Evgeniy created FLINK-35916:
-------------------------------
Summary: AbstractJdbcRowConverter: type conversion to string
Key: FLINK-35916
URL: https://issues.apache.org/jira/browse/FLINK-35916
Project: Flink
Issue Type: Improvement
Components: Connectors / JDBC
Affects Versions: jdbc-3.2.0
Reporter: Evgeniy
Fix For: jdbc-3.1.2, jdbc-3.2.0
*Problem:* When converting a type to a string, Java types are explicitly cast,
which generates a ClassCastException.
{*}Effects{*}: Most Java types, one way or another, have the ability to be
converted to a String type. However, not all types with this capability inherit
a class of type String or similar, where the type can be cast to type String.
As java suggests, any object can be cast to the String: Object#toString type if
its implementation does not imply the opposite. However, explicit casting to
the String type makes this impossible for 99% of custom Java objects.
{*}Goals{*}: Calling the Object#toString method for all objects that are
supposed to be converted to a string.
{*}Solution{*}:
To begin with, I suggest you pay attention to the class that deals with type
conversion - AbstractJdbcRowConverter. Pay attention to the method that deals
with type conversion - createInternalConverter, and specifically to the lambda
expression that deals with converting a type to a String type (CHAR, VARCHAR).
{code:java}
switch (type.getTypeRoot()) {
...
case CHAR:
case VARCHAR:
return val -> StringData.fromString((String) val);
...
} {code}
You can observe (String) val, which is problematic.
My intended solution is the following change.
{code:java}
return val -> StringData.fromString(val.toString()); {code}
val.toString() can give a chance for a new life to most objects that cannot be
processed by Flink by default, and this is very cool because it solves at least
1 problem.
{*}For further research{*}:
For example, pay attention to the type that is used in the podtgres driver to
package PostgreSQL types other than primitive ones - PGobject.
{code:java}
public class PGobject implements Serializable, Cloneable {
protected @Nullable String type;
protected @Nullable String value;
...
...
public String toString() {
return this.getValue();
}
...
} {code}
As you may have noticed, PostgreSQL itself is engaged in converting types to a
string, which is an excellent argument for using val.toString().
Perhaps in the future, you can add PGobject type processing, as was done for
PGarray, but it seems to me that the solution described above is the fastest
and most optimal. Thanks!
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