Data Table doesn't load data

Can someone help me understand why the data isn’t loading in the snippet below?

http://webix.com/snippet/a4c0fd2f

I discovered through trial and error that I can’t programmatically set an id inside the JSON:

`
id: "table_" + 3, ...

`

This code correctly loads the data for a single table.

http://webix.com/snippet/38f43b90

How should I set the column id if I want it programmatically generated?

I found that I didn’t need to set a unique id. Atleast, I didn’t get any errors having multiple data table views displayed with the same column ids.