Greetings.
I want to implement NestedType
<https://clickhouse.yandex/docs/en/data_types/nested_data_structures/nested/>
for the dialect <https://github.com/xzkostyan/clickhouse-sqlalchemy> of
ClickHouse database.
At the first sight it looks like copmosite type, but not not completely:
1. Each subtype considers like separate column
2. `NestedType` is just syntax sugar:
CREATE TABLE test_table1 (
date Date,
object Nested (
type String,
content String
)
)...
CREATE TABLE test_table2 (
date Date,
object.type String,
object.content String
)...
Both of DDL's create tables with the same structure.
3. Queries can be done only using full format, like that:
SELECT count(*), objects.type FROM test_table group by objects.type
or
SELECT count(*), test_table.objects.type FROM test_table group by test_table
.objects.type
My question is how can I implement that behaviour? I've tried to adjust
sqlachemy_utils.CompositeType, but it looks like there are a lot of
differences.
Looks like I need to use separated DeclarativeMeta class and register each
member of nested field (with
sqlalchemy.ext.declarative.base._add_attribute).
Another problem: append parent column name to nested column name, because I
want to make that:
class Test(Base):
__tablename__ = 'test'
object = Column(
Nested(
Column('type', String),
Column('content', String),
)
)
Session.query(Test).filter(Test.object.type == 'type')...
# generates that query...
select ... from test where test.object.type = 'type'
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