary object.</param>
/// <param name="value">The value assoiciated with the key.</param>
public static void SetValue<TKey, TValue>( this IDictionary<TKey,TValue> bag, TKey key, TValue value )
{
if( bag.ContainsKey( key ) )
{
bag[ key ] = value;
}
else
{
bag.Add( key, value );
}
}

.NET C# Extension Methods - DataGridView

Other extension methods:

---------------------------

Extension method for DataGridView. Returns IDictionary with values of all selected rows and columns that are specified by parameter columnName.

        /// <summary>
/// Gets values from selected rows and specified columns.
/// </summary>
/// <param name="grid">The grid.</param>
/// <param name="columnName">Name of the column/s.</param>
/// <returns></returns>
public static IList<IDictionary<string, object>> GetSelectedValuesFrom( this DataGridView grid, params string[] columnName )
{
IList<IDictionary<string,object>> results = new List<IDictionary<string, object>>( grid.SelectedRows.Count );

foreach( DataGridViewRow row in grid.SelectedRows )
{
IDictionary<string,object> rowResult = new Dictionary<string, object>( columnName.Length );

foreach( string column in columnName )
{
rowResult.Add( column, row.Cells[ column ] );
}

results.Add( rowResult );
}

return results;
}

Extension method for DataGridView. Returns a list with values of all selected rows in the columns specified by parameter columnName.

        public static IList<T> GetSelectedValuesFrom<T>( this DataGridView grid, string columnName )
{
IList<T> results = new List<T>( grid.SelectedRows.Count );

foreach( DataGridViewRow row in grid.SelectedRows )
results.Add( GetCurrentValueFrom<T>( grid, columnName ) );

return results;
}

Extension method for DataGridView. Returns a single value of selected row in the columns specified by parameter columnName.

        public static T GetCurrentValueFrom<T>( this DataGridView grid, string columnName )
{
if (grid.CurrentRow != null)
{
return (T)Convert.ChangeType(grid.CurrentRow.Cells[columnName].Value, typeof(T));
}
return (T) Convert.ChangeType(- 1,typeof(T));
}