Hi Arvid, Hi Hao,
thanks for this valuable feedback. Let me clarify a few things before I
go into the details.
Just to avoid any confusion: the FLIP does not propose introducing the
StructuredType. Structured types backed by classes already exist in
Flink for years and are already supported in UDFs, Table.collect(),
StreamTableEnvironment.toDataStream, and connectors. Structured types
have been introduced for a better programmatic story in Table API. They
avoid the need for manually defining the full schema at the edges.
Manual schema work is annoying and with structured types it is possible
to use classes whereever a type is expected.
The goal of this FLIP only to bring Table API and SQL closer together.
In general, this is only the first step of my larger vision of
structured data handling. There are basically 3 kinds of structured types:
1) a typed, fixed field struct like STRUCTURED<'Money', i INT, s STRING>
2) an untyped, fixed field struct like STRUCTURED<i INT, s STRING>
(similar to Snowflake OBJECT(i INT, s STRING))
3) an untyped struct for semi-structured data like STRUCTURED (similar
to Snowflake OBJECT)
RowType represents 2), StructuredType represents 1) and a future
semi-structured type can represent 3) (but out of scope for this FLIP).
If we don't support a typed struct, Money(i INT) and User(i INT) are not
distinct in SQL. For table.collect() or eval(Row row) in UDFs, it would
mean that those need the full schema declaration in order to map to a
target type. Structured types avoid all of that and make Table API very
powerful.
Usually both the UDF and the collect()/toDataStream() are defined in the
same Table API program. Thus, the class is usually present in the same
classpath and this becomes less of an issue in production. Casting
structured types to ROW is also supported.
The implementation effort of this FLIP is very low. It's mostly intended
to fill missing gaps, no major overhaul of the type system. Also to
avoid any backwards compatibility issues.
Let me know what you think.
Cheers,
Timo
On 23.04.25 21:27, Hao Li wrote:
I think Arvid has a good point. Why not define Object type without class
and when you get it in table api, try to cast it to some class? I found
https://docs.oracle.com/javase/1.5.0/docs/guide/jdbc/getstart/mapping.html.
Under `JAVA_OBJECT` type section. They have:
```
ResultSet rs = stmt.executeQuery("SELECT ENGINEERS FROM PERSONNEL");
while (rs.next()) {
Engineer eng = (Engineer)rs.getObject("ENGINEERS");
System.out.println(eng.lastName + ", " + eng.firstName);
}
```
For us, how about add `getFieldAs(int post, Class class)` method in Row
type? Your example:
```
TableEnvironment env = ...
Table t = env.sqlQuery("SELECT OBJECT_OF('com.example.User', 'name', 'Bob',
'age', 42)");
// Tries to resolve `com.example.User` in the classpath, if not present
returns `Row`
t.execute().collect();
```
Will be
```
TableEnvironment env = ...
Table t = env.sqlQuery("SELECT OBJECT_OF('name', 'Bob', 'age', 42)");
// Tries to resolve `com.example.User` in the classpath, if not present
returns `Row`
For (Row row : t.execute().collect()) {
User user = row.getFieldAs(0, User.class);
}
```
For Arvid's question: "However, at that point, why do we actually need
anything beyond ROW?"
Maybe the difference is Row type shouldn't support to be casted as user
defined class but `StructuredType` can be.
Thanks,
Hao
On Wed, Apr 23, 2025 at 2:04 AM Arvid Heise <ahe...@confluent.io.invalid>
wrote:
Hi Timo,
thanks for addressing my points. I'm not set on using STRUCT et al. but
wanted to point out the alternatives.
Regarding the attached class name, I have similar confusion to Hao. I
wonder if Structures types shouldn't be anonymous by default in the sense
that initially we don't attach a class name to it. As you pointed out, it
has no real semantics in SQL and we can't validate it.
Another thing to consider is that if one user creates a table through some
means and another user wants to consume it, the second user may not have
access to the class as is. But the user could easily create a compatible
class on its own.
Consequently, I'm thinking about getting rid of the type at all. Only on
the edges, we can use conversion to the user types when users actually
access the ROW:
* Any table API access that wants to collect results (in your last example
what is t.execute().collect(); returning? How does that work in the
multi-user setup sketched above? Wouldn't it be easier that the consumer
explicitly gives us the POJO type that it expects?)
* Any DataStream conversion
* Any UDF
However, at that point, why do we actually need anything beyond ROW?
Best,
Arvid
On Wed, Apr 23, 2025 at 8:52 AM Timo Walther <twal...@apache.org> wrote:
Hi Hao,
1. Can `StructuredType` be nested?
Yes this is supported.
2. What's the main reason the class won't be enforced in SQL?
SQL should not care about classes. Within the SQL ecosystem, the SQL
engine controls the data serialization and protocols. The SQL engine
will not load the class. Classes are a concept of a JVM or Python API
endpoint. This also the reason why a SQL ARRAY<BIGINT> can be
represented as List<Long>, long[], Long[]. The latter are only concepts
in the target programming language and might look different in Python.
