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https://issues.apache.org/jira/browse/DERBY-2631?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12495236
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Knut Anders Hatlen commented on DERBY-2631:
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I'm +1 to the patch. I don't consider this as introducing differences between
embedded and the client, but rather as making the embedded driver more
complete, which is a good thing. I agree with Kathey that we should open an
issue for the client driver and link it to DERBY-310.
> 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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