[jira] [Created] (IGNITE-14645) Support polymorphic configuration nodes.

["Ivan Bessonov (Jira)" <ji...@apache.org>]

Ivan Bessonov created IGNITE-14645:
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             Summary: Support polymorphic configuration nodes.
                 Key: IGNITE-14645
                 URL: https://issues.apache.org/jira/browse/IGNITE-14645
             Project: Ignite
          Issue Type: Sub-task
            Reporter: Ivan Bessonov
            Assignee: Ivan Bessonov


NOTE: description might not be finished.
h3. Problem

Currently configuration schema structure is very restricted and doesn't allow any variations in it. This approach comes with a set of problems.
 # How do you properly configure {{IpFinder}}? For each type of finder you only need a few properties.
 # How do you configure SQL indexes? Pretty much the same problem.

h3. Interface

For the solution we need to expand abilities of configuration schemas. I propose the following option:
{code:java}
// Configuration schema that contains polymorphic field.
@Config
class TableConfigurationSchema {
    @NamedConfigValue
    public IndexConfigurationSchema indexes;
}

// Base class for polymorphic value. Explicitly has all subclasses
// in its description to simplify incremental code generation.
@PolymorphicConfig(impl = {
    HashIndexConfigurationSchema.class,
    TreeIndexConfigurationSchema.class,
})
class IndexConfigurationSchema {
    // This annotation shows that current field defines implementation.
    // Specific values are present in implementations declarations.
    @Id
    @Immutable
    @Value
    public String type;
}

// One of implementations for index. Id value is defined in annotation.
@PolymorphicInstance(id = "hash")
public static class HashIndexConfigurationSchema extends IndexConfigurationSchema {
    @Immutable
    @Value
    public String column;
}

// Other implementation for index.
@PolymorphicInstance(id = "tree")
public static class TreeIndexConfigurationSchema extends IndexConfigurationSchema {
    @Immutable
    @Value
    public String[] columns;
}
{code}
h3. Generated API

We need to tweak API a little bit. I'd love to see as few changes as possible, so my vision is something like this:
{code:java}
TableConfiguration tableCfg = ...;

tableCfg.indexes().create("hashIndexName", index ->
    // Id sets up automatically by the call.
    index.asHashIndex().changeColumn("columnName")
).get();

tableCfg.indexes().update("hashIndexName", index ->
    // Any cast is allowed to do in change request.
    // But this update will fail during processing.
    index.asTreeIndex().changeColumns(new String[] {"a", "b"})
);

IndexConfiguration indexCfg = tableCfg.indexes().get("hashIndexName");

// This must be an instance of "HashIndexConfiguration".
HashIndexConfiguration hashCfg = (HashIndexConfiguration)indexCfg;

// This must be instance of HashIndexView,
IndexView indexView = indexCfg.value();

// Maybe this is redundant, I don't know.
assert indexView.isHashIndex();

// Returns the same object with a safe cast.
// Maybe this is redundant as well and regular cast would be enough.
HashIndexView hashView = indexView.asHashIndex();{code}
h3. Implementation Notes

TODO



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