Support get_columns and parse protobuf object for Python SDK

[tobegit3hub]

Here is the code to test.

import sqlalchemy as db
from sqlalchemy import inspect

zk_cluster = "127.0.0.1:2181"
zk_path = "/openmldb"

engine = db.create_engine(f'openmldb:///db1?zk={zk_cluster}&zkPath={zk_path}')
connection = engine.connect()

insp = inspect(engine)
print(insp.get_table_names())

columns = insp.get_columns('employees')

for column in columns:
    print(column)

We may add the code in openmldb_dialect.py.

    def get_columns(self, connection, table_name, schema=None, **kw):
        """
        columns_info = [
            {
                'name': 'name',
                'type': sqlalchemy.String(),
                'nullable': False,
                'default': None,
                'primary_key': False,
                'autoincrement': False,
                'comment': 'Unique identifier for the row'
            }
        ]
        return columns_info
        """
        raise NotImplementedError()

[tobegit3hub]

Here is the code to warp C api to get protobuf TableInfo.

--- a/python/openmldb_sdk/openmldb/dbapi/dbapi.py
+++ b/python/openmldb_sdk/openmldb/dbapi/dbapi.py
@@ -417,6 +417,9 @@ class Cursor(object):
     def get_tables(self, db):
         return self.connection._sdk.getTables(db)

+    def get_table_info(self, db, table):
+        return self.connection._sdk.getTableInfo(db, table)
+
     def get_all_tables(self):
         return self.connection._sdk.getAllTables()

diff --git a/python/openmldb_sdk/openmldb/sdk/sdk.py b/python/openmldb_sdk/openmldb/sdk/sdk.py
index bc8454039..05dcbb836 100644
--- a/python/openmldb_sdk/openmldb/sdk/sdk.py
+++ b/python/openmldb_sdk/openmldb/sdk/sdk.py
@@ -120,6 +120,12 @@ class OpenMLDBSdk(object):
             raise Exception("please init sdk first")
         return self.sdk.GetTableNames(db)

+    def getTableInfo(self, db, table):
+        if not self.sdk:
+            raise Exception("please init sdk first")
+        return self.sdk.GetTableInfo(db, table)
+
     def getAllTables(self):
         if not self.sdk:
             raise Exception("please init sdk first")

But we can not call API which may return the share pointer of protobuf TableInfo object. Here is the error message.

Traceback (most recent call last):
  File "/Users/tobe/code/4pd/OpenMLDB/python/openmldb_sdk/tobe/./use_openmldb_sqlalchemy.py", line 15, in <module>
    columns = insp.get_columns('employees')
  File "/Users/tobe/code/4pd/OpenMLDB/python/openmldb_sdk/venv/lib/python3.9/site-packages/sqlalchemy/engine/reflection.py", line 497, in get_columns
    col_defs = self.dialect.get_columns(
  File "/Users/tobe/code/4pd/OpenMLDB/python/openmldb_sdk/openmldb/sqlalchemy_openmldb/openmldb_dialect.py", line 149, in get_columns
    table_info = table_infos[0]
TypeError: 'SwigPyObject' object is not subscriptable
swig/python detected a memory leak of type '::openmldb::nameserver::TableInfo *', no destructor found.
2023-03-31 15:36:08,931:58842(0x7ff855e7f680):ZOO_INFO@zookeeper_close@2564: Closing zookeeper sessionId=0x1000cacd0970038 to [127.0.0.1:2181]

The sql_router_sdk.i only handle the generated code in Java.

// Enable protobuf interfaces
%include "swig_library/java/protobuf.i"
%protobuf(openmldb::nameserver::TableInfo, com._4paradigm.openmldb.proto.NS.TableInfo);
#endif