TreeRepository findDescendants returns everything if parent does not exist or deleted

[astritsh]

Issue Description

findDescendants of TreeRepository using materialised-path design returns everything if parent was deleted before getting children or if we query with a non existing parent id.

In my case when deleting children of a parent that was already deleted I ended up deleting everything from the tree entity table(quite dangerous!).

Expected Behavior

findDescendants should return empty for a non existing parent.

Actual Behavior

findDescendants is returning all tree entity records from database if we query with a non existing parent id.

Steps to Reproduce

1. Save a tree entity parent on db.(e.g saved id is 1)
2. findDescendants({id: -1})(using a non existing id-1)
3. parent with id: 1 saved in step 1 is being returned

// insert code here

My Environment

NestJs.

Dependency	Version
Operating System
Node.js version	12.14.1
Typescript version	x.y.zzz
TypeORM version	0.2.41

Additional Context

Relevant Database Driver(s)

DB Type	Reproducible
aurora-data-api	no
aurora-data-api-pg	no
better-sqlite3	no
cockroachdb	no
cordova	no
expo	no
mongodb	no
mysql	yes
nativescript	no
oracle	no
postgres	yes
react-native	no
sap	no
sqlite	no
sqlite-abstract	no
sqljs	no
sqlserver	yes

Are you willing to resolve this issue by submitting a Pull Request?

• ✅ Yes, I have the time, and I know how to start.
• ✖️ Yes, I have the time, but I don't know how to start. I would need guidance.
• ✖️ No, I don’t have the time, but I can support (using donations) development.
• ✖️ No, I don’t have the time and I’m okay to wait for the community / maintainers to resolve this issue.

[Yuvraj102]

Hello Authors, Can you please point a resource for detailed implementation of materialised path in typeorm ???, the document is very short on this topic and doesn't cover the implementation in detail.

[ashokars]

Tree entity document should be detailed