Add a feature to filter documents by field names and allow concatenation in MongodbLoader

[iamKushagra]

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Feature request

The proposed enhancement aims to add flexibility to the MongodbLoader class in LangChain by introducing an optional feature for field filtering. Currently, the loader retrieves the whole documents. This proposal suggests making field filtering optional, allowing users to choose between filtering specific fields or including the entire document content.

Motivation

The motivation behind this enhancement is to provide users with more control over the loading process. In some scenarios, users may prefer to load some fields or in some case the entire document content as text without specifying individual fields. By making field filtering optional, we accommodate both use cases, enhancing the usability of the MongodbLoader class.

Proposal (If applicable)

Introduce Optional Parameter: Add an optional boolean parameter, filter_fields, to the constructor of MongodbLoader. This parameter will determine whether field filtering should be applied.