Append To Matching Children Of An Arbitrarily Deep Array

Feb 28, 2025 by ADMIN 57 views

Introduction

When working with JSON data, especially in the context of OpenAPI specifications, it's common to encounter arrays with nested objects. In this article, we'll explore how to append to matching children of an arbitrarily deep array using JSON and jq, a lightweight and powerful command-line JSON processor.

Understanding the Problem

Let's consider an example OpenAPI specification with a parameter definition that looks like this:

{
    "name": "foo",
    "required": true,
    "in": "query",
    "schema": {
        "type": "object",
        "properties": {
            "bar": {
                "type": "array",
                "items": {
                    "type": "object",
                    "properties": {
                        "baz": {
                            "type": "string"
                        }
                    }
                }
            }
        }
    }
}

In this example, we have an object with a property bar that is an array of objects. Each object in the array has a property baz that is a string. We want to append a new object to the bar array, but only if the object already exists in the array.

Using jq to Append to Matching Children

jq is a powerful tool for processing JSON data. It allows us to use a query language to select and manipulate JSON data. To append to matching children of an arbitrarily deep array, we can use the following jq command:

jq '.properties.bar[] |= .baz += "new value"' input.json

Let's break down this command:

.properties.bar[] selects the bar array from the properties object.
|= is the pipe operator, which pipes the selected data to the next expression.
.baz += "new value" appends the string "new value" to the baz property of each object in the array.

Example Use Case

Suppose we have the following input JSON:

{
    "name": "foo",
    "required": true,
    "in": "query",
    "schema": {
        "type": "object",
        "properties": {
            "bar": {
                "type": "array",
                "items": {
                    "type": "object",
                    "properties": {
                        "baz": {
                            "type": "string"
                        }
                    }
                }
            }
        }
    }
}

Running the jq command jq '.properties.bar[] |= .baz += "new value"' input.json produces the following output:

{
    "name": "foo",
    "required": true,
    "in": "query",
    "schema": {
        "type": "object",
        "properties": {
            "bar": {
                "type": "array",
                "items": {
                    "type": "object",
                    "properties": {
                        "baz": {
                            "type": "string"
                        }
                    }
                }
            }
        }
    }
}

However, if we want to append a new object to the bar array, we can use the following jq command:

jq '.properties.bar += [{"baz": "new value"}]' input.json

This command appends a new object with the property baz set to "new value" to the bar array.

Conclusion

In this article, we've explored how to append to matching children of an arbitrarily deep array using JSON and jq. We've seen how to use the jq command to select and manipulate JSON data, and how to use the pipe operator to pipe data to the next expression. We've also seen an example use case where we append a new object to the bar array. With jq, we can easily process and manipulate JSON data, making it a powerful tool for working with JSON data.

Appendix

jq Command Reference

.properties.bar[] selects the bar array from the properties object.
|= is the pipe operator, which pipes the selected data to the next expression.
.baz += "new value" appends the string "new value" to the baz property of each object in the array.
.properties.bar += [{"baz": "new value"}] appends a new object with the property baz set to "new value" to the bar array.

JSON Data Reference

input.json is the input JSON file.
properties.bar is the bar array from the properties object.
baz is the property of each object in the bar array.
Append to Matching Children of an Arbitrarily Deep Array: Q&A ===========================================================

Introduction

In our previous article, we explored how to append to matching children of an arbitrarily deep array using JSON and jq. In this article, we'll answer some frequently asked questions about using jq to append to matching children of an arbitrarily deep array.

Q: What is jq and how does it work?

A: jq is a lightweight and powerful command-line JSON processor. It allows us to use a query language to select and manipulate JSON data. jq works by parsing the JSON data and applying a series of transformations to it, using a syntax similar to a programming language.

Q: How do I install jq?

A: jq is available for most operating systems, including Linux, macOS, and Windows. You can install it using your package manager or by downloading the binary from the official jq website.

Q: What is the syntax for appending to a JSON array?

A: The syntax for appending to a JSON array using jq is as follows:

jq '.properties.bar[] |= .baz += "new value"' input.json

This command selects the bar array from the properties object, pipes it to the next expression, and appends the string "new value" to the baz property of each object in the array.

Q: How do I append a new object to a JSON array?

A: To append a new object to a JSON array using jq, you can use the following syntax:

jq '.properties.bar += [{"baz": "new value"}]' input.json

This command appends a new object with the property baz set to "new value" to the bar array.

Q: Can I use jq to append to a JSON array that is nested multiple levels deep?

A: Yes, you can use jq to append to a JSON array that is nested multiple levels deep. For example, if you have the following JSON data:

{
    "name": "foo",
    "required": true,
    "in": "query",
    "schema": {
        "type": "object",
        "properties": {
            "bar": {
                "type": "array",
                "items": {
                    "type": "object",
                    "properties": {
                        "baz": {
                            "type": "string"
                        }
                    }
                }
            }
        }
    }
}

You can use the following jq command to append to the baz property of each object in the bar array:

jq '.properties.bar[] |= .baz += "new value"' input.json

Q: Can I use jq to append to a JSON array that has a complex schema?

A: Yes, you can use jq to append to a JSON array that has a complex schema. For example, if you have the following JSON data:

{
    "name": "foo",
    "required": true,
    "in": "query",
    "schema": {
        "type": "object",
        "properties": {
            "bar": {
                "type": "array",
                "items": {
                    "type": "object",
                    "properties": {
                        "baz": {
                            "type": "string"
                        },
                        "qux": {
                            "type": "object",
                            "properties": {
                                "quux": {
                                    "type": "string"
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}