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http://www.openoffice.org/issues/show_bug.cgi?id=55884
------- Additional comments from [EMAIL PROTECTED] Thu Oct 13 02:56:37 -0700
2005 -------
Sharing the meta data is rather easy. Here is detailed instruction on how to
do:
1) in the common statement base class (exact name depends on the driver), add
a pure virtual function
virtual XXXResultSet* createResultSet() = 0;
(XXX is to be replaced according the driver's notation conventions)
Some drivers, like the file driver, already have such a method. Just make it
pure virtual then.
2) in the statements classes, replace occurences of
= new XXXResultset(...);
with
= createResultSet();
in executeQuery() and similar functions code
3) in the "ordinary" statement class (which derives from the common base
class), implement createResultSet() with code like
return new XXXResultset(... , NULL);
and in the "prepared" statement class (which also derives from the common base
class), implement createResultSet() with code like
return new XXXResultset(... , m_xMetaData);
Explanation : a non-prepared statement has no meta data, it is generated by
the result set when required, so we pass NULL. A prepared statement has meta
data, which it can share with the result set it is currently constructing, so
we pass this meta to the constructor.
4) in the result set, there's normally a member variable named
m_xMetaData
which is a reference to the meta data.
Add an argument to the result set's constructor. Use this argument to
initialize the m_xMetaData member variable.
You are done, meta data is shared between the prepared statement and the
result set.
===
Now the tricky part. Well, it is not necessarily difficult, but I just happen
to have no really clear ideas about that now. Perharps it is very simple, at
the end...
The result set meta data is initialized by passing it the list of selected
columns in the SQL query. This information is used, for example, to determine
the number of columns or the name of the columns.
In a prepared statement, this list of selected columns is known from the very
beginning, when the prepared statement is constructed, because the SQL
statement is passed to the prepared statement's constructor.
In an ordinary statement, the SQL statement is known only when executeQuery()
method is called. So it is the right time to start initializing the meta data.
If the meta data is shared, the initialization might occur twice for a
prepared statement. First time when the prepared statement is constructed,
second time when the query is executed. This might have consequences or not,
depending on how the initialization is done.
Please notice that I did not say it occurs. I just suspect a potential problem
here.
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