Ruby on Rails的+ PostgreSQL的：自定义序列的使用自定义、序列、on、Ruby
说我有一个名为模型交易具有：TRANSACTION_ code 属性。
我想该属性被自动填充可能不同于 ID序列号（例如交易与 ID = 1 可以有 TRANSACTION_ code = 1000 ）。
Say I have a model called Transaction which has a :transaction_code attribute.
I want that attribute to be automatically filled with a sequence number which may differ from id (e.g. Transaction with id=1 could have transaction_code=1000).
我试图创建Postgres的序列，然后庄家对 TRANSACTION_ code 列的默认值 NEXTVAL 。
问题是，如果我不上的回报率，当我发出了一个 @ transaction.save指定任何值的回报率，它试图做的SQL语句： @ transaction.transaction_ code
I have tried to create a sequence on postgres and then making the default value for the transaction_code column the nextval of that sequence.
The thing is, if I do not assign any value to @transaction.transaction_code on RoR, when I issue a @transaction.save on RoR, it tries to do the following SQL:
INSERT INTO交易（TRANSACTION_ code）VALUES（NULL）;
这样做是建立在交易的表里，有TRANSACTION_ code为NULL，而不是计算序列的NEXTVAL和相应的列插入。因此，当我发现，如果你指定NULL给Postgres，它假设你真的想有一个默认值（我是从ORACLE具有不同的行为到来），以NULL插入该列，不管它。
What this does is create a new row on the Transactions table, with transaction_code as NULL, instead of calculating the nextval of the sequence and inserting it on the corresponding column. Thus, as I found out, if you specify NULL to postgres, it assumes you really want to insert NULL into that column, regardless of it having a default value (I'm coming from ORACLE which has a different behavior).
我接受这个任何解决方案，或者如果回报率在数据库或完成的：
I'm open to any solution on this, either if it is done on the database or on RoR:
要么是有办法排除的ActiveRecord的属性保存
或有一种方法插入前改变列的值触发
或有一种方法来生成这些序列号范围内的回报率
或任何其他方式，只要它的工作原理： - ）
either there is a way to exclude attributes from ActiveRecord's
save
or there is a way to change a column's value before insert with a trigger
or there is a way to generate these sequence numbers within RoR
or any other way, as long as it works :-)
在此先感谢。
推荐答案
有关的那一刻，你可能会被卡住获取和分配顺序的ROR模式是这样的：
For the moment, you might be stuck fetching and assigning the sequence in your ROR model like this:
before_create :set_transaction_code_sequence
def set_transaction_code_sequence
self.transaction_code = self.class.connection.select_value("SELECT nextval('transaction_code_seq')")
end
我不particularily喜欢这个解决方案，因为我想看到直接在AR这个修正......但它确实做的伎俩。
I'm not particularily fond of this solution, since I'd like to see this corrected in AR directly... but it does do the trick.
