Monday, January 02, 2012

Lightswitch 2011 - Entity default creation date and time

Creation date and time
Entities have no default property. If the entity needs a creation datetime field that registers the time when an entity record was created you can use the ' <entity> _Created' event from the from the 'Write Code' drop-down menu in the entity designer. 
For instance for an entity called 'Personeel' I want to use a field DatumCreatie that contains the date and time when the record was created. In the '<entity>_Created' event I need to add this code:
        partial void Personeel_Created()
        {
            // set default values for any field of the entity where necessary
            this.DateCreation = DateTime.Now;
        }
DateCreation is set as a required field in the entity designer.
In Lightswitch screens I use the DateTime Viewer control to show this Creation datetime field, since it should not be modifiable by the user.
Modification date and time
To track each time a record has been changed, I have added another datetime field to the entity. In the 'Write Code' I have selected the '<entity>_Updating' event, to change the modification date.
        partial void Personeels_Updating(Personeel entity)
        {
            entity.DateModification = DateTime.Now;
        }
DateModification is not set as required in the entity designer.
Take care NOT to use the '<entity>_Updated' event. Because the change of the date would retrigger the same event endlessly (i.e. until you run into stack overflow).
Creation and modification datetime fields default values and triggers
Creation date can be managed in SQL server by specifying a default value for the DateCreation field. The default value is a sql server GETDATE() function.
For the modification date a trigger after update could be used.

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