Adobe 38043740 Developing Applications - Page 593

DEVELOPING COLDFUSION 9 APPLICATIONS 588 ColdFusion ORM With this strategy, on loading the artists object, its art object is loaded immediately using a separate SQL query. As a result, this strategy is extremely vulnerable to 'N+1 Select problem'. Lazy fetching In this strategy, the associated object or collection is fetched only when required. Although you need to send a new request to the database each time you need data, this strategy controls how much of data is loaded and when is it loaded. This helps in reducing the database load. When you load an entity, by default, ColdFusion ORM loads the entity's data but relations and any mapped collections and are not loaded. They are loaded only when you want to load them by calling the getter method. Therefore, the relations and collection mappings are lazily loaded. For example, when the artist object is loaded, all its artworks are not loaded and they are loaded only when getarts() is called. ColdFusion ORM provides three types of lazy loading for relationships: • lazy: This is the default lazy loading that applies to collection mapping, one-to-many and many-to-many relationship. In this case, when you call the accessor for the collection/relation, the collection is fully loaded. So, when you call EntityLoad() for a particular artist, its artworks are not loaded at that time. When you call artist.getarts(), all the art object belonging to the artist will get loaded. This is achieved by setting lazy="true" on the relationship property definition in the CFC. Example: In artist.cfc • Extra lazy: This applies to one-to-many and many-to-many relationships. This type of lazy loading goes one step ahead of lazy and does not load all the associated objects when the accessor for that relation is called. It just loads the primary keys for those objects and keeps a proxy object for them. When you call any method on the wrapper object, that object's data is loaded from the database. For example, when you call artist.getarts(), it executes a query on the database to fetch the primary key of the related artwork objects and creates a proxy artwork object. So, you do not load the data for all the artwork objects in memory. When you access a particular artwork object and invoke any method on it, then it fires another query to the database to load that particular artwork object. This is achieved by setting lazy="extra" on the relationship property definition in the CFC. Example: In artist.cfc • proxy: This applies to one-to-one and many-to-one relationships. When the owner object is loaded, the related object is not loaded from the database. ColdFusion only creates a proxy object for the related object and when any method is invoked on the related object, the data for the proxy object is loaded from the database and populated in the proxy object. For example, if the art-artist table relation is lazy, when the art object is loaded, the artists object is not loaded and when you call art.getartist(), you would only get a proxy object. When you call any method on the proxy object, query gets executed on the database to load artist object's data. This is achieved by setting lazy="true" on the relationship property definition in the CFC Example: In ART.cfc Last updated 1/20/2012