Transformers do not work for the MongoDB driver

[roderik]

Issue type:

[ ] question
[x] bug report
[ ] feature request
[ ] documentation issue

Database system/driver:

[ ] cordova
[x] mongodb
[ ] mssql
[ ] mysql / mariadb
[ ] oracle
[ ] postgres
[ ] cockroachdb
[ ] sqlite
[ ] sqljs
[ ] react-native
[ ] expo

TypeORM version:

[x] latest
[ ] @next
[ ] 0.x.x (or put your version here)

Steps to reproduce or a small repository showing the problem:

  @Column('text', {
    transformer: {
      from: (value: string): BigNumber => BigNumber.from(value),
      to: (value: BigNumber): string => value.toString(),
    },
  })
  gasUsed!: BigNumber;

gasUsed is stored in the database as the "object", not as the result of the toString() function

The transformer code is correct because the following works correctly in Mongoose

  @Prop({  
    get: (value: string): BigNumber => BigNumber.from(value),
    set: (value: BigNumber): string => value.toString() 
  })
  gasUsed!: BigNumber;

There was a very old ticket about this mentioning some commented out code, but I could not find it and at first glance, the mongodb driver should execute the transformer code here https://github.com/typeorm/typeorm/blob/master/src/driver/mongodb/MongoDriver.ts#L295-L308 triggered by

typeorm/src/query-builder/UpdateQueryBuilder.ts

Line 423 in 33041cc

value = this.connection.driver.preparePersistentValue(value, column);

[imnotjames]

Duplicate of #4268