Adding index on jsonb field fail when running migration

Question

I am using PostgreSQL with TypeORM. My Student entity has a jsonb field, defined like this:

@Entity('students')
export class Student {
  ...
  @Column('jsonb', { name: 'other_data', nullable: true })
  otherData: { nr?: string; hometown?: string } | null;
}

The students table was initially created without the column other_data but added later via the following migration:

await queryRunner.addColumns('students', [
      new TableColumn({
        name: 'other_data',
        type: 'jsonb',
        isNullable: true,
      }),
    ]);

The column adding was successful, I can see on psql console that \d students has the field with type jsonb.

The content of otherData is expected to be a json contains nr and hometown optional fields.

After database table is created, I try to run a migration to add index to the nr field of otherData (please bear in mind otherData is a jsonb type).

This is what I tried in TypeORM migration file:

public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.query(
      `CREATE INDEX "student_nr" ON "students" USING gin (other_data -> 'nr')`
    );

When I run the migration, I get error:

Migration "AddIndexOnOtherDataColumn1647948281597" has been failed, error: syntax error at or near "->"
query: ROLLBACK
Error during migration run:
QueryFailedError: syntax error at or near "->"
    at QueryFailedError.TypeORMError [as constructor] (/Users/john/myproj/src/error/TypeORMError.ts:7:9)
    at new QueryFailedError (/Users/john/myproj/src/error/QueryFailedError.ts:9:9)
    at PostgresQueryRunner.<anonymous> (/Users/john/myproj/src/driver/postgres/PostgresQueryRunner.ts:247:19)
    at step (/Users/john/myproj/node_modules/tslib/tslib.js:143:27)
    at Object.throw (/Users/john/myproj/node_modules/tslib/tslib.js:124:57)
    at rejected (/Users/john/myproj/node_modules/tslib/tslib.js:115:69)
    at processTicksAndRejections (node:internal/process/task_queues:96:5) {
  query: `CREATE INDEX "student_nr" ON "students" USING gin (other_data -> 'nr')`,
  parameters: undefined,
  driverError: error: syntax error at or near "->"

The noticeable part of the error message is parameters: undefined and error near "->". But I get stuck on why this error, where am I wrong?

Answer 1

I eventually solved the problem by adding one more () around other_data->'nr':

await queryRunner.query(
      `CREATE INDEX "student_nr" ON "students" USING gin ((other_data -> 'nr'))`
    );

But it would be nice if someone is experienced with it could verify whether I am right in fixing the issue & also would be nice to explain more on it. Thanks!