Support embedded query in memory connector. Fix memory connector bug

[mazesoul]

Adds support for the ability to query embedsMany models from the parent.

Fix a memory connector bug that could occur when having an "or" or "and"
clause combined with another property. In that case, the and would revert
true for 'Paul McCartney'

{name:'John Lennon',and: [{role:'lead'}, {vip:true}]}}

[mazesoul]

@altsang Are you in a position to give me an ETA for the review/merge. Also, is this something that you can accept?

[raymondfeng]

@mazesoul Thank you for the patch! Contributions are always welcome!

1. Before your PR, the and and or operator cannot be combined with regular clauses. Your case needs to be written as:

{and: [{name:'John Lennon'}, {role:'lead'}, {vip:true}]}

If we allow and/or to be used with regular clauses, we need to make sure other connectors support it too.

1. We already support nested properties for the memory connector even before this PR, see https://github.com/strongloop/loopback-datasource-juggler/blob/master/test/memory.test.js#L397-L428. What else does the PR add?

[mazesoul]

@raymondfeng The memory connector didn't support nested properties over arrays. Like this https://github.com/WyzeLink/loopback-datasource-juggler/blob/feature/support-embedded-query-in-memory/test/memory.test.js#L431-L439. Where friends is an array of object. This is important to be able to test embedsMany relations

Concerning the support for the and/or clauses, from what I can gather the SQL connectors all default to loopback-connector's _buildWhere that does concatenate all the keys together https://github.com/strongloop/loopback-connector/blob/master/lib/sql.js#L827.

Moreover, in the memory connector's implementation, there was a bug even if it doesn't support both. If the and/or clause appeared before another key, it could be reverted because of the forEach iteration. An and that was true, could have been made false if the key was declared after. The pass in the closure, although only setting to false, could in certain circumstances cause confusion by failing the filtering on the secondary case.

• https://github.com/strongloop/loopback-connector-mysql
• https://github.com/strongloop/loopback-connector-postgresql
• https://github.com/strongloop/loopback-connector-oracle/blob/master/lib/oracle.js#L484
• https://github.com/strongloop/loopback-connector-mssql/blob/master/lib/mssql.js#L368

As for mongo, its where build is additive: https://github.com/strongloop/loopback-connector-mongodb/blob/master/lib/mongodb.js#L553

[mazesoul]

And finally, a bug which I forgot to mention in the PR's comment: supposing there are two objects, only one of which having a value for a string key, the regex match would throw because there was no verification: https://github.com/strongloop/loopback-datasource-juggler/pull/697/files#diff-98aa884e786e8c02d53648b6f0afaa82R481

It would be trying undefined.match

[mazesoul]

Thanks :)