referencing columns

[Lukas Eder]

I agree that iterating over columns is very useful and I've noticed that
you've mixed the two paradigms, which is also useful.

If you pursue the thought of this API, will you consider separating the
functionality into two types?

- Columns extends Iterable<Column> (which is essentially ResultMap)
- Column

If not, what would be the motivation to make Column iterate on itself as a
type?

Lukas

2018-05-03 17:33 GMT+02:00 Douglas Surber <douglas.surber at oracle.com>:

> Lukas,
>
> This is orthogonal to the Flow.Processor vs Collector discussion. And
> please note that ADBA has both.
>
> Using a column cursor to access the columns is an attempt to break out of
> the get(int) vs get(String) way of thinking. I came up with this by
> thinking about all the different patterns of column access I’ve seen over
> the years and trying to wrap them up in a reasonably simple API. It quickly
> became clear that I needed to separate column selection from value access.
> Once I did that this class was an obvious consequence.
>
> It provides baked-in support for many different access patterns rather
> than requiring the programmer to roll his own. What I especially like is
> the way it supports mixing access patterns, for example locating a column
> by name, then iterating over a subsequence of successive columns.
>
> The advantage is that it should make it easy to avoid counting columns to
> come up with the desired index and at the same time handle missing and
> duplicate identifiers. From a framework perspective simple iteration over
> columns should be incredibly useful.
>
> Douglas
>
>
> On May 3, 2018, at 1:23 AM, Lukas Eder <lukas.eder at gmail.com> wrote:
>
> Hi Douglas,
>
> This type would be very interesting. Akin to JDBC's ResultSetMetaData
> type, but more object oriented. Mixed with JDBC's ResultSet's notion of
> being a cursor with a current position.
>
> Of course, this cursor-ness is precisely the "old JDBC ResultSet" model,
> which is understandable from the perspective of a result set being a
> flattened stream of column/value pairs, but I think that few people think
> about result sets or records in this way. In JDBC, most people would like
> to fetch a List<Row> style type. In ADBA, being asynchronous, a Consumer<
> Row> style type (simplified Collector) seems appropriate. Putting the
> individual column and its value at the top abstraction level might be
> surprising.
>
> What would be the benefit of this approach?
>
>
> 2018-05-02 19:42 GMT+02:00 Douglas Surber <douglas.surber at oracle.com>:
>
>> Here is another way to approach referencing columns. Replace ResultMap
>> with  Column as defined below. This is not a fully thought out proposal. It
>> is instead an attempt to look at the problem from another direction and not
>> get stuck with the same old JDBC ResultSet model.
>>
>> Douglas
>>
>> /**
>>  * A mutable handle to one value of an ordered sequence of columns or of
>>  * out parameters. Columns have a 1-based index and optionally an
>> identifier.
>>  * Identifiers are not guaranteed to be unique.
>>  */
>> public interface Column extends Iterable<Column>, Iterator<Column>,
>> Cloneable {
>>
>>   /**
>>    * Return the value of this column as an instance of the given type.
>>    *
>>    * @param <T>
>>    * @param type
>>    * @return
>>    */
>>   public <T> T get(Class<T> type);
>>
>>   /**
>>    * Return the identifier of this column. May be null.
>>    *
>>    * @return
>>    */
>>   public String identifier();
>>
>>   /**
>>    * Return the 1-based index of this Column.
>>    *
>>    * @return
>>    */
>>   public int index();
>>
>>   /**
>>    * Return the SQL type of the value of this column.
>>    *
>>    * @return
>>    */
>>   public SqlType type();
>>
>>   /**
>>    * Modify this Column to point to the next value identified by id.
>>    *
>>    * @param id
>>    * @return this Column
>>    */
>>   public Column at(String id);
>>
>>   /**
>>    * Modify this Column to point to the value at index. The first value
>> is at index 1.
>>    * Negative numbers count back from the last value. The last value is at
>>    * index -1.
>>    *
>>    * @param index
>>    * @return this Column
>>    */
>>   public Column at(int index);
>>
>>   /**
>>    * Return a new Column that is a handle to a subsequence of sequence of
>> values
>>    * referenced by this Column. The subsequence consists of the length
>> values in
>>    * order starting with the value this Column points to when this method
>> is
>>    * called. This Column is not modified.
>>    *
>>    * @param length
>>    * @return a new Column.
>>    */
>>   public Column slice(int length);
>>
>>   /**
>>    * Return a new Column that is a duplicate of this Column.
>>    *
>>    * @return a new Column
>>    */
>>   public Column clone();
>>
>>   /**
>>    * Modify this Column to point to the next value in the sequence.
>>    *
>>    * @return this Column
>>    */
>>   @Override
>>   public Column next();
>>
>>   @Override
>>   public boolean hasNext();
>>
>>
>>   static void sample(Column columns) {
>>
>>     Map map = new HashMap();
>>     for (Column m : columns) {
>>       map.put(m.identifier(), m.get(Integer.class));
>>     }
>>
>>     List l = new ArrayList();
>>     for (Column m : columns.at
>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__columns.at&d=DwMFaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=DFcFtomvCycx6XeC1vpTp5TdBqlgkiljGpb5LljiXB4&m=QPvt4Up_aA0V_2p8Wq5SJgPn3Q_4ik1C9rJlyYlvBCk&s=xqp-Xj0rZnZIglqGGccfiy1Q_SbHxh29KAqRT79xdm8&e=>(3).slice(5))
>> {
>>       l.add(m.get(String.class));
>>     }
>>
>>     Column addr = columns.clone().at("street_address_1");
>>     String streetAddress1 = addr.get(String.class);
>>     String streetAddress2 = addr.next().get(String.class);
>>     String city = addr.next().get(String.class);
>>     String state = addr.next().get(String.class);
>>     String postalCode = addr.next().get(String.class);
>>
>>     String givenName = columns.at
>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__columns.at&d=DwMFaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=DFcFtomvCycx6XeC1vpTp5TdBqlgkiljGpb5LljiXB4&m=QPvt4Up_aA0V_2p8Wq5SJgPn3Q_4ik1C9rJlyYlvBCk&s=xqp-Xj0rZnZIglqGGccfiy1Q_SbHxh29KAqRT79xdm8&e=>
>> ("GIVEN_NAME").get(String.class);
>>     String familyName = columns.at
>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__columns.at&d=DwMFaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=DFcFtomvCycx6XeC1vpTp5TdBqlgkiljGpb5LljiXB4&m=QPvt4Up_aA0V_2p8Wq5SJgPn3Q_4ik1C9rJlyYlvBCk&s=xqp-Xj0rZnZIglqGGccfiy1Q_SbHxh29KAqRT79xdm8&e=>
>> ("FAMILY_NAME").get(String.class);
>>
>>   }
>> }
>>
>>
>
>