Hello again,
only now have I returned to this issue. Like two months ago I wrote
some code (MyJdbcPkGenerator) but never had time to actually use it =-O
Now I have invested some hours into it, lurking over cayenne source
code trying to find a way to solve my problem. As suggested I have
overridden the JdbcPkGenerator and implemented my own
createAutoPk(DataNode node, List dbEntities) method. Soon I figured it
out this method is never called by the framework. As it turns out the
generator.runGenerator(dataSource) calls
PkGenerator pkGenerator = adapter.getPkGenerator();
dropPK =
pkGenerator.dropAutoPkStatements(dbEntitiesRequiringAutoPK);
createPK =
pkGenerator.createAutoPkStatements(dbEntitiesRequiringAutoPK);
in its buildStatements() method.
So I have overridden createAutoPkStatements in MyJdbcPkGenerator which
now doesn't delete and insert values in AUTO_PK_SUPPORT table if it
already exists, which is what I wanted (I also check if new tables were
added since last run)
I had a look at DbGenerator class. I think it would be nice if only
tables which do not already exist would be created. This way the
application which calls runGenerator() wouldn't throw
java.sql.SQLException: Table 'foo-bar' already exists. I know there is
a constructor which accepts excludedEntities, but then the application
have to check in advance if the tables are already there and pass
appropriate entities to the constructor. Of course one can always catch
the exception and make it quiet.
I have one more question, more of a architectural nature. I wouldn't
bother to use AUTO_PK_SUPPORT if only one cayenne-aware application
would use the database. I am thinking - if anytime in the near future
some other application will have to have full access to this database
then this is the only way to avoid PK conflicts. Is this correct?
Regards,
Borut
On 24.4.2006 15:41, Andrus Adamchik wrote:
Borut,
I don't have time to do serious review, but looks ok from the first
glance.
How do I use this class, once we agree on the
correct behaviour?
Just set it on adapter. E.g.:
import org.objectstyle.cayenne.property.PropertyUtils;
DbAdapter adapter = ..
// since DbAdapter doesn't define 'setPkGenerator',
// but all implementors do, you can use introspection:
PropertyUtils.setProperty(adapter, "pkGenerator", new
MyJdbcPkGenerator());
Andrus
On Apr 24, 2006, at 3:11 PM, Borut Bolčina wrote:
Hi,
as I need this functionality really bad (production code in three
weeks), I came up with this class. It is in a state we love to call:
"It compiles.". Can you please review it? How do I use this class, once
we agree on the correct behaviour?
public class MyJdbcPkGenerator extends JdbcPkGenerator {
/* (non-Javadoc)
* @see
org.objectstyle.cayenne.dba.JdbcPkGenerator#createAutoPk(org.objectstyle.cayenne.access.DataNode,
java.util.List)
*/
@Override
public void createAutoPk(DataNode node, List dbEntities) throws
Exception {
// check if a table exists
// create AUTO_PK_SUPPORT table
if (!autoPkTableExists(node)) {
runUpdate(node, pkTableCreateString());
}
// will hold only entities to be added to AUTO_PK_SUPPORT table
List<DbEntity> targetDbEntities = new
ArrayList<DbEntity>();
// create a set of model entity names
Set<String> modelDbEntities = new HashSet<String>();
for (Iterator iter = dbEntities.iterator(); iter.hasNext();) {
DbEntity dbEntity = (DbEntity) iter.next();
modelDbEntities.add(dbEntity.getName());
}
// create a set of existing entity names (already in db)
Set<String> existingDbEntities = getExistingTables(node);
if (modelDbEntities.size() >= existingDbEntities.size()) {
// new tables added in modeler after database creation
modelDbEntities.removeAll(existingDbEntities);
// modelDbEntities now contains only entity names to be added
to AUTO_PK_SUPPORT table
for (String dbEntityName : modelDbEntities) {
targetDbEntities.add(new
DbEntity(dbEntityName)); }
dbEntities = targetDbEntities;
}
// TODO if (model < existing) then
existing.removeAll(model) then delete
// TODO if (model={T1, T2} and existing={T3, T4}) then insert
T1,T2 and delete T3,T4
// delete any existing pk entries
// runUpdate(node, pkDeleteString(dbEntities));
// insert all needed entries
Iterator it = dbEntities.iterator();
while (it.hasNext()) {
DbEntity ent = (DbEntity) it.next();
runUpdate(node, pkCreateString(ent.getName()));
}
super.createAutoPk(node, dbEntities);
}
protected Set<String> getExistingTables(DataNode node) throws
SQLException {
Set<String> existingTables = new HashSet<String>();
Connection con = node.getDataSource().getConnection();
Statement stmt = con.createStatement();
String query = "SELECT 'TABLE_NAME' FROM AUTO_PK_SUPPORT";
try {
ResultSet rs = stmt.executeQuery(query);
try {
while (rs.next()) {
String s = rs.getString("TABLE_NAME");
existingTables.add(s);
}
} finally {
rs.close();
}
} finally {
con.close();
}
return existingTables;
}
}
Regards,
Borut
On 23.4.2006 11:34, Andrus Adamchik wrote:
On Apr 23, 2006, at 1:21 PM, Borut Bolčina wrote:
If I understand you correctly, the above
algorithm would create a statement
DELETE FROM AUTO_PK_SUPPORT WHERE TABLE_NAME IN ('tableA', 'tableB',
'tableC')
but not, say, tableD, as it is already present (created before).
In my case this pkDeleteString would look like (empty table names)
DELETE FROM AUTO_PK_SUPPORT WHERE TABLE_NAME IN ('')
INSERT INTO AUTO_PK_SUPPORT (TABLE_NAME, NEXT_ID) VALUES ('', 200)
Sorry, my first message and the correction that followed was a bit
confusing. "DELETE FROM .." is not needed at all. You need to do a
SELECT to see what's there, compare with the full entity list, and only
insert the missing records.
Also see Mike's suggestion on how to figure out the right starting
value. It may work as an alternative or an addition to the algorithm
above.
One "workaround" I can think of is to do
a SELECT on AUTO_PK_SUPPORT and if no error is thrown I must assume the
table exists, so I skip generator.runGenerator(dataSource); altogether.
This is not generic enough as you may end up with missing records if
you added a few new tables since the last run (so AUTO_PK_SUPPORT is
there, but its contents are incomplete).
Andrus
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