typeorm: Unable to delete subordinate relation entity when saving parent entity

Issue type:

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

Database system/driver:

[ ] cordova [ ] mongodb [ ] mssql [x] 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:

My intention was to remove the subordinate entities in a relation from the parent entity.

For example, I’ve a Photo entity which has a one-to-many relation setup with another entity MetaData. So, when I retreive a Photo entity with MetaData relation, the Photo entity should have a shape like this:

    const photoEntity = this.photoRepository.findOne({where: {id: 5}, relations: ['metaData'])
    photoEntity: {
       file: 'someimage.jpg',
       metaDatas: [
          {
             type: 'date',
             data: '12-12-2000'
          },
          {
             type: 'location',
             data: '123.00 123.00'
          }
       ]
    }

Basically, the metaDatas property in Photo entity will be an array. My intention is to remove all MetaData from the Photo entity.

What I did was simply by setting the array of photoEntity.metaDatas to an empty array and then save photoEntity like so:

    const photoEntity = this.photoRepository.findOne({where: {id: 5}, relations: ['metaData'])
    // One photo can have many metadata rows of information in photoEntity.metaDatas
    // Photo entity has a one-to-many relationship setup with MetaData entity
    photoEntity.metaDatas = []   //  Remove all metaDatas in photoEntity
    
    this.photoRepository.save(photoEntity)   // Throws error that ER_BAD_NULL_ERROR: Column 'photoId' cannot be null

However, this throws an error that Column 'photoId' cannot be null. This is because instead of running a DELETE query, the SQL TypeORM did an UPDATE this:

sql: 'UPDATE `metaData` SET `photoId` = NULL, `updatedAt` = CURRENT_TIMESTAMP WHERE `metaDataId` = `123` }

Shouldn’t a DELETE query be run instead of an update one? In this case, how can I remove the MetaData entities from the Photo entity?