Exploring JSON Patch

JSON Patch defines a JSON document structure for expressing a sequence of operations to apply to a JavaScript Object Notation (JSON) document; it is suitable for use with the HTTP PATCH method. The "application/json-patch+json" media type is used to identify such patch documents. You can refer this link (https://tools.ietf.org/html/rfc6902) for more information.

 

JSON Patch document is a JSON document that represents an array of objects, where each object represents a single operation to be applied to the target JSON document.

 

Example of json patch document

[{
    "op": "test",
    "path": "/emp/address/city",
    "value": "Bangalore"
  },
  {
    "op": "remove",
    "path": "/emp/firstName"
  },
  {
    "op": "add",
    "path": "/emp/hobbies",
    "value": ["cricket", "football"]
  },
  {
    "op": "replace",
    "path": "/emp/age",
    "value": 42
  },
  {
    "op": "move",
    "from": "/emp/address/city",
    "path": "/emp/address/state"
  },
  {
    "op": "copy",
    "from": "/emp/firstName",
    "path": "/emp/lastName"
  }
]

As you see above json document structure, "op" key represent the operation to perform.

 

Following table summarizes the operations specified in json patch specification.

 

Operation	Description
add	Add value at given location.   If the target location specifies an array index, a new value is inserted into the array at the specified index.   If the target location specifies an object member that does not already exist, a new member is added to the object.   If the target location specifies an object member that does exist, that member's value is replaced.
remove	removes the value at the target location.
replace	replaces the value at the target location
move	removes the value at a specified location and adds it to the target location.
copy	copies the value at a specified location to the target location.
test	tests that a value at the target location is equal to a specified value.

 

Let’s see it with an example.

 

Source json

{
  "firstName": "Krishna",
  "lastName": "Gurram",
  "hobbies": [
    "Cricket",
    "Football"
  ],
  "address": {
    "city": "Bangalore",
    "state": "Karnataka",
    "country": "India"
  }
}

target json

{
  "firstName": "Ram",
  "lastName": "Gurram",
  "hobbies": [
    "Football",
    "Chess"
  ],
  "address": {
    "city": "Amaravathi",
    "state": "Andhra Pradesh",
    "country": "India"
  }
}

Following patch document is used to transform source json to target json

[
  {
    "op":"replace",
    "path":"/firstName",
    "value":"Ram"
  },
  {
    "op":"replace",
    "path":"/hobbies/0",
    "value":"Football"
  },
  {
    "op":"replace",
    "path":"/hobbies/1",
    "value":"Chess"
  },
  {
    "op":"replace",
    "path":"/address/city",
    "value":"Amaravathi"
  },
  {
    "op":"replace",
    "path":"/address/state",
    "value":"Andhra Pradesh"
  }
]

We need to apply above operations sequentially on source json document to transform source json to target json document. In my next post, I will explain how to get this patch document json from source and target json documents.

 

Reference

https://tools.ietf.org/html/rfc6902

 

 

 

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