REST API for updating informations with empty or null values

Question

I have a general question about how best to build an API that can modify records in a database.

Suppose we have a table with 10 columns and we can query these 10 columns using REST (GET). The JSON response will contain all 10 fields. This is easy and works without problems.

The next step is that someone wants to create a new record via POST. In this case the person sends only 8 of the 10 fields in the JSON Request. We would then only fill the 8 fields in the database (the rest would be NULL). This also works without problems.

But what happens if someone wants to update a record? We see here different possibilities with advantages and disadvantages.

1. Only what should be updated is sent. Problem: How can you explicitly empty / delete a field? If a "NULL" is passed in the JSON, we get NULL in the object, but any other field that is not passed is NULL as well. Therefore we cannot distinguish which field can be deleted and which field cannot be touched.

2. The complete object is sent. Problem: Here the object could be fetched via a GET before, changed accordingly and returned via PUT. Now we get all information back and could write the information directly back into the database. Because empty fields were either already empty before or were cleared by the user.

What happens if the objects are extended by an update of the API. Suppose we extend the database by five more fields. The user of the API makes a GET, gets the 15 fields, but can only read the 10 fields he knows on his page (because he hasn't updated his side yet). Then he changes some of the 10 fields and sends them back via PUT. We would then update only the 10 fields on our site and the 5 new fields would be emptied from the database.

Or do you have to create a separate endpoint for each field? We have also thought about creating a map with key / value, what exactly should be changed.

About the technique: We use the Wildfly 15 with Resteasy and Jackson.

For example:

Database at the beginning

+----+----------+---------------+-----+--------+-------+
| ID | Name     | Country       | Age | Weight | Phone |
+----+----------+---------------+-----+--------+-------+
| 1  | Person 1 | Germany       | 22  | 60     | 12345 |
| 2  | Person 2 | United States | 32  | 78     | 56789 |
| 3  | Person 3 | Canada        | 52  | 102    | 99999 |
+----+----------+---------------+-----+--------+-------+

GET .../person/2

{
   "id" : 2,
   "name" : "Person 2",
   "country" : "United States",
   "age" : 22,
   "weight" :62,
   "phone": "56789"
}

Now I want to update his weight and remove the phone number

PUT .../person/2

{
   "id" : 2,
   "name" : "Person 2",
   "country" : "United States",
   "age" : 22,
   "weight" :78
}

or

{
   "id" : 2,
   "name" : "Person 2",
   "country" : "United States",
   "age" : 22,
   "weight" :78,
   "phone" : null
}

Now the database should look like this:

+----+----------+---------------+-----+--------+-------+
| ID | Name     | Country       | Age | Weight | Phone |
+----+----------+---------------+-----+--------+-------+
| 1  | Person 1 | Germany       | 22  | 60     | 12345 |
| 2  | Person 2 | United States | 32  | 78     | NULL  |
| 3  | Person 3 | Canada        | 52  | 102    | 99999 |
+----+----------+---------------+-----+--------+-------+

The problem is

We extend the table like this (salery)

+----+----------+---------------+-----+--------+--------+-------+
| ID | Name     | Country       | Age | Weight | Salery | Phone |
+----+----------+---------------+-----+--------+--------+-------+
| 1  | Person 1 | Germany       | 22  | 60     | 1929   | 12345 |
| 2  | Person 2 | United States | 32  | 78     | 2831   | NULL  |
| 3  | Person 3 | Canada        | 52  | 102    | 3921   | 99999 |
+----+----------+---------------+-----+--------+--------+-------+

The person using the API does not know that there is a new field in JSON for the salary. And this person now wants to change the phone number of someone again, but does not send the salary. This would also empty the salary:

{
   "id" : 3,
   "name" : "Person 3",
   "country" : "Cananda",
   "age" : 52,
   "weight" :102,
   "phone" : null
}


+----+----------+---------------+-----+--------+--------+-------+
| ID | Name     | Country       | Age | Weight | Salery | Phone |
+----+----------+---------------+-----+--------+--------+-------+
| 1  | Person 1 | Germany       | 22  | 60     | 1929   | 12345 |
| 2  | Person 2 | United States | 32  | 78     | 2831   | NULL  |
| 3  | Person 3 | Canada        | 52  | 102    | NULL   | NULL  |
+----+----------+---------------+-----+--------+--------+-------+

And salary should not be null, because it was not set inside the JSON request

Answer 1

You could deserialize your JSON to a Map. This way, if a property has not been sent, the property is not present in the Map. If its null, its inside the map will a null value.

  ObjectMapper mapper = new ObjectMapper();
  TypeReference<HashMap<String, Object>> typeReference = new TypeReference<>() {};
  HashMap<String, Object> jsonMap = mapper.readValue(json, typeReference);
  jsonMap.entrySet().stream().map(Map.Entry::getKey).forEach(System.out::println);

Not a very convenient solution, but it might work for you.