In my application, every Foo has a Category. Foo.Category is an internal enum in class Foo. When creating a Foo on its given form page, the user selects a Category from a drop down typed to the enum. However, this choice is optional.
Now, on another page, I want to be able to search Foo by name, and also by Category. This search form has a CheckBoxMultipleChoice<Foo.Category> also typed to the same internal enum. The checked values are sent to a DAO which queries my database with a “where category in” clause.
I want to add a “Blank/ None” choice to the check boxes, so that when sent to the DAO I can add a “or where category is null” to the query, if checked. Since my check box is typed to the enum, is this even possible?
EDIT: Not sure if this will be important, but my enum has values designated by a SHORTNAME, but each has a String LongerAndMoreDescriptiveName, and the enum overrides toString() to return this value. The SHORTNAME is what I store in the database, and used in the where clauses, but the Longer is what is shown on the UI. I had briefly thought about changing to CheckBoxMultipleChoice and add the blank choice, but how would I then solve the discrepancy between values?
It’s not possible directly. There’s no such thing as “No value” choice in CheckBoxMultipleChoice (like in DropDownChoice), because component’s model is null when nothing is selected.
I think, you have two options:
1) Add constant Category.NONE to Foo.Category enum, and process it accordingly in the drop down choice where user selects category.
2) Create a wrapper class (something like Optional<Foo.Category>) for Foo.Category constants, and use it in the CheckBoxMultipleChoice instead of using Foo.Category constants directly. Instance of Optional<Foo.Category> will be able to have or not have corresponding Foo.Category constant so your processing of selection model should be appropriate.