Firebird/IBPP: How to retrieve ID generated by a database autoincrement? - c++

Question

I configured my firebird database to autoincrement the primary key of the table.
CREATE GENERATOR GEN_CHANNEL_PARAMETER_SET_ID;
SET GENERATOR GEN_CHANNEL_PARAMETER_SET_ID TO 0;
CREATE TRIGGER CHANNEL_PARAMETER_SETS_BI FOR CHANNEL_PARAMETER_SETS
ACTIVE BEFORE INSERT POSITION 0
AS
BEGIN
if (NEW.CHANNEL_PARAMETER_SET_ID is NULL) then NEW.CHANNEL_PARAMETER_SET_ID = GEN_ID(GEN_CHANNEL_PARAMETER_SET_ID, 1);
END
Now, in my C++ program using IBPP I have the following problem:
When inserting a dataset into an new row of this table I know all values in my C++ program exept the new primary key because the database creates it. How can I retrieve this key form the database?
Maybe someone else inserted an entry too - just a moment after I inserted one. So retrieve the PK with the highest value could create an error. How can I handle this?
Adopting Amir Rahimi Farahani's answer I found the following solution for my problem:
I use a generator:
CREATE GENERATOR GEN_CHANNEL_PARAMETER_SET_ID;
SET GENERATOR GEN_CHANNEL_PARAMETER_SET_ID TO 0;
and the following C++/IBPP/SQL code:
// SQL statement
m_DbStatement->Execute(
"SELECT NEXT VALUE FOR gen_channel_parameter_set_id FROM rdb$database"
);
// Retrieve Data
IBPP::Row ibppRow;
int64_t channelParameterSetId;
m_DbStatement->Fetch(ibppRow);
ibppRow->Get (1, channelParameterSetId);
// SQL statement
m_DbStatement->Prepare(
"INSERT INTO channel_parameter_sets "
"(channel_parameter_set_id, ...) "
"VALUES (?, ...) "
);
// Set variables
m_DbStatement->Set (1, channelParameterSetId);
...
...
// Execute
m_DbStatement->Execute ();
m_DbTransaction->CommitRetain ();

Answer 1

It is possible to generate and use the new id before inserting the new record:
SELECT NEXT VALUE FOR GEN_CHANNEL_PARAMETER_SET_ID FROM rdb$database
You now know the value for new primary key.
Update:
IBPP supports RETURNING too:
// SQL statement
m_DbStatement->Prepare(
"INSERT INTO channel_parameter_sets "
"(...) VALUES (...) RETURNING channel_parameter_set_id"
);
// Execute
m_DbStatement->Execute ();
m_DbTransaction->CommitRetain ();
// Get the generated id
m_DbStatement->Get (1, channelParameterSetId);
...

Answer 2

To retrieve the value of the generated key (or any other column) you can use INSERT ... RETURNING ....
For example:
INSERT INTO myTable (x, y, z) VALUES (1, 2, 3) RETURNING ID
Also a lot of drivers provide extra features to support RETURNING, but I don't know IBPP.
Note that from the perspective of a driver the use of RETURNING will make the insert act like an executable stored procedure; some drivers might require you to execute it in a specific way.