Converting Elastic Search field to Array - json

Question

In elastic search if you have document that has a pre-existing array
"movies": [
"Back to the Future"
]
And then you update it to add more movies like such
{
"script" : "ctx._source.movies += tag",
"params" : {
"tag" : "Pulp Fiction"
}
}
Then the value is added to the field. That works great... but what if the field isn't an arry to start with and instead looks like this
"movies": "Back to the Future"
If you run the same script you will get the following result
"movies":"Back to the FuturePulpFiction"
So my question is how do I take this existing field and "convert" it to an array to tell elastic search that I want to think of it as an array?

Answer 1

You can use this script instead. It checks whether movies is an array and if not it creates one
{
"script" : "if (ctx._source.movies.getClass().isArray()) { ctx._source.movies += tag } else { ctx._source.movies = [ctx._source.movies, tag] }",
"params" : {
"tag" : "Pulp Fiction"
}
}
Another shorter way of doing it is to always assign an array and then "flatten" it using Groovy's Collection.flatten() method
{
"script" : "ctx._source.movies = [ctx._source.movies, tag].flatten()",
"params" : {
"tag" : "Pulp Fiction"
}
}

Answer 2

Adding to the answer from Val, if ctx._source.movies does not exist it will add a null to your resulting list. Following is the script I use to do something similar but not include the null.
{
"script": "if (ctx._source.movie.getClass().isArray()) {ctx._source.event += tag} else if (ctx._source.movie) {ctx._source.movie = [ctx._source.movie, tag]} else {ctx._source.movie=[tag]}",
"params" : {
"tag" : "Pulp Fiction"
}
}