Spring-boot: YAML lists cannot be mapped to Sets

[ejwood79]

I have a YAML application properties file and I'm trying to map a series of items to a Set. This appears to be impossible given the Spring Beans code that processes the properties, but the documentation tells a different story.

YAML:

test:
  - "value"

Code:

@ConfigurationProperties
public class MyTest {

    private Set<String> test;

    public void setTest(Set<String> test) {
        this.test = test;
    }

    public Set<String> getTest() {
        return this.test;
    }
}

The spring-boot documentation states:

To bind to properties like that using the Spring DataBinder utilities (which is what @ConfigurationProperties does) you need to have a property in the target bean of type java.util.List (or Set) and you either need to provide a setter, or initialize it with a mutable value, e.g. this will bind to the properties above

However, Set is not supported. If you attempt to map a YAML property to a Set, you'll get an exception similar to the following:

Property referenced in indexed property path 'test[0]' is neither an array nor a List nor a Map; returned value was [value]

The documentation should be corrected on this point.

[snicoll]

There are tests working with Set in RelaxedDataBinderTests so it should work. Can you put a sample project that reproduces the issue. Ideally here? Thanks

[wilkinsona]

Closing due to lack of response. Please comment again and we can reopen the issue if you're still having trouble.

[dan-nawrocki]

It looks like the RelaxedDataBinderTests are testing that the YAML foo: bar,bat can get mapped to a Set, while this issue appears to be about the YAML:

foo:
-bar
-bat

I duplicated the issue in my Boot 1.2.5.RELEASE app and stumbled across this thread. Once I changed my Set objects back to List everything worked as expected. I don't really think it's a code issue as there is no guarantee of uniqueness in a YAML list, so trying to map them to a Set is incomplete at best. However, I do agree with wooder79 that the (or Set) language in the documentation implies that the two types are interchangeable and is misleading.

[philwebb]

@dan-nawrocki Are you able to share the code that duplicated the issue to https://github.com/spring-projects/spring-boot-issues?

[dan-nawrocki]

Sure. It looks like adding this to RelaxedDataBinderTests does the trick:

    @Test
    public void testBindNestedSetFromList() throws Exception {
        TargetWithNestedSet target = new TargetWithNestedSet();
        this.conversionService = new DefaultConversionService();
        bind(target, "nested[0]: bar");
        assertEquals("[bar]", target.getNested().toString());
    }

[zxkane]

Could you also support below syntax? the object array.

test:
  foo:
    - name: abc
      value: 123
    - name: efg
      value: 456

[ulisesbocchio]

This is still happening in Spring Boot 1.4.0.M3. Trying to set property this way always fails:

security:
  filter-dispatcher-types:
    - REQUEST
    - ERROR

Only workaround I found is:

security:
  filter-dispatcher-types: REQUEST, ERROR

[wilkinsona]

@ulisesbocchio This issue is still open so it's to be expected that 1.4 behaves as you have described

[lhazlewood]

@philwebb or @snicoll is there a reason this has to be pushed all the way to 2.0? This seems like a pretty simple bug fix that is impacting all 1.x users that declare Sets. Thanks!

[philwebb]

@lhazlewood Unfortunately it's not so easy to fix with our current design.

[antoinecarton]

Taking into account Set instances in the processKeyedProperty method of AbstractNestablePropertyAccessor in spring-beans project passes the following test (based on the @dan-nawrocki 's test in this comment):

    @Test
    public void testBindNestedSetFromList() throws Exception {
        TargetWithNestedSet target = new TargetWithNestedSet();
        this.conversionService = new DefaultConversionService();
        bind(target, "nested[0]: bar");
        bind(target, "nested[1]: foo");
        bind(target, "nested[2]: bar");
        assertThat(target.getNested().toString()).isEqualTo("[bar, foo]");
    }

@philwebb Do you think this problem must be managed here? If so, I can make a pull request to spring-framework project.

[philwebb]

@antoinecarton We have plans to rework the binding system entirely. I'd suggest waiting until we get a bit further before suggesting any framework changes. Thanks!

[jacob1182]

try this taken from here

#YAML also has a set type, which looks like this:
set:
    ? item1
    ? item2
    ? item3

#Like Python, sets are just maps with null values; the above is equivalent to:
set2:
    item1: null
    item2: null
    item3: null

[bric3]

@philwebb Any news on this ?

Sorry for the interruption, that was done for Spring Boot 2.x