CODEWITHSUNDEEP
jsonbashjq
Rahul Dess
Rahul Dess

Reputation: 2587

How to check for presence of 'key' in jq before iterating over the values

I get Cannot iterate over null (null) from the below query because .property_history is not present in result object.

How do I check for the presence of .property_history key before proceeding with map(...)?

I tried using something like

sold_year= `echo "$content" | jq 'if has("property_history") then 
map(select(.event_name == "Sold"))[0].date' else null end

Original Query:

sold_year=`echo "$content" | jq '.result.property_history | map(select(.event_name == "Sold"))[0].date'`

JSON:

{
    "result":{
        "property_history":[
            {
                "date":"01/27/2016",
                "price_changed":0,
                "price":899750,
                "event_name":"Listed",
                "sqft":0
            },
            {
                "date":"12/15/2015",
                "price_changed":0,
                "price":899750,
                "event_name":"Listed",
                "sqft":2357
            },
            {
                "date":"08/30/2004",
                "price_changed":0,
                "price":739000,
                "event_name":"Sold",
                "sqft":2357
            }
        ]
    }
}

Upvotes: 116

Views: 175893

Answers (6)

123
123

Reputation: 803

use has("mykey1") (for objects) or has(0) (for arrays):

jq 'has("name")' <<< '{"name": "hello"}'

output:

true

Upvotes: 41

Mohammed Noureldin
Mohammed Noureldin

Reputation: 16806

The shortest you can use (with the bonus that the exit code will be set):

# Example that exits with code 0
jq -e 'has("result")'

# Example that exists with code 0
jq -e '.result[].property_history | has("price")'

# Example that exists with code 1
jq -e '.result[].property_history | has("dummyKey")'

In these examples, because of setting the flag -e, if has returned true, the exit code will be set to 0, otherwise 1. Which saves unnecessary additional steps.

Upvotes: 6

peak
peak

Reputation: 116690

Technically, to test for the presence of a property, you should use has/1, but in the present context, it would probably be better to use the postfix ? operator, e.g.:

$ jq '.result 
  | .property_history[]?
  | select(.event_name == "Sold") 
  | .date'
"08/30/2004"

If there is a possibility that the value of .result is not a JSON object, then you could replace the second line above by:

try(.property_history[])

Upvotes: 40

Curtis Yallop
Curtis Yallop

Reputation: 7309

General pattern:

try (...) // "default_value"

With your logic:

jq 'try (.result.property_history | map(select(.event_name == "Sold"))[0].date) // "default_value"'

try (without a catch) returns empty if the expression fails. // provides a default value if the value is empty.

Upvotes: 7

reegnz
reegnz

Reputation: 927

The trick is to use // together with empty:

jq '.result.property_history // empty | map(select(.event_name == "Sold"))[0:1][].date'

Another alternative is to use an additional select:

jq '.result.property_history | select(.) | map(select(.event_name == "Sold"))[0:1][].date'

Upvotes: 5

Inian
Inian

Reputation: 85560

You can use the select-expression in jq to do what you intend to achieve, something as,

jq '.result 
  | select(.property_history != null) 
  | .property_history 
  | map(select(.event_name == "Sold"))[0].date'

Upvotes: 124

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