Hi Pavel,
Querying the metadata as you suggest is a good approach. You will want
to adjust the arguments to DatabaseMetaData.getTables() however. The
arguments in your example may find false matches in other schemas and
with tables created with double-quoted names. The following example may
help you adjust the arguments to getTable():
public class z
{
public static void main( String... args ) throws Exception
{
Connection conn = DriverManager.getConnection(
"jdbc:derby:memory:db;create=true" );
conn.prepareStatement( "create table myTable( a int )" ).execute();
DatabaseMetaData dbmd = conn.getMetaData();
ResultSet rs;
rs = dbmd.getTables( null, "APP", "MYTABLE", new String[] {
"TABLE" } );
System.out.println( "Table 'MYTABLE' exists = " + rs.next() );
rs = dbmd.getTables( null, "APP", "mytable", new String[] {
"TABLE" } );
System.out.println( "Table 'mytable' exists = " + rs.next() );
}
}
Hope this helps,
-Rick
On 5/22/12 11:33 AM, Pavel Bortnovskiy wrote:
Hello:
When reading derby docs, I noticed that the functionWwdUtils.wwdChk4Tablein
Derby demos is implemented by executing an update on the table and then relying
on the exception mechanism to determine whether or not the table exists.
My approach was to execute DatabaseMetaData.getTables method (pls see implementation below) and iterate through the resultset. I also wanted to assure case insensitivity.
Which method is more preferable from the point of efficiency and database operations (locks, etc).
This code might be executed frequently and by multiple threads.
Thank you,
Pavel.
public static boolean tableExists(final Connection connection,
final String tableName) throws SQLException {
try {
final DatabaseMetaData databaseMetaData =
connection.getMetaData();
final ResultSet resultSet =
databaseMetaData.getTables(null, null, null, new String[]{"TABLE"});
try {
while (resultSet.next()) {
if
(resultSet.getString("TABLE_NAME").equalsIgnoreCase(tableName)) {
return true;
}
}
} finally {
connection.commit();
resultSet.close();
}
return false;
} catch (SQLException e) {
Statement statement = null;
try {
final Connection c =
Components.getMemoryDb().getConnection(true);
statement = c.createStatement();
final String select = "SELECT * FROM
SYSCS_DIAG.LOCK_TABLE";
final ResultSet resultSet =
statement.executeQuery(select);
final int cnt = resultSet.getMetaData().getColumnCount();
final StringBuilder builder = new
StringBuilder("Results of \"" + select + "\":");
while (resultSet.next()) {
builder.append("\n\t");
for (int i = 1; i <= cnt; i++) {
if (i > 1) {
builder.append(",");
}
builder.append(resultSet.getObject(i));
}
}
logger.info(builder.toString());
} finally {
if (statement != null) {
statement.close();
}
}
throw e;
}
}
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