Return Timestamp With Prepared Statement

问题

I have an auto generated timestamp that is created each time a record is inserted or updated in a mysql table. Is there a way to return this timestamp in a way similar to how I would use a keyholder to return a newly created id?

KeyHolder keyHolder = new GeneratedKeyHolder();
JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);

//Insert Contact
jdbcTemplate.update(new PreparedStatementCreator() {
    @Override
    public PreparedStatement createPreparedStatement(Connection connection) throws SQLException {
        PreparedStatement preparedStatement = connection.prepareStatement(SQL_ADD, Statement.RETURN_GENERATED_KEYS);
        preparedStatement.setString(1, contact.getFirstName());
        preparedStatement.setString(2, contact.getLastName());
        preparedStatement.setInt(3, contact.getOrganizationId());
        preparedStatement.setString(4, contact.getType());
        preparedStatement.setInt(5, contact.getUserId());
        return preparedStatement;
        }   
}, keyHolder);
//Use keyholder to obtain newly created id
contact.setId(keyHolder.getKey().intValue());

Is there some way to also return the new timestamp without having to requery the table? I have been looking for ways to return it along with the id as a key in the keyholder, but it doesn't seem to be returned as a key?

回答1:

There are few options for solving this issue on the MySQL database server side. You could start with creating a TRIGGER on the table. As TRIGGER has a restriction and cannot return data, you can set the TIMESTAMP value to a variable:

DEMILITER //
CREATE TRIGGER ai_tbl_name AFTER INSERT ON tbl_name
FOR EACH ROW
BEGIN

SET @TimeStamp = NEW.timestamp_column;

END;//
DELIMITER ;

To retrieve this timestamp value, run the following command:

SELECT @TimeStamp;

Since the variables are stored in the memory, there will be no need to open any tables again.

You go even further. You could create a STORED PROCEDURE in MySQL to automate all the above (sample code, as I do not know your table's details):

DELIMITER //
DROP PROCEDURE IF EXISTS sp_procedure_name //
CREATE PROCEDURE sp_procedure_name (IN col1_val VARCHAR(25),
                                    IN col2_val VARCHAR(25),
                                    IN col3_val INT)
BEGIN
    INSERT INTO tbl_name (col1, col2, col3)
    VALUES (col1_val, col2_val, col3_val);

    SELECT @TimeStamp;
END; //
DELIMITER ;

You can run this procedure with the following code:

CALL sp_procedure_name(col1_val, col2_val, col3_val);

As I'm not familiar with the Java, you'll need to finish it up with your side of code.

回答2:

Not very satisfying, but I think "no" is the answer to your question. I don't know any of the Spring stuff, but I think this is due to the basic JDBC that it's wrapping. See http://docs.oracle.com/javase/6/docs/api/java/sql/Statement.html#getGeneratedKeys%28%29

You only option would be to create a stored procedure on MySQL that has an out parameter and call that. See http://dev.mysql.com/doc/refman/5.0/en/call.html.

回答3:

It seems that the variable contact is an instance for the newly inserted record. As it contains the newly generated id (primary key) field value, you can execute a new query to return the required timestamp field value for this new id.

The query may look like this:

select timestamp_field from my_table where id=?

Use PreparedStatement to input new id value and execute it to fetch required timestamp field value.

回答4:

GeneratedKeyHolder also has two methods: getKeyList() that returns Map<String,Object> of generated fields; and getKeyList() that produces a list of generated keys for all affected rows.

See java doc of GeneratedKeyHolder and Spring tutorial of auto generated keys

In addition Spring's SimpleJdbcInsert has methods for generated key retrieval. See also method SimpleJdbcInsert#usingGeneratedKeyColumns

回答5:

There are 2 methods in java.sql.Connection class causing PreparedStatement execution to return selected key columns :

PreparedStatement prepareStatement(String sql,
                                   int[] columnIndexes)
                                throws SQLException

PreparedStatement prepareStatement(String sql,
                                   String[] columnNames)
                                   throws SQLException

You don't need to use Spring KeyHolder & JDBCTemplate to do this.
The give hope you could number/name your timestamp column. But the javadoc doesn't require or suggest that any JDBC implementation can return non-key columns, so your out of luck with this approach:

Creates a default PreparedStatement object capable of returning the auto-generated keys designated by the given array. This array contains the names of the columns in the target table that contain the auto-generated keys that should be returned.

As suggested in another answer, can switch to a stored procedure that does exactly what you want (CallableStatement is actually a PreparedStatement that executes storedprocedures - i.e. a subclass).
Can populate the timestamp column within the prepared statement via new Timestamp(new Date()) - but you should have in place a mechanism to sync times across your various servers (which is often used in windows and *nix environments). Your trigger could set the timestamp only if a value wasn't already provided.

As part of your app & DB design, you need to commit to a philosophy of where certain operations occur. If the DB derives needed data, the app needs to refresh data - you must pay the price of separate query executions or a combined stored proc that inserts & retrieves.

来源：https://stackoverflow.com/questions/13109982/return-timestamp-with-prepared-statement

标签

java

mysql

Spring

jdbc

timestamp