/// <summary>
/// Reads the latest attribute value using the priority Target -> PreImage -> PostImage
/// </summary>
/// <typeparam name="TValue">The type of the attribute value to read</typeparam>
/// <param name="readProperty">The delegate that defines the property to read</param>
/// <param name="exceptionMessage">The message to appear in the exception message when the value is not available on either target or image</param>
/// <returns>The value read from the prioritised entities</returns>
public TValue ReadValue <TValue>(Func <TEntity, TValue> readProperty, string exceptionMessage = null)
{
var target = _context.LoadTarget <TEntity>(false);
var image = _context.LoadPreImage <TEntity>() ?? _context.LoadPostImage <TEntity>();
var result = readProperty(target ?? image);
//Resharper warnings/recommendations...
//Cannot use Null Coalescing Expression due to not being able to apply class OR nullable constraint
//Value type null compare won't occur as all CRM value types are nullable
if (result == null && !string.IsNullOrEmpty(exceptionMessage))
{
throw new InvalidPluginExecutionException(exceptionMessage);
}
return(result);
}
/// <summary>
/// Helper method for plugins for reading the property defined
/// on the <paramref name="readProperty"/> callback from either the <paramref name="target"/>
/// or <paramref name="image"/> (pre/post) depending on whichever is populated. So if it is an update triggering
/// the plugin it will always read the latest value, regardless of whether the attribute being read was one of the
/// triggering attributes.
/// </summary>
/// <typeparam name="T">The type for the return value (referencee type only)</typeparam>
/// <typeparam name="TE">The entity types for target and image</typeparam>
/// <param name="readProperty">The callback to determine which property on the entity to be read</param>
/// <param name="propertyDisplayName">Friendly display name for the property if an exception is thrown</param>
/// <returns>The value off either the target if it exists or the image</returns>
/// <exception cref="NullReferenceException"></exception>
public static T Read <T, TE>(this IPluginExecutionContext context, Func <TE, T> readProperty,
string propertyDisplayName = "Value")
where T : class
where TE : Entity
{
var image = context.LoadPreImage <TE>() ?? context.LoadPostImage <TE>();
var result = readProperty(context.LoadTarget <TE>()) ?? readProperty(image);
if (result == null)
{
throw new NullReferenceException(propertyDisplayName + " has not been defined.");
}
return(result);
}