[DELTASPIKE-1241] [Config] fallback chain logic

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.7.2
• Component/s: Configuration
• Assignee: Mark Struberg
• Reporter: Mark Struberg
• Created: 02/Apr/17 16:18
• Updated: 16/Dec/19 12:57

Description

We got the request to add handling similar to ConfigResolver#getProjectStageAwarePropertyValue and ConfigResolver#getPropertyAwarePropertyValue but in a more generic way.

Something I've been experimenting with since a long time was to introduce a more generic logic based on different lookup paths with themselves represent a postfix.

The idea is to extend the TypedResolver with a method

TypedResolver#withLookupPath(String... lookupPaths)

where each lookupPath String could either be a hardcoded value (e.g. evaluated upfront) or a variable "${somevariable}" which will be evaluted on the fly.

ConfigResolver.getPropertyAwarePropertyValue("dbvendor") could e.g. also be written as

TypedResolver<String> ds = 
    ConfigResolver.resolve("myprj.datasource")
       .withLookupPath("${dbvendor}", "${deltaspike.projectstage}");
ds.get();

Assuming we are in the ProjectStage UnitTest this would result in the following lookup paths:

• datasource.mysql.UnitTest
• datasource.mysql
• datasource.UnitTest
• datasource

The lookupChain is kind of a binary field with all flags set to 1 (in the sample this would be: 11) and then decremented for each lookup (11, 10, 01, 00). Where 1 means to lookup with the specific postfix and 0 without.