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How to cascade update


Overview
Enabling cascading update
Scenarios
    db.update()
Limitations
See also


Overview

When working with long transactions, you can cascade the db.update() operation, so that, for example, updating the root of a large object graph causes all connected entites to update as well (provided cascading update is enabled on the particular relationships, of course).

Enabling cascading update

To enable cascading update on a relationship you simply set the cascading attribute of the <sql> field describing the relation to "update" (or "all"):

<field name="book" type="myapp.Book" >
  <sql name="book_id" cascading="update" />
</field>

In case of bidirectional relationships, be aware that it matters on which end you enable cascading update. It is also possible to enable it on both ends.

Scenarios

db.update()

Let's say we have the objects Author and Book and they are in a one-to-one relationship, with every Book having exactly one Author. The database looks like this:

Author
id name
1 "John Jackson"
Book
id title author_id
1 "My Life" 1

Now let's change the book's title. Note that we never directly load the book and that the change happens outside of any transaction:

db.begin();
Author a1 = db.load(Author.class, 1);
db.commit();

a1.getBook().setName("My Fantastic Life");

db.begin();
db.update(a1);
db.commit();

Afterwards, the database looks like this:

Author
id name
1 "John Jackson"
Book
id title author_id
1 "My Fantastic Life" 1

Limitations

-

To-many relationships are currently not supported (except many-to-one).

-

As it is now, enabling cascading update will cause db.update() to also create any entities that have not yet been persisted. (In other words: setting cascading to "update" has the same effect as setting it to "update create", but only when invoking db.update().)

See also

- How to use cascading operations - overview
 
   
  
   
 


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