使用jq有条件地将元素添加到json数组

Question

I'm adding strings to a JSON array using jq, and it works great, but I'd like to only add strings that do not already exist. I've experimented with unique, has, not, etc. I'm missing a piece or two to the puzzle.

Here's my starting json file, foo.json:

{
  "widgets": [
    {
      "name": "foo",
      "properties": [
        "baz"
      ]
    },
    {
      "name": "bar"
    }
  ]
}

Here's the jq command I've constructed that adds the string, even if it already exists:

$ cat foo.json | jq '.widgets[] | select(.name=="foo").properties |= .+ ["cat"]'

Here's the latest iteration of my attempt.

$ cat foo.json | jq '.widgets[] | select(.name=="foo").properties | has("cat") | not | .properties += ["cat"]'
jq: error: Cannot check whether array has a string key

Answer 1

There are many ways to do this.

Assuming elements of the array are supposed to be unique, which your use case strongly implies, you can just pass the resulting array after the addition through the unique filter.

$ cat foo.json | jq '.widgets[] | select(.name=="foo").properties |= (.+ ["cat"] | unique)'

Answer 2

There's more than one way to skin a cat, as they say, but perhaps this will give you some ideas:

.widgets[]
| select(.name=="foo")
| select(.properties | index("cat") | not)
| .properties += ["cat"]

With your input, the result is:

{
  "name": "foo",
  "properties": [
    "baz",
    "cat"
  ]
}

The following may be closer to what you're looking for:

.widgets |= [ .[] | if .properties|index("cat")|not
                    then .properties += ["cat"]
                    else .
                    end]