Add dbref field support for mongodb connector;

[academy-codex]

Fixes #3134.

Description: Added explicit case for handling if the type of a field is DBRef. In such case, we extract the id, database name and collection name from the object and convert that into a row. This change enables support at the MongoSession level. With this change, the column starts showing up in the information schema. However, all the values come as null because the writeBlock() method still needs to add the support.

To do this, we need add support at the MongoPageSource. This is done by aadding a case in the writeBlock() method.

[ebyhr]

Thanks for working on this!

Please add a test to TestMongoIntegrationSmokeTest. The test should create DBRef using MongoDB Java library and validate the result in Trino SQL.

CI failure cause is

2021-07-14T06:17:29.7767740Z [ERROR] src/main/java/io/trino/plugin/mongodb/MongoPageSource.java:[84] (regexp) RegexpMultiline: Multiple consecutive blank lines
2021-07-14T06:17:29.7769978Z [ERROR] src/main/java/io/trino/plugin/mongodb/MongoSession.java:[656,69] (whitespace) ParenPad: '(' is followed by whitespace.

If you haven't yet configured codestyle in IntelliJ, I would recommend setting https://github.com/trinodb/trino/blob/master/DEVELOPMENT.md#code-style.

Also, please remove ; from the commit message.

[academy-codex]

@ebyhr Please have a look. Made the changes and added the test case. :)

Test case description: The test case ensures that the column of dbref type is poppulated as well as has a value parsed. This is done by asserting that the count of documents where the dbref column is not null is equal to 1, as we have inserted only one document in the test case.

If column was not found or value was not parsed, the test case would fail.

The test case passes and works and confirms that the dbref value is getting poppulated.

[academy-codex]

Thanks for the review. Let me fix them and get back in a day or two.

[ebyhr]

Almost good to me. Please squash commits into one and update the commit title:
Add DBRef field support for MongoDB connector

[ebyhr]

Looks good except for minor comments.

[academy-codex]

@ebyhr all good in this one now ?

[ebyhr]

Merged, thanks!

[messaoudi-mounir]

I'm testing latest version of trino (docker image 371). He dosn't support BinData as DBRef $id

example
"referencedObject" : DBRef("rig", BinData(3, "lUDptLrw6lXQGoEMLPJ/iQ==")),

[ebyhr]

@messaoudi-mounir It will be supported in #11122.