如何使用Java Document API为OrientDB数据库创建自动递增索引/序列? [英] How do I create an auto-incrementing index/a sequence for an OrientDB database using the Java Document API?
问题描述
我通过Document API使用OrientDB和Java。我有一个名为 items
的简单类,其属性 ID
。我明确地声明了这样的模式:
I am using OrientDB with Java via its Document API. I have a simple Class called items
which has an attribute ID
. I explicitly declare the schema like this:
OSchema schema = db.getMetadata().getSchema();
OClass itemsClass = schema.createClass("items");
itemsClass.createProperty("ID", OType.LONG);
然后在 ID
上创建一个索引: CREATE INDEX items.ID ON项目(ID)UNIQUE
。
and then create an index on ID
: CREATE INDEX items.ID ON items (ID) UNIQUE
.
现在我创建一个新项目(类似于 ODocument doc = new ODocument(items)
等),我想在数据库上生成新项目的ID(类似于RDBMS中的序列) 。
如何使用针对OrientDB的Java Document API执行此操作?
Now when I create a new item (something like ODocument doc = new ODocument("items")
etc.), I would like the ID for the new item to be generated on the database (something like a sequence in RDBMS).
How do I do this with the Java Document API for OrientDB?
推荐答案
OrientDB不支持串行(我们有一个问题,所以你可以用这种方式管理你自己的计数器(例如使用SQL):
OrientDB doesn't support serial (we've an issue for that), so you can manage your own counter in this way (example using SQL):
create class counter
insert into counter set name='mycounter', value=0
然后每次需要新号码时都可以:
And then every time you need a new number you can do:
update counter incr value = 1 where name = 'mycounter'
这在以这种方式在SQL批处理中起作用:
This works in a SQL batch in this way:
begin
let $counter = update counter incr value = 1 where name = 'mycounter' return after
insert into items set id = $counter.value, qty = 10, price = 1000
commit
通过使用Java,你可以做同样的事情:创建单身类计数器,每次我增加文档值并保存。
By using Java you can make the same: create singleton class "Counters" that everytime increment the document value and save it.
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