How to update multiple documents in Solr with JSON?

Question

How to update multiple documents in Solr 4.5.1 with JSON? I tried this but it does not work:

POST /solr/mycore/update/json:

{
  "commit": {},
  "add": {
    "overwrite": true,
    "doc": [{
        "thumbnail": "/images/404.png",
        "url": "/404.html?1",
        "id": "demo:/404.html?1",
        "channel": "demo",
        "display_name": "One entry",
        "description": "One entry is not enough."
      }, {
        "thumbnail": "/images/404.png",
        "url": "/404.html?2",
        "id": "demo:/404.html?2",
        "channel": "demo",
        "display_name": "Another entry",
        "description": "Another entry is required."
      }
    ]
  }
}

Answer 1

I understand that (at least) from versions 4.0 and older of solr, this has been fixed. Look at http://wiki.apache.org/solr/UpdateJSON.

In ./exampledocs/books.json there is an example of a json file with multiple documents.

[
{
"id" : "978-0641723445",
"cat" : ["book","hardcover"],
"name" : "The Lightning Thief",
"author" : "Rick Riordan",
"series_t" : "Percy Jackson and the Olympians",
"sequence_i" : 1,
"genre_s" : "fantasy",
"inStock" : true,
"price" : 12.50,
"pages_i" : 384
}
,
{
"id" : "978-1423103349",
"cat" : ["book","paperback"],
"name" : "The Sea of Monsters",
"author" : "Rick Riordan",
"series_t" : "Percy Jackson and the Olympians",
"sequence_i" : 2,
"genre_s" : "fantasy",
"inStock" : true,
"price" : 6.49,
"pages_i" : 304
}, 
...
]

While @fiskfisk answer is still a valid JSON, it is not easy to be serializable from a data structure. This one is.

Answer 2

Solr expects one "add"-key in the JSON-structure for each document (which might seem weird, if you think about the original meaning of the key in the object), since it maps directly to the XML format when doing the indexing - and this way you can have metadata for each document by itself.

{
    "commit": {},
    "add": {
        "doc": {
            "id": "321321",
            "name": "barfoo"
        }
    },
    "add": {
        "doc": {
            "id": "123123",
            "name": "Foobar"        
        }
    }
}

.. works. I think allowing an array as the element referenced by "add" would make more sense, but I haven't dug further into the source or know the reasoning behind this.