A Guide to Spigot For Seam Developers
Note : Spigot has been renamed to DataValve.
(Edit : I renamed this post so it doesn’t seem like Spigot is just for Seam, Spigot can be used with different frameworks or without any at all. However, I wrote this post since Spigot is so familiar to the Seam EntityQuery that it should be easy for Seam users to get the idea)
Seam developers should become familiar with Spigot concepts fairly quickly since they are very similar to those found in the Seam
EntityQuery which was one of the main inspirations for the framework. If you imagine taking the entity query class and splitting it in two, one part to keep hold of state and the other to actually fetch the data. The stateful part is the
Paginator that keeps track of what the current ordering of the data is, what is the current page and how big the pages are. The stateless part takes the Ejbql and the pagination information and returns a subset of the data. Now imaging that the data provider has the JPA pieces taken out and replaced with an abstract
fetchResults method. This method is implemented in subclasses for specific data providers for text files, sql queries, jpa queries, native jpa queries, xml files, comma delimited or just an in memory dataset.
I also abstracted the concepts of parameterization and parameter resolution so you can have parameters on data providers that are no t query based and your parameters can be resolved using different mechanisms such as EL, reflection, a map, or using custom parameter resolution.
So really, for Seam developers, its like a Seam
EntityQuery that doesn’t just use JPA, but uses any kind of data source you want but still returns just a list of objects.
Spigot works nicely with CDI and there is even a demo of it in the distribution that uses JSF and was generated using the Weld maven archetypes. Also, there is a Seam Jpa Dataset Adapter that you can use as a direct replacement for the
EntityQuery which will adapt the entity query calls to the underlying data provider calls so you can have a seam-less transition if you want to switch over. This is still a little in-progress, but works. The one area that isn’t implemented is the sorting, which may not be possible, but I still need to add in the methods to the adapter even if they don’t do anything. The other issue is of course the configuration of the query from components.xml using the Seam Framework tags. However, you can define the query using regular component xml tags to define the Ejbql, restrictions and page sizes.
Two things to note if you start using Spigot in place of the entity query. All rows are returned by default, and you need to specify both a select statement and a count statement. I separated those two out so you can put join fetch phrases in the select statement without it breaking the count statement. There is an
init method that you can use to set both of these statements for a class type.
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