Regard,
Timo
On 22.04.25 23:54, Hao Li wrote:
Hi Timo,
Thanks for the FLIP. +1 with a few questions:
1. Can `StructuredType` be nested? e.g. `STRUCTURED<'com.example.User',
name STRING, age INT NOT NULL, address
STRUCTURED<'com.example.address',
street STRING, zip STRING>>`
2. What's the main reason the class won't be enforced in SQL? Since
tables
created in SQL can also be used in Table API, will it come as a
surprise
if
it's working in SQL and then failing in Table API? What if
`com.example.User` was not validated in SQL when creating table, then
the
class was created for something else with different fields and then in
Table api, it's not compatible.
Hao
On Tue, Apr 22, 2025 at 9:39 AM Timo Walther <twal...@apache.org>
wrote:
Hi Arvid, Hi Sergey,
thanks for your feedback. I updated the FLIP accordingly but let me
answer your questions
here as well:
> Are we going to enforce that the name is a valid class name? What
is
> happening if it's not a correct name?
> What are the implications of using a class that is not in the
> classpath in Table API? It looks to me that the name is
metadata-only
> until we try to access the objects directly in Table/DataStream
API.
Names are not enforced or validated. They are pure metadata as
mentioned
in Section 2.1. We fallback to Row as the conversion class if the name
cannot be resolved in the current classpath. So when staying in the
SQL
ecosystem (i.e. not switching to Table API, DataStream API, or UDFs),
the class must not be present.
> Should Expressions.objectOf(String, Object... kv); also have an
> overload where you can put in the StructuredType in case where
> the class is not in the CP?
That makes a lot of sense. I added a DataTypes.STRUCTURED(String,
Field...) method and a Expressions.objectOf(String, Object...).
> What is the expected outcome of supplying fewer keys than defined
> in the structured type? Are we going to make use of nullability
here?
> If so, *_INSERT and *_REMOVE may have some use.
Currently, we go with the most conservative approach, which means that
all keys need to be present. Maybe we can reserve this feature to
future
work and make the logic more lenient.
> Talking about nullability: Is there some option to make the
declared
> fields NOT NULL? If so, could you amend one example to show that?
> (Grammar? implies that it's not possible)
NOT NULL is supported similar to ROW<i INT NOT NULL>. I adjusted one
of
the examples.
> One bigger concern is around the naming. For me, OBJECT is used
for
> semi-structured types that are open. Your FLIP implies a closed
design
> and that you want to add an open OBJECT later. I asked ChatGPT
about
> other DB implementations and it seems like STRUCT is used more
often
> (see below). So, I'd propose to call it STRUCT<...>, STRUCT_OF, >
> structOf, UPDATE_STRUCT, and updateStruct respectively.
Naming is hard. I was also torn between STRUCT, STRUCTURED, or OBJECT.
In Flink, the ROW type is rather our STRUCT type, because it works
fully
position based. Structured types might be name-based in the future for
better schema evolution, so they rather model an OBJECT type. This was
my reason for choosing OBJECT_OF (typed to class name and fixed
fields)
vs. OBJECT (semi-structured without fixed fields). Snowflake also uses
OBJECT(i INT) (for structured types) and OBJECT (for semi structured
types).
Also, both structured and semi-structured types can then share
functions
such as UPDATE_OBJECT().
What do others think?
Thanks,
Timo
On 22.04.25 12:08, Sergey Nuyanzin wrote:
Thanks for driving this Timo
The FLIP seems reasonable to me
I have one minor question/clarification
do I understand it correct that after this FLIP we can execute of
`typeof` against result of `OBJECT_OF`
for instance
SELECT typeof(OBJECT_OF(
'com.example.User',
'name', 'Bob',
'age', 42
));
should return `STRUCTURED<'com.example.User', name STRING, age INT>`
?
On Tue, Apr 22, 2025 at 10:57 AM Timo Walther <twal...@apache.org>
wrote:
Hi everyone,
I would like to ask again for feedback on this FLIP. It is a rather
small change but with big impact on usability for structured data.
Are there any objections? Otherwise I would like to continue with
voting
soon.
Thanks,
Timo
On 10.04.25 07:54, Timo Walther wrote:
Hi everyone,
I would like to start a discussion about FLIP-520: Simplify
StructuredType handling [1].
Flink SQL already supports structured types in the engine,
serializers,
UDFs, and connector interfaces. However, currently only Table API
was
able to make use of them. While UDFs can take objects as input and
return types, it is actually quite inconvenient to use them in
transformations.
This FLIP fixes some immediate blockers in the use of structured
types.
Looking forward to feedback.
Cheers,
Timo
[1] https://cwiki.apache.org/confluence/display/FLINK/
FLIP-520%3A+Simplify+StructuredType+handling
