how can I transfer data from the parent data loader to the child data loader

[aymenbraiek]

how can I implements such methods ?
public CompletableFuture<DataFetcherResult<List>> shows(...) {...
public DataFetcherResult<CompletableFuture<List>> shows(...) {...

[GregLyons]

Let me know if I'm misunderstanding the question, but I'm assuming you have a parent field and a child field, both that use data loaders, and you want to use the result of the parent field's DataLoader in the child field's dataloader:

type Parent {
    fieldOnParent: Child
}

type Child {
    fieldOnChild: String
}

In this case, I interpret your question as saying you're in the data fetcher for Child#fieldonChild, which uses a DataLoader, and you want to pass the result of the Parent#fieldOnParent data fetcher (which also uses a DataLoader) in the DataLoader for fieldOnChild. In this case, the result of Parent#fieldOnParent is a Child, and you can pass it down to the DataLoader for Child#fieldOnChild by having the DataLoader for Child#fieldOnChild implement MappedBatchLoaderWithContext and then doing something like:

@DgsData(parentType = DgsConstants.CHILD.TYPE_NAME, field = DgsConstants.CHILD.FieldOnChild)
public CompletableFuture<String> fieldOnChild(DgsDataFetchingEnvironment dfe) {
    DataLoader<String, String> dataLoader = dfe.getDataLoader(ChildDataLoader.class);
    Child source = dfe.getSource();
    // `MappedBatchLoaderWithContext` lets you load in the entire `source` as well
    return dataLoader.load(source.getId(), source);
}

Then you can extract the source (mapped by key) using BatchLoaderEnvironment#getKeyContexts(). I believe you can use other DGS context using BatchLoaderEnvironment#getContext as well, see the bottom of this Data Fetching Cotnext docs page.

Hope this helps