Adobe 38043740 Developing Applications - Page 594

DEVELOPING COLDFUSION 9 APPLICATIONS 589 ColdFusion ORM Important: An entity is loaded only once in the request (in Hibernate session) and there is always only one copy of it in the request. So, for artwork and artist relationship, which is lazy, if the artist is already loaded, calling art.getartist() will not create a proxy object and will return the loaded artist object. Lazy loading can be disabled by setting lazy="false" on the relationship property definition in the CFC. Choosing an appropriate lazy loading option is very important for the performance of your application. Extra lazy means more number of trips to the database (each trip to the database is expensive) but less data in memory whereas no lazy loading means a huge object graph in the memory. So, you need to balance the approach based on the application need. Eager fetching In this strategy, the associated object or collection is fetched together with the owning entity using a single SQL Join query. This strategy reduces the number of trips to the database and is a good optimization technique when you always access the associated object immediately after loading the owning entity. You can define this strategy by setting fetch="join" for the relationship property definition in the CFC. Batch fetching This strategy tells Hibernate to optimize the second SQL select in Immediate fetching or lazy fetching to load batch of objects or collections in a single query. This allows you to load a batch of proxied objects or uninitilized collections that are referenced in the current request. This is generally useful in nested tree loading. You can specify this using "batchsize" attribute for CFC or relationship property. There are two ways you can tune batch fetching: • Batch fetching at CFC level: This allows batch fetching of the proxied objects and is applied to one-to-one and many-to-one relationship. For example, consider artwork and artist example where there are 25 art instances loaded in the request (ORM session). Each artwork has a reference to the artist and the relationship is lazy. Therefore, art objects contain the proxied object for artist. If you now iterate through all the art objects and call getartist() on each, by default 25 SELECT statements are executed to retrieve the proxied owners, one for each artist proxy object. This can be batched by specifying the 'batchsize' attribute on the artist CFC: When you call getartist() on the first art object, it batch fetches 10 artist objects that are proxied in the current request. So for 25 art objects, this type of batch fetching makes Hibernate execute a maximum of three queries in batches of 10, 10, and 5. • Batch fetching at collections: This allows batch fetching of value collections, one-to-many or many-to-many relationships that are uninitialized. For example, consider artist-art one-to-many relationship where there are 25 artists loaded and each artist has a lazy collection of artworks. If you now iterate through the artists and call getarts() on each, by default 25 SELECT statements are executed, one for each artist to load its art objects. This can be optimized by enabling batch fetching, which is done by specifying "batchsize" on the relationship property: Example: In artist.cfc: Last updated 1/20/2012