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When writing plugins to interact with business logic objects, particularly handling events raised by these objects, it is important to understand the behaviours and sequence of events.

The Save

When the Save() method of a business logic object is invoked, the following occurs in order:

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Plugins that wish to use the same SQL transaction to update data to ensure consistency should do this in either the SaveStart or SaveEnding events. If using the SaveEnding event then ensure no user interaction is made.

Common Mistakes

Some of the more common mistakes which can cause significant issues are:

Blocking a SQL Transaction with a UI prompt

An entire organisation can be ground to a halt by displaying a messagebox or dialog at the wrong time.

If a plugin is awaiting user interaction and there are un-committed transactions pending, then other users will be blocked from reading or writing to the same tables or pages of the database.

The SaveEnding event of all business logic objects is raised when the business logic has created a SQL Transaction, issued SQL inserts, updates or deletes and not yet committed the transaction.

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The Read

When the Read(string RecID) of a business logic object is invoked, the following occurs in order:

1. The ReadStart event is raised

2. The Clear() method is invoked to clear contents of properties, private members and collections - this will in turn raise the ClearStart and then ClearEnd events.

3. The data is read

4. The ReadEnd event is raised

JiwaCollections

All collections or lists in Jiwa are of type JiwaCollection. Each item in the collection inherit from the JiwaCollectionItem class.

Sales order lines, purchase order lines, debtor delivery addresses, Bill input items are all JiwaCollections.

There are several events of JiwaCollections which can be subscribed to, via the public property of the business logic object.

Note that the JiwaCollection events are not raised during the normal read of a business logic object.

Adding

The Adding event is raised when an item is being added to the collection. A CancelEventArgs argument allows this add to be cancelled.

Added

The Added event is raised when an item is added to the JiwaCollection. The item argument is the item which was added.

The code below shows a handler for a sales order lines, displaying a message box of the PartNo property of the sales order line when added to the collection.

public class FormPlugin : System.MarshalByRefObject, JiwaFinancials.Jiwa.JiwaApplication.IJiwaFormPlugin
{
	public override object InitializeLifetimeService()
    {
        // returning null here will prevent the lease manager
        // from deleting the Object.
        return null;
    }

    public void SetupBeforeHandlers(JiwaFinancials.Jiwa.JiwaApplication.IJiwaForm JiwaForm, JiwaFinancials.Jiwa.JiwaApplication.Plugin.Plugin Plugin)
    {
    }
	
    public void Setup(JiwaFinancials.Jiwa.JiwaApplication.IJiwaForm JiwaForm, JiwaFinancials.Jiwa.JiwaApplication.Plugin.Plugin Plugin)
    {
		JiwaFinancials.Jiwa.JiwaSalesUI.SalesOrder.SalesOrderEntryForm salesOrderForm = (JiwaFinancials.Jiwa.JiwaSalesUI.SalesOrder.SalesOrderEntryForm)JiwaForm;
		salesOrderForm.SalesOrder.SalesOrderLines.Added += delegate(JiwaFinancials.Jiwa.JiwaSales.SalesOrder.SalesOrderLine salesOrderLine)
			{
				System.Windows.Forms.MessageBox.Show(String.Format("Added '{0}'", salesOrderLine.PartNo));
			};
    }
}

Changed

The Changed even is raised when a property if the item changes. The PropertyChangedEventArgs argument has a PropertyName property which contains the name of the property which changed.

Removing

The Removing event is raised when an item is being removed from the JiwaCollection.

Removed

The Removed event is raised when an item is removed from the JiwaCollection.

Common Mistakes

Some of the more common mistakes which can cause significant issues are:

Blocking a SQL Transaction with a UI prompt

An entire organisation can be ground to a halt by displaying a messagebox or dialog at the wrong time.

If a plugin is awaiting user interaction and there are un-committed transactions pending, then other users will be blocked from reading or writing to the same tables or pages of the database.

The SaveEnding event of all business logic objects is raised when the business logic has created a SQL Transaction, issued SQL inserts, updates or deletes and not yet committed the transaction.

Awaiting user interaction, or any long running operation - such as I/O or external API’s should not be done in handlers of the SaveEnding event.

DRY (Don’t Repeat Yourself)

If there is code that is going to be needed by multiple plugins don’t repeat the code in multiple places, instead create a plugin and create a public class within this plugin to hold the code and then add a plugin reference to each of the plugins that need to access this code and call this new class. By doing this you don’t have to maintain multiple copies of the same code.