feat: Allow view querying with Mongo connector

[auden-woolfson]

Description

Since Mongo treats views as regular documents, the find function that's used in the connector works fine. The change here is to prevent mongo from using functions that are not allowed on views when querying a view. In this instance, get indexes

Motivation and Context

Impact

Test Plan

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== NO RELEASE NOTE ==

 

Summary by Sourcery

Allow MongoDB connector to handle views without invoking unsupported index operations.

New Features:

• Support querying MongoDB views by treating them as collections while avoiding view-incompatible operations.

Enhancements:

• Skip index retrieval for MongoDB tables that are detected to be views by querying collection metadata.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adds view-awareness to the Mongo connector by short-circuiting index lookup for views and introducing a helper to detect MongoDB views via listCollections, ensuring disallowed operations are not used on views.

Sequence diagram for MongoSession.getIndexes handling views

sequenceDiagram
    actor PrestoPlanner
    participant MongoSession
    participant MongoClient
    participant MongoDatabase
    participant MongoCollection

    PrestoPlanner->>MongoSession: getIndexes(SchemaTableName)
    MongoSession->>MongoSession: isView(schema, table)
    MongoSession->>MongoClient: getDatabase(schema)
    MongoClient-->>MongoSession: MongoDatabase
    MongoSession->>MongoDatabase: runCommand(listCollections filter name, type=view)
    MongoDatabase-->>MongoSession: result Document
    MongoSession->>MongoSession: parse cursor.firstBatch
    alt is view
        MongoSession-->>PrestoPlanner: return empty MongoIndex list
    else is not view
        MongoSession->>MongoSession: getCollection(SchemaTableName)
        MongoSession->>MongoCollection: listIndexes()
        MongoCollection-->>MongoSession: indexDocuments
        MongoSession->>MongoSession: MongoIndex.parse(indexDocuments)
        MongoSession-->>PrestoPlanner: List<MongoIndex>
    end

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Updated class diagram for MongoSession view-aware index lookup

classDiagram
    class MongoSession {
        +List~MongoIndex~ getIndexes(SchemaTableName tableName)
        +boolean isView(String schema, String table)
        -MongoClient client
        -LoadingCache~SchemaTableName, MongoTableHandle~ tableCache
        +MongoCollection~Document~ getCollection(SchemaTableName tableName)
        +MongoCollection~Document~ getCollection(String schema, String table)
        +void dropColumn(MongoTableHandle table, String columnName)
    }

    class MongoClient {
        +MongoDatabase getDatabase(String schema)
    }

    class MongoDatabase {
        +Document runCommand(Document command)
    }

    class MongoCollection {
        +ListIndexesIterable~Document~ listIndexes()
    }

    class SchemaTableName {
        +String getSchemaName()
        +String getTableName()
    }

    class MongoIndex {
        +List~MongoIndex~ parse(ListIndexesIterable~Document~ indexes)
    }

    class Document {
    }

    class LoadingCache~SchemaTableName, MongoTableHandle~ {
        +void invalidate(SchemaTableName key)
    }

    class MongoTableHandle {
        +SchemaTableName getSchemaTableName()
    }

    MongoSession --> MongoClient : uses
    MongoSession --> MongoDatabase : via client.getDatabase
    MongoSession --> MongoCollection : uses
    MongoSession --> SchemaTableName : parameter
    MongoSession --> MongoIndex : returns
    MongoSession --> Document : constructs commands
    MongoSession --> LoadingCache~SchemaTableName, MongoTableHandle~ : uses
    MongoSession --> MongoTableHandle : parameter
    MongoClient --> MongoDatabase : creates
    MongoDatabase --> Document : returns
    MongoCollection --> Document : returns
    MongoIndex --> Document : parses from

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File-Level Changes

Change	Details	Files
Skip index retrieval for Mongo views and add a helper to detect views via MongoDB listCollections command.	Guard getIndexes with a view check so that it returns an empty list when the target is a view. Introduce an isView helper that issues a listCollections command with a name and type filter to determine whether a collection is a view. Extract and inspect the cursor.firstBatch result from the listCollections command response and derive the is-view result from whether it is empty.	presto-mongodb/src/main/java/com/facebook/presto/mongodb/MongoSession.java

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[sourcery-ai]

Hey - I've left some high level feedback:

• The new isView check adds a round-trip listCollections command on every getIndexes call; consider caching view metadata or reusing existing table metadata to avoid repeated database commands on hot paths.
• isView currently assumes the listCollections command succeeds and that the result always contains cursor/firstBatch; it would be safer to handle missing fields or command failures explicitly (e.g., permissions issues) to avoid unexpected runtime errors.
• isView is declared public but appears to be an internal helper; if it’s not intended as part of the MongoSession API, consider making it private or package-private and/or taking SchemaTableName directly instead of separate schema/table strings for consistency with the rest of the class.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The new isView check adds a round-trip listCollections command on every getIndexes call; consider caching view metadata or reusing existing table metadata to avoid repeated database commands on hot paths.
- isView currently assumes the listCollections command succeeds and that the result always contains cursor/firstBatch; it would be safer to handle missing fields or command failures explicitly (e.g., permissions issues) to avoid unexpected runtime errors.
- isView is declared public but appears to be an internal helper; if it’s not intended as part of the MongoSession API, consider making it private or package-private and/or taking SchemaTableName directly instead of separate schema/table strings for consistency with the rest of the class.

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[agrawalreetika]

Thanks for the changes. Letf few comments.

Also, can we add test?

[agrawalreetika]

Lets make it private

[agrawalreetika]

Lets use avaiable Driver APIs instead of running raw commands - https://mongodb.github.io/mongo-java-driver/4.11/apidocs/mongodb-driver-sync/com/mongodb/client/MongoDatabase.html#listCollections()