JDBC PreparedStatement - 使用相同的参数，是否可能？

Question

I'm using an "insert or update" query such as the one below:

        String sql = 
            "INSERT INTO servlets (path, applicationId, startTime, numOfRequests, totalResponseTime, totalBytes)" +
            "VALUES (?, ?, NOW(), 1, ?, ?)" +
            "ON DUPLICATE KEY UPDATE numOfRequests = numOfRequests + 1, " +
            "totalResponseTime = totalResponseTime + ?, totalBytes = totalBytes + ?";

I'm using prepared statements and fill it with the relevant arguments in the following manner:

        statement = connection.prepareStatement(sql);
        statement.setString(1, i_ServletModel.GetPath());
        statement.setInt(2, i_ServletModel.GetApplicationId());
        statement.setLong(3, i_RequestStats.GetResponseTime());
        statement.setLong(4, i_RequestStats.GetBytes());
        statement.setLong(5, i_RequestStats.GetResponseTime());
        statement.setLong(6, i_RequestStats.GetBytes());

Notice that argument 3 is exactly the same as argument 5 and argument 4 is exactly the same as argument 6 since they require the same value in the query above.

Is there anything I can change, either in the query or in the arguments filling methods to avoid such an "ugly" syntax?

Answer 1

Using a local variable, you can make the code less ugly and error-prone. But the shortcoming of JDBC that it does not support named parameters still holds. There will be again multiple lines for the same parameter.

    statement = connection.prepareStatement(sql);

    long time = i_RequestStats.GetResponseTime();
    long bytes = i_RequestStats.GetBytes();

    statement.setString(1, i_ServletModel.GetPath());
    statement.setInt(2, i_ServletModel.GetApplicationId());
    statement.setLong(3,time);
    statement.setLong(4, bytes);
    statement.setLong(5, time);
    statement.setLong(6, bytes);

Answer 2

For developers facing same issue I recommend you to create a stored procedure or function, it is a very good practice since you will return a scalar value or list, but avoid to put a lot of logical stuff there. if you adopt this solution you should use "Callable Statement" Hope this will help .

Answer 3

As others have already reported while it is not technically possible with straight JDBC to use named parameters with prepared statements Spring does have some sugar to make it more palatable if that's in your stack already.

Here's an example using the same "named parameter" :personId twice in the query. Under the covers Spring will convert the SQL :personId to ?'s but it will apply the the same values multiple times as desired.

@Repository
public class RoleRepositoryImpl implements RoleRepository {

    private static final String ROLE_ASSIGNMENT_QUERY = "select T.RoleId from \n" +
            "(select RoleId from RoleAssignment where OrganizationId=:orgId and PersonId=:personId\n" +
            "union\n" +
            "select 'TEXTURA_ADMIN' from Administrator where PersonId=:personId) as T\n" +
            "inner join Role R on R.RoleId=T.RoleId\n";


    public static class RoleQuery extends MappingSqlQuery<Role> {

        public RoleQuery(final DataSource ds) {
            super(ds, ROLE_ASSIGNMENT_QUERY);
            declareParameter(new SqlParameter("orgId", Types.INTEGER));
            declareParameter(new SqlParameter("personId", Types.INTEGER));
            compile();
        }

        @Override
        protected Role mapRow(final ResultSet rs, final int rowNum) throws SQLException {
            try {
                return Role.valueOf(rs.getString(1));
            } catch (final IllegalArgumentException ex) {
                return null;
            }
        }
    }
}

And then example usage

    private final RoleQuery roleQuery;

    public RoleRepositoryImpl(final DataSource dataSource) {
        this.roleQuery = new RoleQuery(dataSource);
    }

    @Override
    public List<Role> findRoles(final Long orgId,
                                final Long userId) {

final List<Role> roles = roleQuery.executeByNamedParam(ImmutableMap.of(
                "orgId", orgId, 
                "personId", userId));

You can see the Spring magic happen in this method if you are curious what it does under the covers:

org.springframework.jdbc.object.SqlQuery#executeByNamedParam(java.util.Map, java.util.Map)

Answer 4

Can't you change the SQL syntax to refer back to the 'VALUES' you've already declared? Something like the following:

String sql = 
        "INSERT INTO servlets (path, applicationId, startTime, numOfRequests, totalResponseTime, totalBytes)" +
        "VALUES (?, ?, NOW(), 1, ?, ?)" +
        "ON DUPLICATE KEY UPDATE numOfRequests = numOfRequests + 1, " +
        "totalResponseTime = totalResponseTime + VALUES(5), totalBytes = totalBytes + VALUES(6)";

...that way you need only add each parameter once.

Answer 5

Not possible.

But you could instead, in your query, declare a variable and use the same multiple times. See: http://msdn.microsoft.com/en-IN/library/ms188927.aspx for MSSQL