Execute raw NoSQL queries (e.g. MongoDB)

[bajtos]

Suggestion

As I wrote in #2807 (comment), it is possible to execute raw SQL queries using the recently introduced Repository method execute, see #2681. This works great for SQL connectors.

Unfortunately, this method does not work for MongoDB and possibly for other NoSQL connectors that require more than just a command string and args array.

We need to find a way how to improve LB4 API, MongoDB connector API or both, to make it easy to execute raw MongoDB commands.

Related code:

• loopback-datasource-juggler
• loopback-connector-mongodb

Use Cases

• execute aggregate query, see How to execute raw MongoDB queries #2807, How can i use mongodb aggregate with lb4? #2021

Examples

const result = dataSource.execute('MyCollection', 'aggregate', [
    {
        $lookup:{
            .....   
        }
    },
    {   $unwind:"$data" },
    {
        $match:{
            ...
        }
    },
    {
        $lookup:{
            ... 
        }
    },
    {   $unwind:"$LoanRepayment" },
    { $project : { _id: 0} },
    { $out : "tempData" }
  ],
);

Acceptance criteria

• Improve the typedef signatures for execute possibly with some overloading on both repository classes in LB4 (feat(repository): add support for non-SQL variants of Repository.execute() #6030) and datasource classes in Juggler (see types: support non-SQL styles of ds.execute loopback-datasource-juggler#1855)

• Add API docs on repository classes in LB4 (feat(repository): add support for non-SQL variants of Repository.execute() #6030) and datasource classes in Juggler (see types: support non-SQL styles of ds.execute loopback-datasource-juggler#1855)

• Create a new page about the execute method under https://loopback.io/doc/en/lb4/Working-with-data.html. Mention the connectors that supports the execute method (see Add documentation for executing native database commands #6047)

• Add details about execute method on relevant pages under https://loopback.io/doc/en/lb4/Database-connectors.html.

  See also Add documentation for executing native database commands #6047 (review):

  This is a good content to be mentioned in "Configuring DataSource" page [Spike][Docs] reorganize connector reference into reference, how-to guides, and tutorials #6061

• Add tests to ensure raw NoSQL queries are executing as expected for MongoDB (see test: add acceptance-level tests for repository.execute() #6046)

• Investigate why the acceptance test is failing for PostgreSQL and fix the problem, see test: add acceptance-level tests for repository.execute() #6046 (comment)

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