[CALCITE-204] mapping issue with nested JSON in MongoDB

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Labels: github-import
• Assignee: Unassigned
• Reporter: GitHub Import
• Created: 18/Jun/14 08:35
• Updated: 18/Jun/14 08:35

Description

It looks like nested JSON map-elements cannot be correctly referenced in MongoDB right now. Although I understand MongoDB aggregation framework doesn't allow referencing a specific element from an array (https://jira.mongodb.org/browse/SERVER-4589), but it could be done for JSON/object elements.

For documents like this...
```
{
...
"days_since_join" : NumberLong(0),
"dim_tech" :

{ "calling_medium" : "mobile" }

,
"dim_user" :

{ "age" : NumberLong(19), "age_group" : "18-24", ... }

}
```
If we do aggregation using SQL
```
SELECT calling_medium, count FROM visits GROUP BY calling_medium;
```

The aggregation pipeline should be something like
```
db.visits.aggregate(
{
$group:{
_id:"$dim_tech.calling_medium",
count:{$sum:1}
}
}
)
```
A dot (.) sign could distinguish the hierarchy.

---------------- Imported from GitHub ----------------
Url: https://github.com/julianhyde/optiq/issues/204
Created by: tikazyq
Labels:
Created at: Tue Mar 25 01:41:14 CET 2014
State: open