fix: use psycopg text array decoding in wal2json messages (#490)

Slack thread:
https://meltano.slack.com/archives/C06A1MD6A6L/p1724619858505739

When using log based replication, the wal2json output for columns of
array types returns a string encoded in sql format.
Ex: '{a,b}'

The records produced by the tap in this sutation fails the target schema
validation, since the schema is of type array and the value is a string.

I included a test case for it. Please feel free to modify the PR, I am
by no means a python developer.

Related:

- eulerto/wal2json#221 (comment)

---------

Co-authored-by: Edgar Ramírez Mondragón <[email protected]>

tap_postgres/client.py

@@ -429,7 +429,7 @@ def get_records(self, context: Context | None) -> Iterable[dict[str, Any]]:
         while True:
             message = logical_replication_cursor.read_message()
             if message:
-                row = self.consume(message)
+                row = self.consume(message, logical_replication_cursor)
                 if row:
                     yield row
             else:
@@ -456,7 +456,7 @@ def get_records(self, context: Context | None) -> Iterable[dict[str, Any]]:
         logical_replication_cursor.close()
         logical_replication_connection.close()
 
-    def consume(self, message) -> dict | None:
+    def consume(self, message, cursor) -> dict | None:
         """Ingest WAL message."""
         try:
             message_payload = json.loads(message.payload)
@@ -476,12 +476,12 @@ def consume(self, message) -> dict | None:
 
         if message_payload["action"] in upsert_actions:
             for column in message_payload["columns"]:
-                row.update({column["name"]: column["value"]})
+                row.update({column["name"]: self._parse_column_value(column, cursor)})
             row.update({"_sdc_deleted_at": None})
             row.update({"_sdc_lsn": message.data_start})
         elif message_payload["action"] in delete_actions:
             for column in message_payload["identity"]:
-                row.update({column["name"]: column["value"]})
+                row.update({column["name"]: self._parse_column_value(column, cursor)})
             row.update(
                 {
                     "_sdc_deleted_at": datetime.datetime.utcnow().strftime(
@@ -517,6 +517,15 @@ def consume(self, message) -> dict | None:
 
         return row
 
+    def _parse_column_value(self, column, cursor):
+        # When using log based replication, the wal2json output for columns of
+        # array types returns a string encoded in sql format, e.g. '{a,b}'
+        # https://github.com/eulerto/wal2json/issues/221#issuecomment-1025143441
+        if column["type"] == "text[]":
+            return psycopg2.extensions.STRINGARRAY(column["value"], cursor)
+
+        return column["value"]
+
     def logical_replication_connection(self):
         """A logical replication connection to the database.
 

tests/test_log_based.py

@@ -1,7 +1,7 @@
 import json
 
 import sqlalchemy as sa
-from sqlalchemy.dialects.postgresql import BIGINT, TEXT
+from sqlalchemy.dialects.postgresql import ARRAY, BIGINT, TEXT
 
 from tap_postgres.tap import TapPostgres
 from tests.test_core import PostgresTestRunner
@@ -57,3 +57,53 @@ def test_null_append():
         tap_class=TapPostgres, config=LOG_BASED_CONFIG, catalog=tap_catalog
     )
     test_runner.sync_all()
+
+
+def test_string_array_column():
+    """LOG_BASED syncs failed with array columns.
+
+    This test checks that even when a catalog contains properties with types represented
+    as arrays (ex: "text[]") LOG_BASED replication can properly decode their value.
+    """
+    table_name = "test_array_column"
+    engine = sa.create_engine(
+        "postgresql://postgres:postgres@localhost:5434/postgres", future=True
+    )
+
+    metadata_obj = sa.MetaData()
+    table = sa.Table(
+        table_name,
+        metadata_obj,
+        sa.Column("id", BIGINT, primary_key=True),
+        sa.Column("data", ARRAY(TEXT), nullable=True),
+    )
+    with engine.begin() as conn:
+        table.drop(conn, checkfirst=True)
+        metadata_obj.create_all(conn)
+        insert = table.insert().values(id=123, data=["1", "2"])
+        conn.execute(insert)
+        insert = table.insert().values(id=321, data=['This is a "test"', "2"])
+        conn.execute(insert)
+
+    tap = TapPostgres(config=LOG_BASED_CONFIG)
+    tap_catalog = json.loads(tap.catalog_json_text)
+    altered_table_name = f"public-{table_name}"
+
+    for stream in tap_catalog["streams"]:
+        if stream.get("stream") and altered_table_name not in stream["stream"]:
+            for metadata in stream["metadata"]:
+                metadata["metadata"]["selected"] = False
+        else:
+            stream["replication_method"] = "LOG_BASED"
+            stream["replication_key"] = "_sdc_lsn"
+            for metadata in stream["metadata"]:
+                metadata["metadata"]["selected"] = True
+                if metadata["breadcrumb"] == []:
+                    metadata["metadata"]["replication-method"] = "LOG_BASED"
+
+    test_runner = PostgresTestRunner(
+        tap_class=TapPostgres, config=LOG_BASED_CONFIG, catalog=tap_catalog
+    )
+    test_runner.sync_all()
+    assert test_runner.record_messages[0]["record"]["data"] == ["1", "2"]
+    assert test_runner.record_messages[1]["record"]["data"] == ['This is a "test"', "2"]