Question 1

Does change capture work end to end into MotherDuck?

Accepted Answer

Yes, when change streams are enabled on the sync. Polytomic reads the stream and loads through MotherDuck's Parquet staging path, but staging is transport only: records land in a staging table and are then reconciled with update and insert statements. So a collection with a primary key merges correctly and deletes are applied rather than being silently dropped. Change streams need a replica set or sharded cluster, so a standalone deployment cannot use them.

Question 2

Do nested documents become typed DuckDB structs?

Accepted Answer

Generally no, they arrive as JSON. Contents are preserved in full, so nothing is lost, but MongoDB schema inference is deliberately non recursive, which means MotherDuck usually receives nested objects and arrays as JSON rather than typed STRUCT and LIST columns. DuckDB queries JSON natively so this is workable, and if you query the same paths often it is worth materializing them into typed columns once in MotherDuck rather than extracting on every query.

Question 3

How is schema decided for a schemaless source?

Accepted Answer

By sampling recent documents and inferring fields and types from what is found. That handles most collections immediately. The limitation to watch is sparse fields: an attribute present on a small fraction of documents may fall outside the sample and not be discovered. You can add fields manually and override inferred types, which is worth doing before the first full load rather than after you notice a column missing in MotherDuck.

Question 4

Why pair MongoDB with MotherDuck specifically?

Accepted Answer

Because the two solve opposite problems. Mongo is built for application reads and writes, and aggregation pipelines are not SQL, so most analysts cannot use it directly and heavy queries compete with your production workload. Running ETL into MotherDuck gives everyone SQL over the same data, on a fast analytical engine, without touching the cluster your application depends on. Adding your billing and CRM data alongside is what makes the joins possible.

Connect MotherDuck with MongoDB

Connect MotherDuck and MongoDB with Polytomic

Change streams including deletes

Nested documents kept whole

Documents become SQL

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Step-by-step integration guide

Connect MotherDuck in Polytomic

Connect MongoDB in Polytomic

Create a sync between MotherDuck and MongoDB

Map fields and enable the sync

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