jsonq

JSONQ is XPath inspired JSON processing library for Go. It provides functions for traversing JSON structures and for extracting attributes into Go data structures.

Type-safe getters

Type-safe getters access JSON structures and return type-checked values.

var v interface{}
err := json.Unmarshal([]byte(`{
    "issue": {
        "fields": {
            "project": {
                "name": "Operations"
            }
        }
    }
}`), &v)
if err != nil {
    log.Fatal(err)
}
name, err := GetString(v, "issue.fields.project.name")
if err != nil {
    log.Fatal(err)
}
fmt.Println(name)
// Output: Operations

Extracting JSON attributes to Go data structures

The Context type allows you to select elements from JSON data and extract values into Go data structures. The basic extraction works by annotating Go structurs with the jsonq structure tags:

var v interface{}
err := json.Unmarshal([]byte(`{
    "issue_event_type_name": "issue_assigned",
    "issue": {
        "fields": {
            "project": {
                "name": "Operations"
            }
        },
        "key": "OP-1"
    }
}`), &v)
if err != nil {
    log.Fatal(err)
}
var issue struct {
    Key       string `jsonq:"issue.key"`
    Name      string `jsonq:"issue.fields.project.name"`
    EventType string `jsonq:"issue_event_type_name"`
}
err = Ctx(v).Extract(&issue)
if err != nil {
    log.Fatal(err)
}
fmt.Printf("key=%s, name=%s, type=%s\n", issue.Key, issue.Name, issue.EventType)
// Output: key=OP-1, name=Operations, type=issue_assigned

The Context.Select() function allows you to filter data based on JSON attributes:

var v interface{}
err := json.Unmarshal([]byte(`{
    "issue": {
        "changelog": {
            "items": [
                {
                    "fieldId": "comment",
                    "toString": "This is cool!",
                    "fromString": ""
                },
                {
                    "fieldId": "assignee",
                    "toString": "Veijo Linux",
                    "fromString": null
                }
            ]
        }
    }
}`), &v)
if err != nil {
    log.Fatal(err)
}
var assign struct {
    From string `jsonq:"?fromString"`
    To   string `jsonq:"?toString"`
}
err = Ctx(v).
    Select(`issue.changelog.items[fieldId=="assignee"][0]`).
    Extract(&assign)
if err != nil {
    log.Fatal(err)
}
fmt.Printf("assign from '%s' to '%s'\n", assign.From, assign.To)
// Output: assign from '' to 'Veijo Linux'

Note that if the JSON attribute name is prefixed with question mark, the field is optional.

TODO

• Getters:
  • Number
  • Boolean
• Expressions:
  • Comparison: ==, !=, <, > <=, >=
  • Parenthesized sub-expressions
  • Chaining logical expressions
  • Number expressions