Clarify #dbRef documentation

Author: kibertoad

doc/index.md

@@ -1289,7 +1289,7 @@ await Person
   });
 ```
 
-> If you need to mix inserts and relates inside a single relation, you can use the special property `#dbRef`
+> If you need to mix inserts and relates inside a single relation, you can use the special property `#dbRef` that explicitly points to an id of an entity which already exists in the database. Model `idColumn` of a related entity is used for the `#dbRef`.
 
 ```js
 await Person
@@ -1299,6 +1299,7 @@ await Person
     lastName: 'Lawrence',
 
     movies: [{
+      // This will relate to an existing movie with id 2636
       "#dbRef": 2636
     }, {
       // This will be inserted with an id.
@@ -1378,7 +1379,7 @@ You can read more about graph inserts from [this blog post](https://www.vincit.f
 ```
 
 > By default `upsertGraph` method updates the objects that have an id, inserts objects that don't have an id and deletes
-> all objects that are not present. Off course the delete only applies to relations and not the root. Here's a basic example:
+> all objects that are not present. Of course the delete only applies to relations and not the root. Here's a basic example:
 
 ```js
 // The return value of `upsertGraph` is the input graph converted into model instances.
@@ -1554,6 +1555,8 @@ await Person
   }, options);
 ```
 
+> You can use `upsertGraph` with `#dbRef` (same way as when using `insertGraph`). Alternatively, you can use `relate` option and pass an id as depicted above.
+
 > You can disable updates, inserts, deletes etc. for the whole `upsertGraph` operation or for
 > individual relations by using the `noUpdate`, `noInsert`, `noDelete` etc. options. See
 > [`UpsertGraphOptions`](#upsertgraphoptions) docs for more info.

package.json

@@ -10,6 +10,7 @@
     "test-fast": "mocha --slow 10 --timeout 15000 --reporter spec --recursive tests --bail --exclude \"tests/unit/relations/files/**\"",
     "test-opt": "mocha --slow 10 --timeout 15000 --reporter spec --recursive tests --bail --trace_opt --trace_deopt --exclude \"tests/unit/relations/files/**\"",
     "test-prof": "mocha --slow 10 --timeout 15000 --reporter spec --recursive tests --prof --exclude \"tests/unit/relations/files/**\"",
+    "test-sqlite": "cross-env DATABASES=sqlite3 mocha --slow 10 --timeout 15000 --reporter spec --recursive tests --exclude \"tests/unit/relations/files/**\"",
     "test-typings": "tsc",
     "coveralls": "cat ./testCoverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js",
     "perf": "mocha --slow 60000 --timeout 60000 --reporter spec --recursive perf",
@@ -72,6 +73,7 @@
     "chai": "^4.2.0",
     "chai-subset": "^1.6.0",
     "coveralls": "^3.0.2",
+    "cross-env": "^5.2.0",
     "eslint": "^5.9.0",
     "eslint-plugin-prettier": "^3.0.0",
     "expect.js": "^0.3.1",