support nested property filters

Problem: If there is a class say Person

class Person {
   string name;
   int age;
   Address address;

   .. getters and setters
}

How do we dynamically filter specific nested properties: name, address.state, address.zipcode reusing the same object mapper/writer.

One way is to follow the Spring integration to use property filter https://jira.spring.io/browse/SPR-12586. However, nested property filters are not supported. This is because of the way Jackson integration works. This is a very common use case to get only the fields clients are interested in runtime.

There are a few implementations already available that are slow because they lookup the jgen root context to build the nested path every time a property is checked if it can be filtered. These implementations also won’t work without explicitly adding JsonFilter annotation on all classes that will be filtered: https://github.com/PressAssociation/partial-response/tree/master/filter-json-jackson https://github.com/Antibrumm/jackson-antpathfilter https://github.com/narusas/SpringMvcJacksonFilter

The following won’t work without @JsonFilter(“antPathFilter”) on all classes

objectMapper.addMixIn(Object.class, AntPathFilterMixin.class);
filter = new SimpleFilterProvider()
            .addFilter("antPathFilter",
                    new AntPathPropertyFilter("nestedObj", "nestedObj.nestedProperty")
jacksonValue.setFilters(filter);

One work around is to explicitly set the same @JsonFilter(“antPathFilter”) on all classes that are nested, which did not make any sense to me. What if I wanted to support multiple filters at the same time tomorrow?

I also ended up writing my own implementation that is fast and that uses SimplePropertyFilter per class built on the nested properties.

The problem really is the way Jackson APIs requests a filter for current property without any context on the current class owning that property.

https://github.com/krishna81m/jackson-nested-prop-filter

[bohnman]

I wrote a library called Squiggly Filter, which selects fields based on a subset of the Facebook Graph API syntax. For example, to select the zipCode of the address field of the user object, you would use a filter address{zipCode}.

More information here

[cowtowncoder]

I don’t think I know what should be done here; but I do note that some new functionality has been added in JsonParser; specifically, in Jackson 2.5, ability to set and get “current value” which is the POJO being read. This combined with parent stack of current property names should allow building nested filters. But I don’t see things to work on in Jackson proper itself at this point.

For new specific ideas, requests, feel free to file a new issue.