Create document which nested fields does not work correctly in elasticsearch.js

[katihaumann]

elasticsearch.js. Version: 12.1.3

If I try to create a document which contains nested fields then only the fields of the enclosing document are saved but the nested document not. Here is an example code:

const elasticsearch = require('elasticsearch');
client =  new elasticsearch.Client();
client.indices.create({
   index: 'myindex',
   body: {
      mappings: {
         book: {
            properties: {
               title: {
                  type: 'text'
               },
               authors: {
                  'type': 'nested',
                  'properties': {
                     'name': {
                        'type': 'test'
                     }
                  }
               }
            }
         }
      }
   }
})
.then(function() {
   elasticsearchClient.create( {
      index: 'myindex',
      type: 'book',
      id: 1,
      body: {id:1, title: 'my first book', authors: [{name: 'author1'}, {name: 'author2'}]}
   });
});

The result in elasticsearch is a book document which contains only the title but not the authors.

Can anybody help me?