HTTP PUT使用部分Json更新数据库-Spring，Postgres

Question

I am writing a web api using Spring and Postgres.

• I have a case where I take a Json object item

• The uri is /api/item/{itemId}

• Request type is PUT

Json:

{
   "name":"itemname",
   "description":"item description here"
}

So I do (using JdbcTemplate) a SELECT statement to check if the itemId exists and then update if it does.

I would also like to implement a case with partial puts taking Json that look like this::

{
   "name":"itemname"
}

OR

{
   "description":"item description here"
}

where only the respective fields are updated. In Spring, the variables not present are automatically null .

The way this is implemented now is:

1. SELECT all columns from the items table
2. Sequentially check every single expected variable for null and if they are null, replace the null with the value selected from the table in step 1.
3. UPDATE all columns with the values (none of which should be null if the table has a not null constraint)

Question: How do you do this without == null or != null checks? Is seems to be poor design and involves iterating through every single expected variable for every single PUT request (I will have many of those).

Desired responses (in order of desirability):

1. There's a way in Postgres where if a null value is input, the column-value is simply not written to the database (and no error is produced)
2. There is a way to use Spring (and Jackson) to create a Java object with only the provided values and a way to generate SQL and JdbcTemplate code that only updates those specific columns.
3. Patch is the way of life - implement it
4. Change the front-end to always send everything

Answer 1

You have two choices when working with the database:

1. Just update what has changed, doing everything by yourself.
2. Get Jackson and Hibernate to do it for you.

So let's look at No. 1: Let's say you're looking right now at the contents of an html form that has been sent back to the server. Take every field in the html form and update only those fields in the database using an SQL statement. Anything that is not in the form will not get updated in your database table. Simple! Works well. You don't need to worry about anything that is not in the form. You can restrict your update to the form's contents.

In general this is a simple option, apart from one problem, which is html checkboxes . If you are doing an update, html checkboxes can catch you out because due to a little design quirk, they don't get sent back to the server if they are unchecked.

No. 2: Perhaps you're looking for Hibernate, which you didn't mention. Jackson will fill a json object for you (must have a record id). Use Hibernate to populate a java class with the existing record, update with the new values Jackson has provided, then you tell Hibernate to merge() it into the existing record in the database, which it will. I also use Roo to create my Hibernate-ready classes for me.

No. 2 is hard to learn and set up, but once you've done sussed it, it's very easy to change things, add fields and so on.