How to update embedded document?

Question

How to update the text of second comment to "new content"

{
  name: 'Me',
  comments: [{
        "author": "Joe S.",
        "text": "I'm Thirsty"
    },
    {
        "author": "Adder K.",
        "text":  "old content"
    }]
}

Answer 1

Updating the embedded array basically involves two steps:

1. You create a modified version of the whole array. There are multiple operations that you can use to modify an array, and they are listed here: http://www.rethinkdb.com/api/#js:document_manipulation-insert_at

In your example, if you know that the document that you want to update is the second element of the array, you would write something like

oldArray.changeAt(1, oldArray.nth(1).merge({text: "new content"}))

to generate the new array. 1 here is the index of the second element, as indexes start with 0. If you do not know the index, you can use the indexesOf function to search for a specific entry in the array. Multiple things are happening here: changeAt replaces an element of the array. Here, the element at index 1 is replaced by the result of oldArray.nth(1).merge({text: "new content"}). In that value, we first pick the element that we want to base our new element from, by using oldArray.nth(1). This gives us the JSON object

{
    "author": "Adder K.",
    "text":  "old content"
}

By using merge, we can replace the text field of this object by the new value.

2. Now that we can construct the new object, we still have to actually store it in the original row. For this, we use update and just set the "comments" field to the new array. We can access the value of the old array in the row through the ReQL r.row variable. Overall, the query will look as follows:

r.table(...).get(...).update({
    comments: r.row('comments').changeAt(1,
      r.row('comments').nth(1).merge({text: "new content"}))
  }).run(conn, callback)

Answer 2

Daniel's solution is correct. However, there are several open issues on Github for planned enhancements, including:

• generic object and array modification (https://github.com/rethinkdb/rethinkdb/issues/895)

• being able to specify optional arguments for merge and update (https://github.com/rethinkdb/rethinkdb/issues/872)

• being able to specify a conflict resolution function for merge (https://github.com/rethinkdb/rethinkdb/issues/873)

...among other related issues. Until those are introduced into ReQL (particularly #895), Daniel's approach is the correct one.