Not map correct when property is List

[jamestao83]

public class Demo {
    private List<Long> ids
}

Demo demo1 = new Demo()
    .setIds(Lists.newArrayList(3L));
Demo demo2 = new Demo()
    .setIds(Lists.newArrayList(1L, 2L, 3L));
ModelMapper mapper = new ModelMapper();
mapper.map(demo1, demo2);

After map, I hope the demo2 ids value is 3L, but it still is 1L, 2L, 3L

[chhsiao90]

I guessed you are looking for setCollectionsMergeEnabled.

It's enabled by default, you can disable that the collection of destination was always replaced from the source collection.

[seidhkona]

I know it's an old question, but saw it's still open. I'm new to ModelMapper and I'm using setCollectionMergeEnabled(false) with latest ModelMapper (2.4.4), but it doesn't work. Here is code example:

var foo1 = new Foo();
var test1 = new HashMap<String, String>();
test1.put("key", "val");
foo1.setConfigData(test1);
var foo2= new Foo();
var test2 = new HashMap<String, String>();
test2.put("key1", "val1");
test2.put("key2", "val2");
foo2.setConfigData(test2);
modelMapper.map(foo1,foo2);

I'm expecting that foo2 will have configData with 1 element in it, but it ends up having 3 (merged from test1 and test2)

also, inspecting config of ModelMapper shows that collectionMergeEnabled=true even though I set it to false. I looked through the code and I don't see that property being updated anywhere.. I don't think it's used anywhere, since the real usage is to replace CollectionConverter with NonMergingCollectionConverter (which doesn't work?), but it's confusing still...

[hoangntv-1399]

The reason why the actual result is different from the expected result is because ModelMapper maps fields by name, not by type. In this case, both demo1 and demo2 have a field named ids, so ModelMapper will map the value of demo1.ids to demo2.ids, regardless of the fact that demo1.ids is a list of a single element, while demo2.ids is a list of three elements.

ModelMapper mapper = new ModelMapper();
mapper.addMappings(new PropertyMap<Demo, Demo>() {
    @Override
    protected void configure() {
        map(source.getIds(), destination.getIds(), mapIds);
    }
});

mapper.map(demo1, demo2);