CODEWITHSUNDEEP
springhibernatespring-data-jpaspring-datahibernate-mapping
DanilWH
DanilWH

Reputation: 63

Will Spring Data's save() method update an entity in the database if there are no changes in the entity?

When editing a form, the user may sometimes not change the form and still click the submit button. In one of the controller methods below, will the save() method perform a query to the database and update the fields even if the user didn't change anything?

PostMapping("/edit_entry/{entryId}")
public String update_entry(
        @PathVariable("entryId") Long entryId,
        @RequestParam String title,
        @RequestParam String text
) {
    Entry entry = this.entryRepo.findById(entryId).get();
    
    if (!entry.getTitle().equals(title))
        entry.setTitle(title);
    if (!entry.getText().equals(text))
        entry.setText(text);
        
    this.entryRepo.save(entry);
        
    return "redirect:/entries";
}

And also, are the "if" statements necessary in this case?

Upvotes: 6

Views: 3363

Answers (1)

Oliver Drotbohm
Oliver Drotbohm

Reputation: 83081

What exactly happens during a call to save(…) depends on the underling persistence technology. Fundamentally there a re two categories of implementations:

  1. Implementations that actively manage entities. Examples of this are JPA and Neo4j. Those implementations keep track of the entities returned from the store and thus are able to detect changes in the first place. You pay for this with additional complexity as the entities are usually instrumented in some way and the change detection of course also takes time even if it ends up not detecting any changes. On the upside though the only trigger updates if needed.

  2. Implementations that do not actively manage entities. Examples are JDBC and MongoDB. Those implementations do not keep track of entities loaded from the data store and thus do not instrument them. That also means that there is no way of detecting changes as all the implementation sees is an entity instance without any further context.

In your concrete example, a MongoDB implementation would still issue an update while JPA will not issue an update at all if the request params do not contain differing values.

Upvotes: 7

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