ClickHouse / ClickHouse/clickhouse-java

Map(K, V) type support issue

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bug
Langage dominant
Java
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Forks
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Merge moyen
2 j 23 h
PR mergées (30 j)
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Description

## Description
In Clickhouse `Map(K, V)` is not a collection of unique-by-key pairs, see https://clickhouse.com/docs/sql-reference/data-types/map :

> i.e. a map can contain two elements with the same key

But there is no way to obtain any representation other than a Map<,> of unique entries.

All the key-value pairs are being delivered by the underlying protocol, but they are effectively merged while reading an instance of a map in the corresponding [readMap(..)](https://github.com/ClickHouse/clickhouse-java/blob/601ade16364d667b71a4982bbabf60ed2d941dc1/client-v2/src/main/java/com/clickhouse/client/api/data_formats/internal/BinaryStreamReader.java#L969) method.

The issue affects all scenarios of map usage: top-level value, nested map-in-map, map-in-array, etc.

### Steps to reproduce
1. Execute minimal reproduction program:
```
public class Program {
public static void main(String[] args) throws SQLException {
String queryText = "select map('key', 'X', 'key', 'Y')";
try (
Connection cnn = DriverManager.getConnection("jdbc:clickhouse://localhost:11049/default", "default", "");
PreparedStatement stmt = cnn.prepareStatement(queryText);
ResultSet rs = stmt.executeQuery()
) {
if (rs.next()) {
System.out.println(rs.getObject(1)); // gives {key=Y}
} else {
throw new IllegalStateException();
}
}
}
}
```
2. Observe only one value per key returned.
3. Any attempt to get other value representations than what `getObject()` does gives the same or results in an exception being thrown.

### Expected Behavior

Supporting existing behavior by default, it is expected to be able to use type hints to affect the actual return value of the `getObject(..)` method of the `java.sql.ResultSet` implementation (such overloads as ` T getObject(int columnIndex, Class type)` and `Object getObject(int columnIndex, java.util.Map> map)` specifically, including their counterparts having `columnLabel` instead of `columnIndex`):

```
public class Program {
public static void main(String[] args) throws SQLException {
String queryText = "select map('key', 'X', 'key', 'Y')";
try (
Connection cnn = DriverManager.getConnection("jdbc:clickhouse://localhost:11049/default", "default", "");
PreparedStatement stmt = cnn.prepareStatement(queryText);
ResultSet rs = stmt.executeQuery()
) {
if (rs.next()) {
System.out.println(rs.getObject(1)); // gives {key=Y} by default

System.out.println(rs.getObject(1, List.class)); // to give [key=X, key=Y] only for top level
System.out.println(rs.getObject(1, Map.of("Map", List.class))); // to give [key=X, key=Y] same as above including nested values
} else {
throw new IllegalStateException();
}
}
}
}
```
Consider changing the default behavior by the time of a certain upcoming major release.

### Code Example

```sql
select map('key', 'X', 'key', 'Y');

```

#### Environment
* [ ] Cloud
* Client version: 0.10.0-rc2
* Language version: 21
* OS: Windows 11

#### ClickHouse Server
* ClickHouse Server version: 24.5.3.5

Guide de contribution

Ouvrir le guide de contribution

Piste de recherche

Commencez dans client-v2/src/main/java/com/clickhouse/client/api/data_formats/internal/BinaryStreamReader.java, au niveau de readMap(..), puis suivez les surcharges JDBC ResultSet getObject nommées dans l’issue. Reproduisez la requête avec des clés dupliquées et examinez comment sont lus les maps de niveau supérieur, les maps imbriqués et les maps contenus dans des arrays. C’est terminé lorsque le comportement par défaut reste compatible, tandis que les indications de type demandées préservent les entrées clé-valeur dupliquées dans chacun des scénarios indiqués.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

Évaluation

Stack technique
java
Domaine
api, database
Type d'issue
Bug
Difficulté
4/5
Temps estimé
3-5 jours
Activité
Active
Clarté
Plutôt claire
Accessibilité débutants
48/100

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