JSON Diff and Patch Operations

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How to perform JSON diff & patch operations with a TerminusDB client or with MongoDB
Requirements
Install a client
Install a JavaScript or Python TerminusDB client.
Use the client with TerminusDB
Install and run the docker container on localhost
Use the client with TerminusX
Or to use TerminusX, log into your account or sign-up.
Diff & Patch with Client
TerminusDB represents objects such as documents and schemas in JSON-LD format. Use JSON Diff and Patch to easily compare these objects to obtain differences between them.
The Diff function returns a Patch object containing differences between the objects compared. Use Patch to implement manual or programmatic actions to resolve differences. Actions include:
Retain the original object.
Change to the new (or latest) version of the object.
Create a new version of the object.
The functionality above is demonstrated in three simple steps:
1.​Define documents​
2.​Compare documents​
3.​Implement actions​
Define documents
For simplicity, this demonstration represents JSON documents as client objects. Two 'document' objects are defined - jane and janine.
JavaScript
Python
const jane = {
  "@id": "Person/Jane",
  "@type": "Person",
  age: 18,
  name: "Jane",
};
​
const janine = {
  "@id": "Person/Jane",
  "@type": "Person",
  age: 18,
  name: "Janine",
};
class Person(DocumentTemplate):
    name: str
    age: int
​
jane = Person(name="Jane", age=18)
janine = Person(name="Janine", age=18)
Compare documents
Apply the diff function to jane and janine to populate the patch objectresult_patch. View the contents of result_patch to see any differences.
JavaScript
Python
const result_patch = await client.getDiff(jane, janine);
​
console.log(result_patch);
result_patch = client.diff(jane, janine)
​
pprint(result_patch.content)
Implement actions
After patch
Use the patch function to apply result_patch to the document jane. The object after_patch contains a copy of jane after the patch is applied.
Use after_patch to suit your requirements. The following example compares the modified jane document to the original janine document.
JavaScript
Python
const after_patch = await client.patch(jane, result_patch);
​
console.log(after_patch);
​
console.log(JSON.stringify(after_patch) === JSON.stringify(janine));
after_patch = client.patch(jane, result_patch)
​
pprint(after_patch)
​
assert after_patch == janine._obj_to_dict()
Replace/update document
If there are differences between the two documents, you may wish to replace one document with the other. Use replace document functionality for this.
updateDocument in the JavaScript client.
replace_document in the Python client.
Diff & Patch with MongoDB
An example in four simple steps demonstrating the use JSON Diff and Patch with another JSON-compliant database - MongoDB:
1.​Insert items into a MongoDB database.
2.​Modify an item.
3.​Compare modified and original items.
4.​Update the original item.
Insert items into a MongoDB database
Create a new MongoDB database and insert three items - item_1 to item_3 into a collection object.
