eq object (JSON columns) doesn't work #477

Steps to reproduce

1. Create a model that has an object column, mapped as a JSON type in PostgreSQL
2. Try to do a find searching for a full value in that property/column, e.g. const objectValue = {a: 1, b: 2}; and then repo.find({where: {objectProperty: objectValue}}) or repo.find({where: {objectProperty: {eq: objectValue}}})

Current Behavior

1. The {objectProperty: {eq: value}} is translated down into {objectProperty: value}
2. This line assumes that, if the value is an object, it must contain exactly one field that must be an operator: https://github.com/strongloop/loopback-connector-postgresql/blob/master/lib/postgresql.js#L654
3. It tries to map e.g. a as an operator name
4. The buildExpression operator switch hits its default clause which delegates to the base class in loopback-connector: https://github.com/strongloop/loopback-connector-postgresql/blob/master/lib/postgresql.js#L540-L543
5. That base class method has a switch with no default clause, so it doesn't throw any errors and just concatenates the column name with the placeholder for the value: https://github.com/strongloop/loopback-connector/blob/master/lib/sql.js#L969
6. And so it generates invalid SQL that looks like "columName"$1

Expected Behavior

• I should be able to use object values in where clauses if the property contains object values

Link to reproduction sandbox

WIP -- NB: encountering this in an LB4 app

Additional information

• Running on linux x64 12.22.1
• npm ls doesn't work with rush, but using loopback-connector-postgresql v5.0.1, with loopback-connector v4.11.1, and the following LB4 components:
• "@loopback/boot": "2.2.0"
• "@loopback/context": "3.9.3"
• "@loopback/core": "2.5.0"
• "@loopback/metadata": "2.2.6"
• "@loopback/openapi-v3": "3.3.1"
• "@loopback/openapi-v3-types": "1.2.1"
• "@loopback/repository": "2.4.0"
• "@loopback/rest": "4.0.0"
• "@loopback/rest-explorer": "2.2.0"

Related Issues

Haven't found any yet

Workaround

Create a custom class to represent the value, and then have the equality comparison value use that, e.g. something like this, but without the prototype pollution vulnerabilities:

class JSONWrapper {
  [k: string]: any
  constructor(value: any) {
    Object.assign(this, value)
  }
}

// elsewhere:
repo.find({where: {objectProperty: new JSONWrapper(objectValue)}});

This causes the expression.constructor === Object check to fail, and so it doesn't try to unwrap the value