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https://issues.apache.org/jira/browse/DERBY-2631?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12494570
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A B commented on DERBY-2631:
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> Will it be possible with some future work to implement this functionality for
> client?
I have not looked in detail at how to implement this for client, but I would be
surprised if such a thing was not possible with some future work. My guess,
though, is that it will require more work than was needed for embedded (most of
the embedded code already existed). Since the fish I'm hoping to fry right now
is limited to embedded, and since there does not appear to be a straightforward
mapping to the client code, I was hoping to focus this Jira on embedded only.
But as far as I know there's no reason this functionality couldn't be
implemented in client, once someone has the desire to fry that fish. It may be
more difficult, but it seems like it should be possible...
> Expose existing auto-generated key functionality through more JDBC APIs in
> embedded mode.
> -----------------------------------------------------------------------------------------
>
> Key: DERBY-2631
> URL: https://issues.apache.org/jira/browse/DERBY-2631
> Project: Derby
> Issue Type: Improvement
> Components: JDBC
> Affects Versions: 10.3.0.0
> Environment: Embedded mode only.
> Reporter: A B
> Assigned To: A B
> Priority: Minor
> Attachments: d2631_v1.patch, d2631_v1.stat
>
>
> Derby currently supports the following JDBC methods for auto-generated keys:
> // Indicate that we want to retrieve auto-generated key values.
> Connection.prepareStatement(String sql, int autoGeneratedKeys);
> Statement.execute(String sql, int autoGeneratedKeys);
> Statement.executeUpdate(String sql, int autoGeneratedKeys);
> // Retrieve the auto-generated values (only applies to INSERT statements).
> ResultSet rs = Statement.getGeneratedKeys();
> The current implementation of getGeneratedKeys() internally maps to the
> "IDENTITY_VAL_LOCAL()" method, which means that Derby's implementation only
> returns generated keys for autoincrement columns (no other default columns
> are supported). Further:
> 1. The generated key result set only ever has a single column. This is
> because Derby only allows one autoincrement column per table.
> 2. The type of the single column in the result set will be DECIMAL(31,0).
> This is defined by IDENTITY_VAL_LOCAL().
> 3. The generated key result set will only ever have a single row. This is
> because IDENTITY_VAL_LOCAL() only returns values that were assigned as
> the result of a *single row* INSERT statement using a VALUES clause.
> For a single row INSERT statement, at most one autoincrement value
> will be generated.
> All of that said, JDBC 3.0 also defines the following methods, which allow
> the user to explicitly indicate, via column position or column name, the
> columns for which the auto-generated keys should be made available:
> Connection.prepareStatement(String sql, String[] columnNames);
> Connection.prepareStatement(String sql, int[] columnIndexes);
> Statement.execute(String sql, String[] columNames);
> Statement.execute(String sql, int[] columIndexes);
> Statement.executeUpdate(String sql, String[] columnNames);
> Statement.executeUpdate(String sql, int[] columnIndexes);
> Derby currently throws a "Feature not supported" error for all of these
> methods. However, it seems like the above methods could be "mapped" onto the
> existing Derby behavior with relatively little effort (in embedded mode).
> Most of the required code is already in place.
> Doing so would make it easier for applications that rely on the columnNames
> and/or columnIndexes APIs to work with Derby (assuming the app just wants
> generated keys for identity (autoincrement) columns).
> Note that this Jira does *not* entail removing any of the restrictions nor
> changing any of the behavior outlined above. All of that will remain exactly
> as it is. This Jira simply exposes the existing functionality (restrictions
> and all) through additional (standard) API methods. In particular this means
> that any column specified by index (position) or name must be an
> auto-increment column for the INSERT table; otherwise Derby should throw an
> error. Or put differently, a user who specifies a column name/position will
> get--in the absence of errors--the *exact* same results as s/he would get
> from invoking the "(String sql, int autoGeneratedKeys)" method.
> Note also: This Jira is specifically for embedded mode. I think it would be
> harder to support these methods for Derby Client and so do not plan to
> address that.
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