JavaScript
Python
const { MongoClient } = require("mongodb");
​
// Connection URL
const url = "mongodb://localhost:27017";
const client = new MongoClient(url);
​
// Database Name
const dbName = "user_shopping_list";
​
async function main() {
  // Use connect method to connect to the server
  await client.connect();
  console.log("Connected successfully to server");
​
  // Create the database for our example (we will use the same database throughout the tutorial
  const db = client.db(dbName);
  const collection = db.collection("user_1_items");
​
  let item_1 = {
    _id: "U1IT00001",
    item_name: "Blender",
    max_discount: "10%",
    batch_number: "RR450020FRG",
    price: 340,
    category: "kitchen appliance",
  };
​
  const item_2 = {
    _id: "U1IT00002",
    item_name: "Egg",
    category: "food",
    quantity: 12,
    price: 36,
    item_description: "brown country eggs",
  };
  const insertResult = await collection.insertMany([item_1, item_2]);
  console.log("Inserted documents =>", insertResult);
​
  const item_3 = {
    item_name: "Bread",
    quantity: 2,
    ingredients: "all-purpose flour",
    expiry_date: "2021-07-13 00:00:00",
  };
  await collection.insertOne(item_3);
​
  return "done";
}
​
main()
  .then(console.log)
  .catch(console.error)
  .finally(() => client.close());
client = MongoClient(os.environ["MONGO_CONNECTION_STRING"])
​
# Create the database for our example (we will use the same database throughout the tutorial
connection = client['user_shopping_list']
​
collection_name = connection["user_1_items"]
​
item_1 = {
"_id" : "U1IT00001",
​
"item_name" : "Blender",
"max_discount" : "10%",
"batch_number" : "RR450020FRG",
"price" : 340,
"category" : "kitchen appliance"
}
​
item_2 = {
"_id" : "U1IT00002",
"item_name" : "Egg",
"category" : "food",
"quantity" : 12,
"price" : 36,
"item_description" : "brown country eggs"
}
​
collection_name.insert_many([item_1,item_2])
​
expiry_date = '2021-07-13T00:00:00.000'
expiry = dt.datetime.fromisoformat(expiry_date)
item_3 = {
"item_name" : "Bread",
"quantity" : 2,
"ingredients" : "all-purpose flour",
"expiry_date" : expiry
}
collection_name.insert_one(item_3)
Modify an item
The 'document' new_item_1 represents a modified instance of item_1 with changes to properties max_discount and price.
JavaScript
Python
const new_item_1 = {
  _id: "U1IT00001",
  item_name: "Blender",
  max_discount: "50%",
  batch_number: "RR450020FRG",
  price: 450,
  category: "kitchen appliance",
};
new_item_1 = {
"_id" : "U1IT00001",
"item_ame" : "Blender",
"max_discount" : "50%",
"batch_number" : "RR450020FRG",
"price" : 450,
"category" : "kitchen appliance"
}
Compare modified and original items
Retrieve the original item in the collection and compare it to the modified item new_item_1.
JavaScript
Python
const tbd_endpoint = new TerminusDBClient.WOQLClient("http://127.0.0.1:6363/", {
  user: "admin",
  organization: "admin",
  key: "root",
});
​
// Find the item back from database in case someone already changed it
item_1 = collection.findOne({ item_name: "Blender" });
const patch = tbd_endpoint.getDiff(item_1, new_item_1);
​
console.log(patch);
tbd_endpoint = WOQLClient("http://localhost:6363/")
​
# Find the item back from database in case someone already changed it
item_1 = collection_name.find_one({"item_name" : "Blender"})
patch = tbd_endpoint.diff(item_1, new_item_1)
​
pprint(patch.content)
Update the original item
Update the original item in the MongoDB database. If required, review the differences prior to the update.
JavaScript
Python
Define a function patchMongo to get a patch object:
const mongoPatch = function(patch){
    let query = {};
    let set = {};
​
    if('object' === typeof patch){
        for(var key in patch){
            const entry = patch[key];
​
            if( entry['@op'] == 'SwapValue'){
                query[key] = entry['@before'];
                set[key] = entry['@after'];
            }else if(key === '_id'){
                query[key] = ObjectId(entry);
            }else{
                let [sub_query,sub_set] = mongoPatch(entry);
                query[key] = sub_query;
                if(! sub_set === null){
                    set[key] = sub_set;
                }
            }
        }
        return [query,set]
    }else{
        return [patch,null]
    }
}
Apply the patch:
let [q,s] = mongoPatch(patch);
console.log([q,s]);
​
await collection.updateOne(q, {"$set": s});
collection_name.update_one(patch.before, {"$set": patch.update})
Further Reading
JSON Diff and Patch client functions
JavaScript client diff and patch.
Python client diff and patch.
Demonstration script
The full script for this demonstration (on GitHub.)
Data Modeling in TerminusDB
Manage Access Control with Dashboard
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Requirements
Diff & Patch with Client
Diff & Patch with MongoDB