Collections are used to group documents together so that it is convenient to apply some operation to them,
i.e. subscribing to changes, indexing, querying, ETL, etc.
Every document belongs to exactly one collection.
Typically, a collection holds similarly structured documents based on the entity type of the document.
Note: It is not required that documents within the same collection will share the same structure or have any sort of schema. The only requirement for documents to be in the same collection is that they must have the same @collection metadata property.