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How can I handle auto_increments? For instance, having



user_prescription subscription;

subscription.user_id = user_id;

subscription.service_id = service_id;

query.insert(subscription);

query.execute();





and subscription also has a "id" field which is auto_increment, doesn't
work. The id field gets some seemingly random value. How can I make sure
auto_increment works?


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On Mon, Mar 14, 2005 at 08:35:27PM +0100, Joachim Person wrote:
auto_increment happens at the database level. I don't believe mysql++
automatically updates the struct with the new id, you need to get it yourself
with the insert_id() call.

query.store();
int id = connection.insert_id();// do this right after the
// insert operation

- Chris


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Chris Frey wrote:
I think this may be problematic; if my understanding is correct, the id field
will be filled in by the user_prescription constructor, which is just
going to be an int, which means it'll be an essentially random value
since I doubt the constructor will initialize it to anything.

To get auto_increment to work, you have to either 1) not insert the
value into the table at all, or have the value inserted as NULL.

I *think* -- and this is where it gets quite hazy for me, because I
have not actually used either the specialized structures OR the Null
class (though I do need to use the Null class at some point) you
will need to do something like this:

subscription.id = Null<int>;

However, I'm not 100% sure that works with the specialized type classes
without going into the code and seeing if they respect the Null class.
I should imagine they do, but imagining will not make it so =)

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Joachim Person wrote:
I don't try to use SSQLS inserts when I want to use auto_increment
columns. I manually build my own SQL statement; when you leave the
auto_increment column out of the insert, MySQL picks the value for that
column for you.

I'm not sure that there's an easy way for us to make MySQL++
intelligently handle this for you.

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On Mon, Mar 14, 2005 at 12:58:28PM -0800, Earl Miles wrote:
I tried doing this from the mysql command line, like:

INSERT INTO Category (CategoryID, Name) VALUES (NULL, "hello");

And it worked fine. (CategoryID being auto-increment in my table)

This seems to be vaguely documented on
http://dev.mysql.com/doc/mysql/en/in...functions.html
under LAST_INSERT_ID().

- Chris


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Warren Young wrote:

Sorry, I am in fact using NULL for the column value in this instance.

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