Data Binder: Auto-grow collections as needed to support nested property binding [SPR-6033]

[spring-projects-issues]

Keith Donald opened SPR-6033 and commented

Grails, SpEL, and the new PresentationModel under development for 3.1 all include this feature. We should consider building this natively into DataBnder to benefit existing users & so Grails particularly no-longer has to maintain its own extensions.

Scenario illustrating feature behavior:

• Suppose I have an instance of type Foo
• And I attempt to bind to indexed property path bar.baz[0] = 'hello'
• If baz, a List, is null, it will be created in line with the rules described in Data Binder: Add support for auto-instantiating null values in nested paths [SPR-6032] #10701; 'hello' will then be added as the first element at index = 0, even though the new list was initially empty with a size of 0.

Alternate scenario:

• Attempting to bind to index property path bar.baz[5] = 'hello'; say baz is not null, but only has a size of 1 at index = 0.
• In this scenario, new default instances of the List's parameterized type e.g. String in the case of List<String> will be added at index 1..3; baz[4] would then be set to 'hello'.

As a developer, this frees me from having to pre-populate a indexed object graph ahead of time when binding back a Form post; I can simply rely on what the client is submitting to drive the population of the object graph. This is convenient

---

Affects: 3.0 M4

Issue Links:

• DataBinder should be able to define a different strategy for BeanWrapperImpl how autogrowing should handle gaps in collection properties [SPR-7842] #12498 DataBinder should be able to define a different strategy for BeanWrapperImpl how autogrowing should handle gaps in collection properties
• mvc: Dynamic List use case - allow collections/arrays to grow [SPR-4728] #9405 mvc: Dynamic List use case - allow collections/arrays to grow

Referenced from: commits 3fa533d

1 votes, 2 watchers

[spring-projects-issues]

Keith Donald commented

Added auto-growth for arrays and Lists to BeanWrapper when "autoGrowNestedPaths" is true. Support for sets and Maps will be considered and addressed in a separate JIRA.